101
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Cheng NH, Pittman JK, Shigaki T, Lachmansingh J, LeClere S, Lahner B, Salt DE, Hirschi KD. Functional association of Arabidopsis CAX1 and CAX3 is required for normal growth and ion homeostasis. PLANT PHYSIOLOGY 2005; 138:2048-60. [PMID: 16055687 PMCID: PMC1183394 DOI: 10.1104/pp.105.061218] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Cation levels within the cytosol are coordinated by a network of transporters. Here, we examine the functional roles of calcium exchanger 1 (CAX1), a vacuolar H+/Ca2+ transporter, and the closely related transporter CAX3. We demonstrate that like CAX1, CAX3 is also localized to the tonoplast. We show that CAX1 is predominately expressed in leaves, while CAX3 is highly expressed in roots. Previously, using a yeast assay, we demonstrated that an N-terminal truncation of CAX1 functions as an H+/Ca2+ transporter. Here, we use the same yeast assay to show that full-length CAX1 and full-length CAX3 can partially, but not fully, suppress the Ca2+ hypersensitive yeast phenotype and coexpression of full-length CAX1 and CAX3 conferred phenotypes not produced when either transporter was expressed individually. In planta, CAX3 null alleles were modestly sensitive to exogenous Ca2+ and also displayed a 22% reduction in vacuolar H+-ATPase activity. cax1/cax3 double mutants displayed a severe reduction in growth, including leaf tip and flower necrosis and pronounced sensitivity to exogenous Ca2+ and other ions. These growth defects were partially suppressed by addition of exogenous Mg2+. The double mutant displayed a 42% decrease in vacuolar H+/Ca2+ transport, and a 47% decrease in H+-ATPase activity. While the ionome of cax1 and cax3 lines were modestly perturbed, the cax1/cax3 lines displayed increased PO4(3-), Mn2+, and Zn2+ and decreased Ca2+ and Mg2+ in shoot tissue. These findings suggest synergistic function of CAX1 and CAX3 in plant growth and nutrient acquisition.
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Affiliation(s)
- Ning-Hui Cheng
- United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA
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102
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Shabala S, Hariadi Y. Effects of magnesium availability on the activity of plasma membrane ion transporters and light-induced responses from broad bean leaf mesophyll. PLANTA 2005; 221:56-65. [PMID: 15645306 DOI: 10.1007/s00425-004-1425-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2004] [Accepted: 10/14/2004] [Indexed: 05/20/2023]
Abstract
Considering the physiological significance of Mg homeostasis in plants, surprisingly little is known about the molecular and ionic mechanisms mediating Mg transport across the plasma membrane and the impact of Mg availability on transport processes at the plasmalemma. In this study, a non-invasive ion-selective microelectrode technique (MIFE) was used to characterize the effects of Mg availability on the activity of plasma membrane H+, K+, Ca2+, and Mg2+ transporters in the mesophyll cells of broad bean (Vicia faba L.) plants. Based on the stoichiometry of ion-flux changes and results of pharmacological experiments, we suggest that at least two mechanisms are involved in Mg2+ uptake across the plasma membrane of bean mesophyll cells. One of them is a non-selective cation channel, also permeable to K+ and Ca2+. The other mechanism, operating at concentrations below 30 microM, was speculated to be an H+/Mg+ exchanger. Experiments performed on leaves grown at different levels of Mg availability (from deficient to excessive) showed that Mg availability has a significant impact on the activity of plasma-membrane transporters for Ca2+, K+, and H+. We discuss the physiological significance of Mg-induced changes in leaf electrophysiological responses to light and the ionic mechanisms underlying this process.
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Affiliation(s)
- Sergey Shabala
- School of Agricultural Science, University of Tasmania, Private Bag 254, Hobart, TAS 7001, Australia.
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103
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Nielsen FH, Milne DB. A moderately high intake compared to a low intake of zinc depresses magnesium balance and alters indices of bone turnover in postmenopausal women. Eur J Clin Nutr 2005; 58:703-10. [PMID: 15116072 DOI: 10.1038/sj.ejcn.1601867] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
OBJECTIVES To determine whether moderately high or low intakes of zinc adversely affect the copper status of postmenopausal women to result in unfavorable changes in calcium and magnesium metabolism and other indicators of bone turnover. DESIGN After a 10-day equilibration period in which the diet provided 31.5 micromol (2 mg) Cu and 137.7 micromol (9 mg) Zn/8.4 MJ (2000 kcal), the subjects were randomly divided into two groups, with one group fed the basal diet supplemented to provide 15.7 micromol (1 mg) Cu/8.4 MJ, and the other group fed the same diet supplemented to provide 47.2 micromol (3 mg) Cu/8.4 MJ. After equilibration, both groups were fed the basal diet with no zinc supplemented (provided 45.9 micromol [3 mg] Zn/8.4 MJ) for 90 days; this was followed by another 10-day equilibration period before the basal diet was supplemented with zinc to provide 811 micromol (53 mg)/8.4 MJ for 90 days. SETTING The metabolic unit of the Grand Forks Human Nutrition Research Center, Grand Forks, ND, USA. SUBJECTS A total of 28 postmenopausal women recruited by advertisement throughout the United States of America. Among them, 25 women (64.9+6.7 y) completed the study; 21 as designed. RESULTS The moderately high intake compared to the low intake of zinc increased the excretion of magnesium in the feces and urine, which resulted in a decreased magnesium balance. In the women fed low dietary copper, plasma osteocalcin was higher during the low-zinc than high-zinc dietary period. The urinary excretion of N-telopeptides was increased and the serum calcitonin concentration was decreased by high dietary zinc regardless of dietary copper. CONCLUSIONS A moderately high intake of zinc (811 micromol/day; 53 mg/day) did not induce changes in copper metabolism that resulted in unfavorable changes in bone or mineral metabolism. However, low dietary zinc (45.9 micromol/day; 3 mg/day) apparently resulted in undesirable changes in circulating calcitonin and osteocalcin. As a moderately high intake of zinc decreased magnesium balance, further study of the possibility that a high intake of zinc is a health concern for individuals consuming less than the recommended amounts of magnesium is warranted.
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Affiliation(s)
- F H Nielsen
- US Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202-9034, USA.
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104
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Eapen S, D'Souza SF. Prospects of genetic engineering of plants for phytoremediation of toxic metals. Biotechnol Adv 2005; 23:97-114. [PMID: 15694122 DOI: 10.1016/j.biotechadv.2004.10.001] [Citation(s) in RCA: 324] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/04/2004] [Indexed: 11/26/2022]
Abstract
Bioremediation is gaining a lot of importance in recent times as an alternate technology for removal of elemental pollutants in soil and water, which require effective methods of decontamination. Phytoremediation--the use of green plants to remove, contain or render harmless environmental pollutants--may offer an effective, environmentally nondestructive and cheap remediation method. The use of genetic engineering to modify plants for metal uptake, transport and sequestration may open up new avenues for enhancing efficiency of phytoremediation. Metal chelator, metal transporter, metallothionein (MT), and phytochelatin (PC) genes have been transferred to plants for improved metal uptake and sequestration. Transgenic plants, which detoxify/accumulate cadmium, lead, mercury, arsenic and selenium have been developed. A better understanding of the mechanisms of rhizosphere interaction, uptake, transport and sequestration of metals in hyperaccumulator plants will lead to designing novel transgenic plants with improved remediation traits. As more genes related to metal metabolism are discovered, facilitated by the genome sequencing projects, new vistas will be opened up for development of efficient transgenic plants for phytoremediation.
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Affiliation(s)
- Susan Eapen
- Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Mumbai-40085, India.
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105
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Hanikenne M, Krämer U, Demoulin V, Baurain D. A comparative inventory of metal transporters in the green alga Chlamydomonas reinhardtii and the red alga Cyanidioschizon merolae. PLANT PHYSIOLOGY 2005; 137:428-46. [PMID: 15710683 PMCID: PMC1065346 DOI: 10.1104/pp.104.054189] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Revised: 11/16/2004] [Accepted: 11/18/2004] [Indexed: 05/20/2023]
Affiliation(s)
- Marc Hanikenne
- Metal Homeostasis Group, Max Planck Institute for Plant Molecular Physiology, 14476 Golm, Germany.
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106
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Annunziato L, Pignataro G, Di Renzo GF. Pharmacology of Brain Na+/Ca2+Exchanger: From Molecular Biology to Therapeutic Perspectives. Pharmacol Rev 2004; 56:633-54. [PMID: 15602012 DOI: 10.1124/pr.56.4.5] [Citation(s) in RCA: 254] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
In the last two decades, there has been a growing interest in unraveling the role that the Na+/Ca2+ exchanger (NCX) plays in the function and regulation of several cellular activities. Molecular biology, electrophysiology, genetically modified mice, and molecular pharmacology have helped to delve deeper and more successfully into the physiological and pathophysiological role of this exchanger. In fact, this nine-transmembrane protein, widely distributed in the brain and in the heart, works in a bidirectional way. Specifically, when it operates in the forward mode of operation, it couples the extrusion of one Ca2+ ion with the influx of three Na+ ions. In contrast, when it operates in the reverse mode of operation, while three Na+ ions are extruded, one Ca2+ enters into the cells. Different isoforms of NCX, named NCX1, NCX2, and NCX3, have been described in the brain, whereas only one, NCX1, has been found in the heart. The hypothesis that NCX can play a relevant role in several pathophysiological conditions, including hypoxia-anoxia, white matter degeneration after spinal cord injury, brain trauma and optical nerve injury, neuronal apoptosis, brain aging, and Alzheimer's disease, stems from the observation that NCX, in parallel with selective ion channels and ATP-dependent pumps, is efficient at maintaining intracellular Ca2+ and Na+ homeostasis. In conclusion, although studies concerning the involvement of NCX in the pathological mechanisms underlying brain injury during neurodegenerative diseases started later than those related to heart disease, the availability of pharmacological agents able to selectively modulate each NCX subtype activity and antiporter mode of operation will provide a better understanding of its pathophysiological role and, consequently, more promising approaches to treat these neurological disorders.
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Affiliation(s)
- L Annunziato
- Division of Pharmacology, Department of Neuroscience, School of Medicine, Federico II University of Naples, Via S. Pansini, 5-80131 Naples, Italy.
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107
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Hermans C, Johnson GN, Strasser RJ, Verbruggen N. Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems I and II. PLANTA 2004; 220:344-55. [PMID: 15378366 DOI: 10.1007/s00425-004-1340-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2004] [Accepted: 06/17/2004] [Indexed: 05/03/2023]
Abstract
Magnesium deficiency in plants is a widespread problem, affecting productivity and quality in agriculture, yet at a physiological level it has been poorly studied in crop plants. Here, a physiological characterization of Mg deficiency in Beta vulgaris L., an important crop model, is presented. The impact of Mg deficiency on plant growth, mineral profile and photosynthetic activity was studied. The aerial biomass of plants decreased after 24 days of hydroponic culture in Mg-free nutrient solution, whereas the root biomass was unaffected. Analysis of mineral profiles revealed that Mg decreased more rapidly in roots than in shoots and that shoot Mg content could fall to 3 mg g(-1) DW without chlorosis development and with no effect on photosynthetic parameters. Sucrose accumulated in most recently expanded leaves before any loss in photosynthetic activity. During the development of Mg deficiency, the two photosystems showed sharply contrasting responses. Data were consistent with a down-regulation of PSII through a loss of antenna, and of PSI primarily through a loss of reaction centres. In each case, the net result was a decrease in the overall rate of linear electron transport, preventing an excess of reductant being produced during conditions under which sucrose export away from mature leaf was restricted.
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Affiliation(s)
- Christian Hermans
- Laboratoire de Physiologie et de Génétique Moléculaire des Plantes, Université Libre de Bruxelles, 1050 Brussels, Belgium
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108
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Pittman JK, Shigaki T, Marshall JL, Morris JL, Cheng NH, Hirschi KD. Functional and regulatory analysis of the Arabidopsis thaliana CAX2 cation transporter. PLANT MOLECULAR BIOLOGY 2004; 56:959-71. [PMID: 15821993 DOI: 10.1007/s11103-004-6446-3] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2004] [Accepted: 11/18/2004] [Indexed: 05/05/2023]
Abstract
The vacuolar sequestration of metals is an important metal tolerance mechanism in plants. The Arabidopsis thaliana vacuolar transporters CAX1 and CAX2 were originally identified in a Saccharomyces cerevisiae suppression screen as Ca2+/H+ antiporters. CAX2 has a low affinity for Ca2+ but can transport other metals including Mn2+ and Cd2+. Here we demonstrate that unlike cax1 mutants, CAX2 insertional mutants caused no discernable morphological phenotypes or alterations in Ca2+/H+ antiport activity. However, cax2 lines exhibited a reduction in vacuolar Mn2+/H+ antiport and, like cax1 mutants, reduced V-type H+ -ATPase (V-ATPase) activity. Analysis of a CAX2 promoter beta-glucoronidase (GUS) reporter gene fusion confirmed that CAX2 was expressed throughout the plant and strongly expressed in flower tissue, vascular tissue and in the apical meristem of young plants. Heterologous expression in yeast identified an N-terminal regulatory region in CAX2, suggesting that Arabidopsis contains multiple cation/H+ antiporters with shared regulatory features. Furthermore, despite significant variations in morphological and biochemical phenotypes, cax1 and cax2 lines both significantly alter V-ATPase activity, hinting at coordinate regulation among transporters driven by H+ gradients and the V-ATPase.
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Affiliation(s)
- Jon K Pittman
- United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030, USA.
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109
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Sondergaard TE, Schulz A, Palmgren MG. Energization of transport processes in plants. roles of the plasma membrane H+-ATPase. PLANT PHYSIOLOGY 2004; 136:2475-82. [PMID: 15375204 PMCID: PMC523315 DOI: 10.1104/pp.104.048231] [Citation(s) in RCA: 163] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2004] [Revised: 07/28/2004] [Accepted: 08/02/2004] [Indexed: 05/18/2023]
Affiliation(s)
- Teis E Sondergaard
- Department of Plant Biology, The Royal Veterinary and Agricultural University, DK-1871 Copenhagen, Denmark
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110
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Cai X, Lytton J. The cation/Ca(2+) exchanger superfamily: phylogenetic analysis and structural implications. Mol Biol Evol 2004; 21:1692-703. [PMID: 15163769 DOI: 10.1093/molbev/msh177] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Cation/Ca(2+) exchangers are an essential component of Ca(2+) signaling pathways and function to transport cytosolic Ca(2+) across membranes against its electrochemical gradient by utilizing the downhill gradients of other cation species such as H(+), Na(+), or K(+). The cation/Ca(2+) exchanger superfamily is composed of H(+)/Ca(2+) exchangers and Na(+)/Ca(2+) exchangers, which have been investigated extensively in both plant cells and animal cells. Recently, information from completely sequenced genomes of bacteria, archaea, and eukaryotes has revealed the presence of genes that encode homologues of cation/Ca(2+) exchangers in many organisms in which the role of these exchangers has not been clearly demonstrated. In this study, we report a comprehensive sequence alignment and the first phylogenetic analysis of the cation/Ca(2+) exchanger superfamily of 147 sequences. The results present a framework for structure-function relationships of cation/Ca(2+) exchangers, suggesting unique signature motifs of conserved residues that may underlie divergent functional properties. Construction of a phylogenetic tree with inclusion of cation/Ca(2+) exchangers with known functional properties defines five protein families and the evolutionary relationships between the members. Based on this analysis, the cation/Ca(2+) exchanger superfamily is classified into the YRBG, CAX, NCX, and NCKX families and a newly recognized family, designated CCX. These findings will provide guides for future studies concerning structures, functions, and evolutionary origins of the cation/Ca(2+) exchangers.
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Affiliation(s)
- Xinjiang Cai
- The Cardiovascular Research Group, Departments of Biochemistry and Molecular Biology and Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada.
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111
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Ramesh SA, Choimes S, Schachtman DP. Over-expression of an Arabidopsis zinc transporter in hordeum vulgare increases short-term zinc uptake after zinc deprivation and seed zinc content. PLANT MOLECULAR BIOLOGY 2004; 54:373-85. [PMID: 15284493 DOI: 10.1023/b:plan.0000036370.70912.34] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Increasing the zinc content of cereal grains will be important for improving human nutrition. Improved plant zinc efficiency will lead to increased yields when available zinc is limiting plant growth. The aim of our work was to test how the over-expression of zinc transporters in cereals affects plant growth, seed mineral content, and zinc transport rates. Known zinc transporters from Arabidopsis were over-expressed in Hordeum vulgare cv. Golden Promise by means of a ubiquitin promoter. Multiple transgenic lines were obtained, and the locus number and expression levels were verified. Transgenic lines were tested in long-term growth and short-term uptake experiments. Seeds from transgenic lines grown in soil had higher zinc and iron contents than controls. Short-term uptake rates were higher in the transgenic lines after zinc deprivation. Resupply of zinc after a period of deprivation resulted in the rapid decrease in zinc uptake even in transgenic lines in which a zinc transporter gene was constitutively expressed. Similar to processes in yeast and Arabidopsis, we hypothesize that this rapid decrease in zinc transport activity may be caused by the degradation of transporters in response to zinc-sufficient conditions. In the long-term growth experiments, there were no significant differences between transgenic and control lines in leaf zinc content or shoot biomass under zinc-sufficient or -deficient conditions. However, root-to-shoot ratios were higher in the transgenic plants grown under low-zinc conditions; this could impact zinc acquisition under field conditions. Increased seed zinc and iron content by over-expression of a zinc transporter provides a new strategy for increasing the micronutrient content of cereals.
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Affiliation(s)
- Sunita A Ramesh
- CSIRO Plant Industry - Horticulture Unit, PO Box 350, Glen Osmond, SA 5064, Australia
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112
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Quednau BD, Nicoll DA, Philipson KD. The sodium/calcium exchanger family-SLC8. Pflugers Arch 2004; 447:543-8. [PMID: 12734757 DOI: 10.1007/s00424-003-1065-4] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2003] [Accepted: 03/26/2003] [Indexed: 11/28/2022]
Abstract
The Na(+)/Ca(2+) exchanger gene family encompasses three distinct proteins, NCX1, NCX2, and NCX3, which mediate cellular Ca(2+) efflux and thus contribute to intracellular Ca(2+) homeostasis. NCX1 is expressed ubiquitously while NCX2 and NCX3 are limited to brain and skeletal muscle. NCX1 exchanges 3 extracellular Na(+) for 1 intracellular Ca(2+). In addition to transporting Na(+) and Ca(2+), NCX1 activity is also regulated by these cations. NCX1 is especially important in regulating cardiac contractility.
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Affiliation(s)
- Beate D Quednau
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095-1760, USA
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113
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Ohana E, Segal D, Palty R, Ton-That D, Moran A, Sensi SL, Weiss JH, Hershfinkel M, Sekler I. A Sodium Zinc Exchange Mechanism Is Mediating Extrusion of Zinc in Mammalian Cells. J Biol Chem 2004; 279:4278-84. [PMID: 14581475 DOI: 10.1074/jbc.m309229200] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Zinc influx, driven by a steep inward electrochemical gradient, plays a fundamental role in zinc signaling and in pathophysiologies linked to intracellular accumulation of toxic zinc. Yet, the cellular transport mechanisms that actively generate or maintain the transmembrane gradients are not well understood. We monitored Na+-dependent Zn2+ transport in HEK293 cells and cortical neurons, using fluorescent imaging. Treatment of the HEK293 cells with CaPO4 precipitates induced Na+-dependent Zn2+ extrusion, against a 500-fold transmembrane zinc gradient, or zinc influx upon reversal of Na+ gradient, thus indicating that Na+/Zn2+ exchange is catalyzing active Zn2+ transport. Depletion of intracellular ATP did not inhibit the Na+-dependent Zn2+ extrusion, consistent with a mechanism involving a secondary active transporter. Inhibitors of the Na+/Ca2+ exchanger failed to inhibit Na+-dependent Zn2+ efflux. In addition, zinc transport was unchanged in HEK293 cells heterologously expressing functional cardiac or neuronal Na+/Ca2+ exchangers, thus indicating that the Na+/Zn2+ exchange activity is not mediated by the Na+/Ca2+ exchanger. Sodium-dependent zinc exchange, facilitating the removal of intracellular zinc, was also monitored in neurons. To our knowledge, the Na+/Zn2+ exchanger described here is the first example of a mammalian transport mechanism capable of Na+-dependent active extrusion of zinc. Such mechanism is likely to play an important role, not only in generating the transmembrane zinc gradients, but also in protecting cells from the potentially toxic effects of permeation of this ion.
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Affiliation(s)
- Ehud Ohana
- Department of Physiology, Faculty of Health Science, Ben Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel
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114
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Ferreira A, Rivera A, Romero JR. Na+/Mg2+ exchange is functionally coupled to the insulin receptor. J Cell Physiol 2004; 199:434-40. [PMID: 15095290 DOI: 10.1002/jcp.10463] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Regulation of cellular Mg(2+) levels by insulin has been shown in various tissues. However, the mechanisms for hormonal regulation of cellular Mg(2+) have not been well described. We studied the effect of insulin on Na(+)/Mg(2+) exchange in normal human cells, measuring Na(+)/Mg(2+) exchange activity as net total Mg(2+) efflux driven by an inward Na(+) gradient in Mg(2+)-loaded red blood cells (RBCs). Na(+)/Mg(2+) exchange was increased significantly by the addition of 2.4 nmol/L of insulin to the flux medium (from 0.60 +/- 0.06 mmol/L cell x h to 0.75 +/- 0.08 mmol/L cell x h [P = 0.0098, n = 44]). A dose-response curve for the effects of insulin on the exchanger activity gave an estimated EC(50) for insulin of 0.95 +/- 0.31 nmol/L and a V(max) of 0.86 +/- 0.12 mmol/L cell x h (n = 7). Kinetics of the Na(+)/Mg(2+) exchange were characterized by measuring its activity as a function of Mg(2+) and Na(+) concentrations. The K(0.5) for cellular Mg(2+) was not affected by incubation with insulin. However, the K(0.5) for extracellular Na(+) decreased from 69.9 +/- 6.3 to 40.3 +/- 8.4 mol/L (n = 5, P = 0.03) in the presence of insulin. We also studied the effect of wortmannin (WT), a PI 3-kinase inhibitor, on activity of the exchanger. WT significantly blocked the insulin-stimulated Na(+)/Mg(2+) activity (n = 6, P = 0.048), with an IC(50) of 0.5 nmol/L. LY294002, another PI 3-kinase inhibitor, likewise blocked the insulin-stimulated activity of the exchanger. Therefore, insulin regulates cellular Mg(2+) metabolism in part via an increase in the affinity for Na(+) of the Na(+)/Mg(2+) exchange and PI 3-kinase activation, suggesting another role for the PI 3-kinase pathway in insulin-mediated cellular events.
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Affiliation(s)
- Ana Ferreira
- Division of Endocrinology, Diabetes and Hypertension, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
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115
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Singh OV, Labana S, Pandey G, Budhiraja R, Jain RK. Phytoremediation: an overview of metallic ion decontamination from soil. Appl Microbiol Biotechnol 2003; 61:405-12. [PMID: 12764555 DOI: 10.1007/s00253-003-1244-4] [Citation(s) in RCA: 250] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2002] [Revised: 12/30/2002] [Accepted: 01/03/2003] [Indexed: 11/27/2022]
Abstract
In recent years, phytoremediation has emerged as a promising ecoremediation technology, particularly for soil and water cleanup of large volumes of contaminated sites. The exploitation of plants to remediate soils contaminated with trace elements could provide a cheap and sustainable technology for bioremediation. Many modern tools and analytical devices have provided insight into the selection and optimization of the remediation process by plant species. This review describes certain factors for the phytoremediation of metal ion decontamination and various aspects of plant metabolism during metallic decontamination. Metal-hyperaccumulating plants, desirable for heavily polluted environments, can be developed by the introduction of novel traits into high biomass plants in a transgenic approach, which is a promising strategy for the development of effective phytoremediation technology. The genetic manipulation of a phytoremediator plant needs a number of optimization processes, including mobilization of trace elements/metal ions, their uptake into the root, stem and other viable parts of the plant and their detoxification and allocation within the plant. This upcoming science is expanding as technology continues to offer new, low-cost remediation options.
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Affiliation(s)
- O V Singh
- Institute of Microbial Technology, Sector-39A, 160036 Chandigarh, India
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116
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Thomine S, Lelièvre F, Debarbieux E, Schroeder JI, Barbier-Brygoo H. AtNRAMP3, a multispecific vacuolar metal transporter involved in plant responses to iron deficiency. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2003; 34:685-95. [PMID: 12787249 DOI: 10.1046/j.1365-313x.2003.01760.x] [Citation(s) in RCA: 283] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Metal homeostasis is critical for the survival of living organisms, and metal transporters play central roles in maintaining metal homeostasis in the living cells. We have investigated the function of a metal transporter of the NRAMP family, AtNRAMP3, in Arabidopsis thaliana. A previous study showed that AtNRAMP3 expression is upregulated by iron (Fe) starvation and that AtNRAMP3 protein can transport Fe. In the present study, we used AtNRAMP3 promoter beta-glucoronidase (GUS) fusions to show that AtNRAMP3 is expressed in the vascular bundles of roots, stems, and leaves under Fe-sufficient conditions. This suggests a function in long-distance metal transport within the plant. Under Fe-starvation conditions, the GUS activity driven by the AtNRAMP3 promoter is upregulated without any change in the expression pattern. We analyze the impact of AtNRAMP3 disruption and overexpression on metal accumulation in plants. Under Fe-sufficient conditions, AtNRAMP3 overexpression or disruption does not lead to any change in the plant metal content. Upon Fe starvation, AtNRAMP3 disruption leads to increased accumulation of manganese (Mn) and zinc (Zn) in the roots, whereas AtNRAMP3 overexpression downregulates Mn accumulation. In addition, overexpression of AtNRAMP3 downregulates the expression of the primary Fe uptake transporter IRT1 and of the root ferric chelate reductase FRO2. Expression of AtNRAMP3::GFP fusion protein in onion cells or Arabidopsis protoplasts shows that AtNRAMP3 protein localizes to the vacuolar membrane. To account for the results presented, we propose that AtNRAMP3 influences metal accumulation and IRT1 and FRO2 gene expression by mobilizing vacuolar metal pools to the cytosol.
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Affiliation(s)
- Sébastien Thomine
- Institut des Sciences du Végétal, CNRS UPR2355, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France.
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117
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Abstract
We know very little about the regulation of magnesium uptake and the control of magnesium homeostasis. After years of relative neglect, however, rapid progress is now being made in understanding the molecular biology of magnesium transport in eukaryotes. Several new gene families have been implicated, and tools are in place for the dissection of the biochemical and biological roles played by the encoded proteins.
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Affiliation(s)
- Richard C Gardner
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand.
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118
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Affiliation(s)
- Huguette C Politi
- Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 N 15th Street, Philadelphia, PA 19102, USA
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119
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Shigaki T, Pittman JK, Hirschi KD. Manganese specificity determinants in the Arabidopsis metal/H+ antiporter CAX2. J Biol Chem 2003; 278:6610-7. [PMID: 12496310 DOI: 10.1074/jbc.m209952200] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In plants and fungi, vacuolar transporters help remove potentially toxic cations from the cytosol. Metal/H(+) antiporters are involved in metal sequestration into the vacuole. However, the specific transport properties and the ability to manipulate these transporters to alter substrate specificity are poorly understood. The Arabidopsis thaliana cation exchangers, CAX1 and CAX2, can both transport Ca(2+) into the vacuole. There are 11 CAX-like transporters in Arabidopsis; however, CAX2 was the only characterized CAX transporter capable of vacuolar Mn(2+) transport when expressed in yeast. To determine the domains within CAX2 that mediate Mn(2+) specificity, six CAX2 mutants were constructed that contained different regions of the CAX1 transporter. One class displayed no alterations in Mn(2+) or Ca(2+) transport, the second class showed a reduction in Ca(2+) transport and no measurable Mn(2+) transport, and the third mutant, which contained a 10-amino acid domain from CAX1 (CAX2-C), showed no reduction in Ca(2+) transport and a complete loss of Mn(2+) transport. The subdomain analysis of CAX2-C identified a 3-amino acid region that is responsible for Mn(2+) specificity of CAX2. This study provides evidence for the feasibility of altering substrate specificity in a metal/H(+) antiporter, an important family of transporters found in a variety of organisms.
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Affiliation(s)
- Toshiro Shigaki
- United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA
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120
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Cheng NH, Hirschi KD. Cloning and characterization of CXIP1, a novel PICOT domain-containing Arabidopsis protein that associates with CAX1. J Biol Chem 2003; 278:6503-9. [PMID: 12480930 DOI: 10.1074/jbc.m210883200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulation of Ca(2+) transporters is a vital component of signaling. The Arabidopsis H(+)/Ca(2+) exchanger CAX1 contains an N-terminal autoinhibitory domain that prevents Ca(2+) transport when CAX1 is heterologously expressed in yeast. Using a yeast screen, we have identified three different proteins that activate CAX1. One of these, CXIP1 (CAX-interacting protein-1; 19.3 kDa) has amino acid similarity to the C terminus of PICOT (protein kinase C-interacting cousin of thioredoxin) proteins. Although PICOT proteins are found in a variety of organisms, a function has not been previously ascribed to a plant PICOT protein. We demonstrate that CXIP1 activated the CAX1 homolog CAX4, but not CAX2 or CAX3. An Arabidopsis homolog of CXIP1 (CXIP2) weakly activated CAX4, but not CAX1. In a yeast two-hybrid assay, CXIP1 interacted with the N terminus of CAX1. In competition analysis, CXIP1 and a CAX1 N-terminal peptide appeared to bind to similar N-terminal domains of CAX1. Chimeric CAX3 constructs containing the N terminus of CAX1 were activated by CXIP1. In Arabidopsis, CXIP1 transcripts, like CAX1, accumulated in response to different metal conditions. This work thus characterizes a new class of signaling molecules in plants that may regulate CAX transporters in vivo.
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Affiliation(s)
- Ning-Hui Cheng
- United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA
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121
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Cheng NH, Pittman JK, Barkla BJ, Shigaki T, Hirschi KD. The Arabidopsis cax1 mutant exhibits impaired ion homeostasis, development, and hormonal responses and reveals interplay among vacuolar transporters. THE PLANT CELL 2003; 15:347-64. [PMID: 12566577 PMCID: PMC141206 DOI: 10.1105/tpc.007385] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2002] [Accepted: 11/14/2002] [Indexed: 05/18/2023]
Abstract
The Arabidopsis Ca(2+)/H(+) transporter CAX1 (Cation Exchanger1) may be an important regulator of intracellular Ca(2+) levels. Here, we describe the preliminary localization of CAX1 to the tonoplast and the molecular and biochemical characterization of cax1 mutants. We show that these mutants exhibit a 50% reduction in tonoplast Ca(2+)/H(+) antiport activity, a 40% reduction in tonoplast V-type H(+)-translocating ATPase activity, a 36% increase in tonoplast Ca(2+)-ATPase activity, and increased expression of the putative vacuolar Ca(2+)/H(+) antiporters CAX3 and CAX4. Enhanced growth was displayed by the cax1 lines under Mn(2+) and Mg(2+) stress conditions. The mutants exhibited altered plant development, perturbed hormone sensitivities, and altered expression of an auxin-regulated promoter-reporter gene fusion. We propose that CAX1 regulates myriad plant processes and discuss the observed phenotypes with regard to the compensatory alterations in other transporters.
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Affiliation(s)
- Ning-Hui Cheng
- United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA
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122
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Aharon R, Shahak Y, Wininger S, Bendov R, Kapulnik Y, Galili G. Overexpression of a plasma membrane aquaporin in transgenic tobacco improves plant vigor under favorable growth conditions but not under drought or salt stress. THE PLANT CELL 2003; 15:439-47. [PMID: 12566583 PMCID: PMC141212 DOI: 10.1105/tpc.009225] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2002] [Accepted: 11/26/2002] [Indexed: 05/18/2023]
Abstract
Most of the symplastic water transport in plants occurs via aquaporins, but the extent to which aquaporins contribute to plant water status under favorable growth conditions and abiotic stress is not clear. To address this issue, we constitutively overexpressed the Arabidopsis plasma membrane aquaporin, PIP1b, in transgenic tobacco plants. Under favorable growth conditions, PIP1b overexpression significantly increased plant growth rate, transpiration rate, stomatal density, and photosynthetic efficiency. By contrast, PIP1b overexpression had no beneficial effect under salt stress, whereas during drought stress it had a negative effect, causing faster wilting. Our results suggest that symplastic water transport via plasma membrane aquaporins represents a limiting factor for plant growth and vigor under favorable conditions and that even fully irrigated plants face limited water transportation. By contrast, enhanced symplastic water transport via plasma membrane aquaporins may not have any beneficial effect under salt stress, and it has a deleterious effect during drought stress.
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Affiliation(s)
- Refael Aharon
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel
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123
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Reid R, Hayes J. Mechanisms and Control of Nutrient Uptake in Plants. INTERNATIONAL REVIEW OF CYTOLOGY 2003; 229:73-114. [PMID: 14669955 DOI: 10.1016/s0074-7696(03)29003-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This review is a distillation of the vast amount of physiological and molecular data on plant membrane transport, to provide a concise overview of the main processes involved in the uptake of mineral nutrients in plants. Emphasis has been placed on transport across the plasma membrane, and on the primary uptake from soil into roots, or in the case of aquatic plants, from their aqueous environment. Control of uptake has been mainly considered in terms of local effects on the rate of transport and not in terms of long-distance signaling. The general picture emerging is of a large array of membrane transporters, few of which display any strong selectivity for individual nutrients. Instead, many transporters allow low-affinity uptake of several different nutrients. These features, plus the huge number of potential transporter genes that has been revealed by sequencing of plant genomes, raise some interesting questions about their evolution and likely function.
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Affiliation(s)
- Robert Reid
- Department of Environmental Biology, University of Adelaide, Adelaide 5005, Australia
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124
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Haynes WJ, Kung C, Saimi Y, Preston RR. An exchanger-like protein underlies the large Mg2+ current in Paramecium. Proc Natl Acad Sci U S A 2002; 99:15717-22. [PMID: 12422021 PMCID: PMC137782 DOI: 10.1073/pnas.242603999] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
There are very few molecules known to transport Mg(2+) in eukaryotes. The membrane of Paramecium tetraurelia passes a large Mg(2+)-selective current and exhibits a corresponding backward swimming behavior. Both are missing in a group of mutants called eccentric. By sorting an indexed WT genomic library through microinjection into the macronucleus, we have isolated a DNA fragment that complements the eccentric mutations. The Mg(2+) currents and behavior are restored fully in the transformed cells. Surprisingly, the conceptually translated protein is not homologous to any known ion channel but instead has some similarity to K(+)-dependent Na(+)Ca(2+) exchangers. Exchangers are either electrically silent or only pass very small and slow currents compared with ion-channel currents. In light of recent ion-channel crystal structures and considering the need to have narrow ion-selective filters, we speculate on how an exchanger might evolve to show channel-like activities in special circumstances. The significance of finding the molecular basis of a Mg(2+)-specific pathway is also discussed.
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Affiliation(s)
- W John Haynes
- Laboratory of Molecular Biology and Department of Genetics, University of Wisconsin, Madison 53706, USA.
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125
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Liu GJ, Martin DK, Gardner RC, Ryan PR. Large Mg(2+)-dependent currents are associated with the increased expression of ALR1 in Saccharomyces cerevisiae. FEMS Microbiol Lett 2002; 213:231-7. [PMID: 12167543 DOI: 10.1111/j.1574-6968.2002.tb11311.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Two genes in Saccharomyces cerevisiae, ALR1 and ALR2, encode proteins putatively involved in Mg(2+) uptake. The present study supports this role for ALR1 and provides the first electrophysiological characterisation of this protein. The patch-clamp technique was used to measure whole-cell ion currents in protoplasts prepared from the wild-type strain, the alr1 alr2 double mutant (CM66), and the double mutant over-expressing the ALR1 gene (CM66+ALR1). With 50 mM Mg(2+) in the bathing solution, the inward current in protoplasts of CM66+ALR1 averaged -264+/-48 pA at -150 mV. Inward currents measured in the wild-type and CM66 protoplasts were more than five-fold smaller. When Mg(2+) was the major cation in the pipette solution, time-dependent outward currents were also detected in CM66+ALR1 protoplasts suggesting ALR1 can facilitate Mg(2+) efflux as well as uptake. We conclude that the ALR1 gene encodes a transport protein. The large magnitude of the Mg(2+)-dependent currents suggests that ALR1 could function as a cation channel.
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Affiliation(s)
- Guo Jun Liu
- Department of Health Sciences, University of Technology, Sydney, P.O. Box 123, Broadway, NSW, 2007, Australia
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126
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Gaxiola RA, Fink GR, Hirschi KD. Genetic manipulation of vacuolar proton pumps and transporters. PLANT PHYSIOLOGY 2002; 129:967-73. [PMID: 12114553 PMCID: PMC1540242 DOI: 10.1104/pp.020009] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Affiliation(s)
- Roberto A Gaxiola
- College of Agriculture and Natural Resources, Department of Plant Science, University of Connecticut, Storrs 06269, USA.
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127
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Otegui MS, Capp R, Staehelin LA. Developing seeds of Arabidopsis store different minerals in two types of vacuoles and in the endoplasmic reticulum. THE PLANT CELL 2002; 14:1311-27. [PMID: 12084829 PMCID: PMC150782 DOI: 10.1105/tpc.010486] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2001] [Accepted: 03/01/2002] [Indexed: 05/18/2023]
Abstract
Mineral-accumulating compartments in developing seeds of Arabidopsis were studied using high-pressure-frozen/freeze-substituted samples. Developing seeds store minerals in three locations: in the protein storage vacuoles of the embryo, and transiently in the endoplasmic reticulum (ER) and vacuolar compartments of the chalazal endosperm. Energy dispersive x-ray spectroscopy and enzyme treatments suggest that the minerals are stored as phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate) salts in all three compartments, although they differ in cation composition. Whereas embryo globoids contain Mg, K, and Ca as cations, the chalazal ER deposits show high levels of Mn, and the chalazal vacuolar deposits show high levels of Zn. The appearance of the first Zn-phytate crystals coincides with the formation of network-like extensions of the chalazal vacuoles. The core of these networks consists of a branched network of tubular ER membranes, which are separated from the delineating tonoplast membranes by a layer of cytosolic material. Degradation of the networks starts with the loss of the cytosol and is followed by the retraction of the ER, generating a network of collapsed tonoplast membranes that are resorbed. Studies of fertilized fis2 seeds, which hyperaccumulate Zn-phytate crystals in the chalazal vacuolar compartments, suggest that only the intact network is active in mineral sequestration. Mineral determination analysis and structural observations showed that Zn and Mn are mobilized from the endosperm to the embryo at different developmental stages. Thus, Zn appears to be removed from the endosperm at the late globular stage, and Mn stores appear to be removed at the late bent-cotyledon stage of embryo development. The disappearance of the Mn-phytate from the endosperm coincides with the accumulation of two major Mn binding proteins in the embryo, the 33-kD protein from the oxygen-evolving complex of photosystem II and the Mn superoxide dismutase. The possible functions of transient heavy metal storage in the chalazal endosperm are discussed. A model showing how phytic acid, a potentially cytotoxic molecule, is transported from its site of synthesis, the ER, to the different mineral storage sites is presented.
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Affiliation(s)
- Marisa S Otegui
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
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128
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Abstract
Plant foods can serve as dietary sources of all essential minerals required by humans. Unfortunately, mineral concentrations are low in some plants, especially many staple food crops; thus, efforts are underway to increase the mineral content of these foods as a means to ensure adequate attainment of dietary minerals in all individuals. While these efforts have included classical breeding approaches in the past, it is clear that future progress can be made by utilizing the tools of biotechnology to effect directed changes in plant mineral status. Reviewed are the short- and long-distance mineral transport mechanisms responsible for the root acquisition and whole-plant partitioning of mineral ions in crop plants. This background is used to discuss different transgenic strategies with the potential to enhance mineral content in vegetative and/or reproductive tissues. Due to various constraints imposed by plant transport systems on whole-plant mineral movement, it is argued that modifications designed to increase the supply of minerals to edible organs should have the highest chance for success. Examples of previous efforts to manipulate plant mineral nutrition through the introduction of novel transgenes are presented to demonstrate the utility of these approaches.
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Affiliation(s)
- Michael A Grusak
- US Department of Agriculture, Agricultural Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA.
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129
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Shaked-Sachray L, Weiss D, Reuveni M, Nissim-Levi A, Oren-Shamir M. Increased anthocyanin accumulation in aster flowers at elevated temperatures due to magnesium treatment. PHYSIOLOGIA PLANTARUM 2002; 114:559-565. [PMID: 11975729 DOI: 10.1034/j.1399-3054.2002.1140408.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Temperature is one of the main external factors affecting anthocyanin accumulation in plant tissues: low temperatures cause an increase and elevated temperatures cause a decrease in anthocyanin concentration. Several metals have been shown to increase the half-life time of anthocyanins, by forming complexes with them. We studied the combined effect of elevated temperatures and increased metal concentrations on the accumulation of anthocyanins in aster 'Sungal' flowers. It has been found that magnesium treatment of aster plants or detached flower buds, partially prevents colour fading at elevated temperatures. Anthocyanin concentration of aster 'Sungal' flowers grown at 29 degrees C/21 degrees C day/night, respectively, was about half that of flowers grown at 17 degrees C/9 degrees C. The activity of phenylalanine ammonia-lyase (PAL) and chalcone isomerase (CHI) decreased as the temperature increased. Treatment of both whole plants and detached flower buds grown at elevated temperatures in the presence of magnesium salts, increased flower anthocyanin concentration by up to 80%. Measurement of magnesium following these treatments revealed an increased level of the metal in the petals, suggesting a direct effect. Magnesium treatment does not seem to cause increased synthesis of anthocyanin through a stress-related reaction, since the activities of both PAL and CHI did not increase due to this treatment. The results of this study show that increasing magnesium levels in aster petals prevents the deleterious effect of elevated temperatures on anthocyanin accumulation, thus enhancing flower colour.
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Affiliation(s)
- Liat Shaked-Sachray
- aDepartment of Ornamental Horticulture, Agricultural Research Organization, The Volcani Center, Bet-Dagan 50250, PO Box 6, Israel bDepartment of Horticulture, Faculty of Agriculture, The Hebrew University of Jerusalem, PO Box 12, 76100, Rehovot, Israel
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130
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Cheng NH, Pittman JK, Shigaki T, Hirschi KD. Characterization of CAX4, an Arabidopsis H(+)/cation antiporter. PLANT PHYSIOLOGY 2002; 128:1245-54. [PMID: 11950973 PMCID: PMC154252 DOI: 10.1104/pp.010857] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2001] [Revised: 12/20/2001] [Accepted: 12/27/2001] [Indexed: 05/18/2023]
Abstract
Ion compartmentalization is essential for plant growth and development. The Arabidopsis open reading frames for CAX1, CAX2, and CAX3 (cation exchangers 1, 2, and 3) were previously identified as transporters that may modulate ion fluxes across the vacuolar membrane. To understand the diversity and role of H(+)/cation transporters in controlling plant ion levels, another homolog of the CAX genes, CAX4, was cloned from an Arabidopsis cDNA library. CAX4 is 53% identical to CAX1 at the amino acid level, 42% identical to CAX2, and 54% identical to CAX3. CAX4 transcripts appeared to be expressed at low levels in all tissues and levels of CAX4 RNA increased after Mn(2+), Na(+), and Ni(2+) treatment. An N-terminal CAX4-hemagglutinin fusion appeared to localize to both yeast and plant vacuolar membranes. When expressed in yeast, CAX4, like CAX3, failed to suppress the Ca(2+) sensitivity of yeast strains deficient in vacuolar Ca(2+) transport. Several modifications to CAX4 allowed the protein to transport Ca(2+). Addition of amino acids to the N terminus of CAX4 and CAX3 caused both transporters to suppress the sensitivity of yeast strains deficient in vacuolar Ca(2+) transport. These findings suggest that CAX transporters may modulate their ion transport properties through alterations at the N terminus.
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Affiliation(s)
- Ning-hui Cheng
- Baylor College of Medicine, Plant Physiology Group, United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, 1100 Bates Street, Houston, TX 77030, USA
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131
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Li L, Tutone AF, Drummond RS, Gardner RC, Luan S. A novel family of magnesium transport genes in Arabidopsis. THE PLANT CELL 2001; 13:2761-75. [PMID: 11752386 PMCID: PMC139487 DOI: 10.1105/tpc.010352] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2001] [Accepted: 09/04/2001] [Indexed: 05/18/2023]
Abstract
Magnesium (Mg(2+)) is the most abundant divalent cation in plant cells and plays a critical role in many physiological processes. We describe the identification of a 10-member Arabidopsis gene family (AtMGT) encoding putative Mg(2+) transport proteins. Most members of the AtMGT family are expressed in a range of Arabidopsis tissues. One member of this family, AtMGT1, functionally complemented a bacterial mutant lacking Mg(2+) transport capability. A second member, AtMGT10, complemented a yeast mutant defective in Mg(2+) uptake and increased the cellular Mg(2+) content of starved cells threefold during a 60-min uptake period. (63)Ni tracer studies in bacteria showed that AtMGT1 has highest affinity for Mg(2+) but may also be capable of transporting several other divalent cations, including Ni(2+), Co(2+), Fe(2+), Mn(2+), and Cu(2+). However, the concentrations required for transport of these other cations are beyond normal physiological ranges. Both AtMGT1 and AtMGT10 are highly sensitive to Al(3+) inhibition, providing potential molecular targets for Al(3+) toxicity in plants. Using green fluorescence protein as a reporter, we localized AtMGT1 protein to the plasma membrane in Arabidopsis plants. We suggest that the AtMGT gene family encodes a Mg(2+) transport system in higher plants.
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Affiliation(s)
- L Li
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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132
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Li L, Tutone AF, Drummond RS, Gardner RC, Luan S. A novel family of magnesium transport genes in Arabidopsis. THE PLANT CELL 2001. [PMID: 11752386 DOI: 10.1105/tpc.13.12.2761] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Magnesium (Mg(2+)) is the most abundant divalent cation in plant cells and plays a critical role in many physiological processes. We describe the identification of a 10-member Arabidopsis gene family (AtMGT) encoding putative Mg(2+) transport proteins. Most members of the AtMGT family are expressed in a range of Arabidopsis tissues. One member of this family, AtMGT1, functionally complemented a bacterial mutant lacking Mg(2+) transport capability. A second member, AtMGT10, complemented a yeast mutant defective in Mg(2+) uptake and increased the cellular Mg(2+) content of starved cells threefold during a 60-min uptake period. (63)Ni tracer studies in bacteria showed that AtMGT1 has highest affinity for Mg(2+) but may also be capable of transporting several other divalent cations, including Ni(2+), Co(2+), Fe(2+), Mn(2+), and Cu(2+). However, the concentrations required for transport of these other cations are beyond normal physiological ranges. Both AtMGT1 and AtMGT10 are highly sensitive to Al(3+) inhibition, providing potential molecular targets for Al(3+) toxicity in plants. Using green fluorescence protein as a reporter, we localized AtMGT1 protein to the plasma membrane in Arabidopsis plants. We suggest that the AtMGT gene family encodes a Mg(2+) transport system in higher plants.
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Affiliation(s)
- L Li
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA
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133
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Igamberdiev AU, Kleczkowski LA. Implications of adenylate kinase-governed equilibrium of adenylates on contents of free magnesium in plant cells and compartments. Biochem J 2001; 360:225-31. [PMID: 11696011 PMCID: PMC1222221 DOI: 10.1042/0264-6021:3600225] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
On the basis of the equilibrium of adenylate kinase (AK; EC 2.7.4.3), which interconverts MgATP and free AMP with MgADP and free ADP, an approach has been worked out to calculate concentrations of free magnesium (Mg(2+)), based on concentrations of total ATP, ADP and AMP in plant tissues and in individual subcellular compartments. Based on reported total adenylate contents, [Mg(2+)] in plant tissues and organelles varies significantly depending on light and dark regimes, plant age and developmental stage. In steady-state conditions, [Mg(2+)] in chloroplasts is similar in light and darkness (in the millimolar range), whereas in the cytosol it is very low in the light and increases to about 0.4 mM in darkness. During the dark-to-light transition (photosynthetic induction), the [Mg(2+)] in chloroplasts falls to low values (0.2 mM or less), corresponding to a delay in photosynthetic oxygen evolution. This delay is considered to result from lower activities of Mg-dependent enzymes in the Calvin cycle. In mitochondria, the changes in [Mg(2+)] are similar but smoother. On the other hand, when the transition from light to darkness is considered, an initial increase in [Mg(2+)] occurs in both chloroplasts and mitochondria, which may be of importance for the control of key regulatory enzymes (e.g. mitochondrial malic enzyme and pyruvate dehydrogenase complex) and for processes connected with light-enhanced dark respiration. A rationale is presented for a possible role of [MgATP]/[MgADP] ratio (rather than [ATP(total)]/[ADP(total)]) as an important component of metabolic cellular control. It is postulated that assays of total adenylates may provide an accurate measure of [Mg(2+)] in plant tissues/cells and subcellular compartments, given that the adenylates are equilibrated by AK.
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Affiliation(s)
- A U Igamberdiev
- Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, 901-87 Umeå, Sweden
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134
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Sgambato A, Faraglia B, Ardito R, Torsello A, Boninsegna A, Cittadini A, Wolf FI. Isolation of normal epithelial cells adapted to grow at nonphysiological concentration of magnesium. Biochem Biophys Res Commun 2001; 286:752-7. [PMID: 11520061 DOI: 10.1006/bbrc.2001.5465] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Extracellular magnesium (Mg) depletion inhibits the growth of the HC11 normal mammary epithelial cells. In this study we found that an acute increase in extracellular Mg generally exerts a positive effect on the growth of these cells. We also isolated and characterized two derivatives adapted to grow and proliferate at nonphysiological concentration of Mg. The growth properties of the HC-LMg cells at 25 microM Mg were comparable to those of the parental HC11 cells in the regular medium (0.5 mM Mg) despite an increased expression of the CDK inhibitor p27(Kip1). They also showed a reduced dependence from serum to grow. The HC-HMg cells have been adapted to grow and proliferate at an increased (45 mM) Mg concentration. Cell total Mg content was 19.6, 9.7, and 20.1 nmol/mg protein in the HC11, HC-LMg, and HC-HMg cells, respectively. Thus, we have isolated derivatives of normal epithelial cells which are able to maintain Mg content in a physiological range in the face of different extracellular concentration gradients and will be a valuable tool for further studies on the regulation of Mg homeostasis in eukaryotic cells.
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Affiliation(s)
- A Sgambato
- Centro di Ricerche Oncologiche Giovanni XXIII, Istituto di Patologia Generale, Università Cattolica del Sacro Cuore, Largo Francesco Vito 1, 00168 Rome, Italy.
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135
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Borrelly G, Boyer JC, Touraine B, Szponarski W, Rambier M, Gibrat R. The yeast mutant vps5Delta affected in the recycling of Golgi membrane proteins displays an enhanced vacuolar Mg2+/H+ exchange activity. Proc Natl Acad Sci U S A 2001; 98:9660-5. [PMID: 11493679 PMCID: PMC55508 DOI: 10.1073/pnas.161215198] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Growth of the yeast vacuolar protein-sorting mutant vps5Delta affected in the endosome-to-Golgi retromer complex was more sensitive to Mg2+-limiting conditions than was the growth of the wild-type (WT) strain. This sensitivity was enhanced at acidic pH. The vps5Delta strain was also sensitive to Al3+, known to inhibit Mg2+ uptake in yeast cells. In contrast, it was found to be resistant to Ni2+ and Co2+, two cytotoxic analogs of Mg2+. Resistance to Ni2+ did not seem to result from the alteration of plasma-membrane transport properties because mutant and WT cells displayed similar Ni2+ uptake. After plasma-membrane permeabilization, intracellular Ni2+ uptake in vps5Delta cells was 3-fold higher than in WT cells, which is consistent with the implication of the vacuole in the observed phenotypes. In reconstituted vacuolar vesicles prepared from vps5Delta, the rates of H+ exchange with Ni2+, Co2+, and Mg2+ were increased (relative to WT) by 170%, 130%, and 50%, respectively. The rates of H+ exchange with Ca2+, Cd2+, and K+ were similar in both strains, as were alpha-mannosidase and H+-ATPase activities, and SDS/PAGE patterns of vacuolar proteins. Among 14 other vacuolar protein-sorting mutants tested, only the 8 mutants affected in the recycling of trans-Golgi network membrane proteins shared the same Ni2+ resistance phenotype as vps5Delta. It is proposed that a trans-Golgi network Mg2+/H+ exchanger, mislocalized to vps5Delta vacuole, could be responsible for the phenotypes observed in vivo and in vitro.
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Affiliation(s)
- G Borrelly
- Biochimie et Physiologie Moléculaire des Plantes, Ecole Nationale Supérieure d'Agronomie de Montpellier (Agro-M)/Institut National de la Recherche Agronomique, France
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136
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Mäser P, Thomine S, Schroeder JI, Ward JM, Hirschi K, Sze H, Talke IN, Amtmann A, Maathuis FJ, Sanders D, Harper JF, Tchieu J, Gribskov M, Persans MW, Salt DE, Kim SA, Guerinot ML. Phylogenetic relationships within cation transporter families of Arabidopsis. PLANT PHYSIOLOGY 2001; 126:1646-1667. [PMID: 11500563 DOI: 10.2307/4280038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Uptake and translocation of cationic nutrients play essential roles in physiological processes including plant growth, nutrition, signal transduction, and development. Approximately 5% of the Arabidopsis genome appears to encode membrane transport proteins. These proteins are classified in 46 unique families containing approximately 880 members. In addition, several hundred putative transporters have not yet been assigned to families. In this paper, we have analyzed the phylogenetic relationships of over 150 cation transport proteins. This analysis has focused on cation transporter gene families for which initial characterizations have been achieved for individual members, including potassium transporters and channels, sodium transporters, calcium antiporters, cyclic nucleotide-gated channels, cation diffusion facilitator proteins, natural resistance-associated macrophage proteins (NRAMP), and Zn-regulated transporter Fe-regulated transporter-like proteins. Phylogenetic trees of each family define the evolutionary relationships of the members to each other. These families contain numerous members, indicating diverse functions in vivo. Closely related isoforms and separate subfamilies exist within many of these gene families, indicating possible redundancies and specialized functions. To facilitate their further study, the PlantsT database (http://plantst.sdsc.edu) has been created that includes alignments of the analyzed cation transporters and their chromosomal locations.
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Affiliation(s)
- P Mäser
- Division of Biology, Cell and Developmental Biology Section and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116, USA
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137
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Mäser P, Thomine S, Schroeder JI, Ward JM, Hirschi K, Sze H, Talke IN, Amtmann A, Maathuis FJ, Sanders D, Harper JF, Tchieu J, Gribskov M, Persans MW, Salt DE, Kim SA, Guerinot ML. Phylogenetic relationships within cation transporter families of Arabidopsis. PLANT PHYSIOLOGY 2001; 126:1646-67. [PMID: 11500563 PMCID: PMC117164 DOI: 10.1104/pp.126.4.1646] [Citation(s) in RCA: 719] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2001] [Revised: 04/12/2001] [Accepted: 05/01/2001] [Indexed: 05/17/2023]
Abstract
Uptake and translocation of cationic nutrients play essential roles in physiological processes including plant growth, nutrition, signal transduction, and development. Approximately 5% of the Arabidopsis genome appears to encode membrane transport proteins. These proteins are classified in 46 unique families containing approximately 880 members. In addition, several hundred putative transporters have not yet been assigned to families. In this paper, we have analyzed the phylogenetic relationships of over 150 cation transport proteins. This analysis has focused on cation transporter gene families for which initial characterizations have been achieved for individual members, including potassium transporters and channels, sodium transporters, calcium antiporters, cyclic nucleotide-gated channels, cation diffusion facilitator proteins, natural resistance-associated macrophage proteins (NRAMP), and Zn-regulated transporter Fe-regulated transporter-like proteins. Phylogenetic trees of each family define the evolutionary relationships of the members to each other. These families contain numerous members, indicating diverse functions in vivo. Closely related isoforms and separate subfamilies exist within many of these gene families, indicating possible redundancies and specialized functions. To facilitate their further study, the PlantsT database (http://plantst.sdsc.edu) has been created that includes alignments of the analyzed cation transporters and their chromosomal locations.
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Affiliation(s)
- P Mäser
- Division of Biology, Cell and Developmental Biology Section and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116, USA
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138
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Graschopf A, Stadler JA, Hoellerer MK, Eder S, Sieghardt M, Kohlwein SD, Schweyen RJ. The yeast plasma membrane protein Alr1 controls Mg2+ homeostasis and is subject to Mg2+-dependent control of its synthesis and degradation. J Biol Chem 2001; 276:16216-22. [PMID: 11279208 DOI: 10.1074/jbc.m101504200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Saccharomyces cerevisiae ALR1 (YOL130w) gene product Alr1p is the first known candidate for a Mg(2+) transport system in eukaryotic cells and is distantly related to the bacterial CorA Mg(2+) transporter family. Here we provide the first experimental evidence for the location of Alr1p in the yeast plasma membrane and for the tight control of its expression and turnover by Mg(2+). Using well characterized npi1 and end3 mutants deficient in the endocytic pathway, we demonstrate that Alr1 protein turnover is dependent on ubiquitination and endocytosis. Furthermore, cells lacking the vacuolar protease Pep4p accumulated Alr1p in the vacuole. Mutants lacking Alr1p (Deltaalr1) showed a 60% reduction of total intracellular Mg(2+) compared with the wild type and failed to grow in standard media. When starved of Mg(2+), mutant and wild-type cells had similar low levels of intracellular Mg(2+); but upon addition of Mg(2+), wild-type cells replenished the intracellular Mg(2+) pool within a few hours, whereas Deltaalr1 mutant cells did not. Expression of the bacterial Mg(2+) transporter CorA in the yeast Deltaalr1 mutant partially restored growth in standard media. The results are discussed in terms of Alr1p being a plasma membrane transporter with high selectivity for Mg(2+).
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Affiliation(s)
- A Graschopf
- Vienna Biocenter, Institute of Microbiology and Genetics, University of Vienna, A-1030 Vienna, Austria
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139
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Hirschi KD, Miranda ML, Wilganowski NL. Phenotypic changes in Arabidopsis caused by expression of a yeast vacuolar Ca2+/H+ antiporter. PLANT MOLECULAR BIOLOGY 2001; 46:57-65. [PMID: 11437250 DOI: 10.1023/a:1010620227913] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In plants, cytosolic Ca2+ levels are tightly regulated, and changes in cytosolic Ca2+ have been implicated in converting numerous signals into adapted responses. Vacuolar ion transporters are thought to be key mediators of cytosolic Ca2+ concentrations. In an attempt to interpret the role of vacuolar Ca2+ transport in plant processes, we have expressed the yeast vacuolar Ca2+/H+ antiporter, VCX1, in Arabidopsis and tobacco. This transporter localizes to the plant vacuolar membrane. VCX1-expressing Arabidopsis plants displayed increased sensitivity to sodium and other ions. These ion sensitivities could be suppressed by addition of calcium to the media. VCX1-expressing plants demonstrated increased tonoplast-enriched Ca2+/H+ antiport activity as well as increased Ca2+ accumulation. These results suggest that VCX1 expression in Arabidopsis could be a valuable tool with which to experimentally dissect the role of Ca2+ transport around the plant vacuole.
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Affiliation(s)
- K D Hirschi
- Baylor College of Medicine, Plant Physiology Group, U.S. Department of Agriculture, Agricultural Research Service, Children's Nutrition Research Center, Houston, TX 77030, USA.
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140
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Touyz RM, Mercure C, Reudelhuber TL. Angiotensin II type I receptor modulates intracellular free Mg2+ in renally derived cells via Na+-dependent Ca2+-independent mechanisms. J Biol Chem 2001; 276:13657-63. [PMID: 11278387 DOI: 10.1074/jbc.m008101200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Treatment of Madin-Darby canine kidney (MDCK) cells with the peptide hormone angiotensin II (Ang II) results in an increase in the concentrations of cytosolic free calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) with a concomitant decrease in cytosolic free Mg(2+) concentration ([Mg(2+)](i)). In the present study we demonstrate that this hormone-induced decrease in [Mg(2+)](i) is independent of [Ca(2+)](i) but dependent on extracellular Na(+). [Mg(2+)](i), [Ca(2+)](i), and [Na(+)](i) were measured in Ang II-stimulated MDCK cells by fluorescence digital imaging using the selective fluoroprobes mag-fura-2AM, fura-2AM, and sodium-binding benzofuran isophthalate (acetoxymethyl ester), respectively. Ang II decreased [Mg(2+)](i) and increased [Na(+)](i) in a dose-dependent manner. These effects were inhibited by irbesartan (selective AT(1) receptor blocker) but not by PD123319 (selective AT(2) receptor blocker). Imipramine and quinidine (putative inhibitors of the Na(+)/Mg(2+) exchanger) and removal of extracellular Na(+) abrogated Ang II-mediated [Mg(2+)](i) effects. In cells pretreated with thapsigargin (reticular Ca(2+)-ATPase inhibitor), Ang II-stimulated [Ca(2+)](i) transients were attenuated (p < 0.01), whereas agonist-induced [Mg(2+)](i) responses were unchanged. Clamping the [Ca(2+)](i) near 50 nmol/liter with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) inhibited Ang II-induced [Ca(2+)](i) increases but failed to alter Ang II-induced [Mg(2+)](i) responses. Benzamil, a selective blocker of the Na(+)/Ca(2+) exchanger, inhibited [Na(+)](i) but not [Mg(2+)](i) responses. Our data demonstrate that in MDCK cells, AT(1) receptors modulate [Mg(2+)](i) via a Na(+)-dependent Mg(2+) transporter that is not directly related to [Ca(2+)](i). These data support the notion that rapid modulation of [Mg(2+)](i) is not simply a result of Mg(2+) redistribution from intracellular buffering sites by Ca(2+) and provide evidence for the existence of a Na(+)-dependent, hormonally regulated transporter for Mg(2+) in renally derived cells.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Adrenergic Uptake Inhibitors/pharmacology
- Adrenergic alpha-Antagonists/pharmacology
- Amiloride/analogs & derivatives
- Amiloride/pharmacology
- Angiotensin II/pharmacology
- Animals
- Antihypertensive Agents/pharmacology
- Benzofurans/pharmacology
- Biphenyl Compounds/pharmacology
- Calcium/metabolism
- Calcium Channel Agonists/pharmacology
- Cell Line
- Cells, Cultured
- Chelating Agents/pharmacology
- Cytosol/metabolism
- Dogs
- Dose-Response Relationship, Drug
- Egtazic Acid/analogs & derivatives
- Egtazic Acid/pharmacology
- Ethers, Cyclic/pharmacology
- Fluorescent Dyes/pharmacology
- Fura-2/analogs & derivatives
- Fura-2/pharmacology
- Imidazoles/pharmacology
- Imipramine/pharmacology
- Irbesartan
- Kidney/metabolism
- Kinetics
- Magnesium/metabolism
- Microscopy, Fluorescence
- Peptides/pharmacology
- Pyridines/pharmacology
- Quinidine/pharmacology
- Receptor, Angiotensin, Type 1
- Receptor, Angiotensin, Type 2
- Receptors, Angiotensin/physiology
- Sodium/metabolism
- Sodium/pharmacology
- Tetrazoles/pharmacology
- Time Factors
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Affiliation(s)
- R M Touyz
- Multidisciplinary Research Group on Hypertension, Clinical Research Institute of Montreal, University of Montreal, Montreal, Quebec H2W 1R7, Canada.
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141
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Schlatterer C, Walther P, Müller M, Mendgen K, Zierold K, Knoll G. Calcium stores in differentiated Dictyostelium discoideum: prespore cells sequester calcium more efficiently than prestalk cells. Cell Calcium 2001; 29:171-82. [PMID: 11162854 DOI: 10.1054/ceca.2000.0181] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Dictyostelium discoideum pseudoplasmodia exhibit a gradient of the cytosolic free Ca2+-concentration ([Ca2+]i) along their anterior-posterior axis involved in cell-type specific differentiation. [Ca2+]i is high in prestalk and low in prespore cells. We determined the content and localization of calcium and other elements in cryosectioned cells of pseudoplasmodia and fruiting bodies by X-ray microanalysis. Granular stores rich in Ca, Mg and P were identified. Average Ca was higher in prespore than prestalk granules (225vs 111 mmol/kg dry weight). Total Ca stored in granules was also higher in prespore than prestalk cells. The amount of P and S in granules differed between the two cell types indicating different store composition. In spores mean granular Ca was 120 mmol/kg dry weight. Stalk cells had smaller granules with 360 mmol Ca/kg dry weight. Complementary to microanalysis, vesicular Ca2+-fluxes were studied in fractionated cell homogenates. The rate of Ca2+-uptake was higher in pellet fractions of prespore than prestalk amoebae (4.7 vs 3.4 nmol/min x mg). Ca2+-release was greater in supernatant fractions from prestalk than prespore cells (16.5vs 7.7 nmol/10(8)cells). In summary, prestalk and prespore cells possess qualitatively different, high-capacity stores containing distinct amounts of Ca and probably being involved in regulation of the anterior-posterior [Ca2+]i-gradient.
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Affiliation(s)
- C Schlatterer
- Faculty of Biology, University of Konstanz, Konstanz, Germany.
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142
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Abstract
Physiological studies have established the role of plant high-capacity vacuolar H+/Ca2+ exchange activity in ion homeostasis and signal transduction. The molecular characterization and structure-function analyses of these transporters are just beginning to emerge. In yeast, Ca2+ signaling molecules regulate vacuolar H+/Ca2+ exchange. Recently, some of the Ca2+ dependent "molecular relay" molecules have been characterized in plants; however, the regulation of plant vacuolar H+/Ca2+ exchange remains an open question.
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Affiliation(s)
- K Hirschi
- Baylor College of Medicine, Plant Physiology Group, Dept of Pediatrics, US Dept of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, 1100 Bates St, Houston, TX 77030, USA.
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143
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Iwamoto T, Uehara A, Imanaga I, Shigekawa M. The Na+/Ca2+ exchanger NCX1 has oppositely oriented reentrant loop domains that contain conserved aspartic acids whose mutation alters its apparent Ca2+ affinity. J Biol Chem 2000; 275:38571-80. [PMID: 10967097 DOI: 10.1074/jbc.m003788200] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
We examined the membrane topology and functional importance of residues in regions of the Na(+)/Ca(2+) exchanger NCX1 encompassing the conserved internal alpha repeats by substituted cysteine scanning analysis and kinetic analysis of site-directed mutants. The results suggest that both the alpha-1 repeat and a region encompassing the alpha-2 repeat and its immediately C-terminal segment contain reentrant loop domains, each oriented in an opposite direction with respect to the membrane. We found that single or multiple mutations of six residues including Asn-125 and conserved aspartates Asp-130, Asp-825, and Asp-829 in the alpha repeat reentrant domains reduce the apparent affinity of the exchanger for extracellular Ca(2+) by up to 6-fold. In contrast, the triple cysteine mutation D130C/D825C/D829C did not influence the current-voltage (I-V) relationship of the exchange current. Cysteine accessibility scanning with different thiol modifiers suggested that N125C, D130C, and D825C may be located in a restricted aqueous space in the membrane accessible only to ions when examined with external probes, although N125C and D825C were previously shown to be internally accessible during exchange reaction. The results suggest that these reentrant domains in the alpha repeats may participate in the formation of the ion transport pathway in the exchanger with some of the aspartates possibly lining it or located close to it.
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Affiliation(s)
- T Iwamoto
- Department of Molecular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka, Japan
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144
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Zhu X, Tang G, Galili G. Characterization of the two saccharopine dehydrogenase isozymes of lysine catabolism encoded by the single composite AtLKR/SDH locus of Arabidopsis. PLANT PHYSIOLOGY 2000; 124:1363-1372. [PMID: 11080311 PMCID: PMC59233 DOI: 10.1104/pp.124.3.1363] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2000] [Accepted: 08/01/2000] [Indexed: 05/23/2023]
Abstract
Arabidopsis plants possess a composite AtLKR/SDH locus encoding two different polypeptides involved in lysine catabolism: a bifunctional lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH) enzyme and a monofunctional SDH enzyme. To unravel the physiological significance of these two enzymes, we analyzed their subcellular localization and detailed biochemical properties. Sucrose gradient analysis showed that the two enzymes are localized in the cytosol and therefore may operate at relatively neutral pH values in vivo. Yet while the physiological pH may provide an optimum environment for LKR activity, the pH optima for the activities of both the linked and non-linked SDH enzymes were above pH 9, suggesting that these two enzymes may operate under suboptimal conditions in vivo. The basic biochemical properties of the monofunctional SDH, including its pH optimum as well as the apparent Michaelis constant (K(m)) values for its substrates saccharopine and nicotinamide adenine dinucleotide at neutral and basic pH values, were similar to those of its SDH counterpart that is linked to LKR. Taken together, our results suggest that production of the monofunctional SDH provides Arabidopsis plants with enhanced levels of SDH activity (maximum initial velocity), rather than with an SDH isozyme with significantly altered kinetic parameters. Excess levels of this enzyme might enable efficient flux of lysine catabolism via the SDH reaction in the unfavorable physiological pH of the cytosol.
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Affiliation(s)
- X Zhu
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel
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145
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Hirschi KD, Korenkov VD, Wilganowski NL, Wagner GJ. Expression of arabidopsis CAX2 in tobacco. Altered metal accumulation and increased manganese tolerance. PLANT PHYSIOLOGY 2000; 124:125-33. [PMID: 10982428 PMCID: PMC59128 DOI: 10.1104/pp.124.1.125] [Citation(s) in RCA: 235] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2000] [Accepted: 05/21/2000] [Indexed: 05/17/2023]
Abstract
Metal transport from the cytosol to the vacuole is thought to be an important component of ion tolerance and of a plant's potential for use in phytoremediation. The Arabidopsis antiporter CAX2 (calcium exchanger 2) may be a key mediator of this process. CAX2 expression in yeast suppressed both Ca(2+) and Mn(2+) growth defects. A peptide-specific antibody to the antiporter reacted with a 39-kD protein from plant vacuolar membranes. Tobacco (Nicotiana tabacum) plants expressing CAX2 accumulated more Ca(2+), Cd(2+), and Mn(2+) and were more tolerant to elevated Mn(2+) levels. Expression of CAX2 in tobacco increased Cd(2+) and Mn(2+) transport in isolated root tonoplast vesicles. These results suggest that CAX2 has a broad substrate range and modulation of this transporter may be an important component of future strategies to improve plant ion tolerance.
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Affiliation(s)
- K D Hirschi
- Baylor College of Medicine, Plant Physiology Group, United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Houston, Texas 77030, USA.
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146
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Tang G, Zhu X, Tang X, Galili G. A novel composite locus of Arabidopsis encoding two polypeptides with metabolically related but distinct functions in lysine catabolism. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2000; 23:195-203. [PMID: 10929113 DOI: 10.1046/j.1365-313x.2000.00770.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Both plants and animals catabolize lysine via saccharopine by two consecutive enzymes, lysine-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH), which are linked on a single polypeptide. We recently demonstrated that Arabidopsis plants possess not only a bifunctional LKR/SDH but in addition a monofunctional SDH enzyme. We also speculated that these two enzymes may be controlled by a single gene (G. Tang et al. Plant Cell, 1997, 9, 1305-1316). By expressing several epitope-tagged and GUS reporter constructs, we demonstrate in the present study that the Arabidopsis monofunctional SDH is encoded by a distinct gene, which is, however, nested entirely within the coding and 3' non-coding regions of the larger bifunctional LKR/SDH gene. The entire open reading frame of the monofunctional SDH gene, as well as some components of its promoter, are also parts of the translated coding sequence of the bifunctional LKR/SDH gene. These special structural characteristics, combined with the fact that the two genes encode simultaneously two metabolically related but distinct enzymes, render the LKR/SDH locus a novel type of a composite locus. Not all plant species possess an active monofunctional SDH gene and the production of this enzyme is correlated with an increased flux of lysine catabolism. Taken together, our results suggest that the composite LKR/SDH locus serves to control an efficient, highly regulated flux of lysine catabolism
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Affiliation(s)
- G Tang
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel
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147
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Diener A, Hirschi H. Heterologous expression for dominant-like gene activity. TRENDS IN PLANT SCIENCE 2000; 5:10-11. [PMID: 10637655 DOI: 10.1016/s1360-1385(99)01512-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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