1
|
The Effects of Salts and Osmoprotectants on Enzyme Activities of Fructose-1,6-biphosphate Aldolases in a Halotolerant Cyanobacterium, Halothece sp. PCC 7418. Life (Basel) 2020; 10:life10030023. [PMID: 32182767 PMCID: PMC7151593 DOI: 10.3390/life10030023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 02/04/2023] Open
Abstract
The halotolerant cyanobacterium, Halothece sp. PCC 7418, possesses two classes of fructose-1,6-bisphosphate aldolase (FBA): H2846 and H2847. Though class I (CI)-FBA H2846 is thought to be associated with salt tolerance, the regulatory mechanisms, molecular characteristics, and expression profiles between H2846 and class II (CII)-FBA H2847 have scarcely been investigated. Here, we show that the accumulation of the H2846 protein is highly responsive to both up- and down-shock with NaCl, whereas H2847 is constitutively expressed. The activity of CI- and CII-FBA in cyanobacterial extracts is correlated with the accumulation patterns of H2846 and H2847, respectively. In addition, it was found that these activities were inhibited by NaCl and KCl, with CII-FBA activity strikingly inhibited. It was also found that the CI-FBA activity of recombinant H2846 was hindered by salts and that this hindrance could be moderated by the addition of glycine betaine (GB), whereas no moderation occurred with other potential osmoprotectant molecules (proline, sucrose, and glycerol). In addition, a phylogenetic analysis showed that CI-FBAs with higher similarities to H2846 tended to be distributed among potential GB-synthesizing cyanobacteria. Taken together, our results provide insights into the independent evolution of the CI- and CII-FBA gene families, which show distinct expression profiles and functions following salt stress.
Collapse
|
2
|
Borowitzka LJ, Demmerle S, Mackay MA, Norton RS. Carbon-13 nuclear magnetic resonance study of osmoregulation in a blue-green alga. Science 2010; 210:650-1. [PMID: 17815155 DOI: 10.1126/science.210.4470.650] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The process of osmoregulation in a unicellular blue-green alga, Synechococcus sp., has been studied by natural-abundance carbon-13 nuclear magnetic resonance spectroscopy of intact cells and cell extracts. 2-O-alpha-D-Glucopyranosylglycerol was identified as the major organic osmoregulatory solute. This demonstrates the presence of a major osmoregulatory solute in a blue-green alga and is also an example of an osmoregulatory role for glucosylglycerol.
Collapse
|
3
|
Fernandes TA, Iyer V, Apte SK. Differential responses of nitrogen-fixing cyanobacteria to salinity and osmotic stresses. Appl Environ Microbiol 2010; 59:899-904. [PMID: 16348897 PMCID: PMC202205 DOI: 10.1128/aem.59.3.899-904.1993] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Two nitrogen-fixing Anabaena strains were found to be differentially tolerant to salinity and osmotic stresses. Anabaena torulosa, a brackish-water, salt-tolerant strain, was relatively osmosensitive. Anabaena sp. strain L-31, a freshwater, salt-sensitive strain, on the other hand, displayed significant osmotolerance. Salinity and osmotic stresses affected nitrogenase activity differently. Nitrogen fixation in both of the strains was severely inhibited by the ionic, but not by the osmotic, component of salinity stress. Such differential sensitivity of diazotrophy to salinity-osmotic stresses was observed irrespective of the inherent tolerance of the two strains to salt-osmotic stress. Exogenously added ammonium conferred significant protection against salinity stress but was ineffective against osmotic stress. Salinity and osmotic stresses also affected stress-induced gene expression differently. Synthesis of several proteins was repressed by salinity stress but not by equivalent or higher osmotic stress. Salinity and osmotic stresses induced many common proteins. In addition, unique salt stress- or osmotic stress-specific proteins were also induced in both strains, indicating differential regulation of protein synthesis by the two stresses. These data show that cyanobacterial sensitivity and responses to salinity and osmotic stresses are distinct, independent phenomena.
Collapse
Affiliation(s)
- T A Fernandes
- Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre, Trombay, Bombay 400 085, India
| | | | | |
Collapse
|
4
|
Yin X, Proteau PJ. Characterization of native and histidine-tagged deoxyxylulose 5-phosphate reductoisomerase from the cyanobacterium Synechocystis sp. PCC6803. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2003; 1652:75-81. [PMID: 14580998 DOI: 10.1016/j.bbapap.2003.08.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The dxr gene encoding the 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) from the cyanobacterium Synechocystis sp. PCC6803 was expressed in Escherichia coli to produce both the native and N-terminal histidine-tagged forms of DXR. The enzymes were purified from the cell extracts using either anion exchange chromatography or metal affinity chromatography and gel filtration. The purified recombinant native and histidine-tagged enzymes each displayed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels, corresponding to the calculated subunit molecular weights of 42,500 and 46,700, respectively. By native PAGE, both enzymes were dimers under reducing conditions. The kinetic properties for the enzymes were characterized and only minor variations were observed, demonstrating that the N-terminal histidine tag does not greatly affect the activity of the enzyme. Both enzymes had similar properties to previously characterized reductoisomerases from other sources. The K(m)'s for the metal ions Mn(2+), Mg(2+), and Co(2+) were determined for native DXR for the first time, with the K(m) for Mg(2+) being approximately 200-fold higher than the K(m)'s for Mn(2+) and Co(2+).
Collapse
Affiliation(s)
- Xihou Yin
- College of Pharmacy, Pharmacy Building, Room 203, Oregon State University, Corvallis, OR 97331-3507, USA
| | | |
Collapse
|
5
|
Alahari A, Apte SK. Pleiotropic effects of potassium deficiency in a heterocystous, nitrogen-fixing cyanobacterium, Anabaena torulosa. MICROBIOLOGY (READING, ENGLAND) 1998; 144 ( Pt 6):1557-1563. [PMID: 9639926 DOI: 10.1099/00221287-144-6-1557] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Omission of potassium from the growth medium caused multiple metabolic impairments and resulted in cessation of growth of the filamentous, heterocystous, nitrogen-fixing cyanobacterium Anabaena torulosa, during both diazotrophic and nitrogen-supplemented growth. Prominent defects observed during potassium deprivation were: (i) the loss of photosynthetic pigments, (ii) impairment of photosynthetic functions, (iii) reduced synthesis of dinitrogenase reductase (Fe-protein), (iv) inhibition of nitrogenase activity, and (v) specific qualitative modifications of protein synthesis leading to the repression of twelve polypeptides and synthesis and accumulation of nine novel polypeptides. The observed metabolic defects were reversible, and growth arrested under prolonged potassium deficiency was fully restored upon re-addition of potassium. Such pleiotropic effects of potassium deficiency demonstrate that apart from its well-known requirement for pH and turgor homeostasis, K+ plays other vital specific roles in cyanobacterial growth and metabolism.
Collapse
Affiliation(s)
- Anuradha Alahari
- Cell Biology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Shree K Apte
- Cell Biology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| |
Collapse
|
6
|
Papageorgiou GC, Alygizaki-Zorba A. A sensitive method for the estimation of the cytoplasmic osmolality of cyanobacterial cells using chlorophyll a fluorescence. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1335:1-4. [PMID: 9133636 DOI: 10.1016/s0304-4165(96)00156-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- G C Papageorgiou
- National Research Center Demokritos, Institute of Biology, Athens, Greece.
| | | |
Collapse
|
7
|
Kumar Rai A. Biochemical characteristics of photosynthetic response to various external salanities in halotolerant and fresh water cyanobacteria. FEMS Microbiol Lett 1990. [DOI: 10.1111/j.1574-6968.1990.tb04196.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
8
|
Apte SK, Bhagwat AA. Salinity-stress-induced proteins in two nitrogen-fixing Anabaena strains differentially tolerant to salt. J Bacteriol 1989; 171:909-15. [PMID: 2492516 PMCID: PMC209682 DOI: 10.1128/jb.171.2.909-915.1989] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Salinity altered the protein synthesis patterns in two cyanobacterial strains: Anabaena torulosa, a salt-tolerant brackish water strain, and Anabaena sp. strain L-31, a salt-sensitive freshwater strain. The cyanobacterial response to salinity was very rapid, varied with time, and was found to be correlated with the external salt (NaCl) concentration during stress. Salinity induced three prominent types of modification. First, the synthesis of several proteins was inhibited, especially in the salt-sensitive strain; second, the synthesis of certain proteins was significantly enhanced; and third, synthesis of a specific set of proteins was induced de novo by salinity stress. Proteins which were selectively synthesized or induced de novo during salt stress, tentatively called the salt-stress proteins, were confined to an isoelectric pI range of 5.8 to 7.5 and were distributed in a molecular mass range of 12 to 155 kilodaltons. These salt-stress proteins were unique to each Anabaena strain, and their expression was apparently regulated coordinately during exposure to salt stress. In Anabaena sp. strain L-31, most of the salt-stress-induced proteins were transient in nature and were located mainly in the cytoplasm. In A. torulosa, salt-stress-induced proteins were evenly distributed in the membrane and cytoplasmic fractions and were persistent, being synthesized at high rates throughout the period of salinity stress. These initial studies reveal that salinity-induced modification of protein synthesis, as has been demonstrated in higher plant species, also occurs in cyanobacteria and that at least some of the proteins preferentially synthesized during salt stress may be important to cyanobacterial osmotic adaptation.
Collapse
Affiliation(s)
- S K Apte
- Molecular Biology & Agriculture Division, Bhabha Atomic Research Centre, Trombay, Bombay, India
| | | |
Collapse
|
9
|
|
10
|
Niven GW, Kerby NW, Rowell P, Reed RH, Stewart WD. The effects of salt on nitrogen-fixation and ammonium assimilation inAnabaena variabilis. ACTA ACUST UNITED AC 1987. [DOI: 10.1080/00071618700650471] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
|
11
|
Regulation of S-adenosylhomocysteine hydrolase in the halophilic cyanobacterium Aphanothece halophytica: a possible role in glycinebetaine biosynthesis. Arch Microbiol 1987. [DOI: 10.1007/bf00423134] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
12
|
Apte SK, Reddy BR, Thomas J. Relationship between Sodium Influx and Salt Tolerance of Nitrogen-Fixing Cyanobacteria. Appl Environ Microbiol 1987; 53:1934-9. [PMID: 16347419 PMCID: PMC204028 DOI: 10.1128/aem.53.8.1934-1939.1987] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The relationship between sodium uptake and cyanobacterial salt (NaCl) tolerance has been examined in two filamentous, heterocystous, nitrogen-fixing species of
Anabaena.
During diazotrophic growth at neutral pH of the growth medium,
Anabaena
sp. strain L-31, a freshwater strain, showed threefold higher uptake of Na
+
than
Anabaena torulosa
, a brackish-water strain, and was considerably less salt tolerant (50% lethal dose of NaCl, 55 mM) than the latter (50% lethal dose of NaCl, 170 mM). Alkaline pH or excess K
+
(>25 mM) in the medium causes membrane depolarization and inhibits Na
+
influx in both cyanobacteria (S. K. Apte and J. Thomas, Eur. J. Biochem. 154:395-401, 1986). The presence of nitrate or ammonium in the medium caused inhibition of Na
+
influx accompanied by membrane depolarization. These experimental manipulations affecting Na
+
uptake demonstrated a good negative correlation between Na
+
influx and salt tolerance. All treatments which inhibited Na
+
influx (such as alkaline pH, K
+
above 25 mM, NO
3
−
, and NH
4
+
), enhanced salt tolerance of not only the brackish-water but also the freshwater cyanobacterium. The results indicate that curtailment of Na
+
influx, whether inherent or effected by certain environmental factors (e.g., combined nitrogen, alkaline pH), is a major mechanism of salt tolerance in cyanobacteria.
Collapse
Affiliation(s)
- S K Apte
- Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre, Trombay, Bombay 400 085, India
| | | | | |
Collapse
|
13
|
A glycine betaine transport system in Aphanothece halophytica and other glycine betaine-synthesising cyanobacteria. Arch Microbiol 1987. [DOI: 10.1007/bf00406140] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
14
|
Abstract
Microorganisms have the ability to adapt to a wide range of NaCl concentrations. In general the NaCl tolerance shown by microbes far exceeds the salt tolerance of any other organism, procryote or eukaryote. There are at least three mechanisms available for adaptation to different salt concentrations. The first would be a passive one in which the cytoplasmic ion content would always equal that in the medium. A second mechanism which is used by many organisms involves concentrating compatible solutes to create an osmotic balance between the cytoplasm and the external environment. The third mechanism involves changing the cell physiology to control the movement of water allowing the cell to exist with an ionically dilute cytoplasm. This article will review the major developments and discuss the implications of increasing knowledge about salt tolerance in microorganisms.
Collapse
Affiliation(s)
- R H Vreeland
- Department of Biology, University of New Orleans, Louisiana
| |
Collapse
|
15
|
Reed R, Borowitzka L, Mackay M, Chudek J, Foster R, Warr S, Moore D, Stewart W. Organic solute accumulation in osmotically stressed cyanobacteria. FEMS Microbiol Lett 1986. [DOI: 10.1111/j.1574-6968.1986.tb01842.x] [Citation(s) in RCA: 150] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
|
16
|
Apte SK, Thomas J. Membrane electrogenesis and sodium transport in filamentous nitrogen-fixing cyanobacteria. EUROPEAN JOURNAL OF BIOCHEMISTRY 1986; 154:395-401. [PMID: 3080316 DOI: 10.1111/j.1432-1033.1986.tb09411.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Transport of Na+ and its relationship with membrane potential (delta psi m) was examined in Anabaena L-31 (a fresh water cyanobacterium) and Anabaena torulosa (a brackish water cyanobacterium) which require Na+ for diazotrophic growth. The data on the effect of N,N'-dicyclohexylcarbodiimide indicated that delta psi m was generated by electrogenic proton extrusion predominantly mediated by ATPase(s). In addition, operation of a plasmalemmabound, non-ATP-requiring, H+-pumping terminal oxidase was suggested by the sensitivity of delta psi m to anaerobiosis, cyanide and azide, all of which inhibit aerobic respiration. The response of delta psi m to external pH and external Na+ or K+ concentrations indicated that a diffusion potential of Na+ or K+ may not contribute significantly to delta psi m. Kinetic studies showed that Na+ influx was unlikely to be a result of Na+/NA+ exchange but was a carrier-mediated secondary active transport insensitive to low concentrations (less than 10 mM) of external K+. There was a close correspondence between changes in delta psi m and Na+ influx; all the treatments which caused depolarisation (such as low temperature, dark, cyanide, azide, anaerobiosis, ATPase inhibitors) lowered Na+ influx whereas treatments which caused hyperpolarisation (such as 2,4-dinitrophenol, nigericin) enhanced Na+ influx. Remarkably low intracellular Na+ concentrations were maintained by these cyanobacteria by means of active efflux of the cation. The basic mechanism of Na+ transport in the fresh water and the brackish water cyanobacterium was similar but the latter demonstrated less influx, more efficient efflux, more affinity of carriers for Na+ and less accumulation of Na+, all attributes favouring salt tolerance.
Collapse
|
17
|
Changes in turgor pressure in response to increases in external NaCl concentration in the gas-vacuolate cyanobacterium Microcystis sp. Arch Microbiol 1985. [DOI: 10.1007/bf00411252] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
|
18
|
Reed RH, Warr SR, Richardson DL, Moore DJ, Stewart WD. Multiphasic osmotic adjustment in a euryhaline cyanobacterium. FEMS Microbiol Lett 1985. [DOI: 10.1111/j.1574-6968.1985.tb00796.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
|
19
|
Reed RH, Richardson DL, Stewart WD. Na+ uptake and extrusion in the cyanobacterium SynechocystisPCC6714 in response to hypersaline treatment. Evidence for transient changes in plasmalemma Na+ permeability. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1985. [DOI: 10.1016/0005-2736(85)90455-9] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
20
|
|
21
|
Reed RH, Chudek JA, Foster R, Stewart WDP. Osmotic adjustment in cyanobacteria from hypersaline environments. Arch Microbiol 1984. [DOI: 10.1007/bf00410900] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
22
|
Takabe T, Rai AK, Akazawa T. Interaction of constituent subunits in ribulose 1,5-bisphosphate carboxylase from Aphanothece halophytica. Arch Biochem Biophys 1984; 229:202-11. [PMID: 6422849 DOI: 10.1016/0003-9861(84)90145-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) from the halophilic cyanobacterium, Aphanothece halophytica, dissociates into catalytic core (large subunit A oligomer) and small subunit B under low ionic strength during sucrose density gradient centrifugation. Supplementation of KCl, NaCl, or K2SO4 ( [I] = 0.3 M) partly prevents the dissociation, the preventive effect of divalent cation salts such as MgCl2 and CaCl2 being more effective than monovalent cation salts. RuBisCO with its higher-plant-type molecular form can be isolated from the cyanobacterial extracts using gradient medium containing 0.3 M KCl, 20 mM MgCl2, and 10 mM CaCl2. The isolated enzyme contains large subunit A and small subunit B in a molar ratio of approximately 1:1, estimated from the densitometric scanning of Coomassie blue-stained gels. During the second sucrose density gradient centrifugation to remove minor contaminants, a small amount of subunit B is depleted from the holoenzyme. Determination of the molecular weight by equilibrium centrifugation and electron microscopic observation have confirmed that the cyanobacterial RuBisCO has an A8B8-type structure. The enzyme activity per se is found to be sensitive to concentrations of salts, and small subunit B is obligatory for the enzyme catalysis. It has been shown that the more the enzyme activity is inhibited by salts, the tighter the association of subunit B becomes. It is likely that the active enzyme retains the loose conformational structure to such an extent that the dissociable release of subunit B from the holoenzyme in vivo is not allowed.
Collapse
|
23
|
Mohammad F, Reed R, Stewart W. The halophilic cyanobacteriumSynechocystisDUN52 and its osmotic responses. FEMS Microbiol Lett 1983. [DOI: 10.1111/j.1574-6968.1983.tb00304.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
24
|
Reed RH, Rowell P, Stewart WD. Characterization of the transport of potassium ions in the cyanobacterium Anabaena variabilis Kütz. EUROPEAN JOURNAL OF BIOCHEMISTRY 1981; 116:323-30. [PMID: 6788551 DOI: 10.1111/j.1432-1033.1981.tb05337.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Interrelationships between potassium-ion transport and transplasmalemma electrical-potential difference (delta psi m) have been investigated in Anabaena variabilis (ATCC 29413) by measuring K+ translocation and membrane potential in parallel. At pH 7.0, 5 mmol . dm-3 external K+, there was a thirtyfold accumulation of K+. The K+ equilibrium potential was lower (more negative) than the measured membrane potential by up to 20 mV, (delta psi K+ = -90 mV; delta psi m = -70 mV to -75 mV, respectively). Dark pretreatment and low temperature (4 degrees C) reduced internal K+ and depolarized delta psi m. External pH affected K+ translocation and membrane potential; delta psi m was hyperpolarized at high external pH; transplasmalemma K+ fluxes and internal K+ concentration were also increased at high pH. The effects of pH upon delta psi m, coupled with the finding that the membrane potential was relatively insensitive to external K+, suggest that delta psi m is unlikely to be due primarily to a diffusion potential of K+, but that the membrane potential is maintained by an electrogenic proton-extrusion mechanism. There was no close (obligate) link between K+ transport and changes in delta psi m. Carbonylcyanide m-chlorophenylhydrazone decreased K+ fluxes, internal K+ and delta psi m when added in amounts up to 100 mumol . dm-3. However, delta psi K+ was always more negative than delta psi m. Valinomycin up to concentrations of 50 mumol . dm-3 increased transplasmalemma K+ fluxes by up to 300%, while changes in delta psi m were negligible. Internal K+ was unaffected by valinomycin. N,N'-Dicyclohexylcarbodiimide at concentrations up to 100 mumol . dm-3, reduced K+ flux rates and caused a hyperpolarization of delta psi m. These observations suggest that delta psi m is primarily due to electron transport reactions at the plasmalemma and that K+ transport is energy-dependent. In the presence of dicyclohexylcarbodiimide, internal K+ redistributed in accordance with the membrane potential, suggesting that passive uniport in response to delta psi m (i.e. secondary active transport) is not usually important but may operate when primary active mechanisms are blocked.
Collapse
|
25
|
|
26
|
|
27
|
Larsen H. Chapter 3 Ecology of Hypersaline Environments. ACTA ACUST UNITED AC 1980. [DOI: 10.1016/s0070-4571(08)70227-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
|
28
|
Maier M, Kappen L. Cellular compartmentalization of salt ions and protective agents with respect to freezing tolerance of leaves : Investigations with the Halophyte Halimione portulacoides (L.) aellen. Oecologia 1979; 38:303-316. [PMID: 28309490 DOI: 10.1007/bf00345190] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/1978] [Indexed: 10/26/2022]
Abstract
Evidence was given that the freezing tolerance of Halimione portulacoides, a wintergreen halophyte, can be explained by protection of sensitive cellular membranes in vivo. Experiments were done with cloned cuttings of a plant from the German North Sea coast. One series received no NaCl (O-plants) the other 3% NaCl (NaCl-plants) in the nutrient solution. During the annual course Na+ and Cl- of the O-plant leaves remained on a nearly constant low level. In the leaves of the NaCl-plants Na+ and Cl- concentrations changed strongly during year and reached a maximum in winter. Potassium was always on a low level. The freezing tolerance curves showed a minimum in summer and a maximum in winter. The small difference between the freezing tolerance peaks of the NaCl- and O-plants indicated that the increased salt stress did not affect freezing tolerance very much. Freezing stress in cellular membranes, like thylacoids, acts in the same way as increasing salt concentration; consequently both together must amplify the stress. For the analysis of their ion contents chloroplasts of H. portulacoides were non-aqueously isolated from leaves with different freezing tolerance during the year. In midwinter, when freezing tolerance was highest, the chloroplasts of the NaCl-plants contained about 250 mM chloride (O-plants c. 150 mM), while the non-plastidic fraction of the cell contained about 1 M (O-plants c. 400 mM) chloride. On the other hand citrate reached high concentrations in the chloroplasts in winter. Non-volatile organic acids like citrate are known to compensate colligatively the injurious action of the inorganic salt ions on thylacoids in vitro (Heber and Santarius, 1976). The molar proportion between chloride and citrate in H. portulacoides chloroplasts decreased with increasing freezing tolerance and reached values which were protective on chloroplast membranes in vitro. This relationship in vivo with H. portulacoides provides evidence supplying the concept of colligative protection of cellular membranes. Besides citrate also malate may act as a colligatively protecting agent against the amplified salt stress by freezing.
Collapse
Affiliation(s)
- Maria Maier
- Lehrstuhl für Botanik II der Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany
| | - Ludger Kappen
- Lehrstuhl für Botanik II der Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany
| |
Collapse
|