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Wall S, Vialet‐Chabrand S, Davey P, Van Rie J, Galle A, Cockram J, Lawson T. Stomata on the abaxial and adaxial leaf surfaces contribute differently to leaf gas exchange and photosynthesis in wheat. THE NEW PHYTOLOGIST 2022; 235:1743-1756. [PMID: 35586964 PMCID: PMC9545378 DOI: 10.1111/nph.18257] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 04/06/2022] [Indexed: 05/12/2023]
Abstract
Although stomata are typically found in greater numbers on the abaxial surface, wheat flag leaves have greater densities on the adaxial surface. We determine the impact of this less common stomatal patterning on gaseous fluxes using a novel chamber that simultaneously measures both leaf surfaces. Using a combination of differential illuminations and CO2 concentrations at each leaf surface, we found that mesophyll cells associated with the adaxial leaf surface have a higher photosynthetic capacity than those associated with the abaxial leaf surface, which is supported by an increased stomatal conductance (driven by differences in stomatal density). When vertical gas flux at the abaxial leaf surface was blocked, no compensation by adaxial stomata was observed, suggesting each surface operates independently. Similar stomatal kinetics suggested some co-ordination between the two surfaces, but factors other than light intensity played a role in these responses. Higher photosynthetic capacity on the adaxial surface facilitates greater carbon assimilation, along with higher adaxial stomatal conductance, which would also support greater evaporative leaf cooling to maintain optimal leaf temperatures for photosynthesis. Furthermore, abaxial gas exchange contributed c. 50% to leaf photosynthesis and therefore represents an important contributor to overall leaf gas exchange.
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Affiliation(s)
- Shellie Wall
- School of Life SciencesUniversity of EssexColchesterCO4 3SQUK
| | | | - Phillip Davey
- School of Life SciencesUniversity of EssexColchesterCO4 3SQUK
| | - Jeroen Van Rie
- BASF BBCC – Innovation Center GentTechnologiepark‐Zwijnaarde 1019052GhentBelgium
| | - Alexander Galle
- BASF BBCC – Innovation Center GentTechnologiepark‐Zwijnaarde 1019052GhentBelgium
| | | | - Tracy Lawson
- School of Life SciencesUniversity of EssexColchesterCO4 3SQUK
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2
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Santelia D, Lawson T. Rethinking Guard Cell Metabolism. PLANT PHYSIOLOGY 2016; 172:1371-1392. [PMID: 27609861 PMCID: PMC5100799 DOI: 10.1104/pp.16.00767] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 08/27/2016] [Indexed: 05/18/2023]
Abstract
Stomata control gaseous fluxes between the internal leaf air spaces and the external atmosphere and, therefore, play a pivotal role in regulating CO2 uptake for photosynthesis as well as water loss through transpiration. Guard cells, which flank the stomata, undergo adjustments in volume, resulting in changes in pore aperture. Stomatal opening is mediated by the complex regulation of ion transport and solute biosynthesis. Ion transport is exceptionally well understood, whereas our knowledge of guard cell metabolism remains limited, despite several decades of research. In this review, we evaluate the current literature on metabolism in guard cells, particularly the roles of starch, sucrose, and malate. We explore the possible origins of sucrose, including guard cell photosynthesis, and discuss new evidence that points to multiple processes and plasticity in guard cell metabolism that enable these cells to function effectively to maintain optimal stomatal aperture. We also discuss the new tools, techniques, and approaches available for further exploring and potentially manipulating guard cell metabolism to improve plant water use and productivity.
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Affiliation(s)
- Diana Santelia
- Department of Plant and Microbial Biology, University of Zürich, 8008 Zurich, Switzerland (D.S.); and
- School of Biological Science, University of Essex, Colchester CO4 3SQ, United Kingdom (T.L.)
| | - Tracy Lawson
- Department of Plant and Microbial Biology, University of Zürich, 8008 Zurich, Switzerland (D.S.); and
- School of Biological Science, University of Essex, Colchester CO4 3SQ, United Kingdom (T.L.)
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3
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Krabel D, Bodson M, Eschrich W. Seasonal Changes in the Cambium of Trees. I. Sucrose Content inThuja occidentalis. ACTA ACUST UNITED AC 2014. [DOI: 10.1111/j.1438-8677.1994.tb00408.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
Chloroplasts are a key feature of most guard cells; however, the function of these organelles in stomatal responses has been a subject of debate. This review examines evidence for and against a role of guard cell chloroplasts in stimulating stomatal opening. Controversy remains over the extent to which guard cell Calvin cycle activity contributes to stomatal regulation. However, this is only one of four possible functions of guard cell chloroplasts; other roles include supply of ATP, blue-light signalling and starch storage. Evidence exists for all these mechanisms, but is highly dependent upon species and growth/measurement conditions, with inconsistencies between different laboratories reported. Significant plasticity and extreme flexibility in guard cell osmoregulatory, signalling and sensory pathways may be one explanation. The use of chlorophyll a fluorescence analysis of individual guard cells is discussed in assessing guard and mesophyll cell physiology in relation to stomatal function. Developments in transgenic and molecular techniques have recently provided interesting, albeit contrasting, data regarding the role of these highly conserved organelles in stomatal function. Recent studies examining the link between mesophyll photosynthesis and stomatal conductance are discussed. An enhanced understanding of these processes may be fundamental in generating crop plants with greater water use efficiencies, capable of combating future climatic changes.
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Affiliation(s)
- Tracy Lawson
- Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK
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Roelfsema MRG, Hedrich R. In the light of stomatal opening: new insights into 'the Watergate'. THE NEW PHYTOLOGIST 2005; 167:665-91. [PMID: 16101906 DOI: 10.1111/j.1469-8137.2005.01460.x] [Citation(s) in RCA: 303] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO2 uptake and close to prevent excessive loss of water. Movement of these 'Watergates' is regulated by environmental conditions, such as light, CO2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K+ salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light-specific and photosynthetic-active radiation-dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross-talk, as multiple signaling pathways induce both short- and long-term responses in these sensory cells.
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Affiliation(s)
- M Rob G Roelfsema
- Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Würzburg University, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany
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6
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Stadler R, Büttner M, Ache P, Hedrich R, Ivashikina N, Melzer M, Shearson SM, Smith SM, Sauer N. Diurnal and light-regulated expression of AtSTP1 in guard cells of Arabidopsis. PLANT PHYSIOLOGY 2003; 133:528-37. [PMID: 12972665 PMCID: PMC219029 DOI: 10.1104/pp.103.024240] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2003] [Revised: 04/21/2003] [Accepted: 05/15/2003] [Indexed: 05/18/2023]
Abstract
Guard cell chloroplasts are unable to perform significant photosynthetic CO2 fixation via Rubisco. Therefore, guard cells depend on carbon supply from adjacent cells even during the light period. Due to their reversible turgor changes, this import cannot be mediated by plasmodesmata. Nevertheless, guard cells of several plants were shown to use extracellular sugars or to accumulate sucrose as an osmoticum that drives water influx to increase stomatal aperture. This paper describes the first localization of a guard cell-specific Arabidopsis sugar transporter involved in carbon acquisition of these symplastically isolated cells. Expression of the AtSTP1 H+-monosacharide symporter gene in guard cells was demonstrated by in situ hybridization and by immunolocalization with an AtSTP1-specific antiserum. Additional RNase protection analyses revealed a strong increase of AtSTP1 expression in the dark and a transient, diurnally regulated increase during the photoperiod around midday. This transient increase in AtSTP1 expression correlates in time with the described guard cell-specific accumulation of sucrose. Our data suggest a function of AtSTP1 in monosaccharide import into guard cells during the night and a possible role in osmoregulation during the day.
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Affiliation(s)
- Ruth Stadler
- Molekulare Pflanzenphysiologie, Universität Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany
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7
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Outlaw WH, De Vlieghere-He X. Transpiration rate. An important factor controlling the sucrose content of the guard cell apoplast of broad bean. PLANT PHYSIOLOGY 2001; 126:1716-24. [PMID: 11500569 PMCID: PMC117170 DOI: 10.1104/pp.126.4.1716] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2001] [Revised: 05/05/2001] [Accepted: 05/22/2001] [Indexed: 05/20/2023]
Abstract
Evaporation of water from the guard cell wall concentrates apoplastic solutes. We hypothesize that this phenomenon provides two mechanisms for responding to high transpiration rates. First, apoplastic abscisic acid is concentrated in the guard cell wall. Second, by accumulating in the guard cell wall, apoplastic sucrose (Suc) provides a direct osmotic feedback to guard cells. As a means of testing this second hypothesized mechanism, the guard cell Suc contents at a higher transpiration rate (60% relative humidity [RH]) were compared with those at a lower transpiration rate (90% RH) in broad bean (Vicia faba), an apoplastic phloem loader. In control plants (constant 60% RH), the guard cell apoplast Suc content increased from 97 +/- 81 femtomol (fmol) guard cell pair(-1) to 701 +/- 142 fmol guard cell pair(-1) between daybreak and midday. This increase is equivalent to approximately 150 mM external, which is sufficient to decrease stomatal aperture size. In plants that were shifted to 90% RH before daybreak, the guard cell apoplast Suc content did not increase during the day. In accordance, in plants that were shifted to 90% RH at midday, the guard cell apoplast Suc content declined to the daybreak value. Under all conditions, the guard cell symplast Suc content increased during the photoperiod, but the guard cell symplast Suc content was higher (836 +/- 33 fmol guard cell pair(-1)) in plants that were shifted to 90% RH. These results indicate that a high transpiration rate may result in a high guard cell apoplast Suc concentration, which diminishes stomatal aperture size.
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Affiliation(s)
- W H Outlaw
- Department of Biological Science, Biology Unit I, Florida State University, Tallahassee, Florida 32306-4370, USA
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La Cognata U, Willmitzer L, Müller-Röber B. Molecular cloning and characterization of novel isoforms of potato ADP-glucose pyrophosphorylase. MOLECULAR & GENERAL GENETICS : MGG 1995; 246:538-48. [PMID: 7700228 DOI: 10.1007/bf00298960] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
ADP-glucose pyrophosphorylase (AGPase) is one of the major enzymes involved in starch biosynthesis in higher plants. We report here the molecular cloning of two cDNAs encoding so far uncharacterized isoforms (AGP S2 and AGP S3) of the potato enzyme. Sequence analysis shows that the two polypeptides are more homologous to previously identified large subunit polypeptides from potato and other plant species than to small subunit isoforms. This observation suggest that AGP S2 and AGP S3 represent novel large subunit polypeptides. agpS2 is expressed in several tissues of the potato plant, including leaves and tubers. Expression was stronger in sink leaves than in source leaves, indicating developmental regulation. In leaves, agpS2 expression was induced 2- to 3-fold by exogenous sucrose; therefore, agpS2 represents a new sucrose-responsive gene of starch metabolism. Expression of agpS3 was restricted to tubers: no agpS3 expression could be seen in leaves of different developmental stages, or when leaves were incubated in sucrose. Therefore, agpS3 represents the only AGPase gene so far characterized from potato, which is not expressed in leaves. Conversely, all four AGPase isoforms known from potato are expressed in tubers.
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Affiliation(s)
- U La Cognata
- Institut für Genbiologische Forschung Berlin GmbH, Germany
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9
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Müller-Röber B, La Cognata U, Sonnewald U, Willmitzer L. A truncated version of an ADP-glucose pyrophosphorylase promoter from potato specifies guard cell-selective expression in transgenic plants. THE PLANT CELL 1994; 6:601-612. [PMID: 8038601 PMCID: PMC160462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
ADP-glucose pyrophosphorylase (AGPase) is a key regulatory enzyme in starch biosynthesis in higher plants. A 3.2-kb promoter of the large subunit gene of the AGPase from potato has been isolated and its activity analyzed in transgenic potato and tobacco plants using a promoter-beta-glucuronidase fusion system. The promoter was active in various starch-containing cells, including guard cells, tuber parenchyma cells, and the starch sheath layer of stems and petioles. No expression was observed in mesophyll cells. Analysis of various promoter derivatives showed that with respect to expression in petioles and stems, essential elements must be located in the 5' distal region of the promoter, whereas elements important for expression in tuber parenchyma cells are located in an internal fragment comprising nucleotides from positions -500 to -1200. Finally, a 0.3-kb 5' proximal promoter fragment was identified that was sufficient to obtain exclusive expression in guard cells of transgenic potato and tobacco plants. The implications of our observations are discussed with respect to starch synthesis in various tissues and the use of the newly identified promoter as a tool for stomatal biology.
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Affiliation(s)
- B Müller-Röber
- Institut für Genbiologische Forschung Berlin GmbH, Germany
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Rieger A, Hampp R. Intercellular compartmentation of basic carbon pathways in motor organs (pulvini) of leaves of Phaseolus coccineus L. PLANTA 1991; 184:415-421. [PMID: 24194161 DOI: 10.1007/bf00195345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/1990] [Accepted: 01/28/1991] [Indexed: 06/02/2023]
Abstract
The activities of enzymes which catalyze one step in each of the five major carbon pathways in green plants were measured in secondary pulvini and other tissues of Phaseolus coccineus L. leaves. We were able to detect activities of fumarase (EC 4.2.1.2; tricarboxylic-acid pathway), NAD-glyceraldehyde-phosphate dehydrogenase (NAD-GAPDH, EC 1.2.1.12; glycolysis), 6-phosphogluconate dehydrogenase (6-PGDH, EC 1.1.1.44; oxidative pentose-phosphate pathway), ribulose-1, 5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39; photosynthetic carbon-reduction pathway), and of hydroxypyruvate reductase (HP-R, EC 1.1.1.81; photosynthetic carbon-oxidation pathway). On a protein basis the activities of Rubisco and HP-R in pulvinar regions were very low (below 1 and 2 mol · (kg protein) (--1) · h(--1), respectively), but the activities of fumarase and NAD-GAPDH were between 10- and 5-fold higher compared with the laminar tissue (up to 7 and 50 mol · (kg protein)(--1) · h(--1), respectively). Similarly, the protein specific activities of 6-PGDH were increased in the pulvinus (3-4 compared with approx. 1 mol · (kg protein)(--1) · h(--1) in the leaf blade). No differences in specific activities were detected between day and night positions of the leaves. By applying quantitative histochemical techniques we determined the longitudinal and transversal compartmentation of the activities of fumarase, NAD-GAPDH, and 6-PGDH in pulvinar tissues. Levels of activity of all three enzymes increased towards the middle part of the pulvinus. Here, expressed on a dry-weight (DW) basis, the analysis of cross sections showed highest activities in the outer parts of the extensor in the order given, approx. 0.6, 5, and 0.25 mol · (kg DW)(--1) · h(--1) for fumarase, NAD-GAPDH and 6-PGDH. When related to protein, levels of activity were comparably high within the inner parts of extensor and flexor, and partly also in the abaxial part of the bundle (fumarase, 6-PGDH). The tissue-specific compartmentation of the respective activities is discussed in relation to leaf movement and shows parallels with guard-cell function.
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Affiliation(s)
- A Rieger
- Physiologische Ökologie der Pflanzen, Universität Tübingen, Auf der Morgenstelle 1, W-7400, Tübingen, Germany
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12
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Robinson NL, Preiss J. Localization of Carbohydrate Metabolizing Enzymes in Guard Cells of Commelina communis. PLANT PHYSIOLOGY 1987; 85:360-4. [PMID: 16665702 PMCID: PMC1054260 DOI: 10.1104/pp.85.2.360] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The localization of enzymes involved in the flow of carbon into and out of starch was determined in guard cells of Commelina communis. The guard cell chloroplasts were separated from the rest of the cellular components by a modification of published microfuge methods. The enzymes of interest were then assayed in the supernatant and chloroplast fractions. The chloroplast yield averaged 75% with 10% cytoplasmic contamination. The enzymes involved in starch biosynthesis, ADPglucose pyrophosphorylase, starch synthase, and branching enzyme, are located exclusively in the chloroplast fraction. The enzymes involved in starch degradation show a more complex distribution. Phosphorylase is located in both the supernatant and chloroplast fraction, 50% in each fraction. Most of the amylase and debranching enzyme activity is present in the supernatant (70%) fraction. The majority of the rest of the enzymes involved in the degradation of starch to malate and synthesis of starch from a hexose precursor were also investigated. All of the enzymes were present in the chloroplast except for hexokinase and phosphofructokinase. The inability to assay these enzymes could possibly have been due to the lack of or low activity of the enzymes or to nonoptimal assay conditions.
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Affiliation(s)
- N L Robinson
- Department of Biochemistry and Biophysics, University of California, Davis, California 95616
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13
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Pospišilová J, Solárová J. References no. 12912-14765/ABD-ZUR. WATER-IN-PLANTS BIBLIOGRAPHY 1986:1-121. [DOI: 10.1007/978-94-009-4816-7_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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Caspar T, Huber SC, Somerville C. Alterations in Growth, Photosynthesis, and Respiration in a Starchless Mutant of Arabidopsis thaliana (L.) Deficient in Chloroplast Phosphoglucomutase Activity. PLANT PHYSIOLOGY 1985; 79:11-7. [PMID: 16664354 PMCID: PMC1074821 DOI: 10.1104/pp.79.1.11] [Citation(s) in RCA: 374] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
A mutant of Arabidopsis thaliana (L.) Heynh. which lacks leaf starch was isolated by screening for plants which did not stain with iodine. The starchless phenotype, confirmed by quantitative enzymic analysis, is caused by a single recessive nuclear mutation which results in a deficiency of the chloroplast isozyme of phosphoglucomutase. When grown in a 12-h photoperiod, leaves of the wild-type accumulated substantial amounts of starch but lower levels of soluble sugars. Under these conditions, the mutant accumulated relatively high levels of soluble sugars. Rates of growth and net photosynthesis of the mutant and wild-type were indistinguishable when the plants were grown in constant illumination. However, in a short photoperiod, the growth of the mutant was severely impaired, the rate of photosynthesis was depressed relative to the wild-type, and the rate of dark respiration, which was high following the onset of darkness, exhibited an uncharacteristic decay throughout the dark period. The altered control of respiration by the mutant, which may be related to the relatively high levels of soluble carbohydrate that accumulate in the leaf and stem tissue, is believed to be partially responsible for the low growth rate of the mutant in short days. The depressed photosynthetic capacity of the mutant may also reflect a metabolic adaptation to the accumulation of high levels of soluble carbohydrate which mimics the effects of alterations in source/sink ratio. The activities of sucrose phosphate synthase and acid invertase are significantly higher in the mutant than in the wild-type whereas ADP-glucose pyrophosphorylase activity is lower. This suggests that the activities of these enzymes may be modulated in response to metabolite concentrations or flux through the pathways.
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Affiliation(s)
- T Caspar
- DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824
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Outlaw WH, Springer SA, Tarczynski MC. Histochemical technique : a general method for quantitative enzyme assays of single cell ;extracts' with a time resolution of seconds and a reading precision of femtomoles. PLANT PHYSIOLOGY 1985; 77:659-66. [PMID: 16664116 PMCID: PMC1064582 DOI: 10.1104/pp.77.3.659] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Biochemists who study single cells have been constrained by the lack of a general methodology of high time resolution and high measurement sensitivity for quantitatively assaying enzyme activities using natural substrates in solution. The methods we describe will remove this limitation. In brief, nanogram tissue samples are dissected from frozen-dried tissue. The samples are ;extracted' in microdroplets of assay cocktail. The enzyme activity, indicated fluorometrically by the oxidation/reduction of NAD(P), is followed in real time on a computer display. In the development of this method, we evaluated several parameters required for optimization; the most important of these evaluations, including numerous empirically derived relationships, are reported here and in supplemental material provided with reprints.With these methods, assays of pyruvate orthophosphate dikinase on samples enriched in bundlesheath cells and mesophyll cells of Flaveria brownii yielded the predictable results. Assays of this enzyme in guard cells dissected from Vicia faba leaflets gave results like those recently reported by another laboratory for protoplasts derived from these cells. The results of assays by this method and by enzymic cycling for NAD(P)triose-P dehydrogenase were comparable. Phosphoenolpyruvate carboxylase, the most extensively studied enzyme activity, was present at high levels in guard cells, which has been demonstrated previously in other reports based on diverse assay approaches.
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Affiliation(s)
- W H Outlaw
- Biology Unit I, Florida State University, Tallahassee, Florida 32306
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Outlaw WH, Tarczynski MC, Miller WI. Histological Compartmentation of Phosphate in Vicia faba L. Leaflet : Possible Significance to Stomatal Functioning. PLANT PHYSIOLOGY 1984; 74:430-3. [PMID: 16663435 PMCID: PMC1066695 DOI: 10.1104/pp.74.2.430] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Guard cells, epidermal cells, palisade parenchyma cells, and spongy parenchyma cells of Vicia faba L. leaflet were analyzed for inorganic phosphate and phosphorus. On a molar basis, cells in the epidermal layer contained about 15-fold more inorganic phosphate than mesophyll cells did. Although a metabolic role for this asymmetric distribution cannot be defined unequivocally, we note that high epidermal inorganic phosphate would buffer against pH changes in the epidermis during stomatal movements.
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Affiliation(s)
- W H Outlaw
- Biology Unit 1, Florida State University, Tallahassee, Florida 32306
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