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Author

Gerald E. Edwards

Other affiliations: Teikyo University, University of Karachi, Kettering University  ...read more
Bio: Gerald E. Edwards is an academic researcher from Washington State University. The author has contributed to research in topics: Photosynthesis & Phosphoenolpyruvate carboxylase. The author has an hindex of 73, co-authored 348 publications receiving 19967 citations. Previous affiliations of Gerald E. Edwards include Teikyo University & University of Karachi.


Papers
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Journal ArticleDOI
TL;DR: A new parameter, qL, is introduced, based on a Stern–Volmer approach using a lake model, which estimates the fraction of open PS II centers and should be a useful parameter for terrestrial plants consistent with a high connectivity of PS II units, whereas some marine species with distinct antenna architecture may require the use of more complex parameters based on intermediate models of the photosynthetic unit.
Abstract: A number of useful photosynthetic parameters are commonly derived from saturation pulse-induced fluorescence analysis. We show, that qP, an estimate of the fraction of open centers, is based on a pure ‘puddle’ antenna model, where each Photosystem (PS) II center possesses its own independent antenna system. This parameter is incompatible with more realistic models of the photosynthetic unit, where reaction centers are connected by shared antenna, that is, the so-called ‘lake’ or ‘connected units’ models. We thus introduce a new parameter, qL, based on a Stern–Volmer approach using a lake model, which estimates the fraction of open PS II centers. We suggest that qL should be a useful parameter for terrestrial plants consistent with a high connectivity of PS II units, whereas some marine species with distinct antenna architecture, may require the use of more complex parameters based on intermediate models of the photosynthetic unit. Another useful parameter calculated from fluorescence analysis is ΦII, the yield of PS II. In contrast to qL, we show that the ΦII parameter can be derived from either a pure ‘lake’ or pure ‘puddle’ model, and is thus likely to be a robust parameter. The energy absorbed by PS II is divided between the fraction used in photochemistry, ΦII, and that lost non-photochemically. We introduce two additional parameters that can be used to estimate the flux of excitation energy into competing non-photochemical pathways, the yield induced by downregulatory processes, ΦNPQ, and the yield for other energy losses, ΦNO.

1,383 citations

Journal ArticleDOI
19 Nov 1998-Nature
TL;DR: The results show that fluctuations in K+ levels originating within the blood vessel itself are important in regulating mammalian blood pressure and flow.
Abstract: In arteries, muscarinic agonists such as acetylcholine release an unidentified, endothelium-derived hyperpolarizing factor (EDHF) which is neither prostacyclin nor nitric oxide. Here we show that EDHF-induced hyperpolarization of smooth muscle and relaxation of small resistance arteries are inhibited by ouabain plus Ba2+; ouabain is a blocker of Na+/K+ ATPase and Ba2+ blocks inwardly rectifying K+ channels. Small increases in the amount of extracellular K+ mimic these effects of EDHF in a ouabain- and Ba2+-sensitive, but endothelium-independent, manner. Acetylcholine hyperpolarizes endothelial cells and increases the K+ concentration in the myoendothelial space; these effects are abolished by charbdotoxin plus apamin. Hyperpolarization of smooth muscle by EDHF is also abolished by this toxin combination, but these toxins do not affect the hyperpolarizaiton of smooth muscle by added K+. These data show that EDHF is K+ that effluxes through charybdotoxin- and apamin-sensitive K+ channels on endothelial cells. The resulting increase in myoendothelial K+ concentration hyperpolarizes and relaxes adjacent smooth-muscle cells by activating Ba2+-sensitive K+ channels and Na+/K+ ATPase. These results show that fluctuations in K+ levels originating within the blood vessel itself are important in regulating mammalian blood pressure and flow.

1,056 citations

Journal ArticleDOI
TL;DR: In this paper, a measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system.
Abstract: There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO2 fixed. A measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals ΦII times incident light intensity times the fraction of incident light absorbed by PSII. In C4 plants, there is a linear relationship between PSII activity and CO2 fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C4 species. In C3 plants, both CO2 fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO2, or per O2 reacting with RuBP). The rates of PSII activity associated with photosynthesis in C3 plants, based on estimates of the rates of carboxylation (vo) and oxygenation (vo) at various levels of CO2 and O2, largely account for the PSII activity determined from fluorescence measurements. Thus, in C3 plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO2 fixation.

652 citations

Journal ArticleDOI
TL;DR: Chlorophyll determinations made for leaves harvested at intervals after an ozone treatment indicated that maximum chlorophyll reduction had occurred by 4 days, which should be useful in eliminating the human bias associated with visible estimates of injury.
Abstract: A simple, rapid procedure is described for evaluating ozone injury to leaves of Phaseolus vulgaris L. cv. Pinto. Leaf chlorophyll is extracted with ethanol and analyzed spectrophotometrically; the concentration is expressed on the basis of leaf dry weight. The per cent chlorophyll reduction of ozone-injured leaves was highly correlated with the per cent visible necrosis and chlorosis ( r = 0.96). The variability in injury estimates with chlorophyll analysis was slightly less than with visual evaluation. An evaluation of chlorophyll a and b concentrations separately showed that the chlorophyll a/b ratio decreased with increasing amounts of injury. Chlorophyll determinations made for leaves harvested at intervals after an ozone treatment indicated that maximum chlorophyll reduction had occurred by 4 days. This procedure for measuring ozone injury should be useful in eliminating the human bias associated with visible estimates of injury.

388 citations

Journal ArticleDOI
TL;DR: It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO2 assimilation rates in maize.
Abstract: Analysis is made of the energetics of CO2 fixation, the photochemical quantum requirement per CO2 fixed, and sinks for utilising reductive power in the C4 plant maize. CO2 assimilation is the primary sink for energy derived from photochemistry, whereas photorespiration and nitrogen assimilation are relatively small sinks, particularly in developed leaves. Measurement of O2 exchange by mass spectrometry and CO2 exchange by infrared gas analysis under varying levels of CO2 indicate that there is a very close relationship between the true rate of O2 evolution from PS II and the net rate of CO2 fixation. Consideration is given to measurements of the quantum yields of PS II (φ PS II) from fluorescence analysis and of CO2 assimilation ( $$\phi _{CO_2 } $$ ) in maize over a wide range of conditions. The $${{\phi _{PSII} } \mathord{\left/ {\vphantom {{\phi _{PSII} } {\phi _{CO_2 } }}} \right. \kern- ulldelimiterspace} {\phi _{CO_2 } }}$$ ratio was found to remain reasonably constant (ca. 12) over a range of physiological conditions in developed leaves, with varying temperature, CO2 concentrations, light intensities (from 5% to 100% of full sunlight), and following photoinhibition under high light and low temperature. A simple model for predicting CO2 assimilation from fluorescence parameters is presented and evaluated. It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO2 assimilation rates in maize.

371 citations


Cited by
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Journal ArticleDOI
TL;DR: The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level and the role of the HKT gene family in Na(+) exclusion from leaves is increasing.
Abstract: The physiological and molecular mechanisms of tolerance to osmotic and ionic components of salinity stress are reviewed at the cellular, organ, and whole-plant level. Plant growth responds to salinity in two phases: a rapid, osmotic phase that inhibits growth of young leaves, and a slower, ionic phase that accelerates senescence of mature leaves. Plant adaptations to salinity are of three distinct types: osmotic stress tolerance, Na + or Cl − exclusion, and the tolerance of tissue to accumulated Na + or Cl − . Our understanding of the role of the HKT gene family in Na + exclusion from leaves is increasing, as is the understanding of the molecular bases for many other transport processes at the cellular level. However, we have a limited molecular understanding of the overall control of Na + accumulation and of osmotic stress tolerance at the whole-plant level. Molecular genetics and functional genomics provide a new opportunity to synthesize molecular and physiological knowledge to improve the salinity tolerance of plants relevant to food production and environmental sustainability.

9,966 citations

Journal ArticleDOI
TL;DR: An introduction for the novice into the methodology and applications of chlorophyll fluorescence is provided and a selection of examples are used to illustrate the types of information that fluorescence can provide.
Abstract: typically written from a biophysicist’s or a molecular plant physiologist’s point of view (Horton and Bowyer, Chlorophyll fluorescence analysis has become one of 1990; Krause and Weis, 1991; Govindjee, 1995). The aim the most powerful and widely used techniques avail- of this review is to provide a simple, practical guide to able to plant physiologists and ecophysiologists. This chlorophyll fluorescence for those beginners who are review aims to provide an introduction for the novice interested in applying the technique in both field and into the methodology and applications of chlorophyll laboratory situations. Whilst the principles behind the fluorescence. After a brief introduction into the theor- measurements will be discussed briefly, the emphasis will etical background of the technique, the methodology be on the applications and limitations of this technique and some of the technical pitfalls that can be encoun- in plant ecophysiology. tered are explained. A selection of examples is then used to illustrate the types of information that fluorescence can provide. The basis of chlorophyll fluorescence measurements

7,721 citations

Journal ArticleDOI
01 Jun 1980-Planta
TL;DR: Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves.
Abstract: Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.

7,312 citations

Journal ArticleDOI
TL;DR: A revised and updated classification for the families of the flowering plants is provided in this paper, which includes Austrobaileyales, Canellales, Gunnerales, Crossosomatales and Celastrales.

7,299 citations

Journal ArticleDOI
01 Jan 1989
TL;DR: In this article, the physical and enzymatic bases of carbone isotope discrimination during photosynthesis were discussed, noting how knowledge of discrimination can be used to provide additional insight into photosynthetic metabolism and the environmental influences on that process.
Abstract: We discuss the physical and enzymatic bases of carbone isotope discrimination during photosynthesis, noting how knowledge of discrimination can be used to provide additional insight into photosynthetic metabolism and the environmental influences on that process

6,246 citations