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PubMed1997

The effect of reciprocal treatments with ozone and ultraviolet-B radiation on photosynthesis and growth of perennial grass Elymus athericus.

The impact on plant growth of the simultaneously changing factors of the global climate, rising tropospheric O3 concentrations and increasing UV-B radiation fluxes, has been tested in a combined glasshouse and growth chamber experiment. The saltmarsh grass species Elymus athericus was sequentially fumigated for two weeks with O3 and for another two weeks irradiated with UV-B (vv). Exposure to elevated UV-B did not negatively affect photosynthesis or plant growth. Fumigation with O3 had a depressing effect on net photosynthesis, the number and biomass of flowers, the number of leaves and the number of shoots. O3-induced damage only was observed in plants which had been fumigated during the last two weeks of the experiment. Since interactive responses were not observed, results suggest different primary target sites for O3 and UV-B within the plant.

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PubMed2000

Bicentenary homage to Dr Jan Ingen-Housz, MD (1730-1799), pioneer of photosynthesis research.

On September 7, 1999, the 200th anniversary of the death of Dr Jan Ingen-Housz was commemorated by ceremonies in Calne, England. Ingen-Housz discovered the action of light in photosynthesis in 1779, following Joseph Priestley's demonstration that green plants had the capacity to produce oxygen. Priestley's claim for priority in discovering the light requirement of photosynthesis is examined.

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PubMed2000

The golden age of biochemical research in photosynthesis.

The perspectives and enthusiasms recorded in this review describe the events I witnessed and, in small ways, contributed to. Two great rewards emerged from my experiences - the pleasure of doing experiments and the great wealth of friendships with students and colleagues. As a graduate student, phenomena appeared at the bench before me which clarified the coupling of electron transport to ATP synthesis. My first PhD graduate student measured concentrations of pyridine nucleotides in chloroplasts and his results have been often confirmed and well used. All of the many graduate students who followed contributed to our understanding of photosynthesis. I have taken much pleasure from documenting the details of photosynthetic phosphorylation and electron transport in cyanobacteria. Studies of the 'c' type cytochromes in these organisms continue to fascinate me. My experiences in government in its efforts to promote research are unusual, perhaps unique. A rare event outside the laboratory - a natural bloom of cyanobacteria - stimulated new thoughts and special opportunities for laboratory science. Photosynthesis seems magisterial in its shaping of our planet and its biology and in the details of its cleverness that were revealed in the time of my witness.

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PubMed2000

A mathematical model of C(4) photosynthesis: The mechanism of concentrating CO(2) in NADP-malic enzyme type species.

A computer model comprising light reactions in PS II and PS I, electron-proton transport reactions in mesophyll and bundle sheath chloroplasts, all enzymatic reactions and most of the known regulatory functions of NADP-ME type C(4) photosynthesis has been developed as a system of differential budget equations for intermediate compounds. Rate-equations were designed on principles of multisubstrate-multiproduct enzyme kinetics. Some of the 275 constants needed (DeltaG(0)' and K (m) values) were available from literature and others (V (m)) were estimated from reported rates and pool sizes. The model provided good simulations for rates of photosynthesis and pool sizes of intermediates under varying light, CO(2) and O(2). A basic novelty of the model is coupling of NADPH production via NADP-ME with ATP production and regulation of the C(3) cycle in bundle sheath chloroplasts. The functional range of the ATP/NADPH ratio in bundle sheath chloroplasts extends from 1.5 to 2.1, being energetically most efficient around 2. In the presence of such stoichiometry, the CO(2) concentrating function can be explained on the basis of two processes: (a) extra ATP consumption for starch and protein synthesis in bundle sheath leads to a faster NADPH and CO(2) import compared with CO(2) fixation in bundle sheath, and (b) the residual photorespiratory activity consumes RuBP by oxygenation, NADPH and ATP and causes the imported CO(2) to accumulate in bundle sheath cells. As a wider application, the model may be used for predicting results of genetic engineering of plants.

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PubMed2001

Inhibition of photosynthesis by intracellular carbonic anhydrase in microalgae under excess concentrations of CO(2).

When cells of Chlorococcum littorale that had been grown in air (air-grown cells) were transferred to extremely high CO(2) concentrations (>20%), active photosynthesis resumed after a lag period which lasted for 1-4 days. In contrast, C. littorale cells which had been grown in 5% CO(2) (5% CO(2)-grown cells) could grow in 40% CO(2) without any lag period. When air-grown cells were transferred to 40% CO(2), the quantum efficiency of PS II (Phi(II)) decreased greatly, while no decrease in Phi(II) was apparent when the 5% CO(2)-grown cells were transferred to 40% CO(2). In contrast to air-grown cells, 5% CO(2)-grown cells showed neither extracellular nor intracellular carbonic anhydrase (CA) activity. Upon the acclimation of 5% CO(2)-grown cells to air, photosynthetic susceptibility to 40% CO(2) was induced. This change was associated with the induction of CA. In addition, neither suppression of photosynthesis nor arrest of growth was apparent when ethoxyzolamide (EZA), a membrane-permeable inhibitor of CA, had been added before transferring air-grown cells of C. littorale to 40% CO(2). The intracellular pH value (pH(i)) decreased from 7.0 to 6.4 when air-grown C. littorale cells were exposed to 40% CO(2) for 1-2 h, but no such decrease in pH(i) was apparent in the presence of EZA. Both air- and 5% CO(2)-grown cells of Chlorella sp. UK001, which was also resistant to extremely high CO(2) concentrations, grew in 40% CO(2) without any lag period. The activity of CA was much lower in air-grown cells of this alga than those in air-grown C. littorale cells. These results prompt us to conclude that intracellular CA caused intracellular acidification and hence inhibition of photosynthetic carbon fixation when air-grown C. littorale cells were exposed to excess concentrations of CO(2). No such harmful effect of intracellular CA was observed in Chlorella sp. UK001 cells.

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PubMed2002

Photosynthetic characteristics and tolerance to photo-oxidation of transgenic rice expressing C(4) photosynthesis enzymes.

The photosynthetic characteristics of four transgenic rice lines over-expressing rice NADP-malic enzyme (ME), and maize phosphoenolpyruvate carboxylase (PC), pyruvate,orthophosphate dikinase (PK), and PC+PK (CK) were investigated using outdoor-grown plants. Relative to untransformed wild-type (WT) rice, PC transgenic rice exhibited high PC activity (25-fold increase) and enhanced activity of carbonic anhydrase (more than two-fold increase), while the activity of ribulose-bisphosphate carboxylase/oxygenase (Rubisco) and its kinetic property were not significantly altered. The PC transgenic plants also showed a higher light intensity for saturation of photosynthesis, higher photosynthetic CO(2) uptake rate and carboxylation efficiency, and slightly reduced CO(2) compensation point. In addition, chlorophyll a fluorescence analysis indicates that PC transgenic plants are more tolerant to photo-oxidative stress, due to a higher capacity to quench excess light energy via photochemical and non-photochemical means. Furthermore, PC and CK transgenic rice produced 22-24% more grains than WT plants. Taken together, these results suggest that expression of maize C(4) photosynthesis enzymes in rice, a C(3) plant, can improve its photosynthetic capacity with enhanced tolerance to photo-oxidation.

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PubMed2002

Leaf discs floated on water are different from intact leaves in photosynthesis and photoinhibition.

Photoinhibition has been often evaluated with leaf discs floated on water or placed on wet papers to prevent desiccation. Under these conditions, there is a possibility that CO(2) diffusion is blocked by water, which may lead to reduction in photosynthetic CO(2) assimilation. Using Chenopodium album L. grown at two irradiances, photosynthesis, quantum yield of Photosystem II (DeltaF/F (m)'), non-photochemical quenching (qN), and photoinhibition were compared between detached leaves and leaf discs. In low-light-grown plants, photoinhibition was greater in leaf discs than in detached leaves, while in high-light-grown plants, there was little difference. Leaf discs showed lower rates of photosynthesis and DeltaF/F (m)', and higher qN. The DeltaF/F (m)' in leaf discs increased when leaf discs were exposed to high concentration of CO(2), suggesting that CO(2) diffusion to chloroplasts was limited in leaf discs floated on water.

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PubMed2002

Gene-targeted and site-directed mutagenesis of photosynthesis genes in cyanobacteria.

This historical minireview traces the development and application of methods for gene-targeted and site-directed mutagenesis of photosynthesis genes in cyanobacteria (mainly Synechocystis sp. PCC 6803). This approach allowed important data to be obtained on the structure and function of Photosystem I and Photosystem II complexes. I describe some of the major contributions of molecular genetics and subsequent mutant analysis in the 1980s and early 1990s that led to substantial advances in our knowledge of basic principles regarding the organization of the photosynthetic apparatus. This molecular-genetic research on cyanobacteria has initiated a fresh wave of photosynthesis research and created a solid foundation for rapid progress at the threshold of the twenty-first century.

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PubMed2002

Photosynthesis genes and their expression in Rhodobacter sphaeroides 2.4.1: a tribute to my students and associates.

This minireview traces the photosynthesis genes, their structure, function and expression in Rhodobacter sphaeroides 2.4.1, as applied to our understanding of the inducible photosynthetic intracytoplasmic membrane system or ICM. This focus has represented the research interests of this laboratory from the late 1960s to the present. This opportunity has been used to highlight the contributions of students and postdoctorals to this research effort. The work described here took place in a much greater and much broader context than what can be conveyed here. The 'timeline' begins with a clear acknowledgment of the work of June Lascelles and William Sistrom, whose foresight intuitively recognized the necessity of a 'genetic' approach to the study of photosynthesis in R. sphaeroides. The 'timeline' concludes with the completed genome sequence of R. sphaeroides 2.4.1. However, it is hoped the reader will recognize this event as not just a new beginning, but also as another hallmark describing this continuum.

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PubMed2003

The low-light reduction in the quantum yield of photosynthesis: potential errors and biases when calculating the maximum quantum yield.

Photosynthesis-irradiance (P-E) curves are widely used to describe photosynthetic efficiency and potential. Contemporary models assume maximal photosynthetic quantum yield (phi) at low irradiances. But P-E observations made with both oxygen evolution and carbon uptake techniques show that this is not always the case. Using new and published data in conjunction with modeling exercises, we demonstrate that regardless of the mechanism there can be reductions in phi at low irradiances that are not readily observable using conventional P-E analyses. We also show that analytical errors, such as inaccurate estimation of dark oxygen consumption or carbon uptake, can markedly affect the structure of phi-E curves with negligible effect on P-E curve structure. Whether from respiration ;corrections' or other mechanisms, these deviations in phi at low light levels from the maximum quantum yield of photosynthesis (phi(max)) can lead to significant errors (> 50%) in the estimation of the linear portion of the P-E curve and ultimately phi(max). Non-linear models of P-E, such as the rectangular hyperbola, quadratic, exponential and hyperbolic tangent that are commonly used to estimate the initial slope (alpha) of the P-E curve assume that phi is maximal at low light levels and therefore can err in the estimation of phi(max) when phi is reduced at low light levels. Using a diverse data set of 622 P-E curves with a total of 7623 points, we show that although model skills are high (r (2) = 0.96 +/- 0.05, 0.97 +/- 0.04, 0.97 +/- 0.04 and 0.97 +/- 0.04, respectively), a large fraction of the model-predicted phi(max) differ by greater than 10% from true phi(max) values (91%, 50%, 82% and 46%, respectively). Data from these observations and modeling exercises lead us to suggest that phi(max) be determined by directly estimating the true maximum of a phi-E curve rather than using the more conventional methodology employing the initial slope of the P-E curve.

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PubMed2003

Photosynthesis research in Greece: a historical snapshot (1960-2001).

The origin of photosynthesis research in Greece can be traced to the early 1960s, and the first dedicated laboratory was established by George Akoyunoglou in the Nuclear Reseach Center (now National Center for Scientific Research) Demokritos, in Athens. More photosynthesis groups subsequently emerged, in Demokritos and in the universities. Research in Greece benefited greatly from the links of Greek scientists with laboratories and personalities, primarily in the USA and western Europe. The local research output is a proportional part of global research and, more or less, in tune with the shifting priorities of the latter. The list of references provided includes only a sample of publications: it is not inclusive.

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PubMed2003

Photosynthesis research in the People's Republic of China.

The first research paper on photosynthesis in China was published by T.T. Li(2) in 1929. Two photosynthesis laboratories were established in Shanghai and Beijing in the 1950s and the 1960s, respectively. A photophosphorylation 'intermediate' was discovered after the energy conversion process was separated into light and dark phases in the 1960s. Since the 1980s, research has accelerated at several different levels through efforts of a large number of scientists in China.

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PubMed2003

Photosynthesis research: advances through molecular biology - the beginnings, 1975-1980s and on...

Restriction endonuclease recognition sites and genes for rRNAs were first mapped on chloroplast chromosomes in 1975-1976. This marked the beginning of the application of molecular biology tools to photosynthesis research. In the first phase, knowledge about proteins involved in photosynthesis was used to identify plastid and nuclear genes encoding these proteins on cloned segments of DNA. Soon afterwards the DNA sequences of the cloned genes revealed the full primary sequences of the proteins. Knowledge of the primary amino acid sequences provided deeper understanding of the functioning of the protein and interactions among proteins of the photosynthetic apparatus. Later, as chloroplast DNA sequencing proceeded, genes were discovered that encoded proteins that had not been known to be part of the photosynthetic apparatus. This more complete knowledge of the composition of reaction centers and of the primary amino acid sequences of individual proteins comprising the reaction centers opened the way to determining the three-dimensional structures of reaction centers. At present, the availability of cloned genes, knowledge of the gene sequences and systems developed to genetically manipulate photosynthetic organisms is permitting experimental inquiries to be made into crucial details of the photosynthetic process.

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PubMed2004

Passage of a Young Indian Physical Chemist through the World of Photosynthesis Research at Urbana, Illinois, in the 1960s: A Personal Essay.

In September 1963, I came to the famous Photosynthesis Laboratory of Eugene Rabinowitch (1901-1973) at the University of Illinois at Urbana, Illinois, after submitting my doctoral thesis, under Professor Pasupati Mukerjee, in physical chemistry, then at the Indian Association for the Cultivation of Science, Calcutta, India. I present here my personal impressions, my research and interactions at the then International Center of Photosynthesis at Urbana, Illinois. A brief mention is made of research of others at this center, my collaboration with Govindjee (Urbana) and with John Olson (at Brookhaven National Laboratory).

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PubMed2003

Effects of season-dependent irradiance levels and nitrogen-deficiency on photosynthesis and photoinhibition in field-grown rice (Oryza sativa).

Photoinhibition and acclimation of photosynthesis in rice plants grown under N-sufficient (NS) and N-deficient (ND) field conditions were investigated during the tropical wet (WS) and dry (DS) seasons in the Philippines. Diurnal patterns of CO2 assimilation were examined. There was a transient peak in CO2 assimilation in the leaves of the NS plants in the early morning during the DS and the WS, which was not seen in the ND plants in either season. ND leaves had lower Ribulose bisphosphate carboxylase/oxygenase (Rubisco) contents and lower chlorophyll contents. A lowered quantum yield of photosystem II (phiPSII) was observed in the ND plants at an intermediate irradiance though no differences between N treatments were seen at high irradiance. Analysis of carotenoids indicated a small increase in the de-epoxidation state of the xanthophyll cycle (DES) at mid-day in the ND leaves compared to NS. Photoinhibition was greater in ND leaves when incident mid-day irradiance was increased by altering the leaf angle. Although Rubisco contents were lower in ND plants, photosynthesis in situ did not decline proportionally. For NS plants, Chlorophyll content, but not Rubisco content, was season-dependent and results are discussed in terms of the interaction between irradiance use and N content of rice leaves.

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PubMed1969

A concept of three light reactions in photosynthesis by green plants.

It has generally been accepted that plant photosynthesis involves two light reactions, one that proceeds best in short-wavelength light and is identified with oxygen evolution (System II) and another that proceeds best in long-wavelength light and is identified with a cycle electron flow (System I). This paper presents a concept of three light reactions in photosynthesis, based on new evidence that System II comprises two rather than one short-wavelength light reaction. These appear to operate in series and to be connected by an electron transport chain peculiar to System II. Parallel to System II is the long-wavelength light reaction of System I.

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PubMed1988

Cytochrome b-559 and proton conductance in oxygenic photosynthesis.

Although cytochrome b-559 has long been known as a membrane-bound redox component closely linked to the reaction center of the oxygen-generating photosystem (PSII), its role in photosynthesis has remained obscure. This paper reports evidence and outlines a hypothesis in support of a "b-559 cycle"-i.e., a light-induced, cytochrome b-559-dependent, cyclic electron transport pathway around PSII that promotes translocation of protons from plastoquinol into the aqueous domain (lumen) of photosynthetic membranes (thylakoids). Light-induced proton transport coupled to light-induced electron transport is an essential aspect of energy transduction in photosynthesis because it generates an electrochemical proton gradient that drives ATP synthesis by the process of photosynthetic phosphorylation. The principal carrier of electrons and protons in thylakoids is the plastoquinone/plastoquinol couple. We propose that the b-559 cycle functions as a redox-linked proton pump that may operate jointly with the Rieske iron-sulfur pathway in oxidizing plastoquinol. The overall effect of such concerted oxidation of plastoquinol would be the translocation into the thylakoid lumen of two protons for each electron transferred from water to plastocyanin via plastoquinone.

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PubMed1997

Evolution of plastid gene rps2 in a lineage of hemiparasitic and holoparasitic plants: many losses of photosynthesis and complex patterns of rate variation.

The plastid genomes of some nonphotosynthetic parasitic plants have experienced an extreme reduction in gene content and an increase in evolutionary rate of remaining genes. Nothing is known of the dynamics of these events or whether either is a direct outcome of the loss of photosynthesis. The parasitic Scrophulariaceae and Orobanchaceae, representing a continuum of heterotrophic ability ranging from photosynthetic hemiparasites to nonphotosynthetic holoparasites, are used to investigate these issues. We present a phylogenetic hypothesis for parasitic Scrophulariaceae and Orobanchaceae based on sequences of the plastid gene rps2, encoding the S2 subunit of the plastid ribosome. Parasitic Scrophulariaceae and Orobanchaceae form a monophyletic group in which parasitism can be inferred to have evolved once. Holoparasitism has evolved independently at least five times, with certain holoparasitic lineages representing single species, genera, and collections of nonphotosynthetic genera. Evolutionary loss of the photosynthetic gene rbcL is limited to a subset of holoparasitic lineages, with several holoparasites retaining a full length rbcL sequence. In contrast, the translational gene rps2 is retained in all plants investigated but has experienced rate accelerations in several hemi- as well as holoparasitic lineages, suggesting that there may be substantial molecular evolutionary changes to the plastid genome of parasites before the loss of photosynthesis. Independent patterns of synonymous and nonsynonymous rate acceleration in rps2 point to distinct mechanisms underlying rate variation in different lineages. Parasitic Scrophulariaceae (including the traditional Orobanchaceae) provide a rich platform for the investigation of molecular evolutionary process, gene function, and the evolution of parasitism.

Arabidopsis Proteins↗