Showing papers on "Photosynthesis published in 2003"

Crystal structure of plant photosystem I

Abstract: Oxygenic photosynthesis is the principal producer of both oxygen and organic matter on Earth. The conversion of sunlight into chemical energy is driven by two multisubunit membrane protein complexes named photosystem I and II. We determined the crystal structure of the complete photosystem I (PSI) from a higher plant (Pisum sativum var. alaska) to 4.4 A resolution. Its intricate structure shows 12 core subunits, 4 different light-harvesting membrane proteins (LHCI) assembled in a half-moon shape on one side of the core, 45 transmembrane helices, 167 chlorophylls, 3 Fe-S clusters and 2 phylloquinones. About 20 chlorophylls are positioned in strategic locations in the cleft between LHCI and the core. This structure provides a framework for exploration not only of energy and electron transfer but also of the evolutionary forces that shaped the photosynthetic apparatus of terrestrial plants after the divergence of chloroplasts from marine cyanobacteria one billion years ago.

CO2 concentrating mechanisms in cyanobacteria: molecular components, their diversity and evolution

Abstract: Cyanobacteria have evolved an extremely effective single-cell CO(2) concentrating mechanism (CCM). Recent molecular, biochemical and physiological studies have significantly extended current knowledge about the genes and protein components of this system and how they operate to elevate CO(2) around Rubisco during photosynthesis. The CCM components include at least four modes of active inorganic carbon uptake, including two bicarbonate transporters and two CO(2) uptake systems associated with the operation of specialized NDH-1 complexes. All these uptake systems serve to accumulate HCO(3)(-) in the cytosol of the cell, which is subsequently used by the Rubisco-containing carboxysome protein micro-compartment within the cell to elevate CO(2) around Rubisco. A specialized carbonic anhydrase is also generally present in this compartment. The recent availability of at least nine cyanobacterial genomes has made it possible to begin to undertake comparative genomics of the CCM in cyanobacteria. Analyses have revealed a number of surprising findings. Firstly, cyanobacteria have evolved two types of carboxysomes, correlated with the form of Rubisco present (Form 1A and 1B). Secondly, the two HCO(3)(-) and CO(2) transport systems are distributed variably, with some cyanobacteria (Prochlorococcus marinus species) appearing to lack CO(2) uptake systems entirely. Finally, there are multiple carbonic anhydrases in many cyanobacteria, but, surprisingly, several cyanobacterial genomes appear to lack any identifiable CA genes. A pathway for the evolution of CCM components is suggested.

Light-harvesting antennas in photosynthesis

Abstract: Editorial. Preface. Color Plates. I: Introduction to Light-Harvesting. 1. Photosynthetic Membranes and Their Light-Harvesting Antennas B.R. Green, J.M. Anderson, W.W. Parson. 2. The Pigments H. Scheer. 3. Optical Spectroscopy in Photosynthetic Antennas W.W. Parson, V. Nagarajan. 4. The Evolution of Light-Harvesting Antennas B.R. Green. II: Structure and Function in Light-Harvesting. 5. The Light-Harvesting System of Purple Bacteria B. Robert, R.J. Cogdell, R. van Grondelle. 6. Antenna Complexes from Green Photosynthetic Bacteria R.E. Blankenship, K. Matsuura. 7. Light-Harvesting in Photosystem II H. van Amerongen, J.P. Dekker. 8. Structure and Function of the Antenna System in Photsystem I P. Fromme, E. Schlodder, S. Jansson. 9. Antenna Systems and Energy Transfer in Cyanophyta and Rhodophyta M. Mimuro, H. Kikuchi. 10. Antenna Systems of Red Algae: Phycobilisomes with Photosystem II and Chlorophyll Complexes with Photosystem I E. Gantt, B. Grabowski, F.X. Cunningham Jr. 11. Light-Harvesting Systems in Chlorophyll c-Containing Algae A.N. Macpherson, R.G. Hiller. III: Biogenesis, Regulation and Adaptation. 12. Biogenesis of Green Plant Thylakoid Membranes K. Cline. 13. Pulse Amplitude Modulated Chlorophyll Fluorometry and its Application in Plant Science G.H. Krause, P. Jahns. 14. Photostasis in Plants, Green Algae and Cyanobacteria: The Role of Light-Harvesting Antenna Complexes N.P.A. Huner, G. Oquist, A. Melis. 15. Photoacclimation of Light-Harvesting Systems in EukaryoticAlgae P.G. Falkowski, Yi-Bu Chen. 16. Multi-level Regulation of Purple Bacterial Light-Harvesting Complexes C.S. Young, J.T. Beatty. 17. Environmental Regulation of Phycobilisome Biosynthesis A.R. Grossman, L.G. van Waasbergen, D. Kehoe. Index.

Carbon metabolite feedback regulation of leaf photosynthesis and development

Abstract: Photosynthesis is regulated as a two-way process Light regulates the expression of genes for photosynthesis and the activity of the gene products (feedforward control) Rate of end-product use down-stream of the Calvin cycle, determined largely by nutrition and temperature, also affects photosynthetic activity and photosynthetic gene expression (feedback control) Whereas feedforward control ensures efficient light use, feedback mechanisms ensure that carbon flow is balanced through the pathways that produce and consume carbon, so that inorganic phosphate is recycled and nitrogen is distributed optimally to different processes to ensure growth and survival Actual mechanisms are sketchy and complex, but carbon to nitrogen balance rather than carbon status per se is central to understanding carbon metabolite feedback control of photosynthesis In addition to determining the activity of the metabolic machinery, carbon metabolite feedback mechanisms also regulate photosynthesis at the leaf level through the regulation of leaf development This review summarizes the current sketchy, but growing, knowledge of the mechanisms through which carbon metabolite feedback mechanisms regulate leaf photosynthesis

In vivo temperature response functions of parameters required to model RuBP-limited photosynthesis

Abstract: The leaf model of C 3 photosynthesis of Farquhar, von Caemmerer & Berry ( Planta 149, 78‐90, 1980) provides the basis for scaling carbon exchange from leaf to canopy and Earth-System models, and is widely used to project biosphere responses to global change. This scaling requires using the leaf model over a wider temperature range than that for which the model was originally parameterized. The leaf model assumes that photosynthetic CO 2 uptake within a leaf is either limited by the rate of ribulose-1,5bisphosphate (RuBP) regeneration or the activity of RuBP carboxylase-oxygenase (Rubisco). Previously we reported a re-parameterization of the temperature responses of Rubisco activity that proved robust when applied to a range of species. Herein this is extended to re-parameterizing the response of RuBP-limited photosynthesis to temperature. RuBP-limited photosynthesis is assumed to depend on the whole chain electron transport rate, which is described as a three-parameter non-rectangular hyperbolic function of photon flux. Herein these three parameters are determined from simultaneous measurement of chlorophyll fluorescence and CO 2 exchange of tobacco leaves, at temperatures from 10 to 40 ∞ C. All varied significantly with temperature and were modified further with variation in growth temperature from 15 to 35 ∞ C. These parameters closely predicted the response of RuBP-limited photosynthesis to temperature measured in both lemon and poplar and showed a significant improvement over predictions based on earlier parameterizations. We provide the necessary equations for use of the model of Farquhar et al . (1980) with our newly derived temperature functions for predicting both Rubiscoand RuBP-limited photosynthesis.

The Calvin cycle revisited.

Abstract: The sequence of reactions in the Calvin cycle, and the biochemical characteristics of the enzymes involved, have been known for some time. However, the extent to which any individual enzyme controls the rate of carbon fixation has been a long standing question. Over the last 10 years, antisense transgenic plants have been used as tools to address this and have revealed some unexpected findings about the Calvin cycle. It was shown that under a range of environmental conditions, the level of Rubisco protein had little impact on the control of carbon fixation. In addition, three of the four thioredoxin regulated enzymes, FBPase, PRKase and GAPDH, had negligible control of the cycle. Unexpectedly, non-regulated enzymes catalysing reversible reactions, aldolase and transketolase, both exerted significant control over carbon flux. Furthermore, under a range of growth conditions SBPase was shown to have a significant level of control over the Calvin cycle. These data led to the hypothesis that increasing the amounts of these enzymes may lead to an increase in photosynthetic carbon assimilation. Remarkably, photosynthetic capacity and growth were increased in tobacco plants expressing a bifunctional SBPase/FBPase enzyme. Future work is discussed which will further our understanding of this complex and important pathway, particularly in relation to the mechanisms that regulate and co-ordinate enzyme activity.

Interaction of drought and high temperature on photosynthesis and grain-filling of wheat

Abstract: Drought and high temperature often occur simultaneously, but their effects on crops are usually investigated individually. Our objective was to compare effects of drought, high temperature, and their interactions on photosynthesis and grain-growth of wheat (Triticum aestivum L.). Plants (cv. Len) were grown uniformly in well-watered soil at 25/20 ± 2 °C day/night until anthesis, when they were subjected to regimes of no drought (soil at field capacity) and drought (plant water potential of −.0 to −2.4 MPa) at 15/10, 25/20, and 35/30 °C in controlled environments until physiological maturity. Drought decreased photosynthesis, stomatal conductance, viable leaf area, shoot and grain mass, and weight and soluble sugar content of kernels but increased plant water-use efficiency. High temperature hastened the decline in photosynthesis and leaf area, decreased shoot and grain mass as well as weight and sugar content of kernels, and reduced water-use efficiency. Interactions between the two stresses were pronounced, and consequences of drought on all physiological parameters were more severe at high temperature than low temperature. The synergistic interactions indicated that productivity of wheat is reduced considerably more by the combined stresses than by either stress alone, and that much of the effect is on photosynthetic processes.

The use of low [CO2] to estimate diffusional and non‐diffusional limitations of photosynthetic capacity of salt‐stressed olive saplings

Abstract: In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO 2 ] ( ~ ~ ~ 50 m mol mol - - 1 ), and, thus a non-destructive- in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, g s , and mesophyll conductance to CO 2 , g m ) and biochemical limitations to photosynthesis ( A ) were measured in two 1-yearold Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 m M NaCl to the irrigation water. Two sets of A ‐ C i curves were measured. A first set of standard A ‐ C i curves (i.e. without pre-conditioning plants at low [CO 2 ]), were generated for salt-stressed plants. A second set of A ‐ C i curves were measured, on both control and salt-stressed plants, after pre-conditioning leaves at [CO 2 ] of ~ 50 m mol mol - 1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and g s increased to similar values in control and salt-stressed plants of both cultivars. After g s had approached the maximum value, the A ‐ C i response was again measured. The analysis of the photosynthetic capacity of the salt-stressed plants based on the standard A ‐ C i curves, showed low values of the J max (maximum rate of electron transport) to V cmax (RuBP-saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the A ‐ C i curves made on pre-conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard A ‐ C i responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger ( Journal of Experimental Botany 44, 907‐920, 1993) in a survey of 109 C 3 species. These findings clearly indicates that: (1) salt stress did affect g s and g m but not the biochemical capacity to assimilate CO 2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship ( r 2 = = = 0.68) between g m and g s , and, thus, changes of g m can be as fast as those of g s ; (3) the estimates of photosynthetic capacity based on A ‐ C i curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non-stomatal limitations should be replaced by the analysis of diffusional and non-diffusional limitations of photosynthesis. Finally, the C 3 photosynthesis model parameterization using in vitro -measured and in vivo measured kinetics parameters was compared. Applying the in vivo -measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model.

Anthocyanins in leaves: light attenuators or antioxidants?

Abstract: Anthocyanins have the potential to mitigate photooxidative injury in leaves, both by shielding chloroplasts from excess high-energy quanta, and by scavenging reactive oxygen species. To distinguish between the impacts of these two putative mechanisms, superoxide (O2•–) concentration and chlorophyll oxidation were measured for Lactuca sativa L. chloroplast suspensions under various light and antioxidant-supplemented environments. A red cellulose filter, the optical properties of which approximated that of anthocyanin, effected a 33% decline in rate of O2•– generation and 37% reduction in chlorophyll bleaching, when used to shield irradiated chloroplasts. Colourless and blue tautomers of cyanidin 3-(6-malonyl)glucoside at pH 7 removed up to 17% of O2•– generated by chloroplasts, indicating that cytosolic anthocyanins can serve as effective antioxidants. Red tautomers, typical of vacuolar anthocyanins, also showed strong reducing potentials as indicated by cyclic voltammetry. These potentials declined by 40% after 15 min exposure to O2•–. Maximum quantum efficiencies of photosynthesis were similar for red and green portions of intact L. sativa leaves, but the red regions were less photoinhibited, and recovered more extensively after exposures to strong light. Anthocyanins evidently offer effective and versatile protection to leaves without significantly compromising photosynthesis.

Interaction of cadmium with glutathione and photosynthesis in developing leaves and chloroplasts of Phragmites australis (Cav.) Trin. ex Steudel.

Abstract: We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg 1 chlorophyll was found in leaves, and 0.83 nmol Cd mg 1 chlorophyll was found in chloroplasts of plants treated with 50 m Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 m treatment and the efficiency of photosystem II, measured as the fluorescence ratio Fv/Fm, remained high because F0 and Fm were proportionally decreased. In plants treated with 100 m Cd, all effects were exacerbated, but Fv/Fm remained close to that of control leaves and the glutathione and pyridine nucleotides pools were lowered. The results suggest that glutathione exerted a direct important protective role on photosynthesis in the presence of Cd. Most plants respond to cadmium (Cd) present in the root environment: the metal ion is absorbed on cortical cell walls or it is channeled into roots, where it is then subsumed into the closest vacuoles or loaded into the xylem for transport into leaves

Thermal acclimation of leaf and root respiration: An investigation comparing inherently fast- and slow-growing plant species

Abstract: We investigated the extent to which leaf and root respiration W differ in their response to short- and long-term changes in temperature in several contrasting plant species (herbs, grasses, shrubs and trees) that differ in inherent relative growth rate (RGR, increase in mass per unit starting mass and time). Two experiments were conducted using hydroponically grown plants. In the long-term (LT) acclimation experiment, 16 species were grown at constant 18,23 and 28degreesC. In the short-term (ST) acclimation experiment, 9 of those species were grown at 25/20degreesC (day/night) and then shifted to a 15/10degreesC for 7 days. Short-term Q(10) values (proportional change in R per 10degreesC) and the degree of acclimation to. longer-term changes in temperature were compared. The effect of growth temperature on root and leaf soluble sugar and nitrogen concentrations was examined. Light-saturated photosynthesis (A(sat)) was also measured in the LT acclimation experiment. Our results show that Q(10) values and the degree of acclimation are highly variable amongst species and that roots exhibit lower Q(10) values than leaves over the 15-25degreesC measurement temperature range. Differences in RGR or concentrations of soluble sugars/nitrogen could not account for the inter-specific differences in the Q(10) or degree of acclimation. There were no systematic differences in the ability of roots and leaves to acclimate when plants developed under contrasting temperatures (LT acclimation). However, acclimation was greater in both leaves and roots that developed at the growth temperature (LT acclimation) than in pre-existing leaves and roots shifted from one temperature to another (ST acclimation). The balance between leaf R and A(sat) was maintained in plants grown at different temperatures, regardless of their inherent relative growth rate. We conclude that there is tight coupling between the respiratory acclimation and the temperature under which leaves and roots developed and that acclimation plays an important role in determining the relationship between respiration and photosynthesis.

Functional Mitochondrial Complex I Is Required by Tobacco Leaves for Optimal Photosynthetic Performance in Photorespiratory Conditions and during Transients

Abstract: The importance of the mitochondrial electron transport chain in photosynthesis was studied using the tobacco (Nicotiana sylvestris) mutant CMSII, which lacks functional complex I. Rubisco activities and oxygen evolution at saturating CO(2) showed that photosynthetic capacity in the mutant was at least as high as in wild-type (WT) leaves. Despite this, steady-state photosynthesis in the mutant was reduced by 20% to 30% at atmospheric CO(2) levels. The inhibition of photosynthesis was alleviated by high CO(2) or low O(2). The mutant showed a prolonged induction of photosynthesis, which was exacerbated in conditions favoring photorespiration and which was accompanied by increased extractable NADP-malate dehydrogenase activity. Feeding experiments with leaf discs demonstrated that CMSII had a lower capacity than the WT for glycine (Gly) oxidation in the dark. Analysis of the postillumination burst in CO(2) evolution showed that this was not because of insufficient Gly decarboxylase capacity. Despite the lower rate of Gly metabolism in CMSII leaves in the dark, the Gly to Ser ratio in the light displayed a similar dependence on photosynthesis to the WT. It is concluded that: (a) Mitochondrial complex I is required for optimal photosynthetic performance, despite the operation of alternative dehydrogenases in CMSII; and (b) complex I is necessary to avoid redox disruption of photosynthesis in conditions where leaf mitochondria must oxidize both respiratory and photorespiratory substrates simultaneously.

A ten-year study on the physiology of two Spanish grapevine cultivars under field conditions: effects of water availability from leaf photosynthesis to grape yield and quality

Abstract: The effects of moderate irrigation, compared with non-irrigation, on leaf photosynthesis and transpiration, grape yield, and quality parameters, were studied over ten years in two Spanish cultivars (Tempranillo and Manto Negro) of field-grown grapevines (Vitis vinifera L.). The aim was to increase our knowledge of the relationships between water availability, canopy water losses, photosynthesis, and fruit yield and quality. A second aim was to analyse some of the mechanisms of photosynthetic down-regulation under drought, such as the capacity for RuBP regeneration and Rubisco activity. Moderate irrigation improved plant water status, leaf photosynthesis and transpiration. Considering the results over ten years, soil water availability (estimated as pre-dawn leaf water potential, ΨPD) largely determined leaf photosynthesis and leaf transpiration. Decreased photosynthesis was due to both stomatal and non-stomatal factors. The latter were related to decayed electron transport rate and reduced RuBP regeneration capacity, but not to decreased Rubisco activity. Moderate irrigation also improved grape yield, although this effect was much larger in Tempranillo than in Manto Negro. Moreover, the correlation between photosynthesis and grape yield was significant in Tempranillo, but not in Manto Negro. In contrast, the correlation between ΨPD and several parameters reflecting fruit quality (such as soluble solids and total polyphenol content) was significant only in Manto Negro. These results suggest that there is a close link between water availability and grape yield, mostly through water stress effects on photosynthesis. Drought effects on grape quality are linked to water availability but not to photosynthesis or yield.

Photosynthetic limitations in olive cultivars with different sensitivity to salt stress

Abstract: Olive ( Olea europea L) is one of the most valuable and widespread fruit trees in the Mediterranean area. To breed olive for resistance to salinity, an environmental constraint typical of the Mediterranean, is an important goal. The photosynthetic limitations associated with salt stress caused by irrigation with saline (200 m M ) water were assessed with simultaneous gas-exchange and fluorescence field measurements in six olive cultivars. Cultivars were found to possess inherently different photosynthesis when non-stressed. When exposed to salt stress, cultivars with inherently high photosynthesis showed the highest photosynthetic reductions. There was no relationship between salt accumulation and photosynthesis reduction in either young or old leaves. Thus photosynthetic sensitivity to salt did not depend on salt exclusion or compartmentalization in the old leaves of the olive cultivars investigated. Salt reduced the photochemical efficiency, but this reduction was also not associated with photosynthesis reduction. Salt caused a reduction of stomatal and mesophyll conductance, especially in cultivars with inherently high photosynthesis. Mesophyll conductance was generally strongly associated with photosynthesis, but not in salt-stressed leaves with a mesophyll conductance higher than 50 mmol m - - 2 s - 1 . The combined reduction of stomatal and mesophyll conductances in saltstressed leaves increased the CO 2 draw-down between ambient air and the chloroplasts. The CO 2 draw-down was strongly associated with photosynthesis reduction of saltstressed leaves but also with the variable photosynthesis of controls. The relationship between photosynthesis and CO 2 draw-down remained unchanged in most of the cultivars, suggesting no or small changes in Rubisco activity of saltstressed leaves. The present results indicate that the low chloroplast CO 2 concentration set by both low stomatal and mesophyll conductances were the main limitations of photosynthesis in salt-stressed olive as well as in cultivars with inherently low photosynthesis. It is consequently suggested that, independently of the apparent sensitivity of photosynthesis to salt, this effect may be relieved if conductances to CO 2 diffusion are restored.

Evolution of cam and c4 carbon-concentrating mechanisms

Abstract: Mechanisms for concentrating carbon around the Rubisco enzyme, which drives the carbon‐reducing steps in photosynthesis, are widespread in plants; in vascular plants they are known as crassulacean acid metabolism (CAM) and C4 photosynthesis CAM is common in desert succulents, tropical epiphytes, and aquatic plants and is characterized by nighttime fixation of CO2 The proximal selective factor driving the evolution of this CO2‐concentrating pathway is low daytime CO2, which results from the unusual reverse stomatal behavior of terrestrial CAM species or from patterns of ambient CO2 availability for aquatic CAM species In terrestrials the ultimate selective factor is water stress that has selected for increased water use efficiency In aquatics the ultimate selective factor is diel fluctuations in CO2 availability for palustrine species and extreme oligotrophic conditions for lacustrine species C4 photosynthesis is based on similar biochemistry but carboxylation steps are spatially separated in the leaf

Absence of the Lhcb1 and Lhcb2 proteins of the light-harvesting complex of photosystem II - effects on photosynthesis, grana stacking and fitness

Abstract: We have constructed Arabidopsis thaliana plants that are virtually devoid of the major light-harvesting complex, LHC II. This was accomplished by introducing the Lhcb2.1 coding region in the antisense orientation into the genome by Agrobacterium-mediated transformation. Lhcb1 and Lhcb2 were absent, while Lhcb3, a protein present in LHC II associated with photosystem (PS) II, was retained. Plants had a pale green appearance and showed reduced chlorophyll content and an elevated chlorophyll a/b ratio. The content of PS II reaction centres was unchanged on a leaf area basis, but there was evidence for increases in the relative levels of other light harvesting proteins, notably CP26, associated with PS II, and Lhca4, associated with PS I. Electron microscopy showed the presence of grana. Photosynthetic rates at saturating irradiance were the same in wild-type and antisense plants, but there was a 10-15% reduction in quantum yield that reflected the decrease in light absorption by the leaf. The antisense plants were not able to perform state transitions, and their capacity for non-photochemical quenching was reduced. There was no difference in growth between wild-type and antisense plants under controlled climate conditions, but the antisense plants performed worse compared to the wild type in the field, with decreases in seed production of up to 70%.

tla1, a DNA insertional transformant of the green alga Chlamydomonas reinhardtii with a truncated light-harvesting chlorophyll antenna size.

Abstract: DNA insertional mutagenesis and screening of the green alga Chlamydomonas reinhardtii was employed to isolate tla1, a stable transformant having a truncated light-harvesting chlorophyll antenna size. Molecular analysis showed a single plasmid insertion into an open reading frame of the nuclear genome corresponding to a novel gene (Tla1) that encodes a protein of 213 amino acids. Genetic analysis showed co-segregation of plasmid and tla1 phenotype. Biochemical analyses showed the tla1 mutant to be chlorophyll deficient, with a functional chlorophyll antenna size of photosystem I and photosystem II being about 50% and 65% of that of the wild type, respectively. It contained a correspondingly lower amount of light-harvesting proteins than the wild type and had lower steady-state levels of Lhcb mRNA. The tla1 strain required a higher light intensity for the saturation of photosynthesis and showed greater solar conversion efficiencies and a higher photosynthetic productivity than the wild type under mass culture conditions. Results are discussed in terms of the tla1 mutation, its phenotype, and the role played by the Tla1 gene in the regulation of the photosynthetic chlorophyll antenna size in C. reinhardtii.

Effects of Extracellular pH on the Metabolic Pathways in Sulfur-Deprived, H2-Producing Chlamydomonas reinhardtii Cultures

Abstract: Sustained photoproduction of H(2) by the green alga, Chlamydomonas reinhardtii, can be obtained by incubating cells in sulfur-deprived medium [Ghirardi et al. (2000b) Trends Biotechnol. 18: 506; Melis et al. (2000) Plant Physiol. 122: 127]. The current work focuses on (a) the effects of different initial extracellular pHs on the inactivation of photosystem II (PSII) and O(2)-sensitive H(2)-production activity in sulfur-deprived algal cells and (b) the relationships among H(2)-production, photosynthetic, aerobic and anaerobic metabolisms under different pH regimens. The maximum rate and yield of H(2) production occur when the pH at the start of the sulfur deprivation period is 7.7 and decrease when the initial pH is lowered to 6.5 or increased to 8.2. The pH profile of hydrogen photoproduction correlates with that of the residual PSII activity (optimum pH 7.3-7.9), but not with the pH profiles of photosynthetic electron transport through photosystem I or of starch and protein degradation. In vitro hydrogenase activity over this pH range is much higher than the actual in situ rates of H(2) production, indicating that hydrogenase activity per se is not limiting. Starch and protein catabolisms generate formate, acetate and ethanol; contribute some reductant for H(2) photoproduction, as indicated by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone inhibition results; and are the primary sources of reductant for respiratory processes that remove photosynthetically generated O(2). Carbon balances demonstrate that alternative metabolic pathways predominate at different pHs, and these depend on whether residual photosynthetic activity is present or not.

Photosynthesis in algae

Abstract: Introductory Chapters.- 1 The Algae and their General Characteristics.- Summary.- I. Introduction.- II. The Algae: Their Origins and Diversity.- III. The Green, Red and Brown Algae.- IV. The Chromophytes.- V. The Chlorarachniophytes.- VI. The Euglenophytes.- VII. Algal Genomes.- VIII. Algae as Sources of Natural Products.- IX. Concluding Remarks.- Acknowledgements.- References.- 2 Algal Plastids: Their Fine Structure and Properties.- Summary.- I. Introduction.- II. Origin of Plastids.- III. Chlorophyte Plastids.- IV. Rhodophyte Plastids.- V. Cyanelles (Glaucocystophyte Plastids).- VI. Cryptophyte Plastids.- VII. Chlorarachniophyte Plastids.- VIII. Euglenophyte Plastids.- IX. Dinoflagellate Plastids.- X. Chrysophyte (Ochrophyte) Plastids.- XI. Phaeophyte, Bacillariophyte, Eustigmatophyte, Raphidophyte, Synurophyte, Pelagophyte, Silicoflagellate, Pedinellid and Xanthophyte Plastids.- XII. Haptophyte Plastids.- XIII. Apicomplexan Plastids.- XIV. Kleptoplastids.- XV. Microstructure of the Thylakoid Membrane.- Acknowledgments.- References.- 3 The Photosynthetic Apparatus of Chlorophyll b- and d-Containing Oxyphotobacteria.- Summary.- I. Introduction.- II. Advances in Photosynthesis in Chlorophyll b- and d-Containing Oxyphotobacteria.- III. Green Oxyphotobacteria and the Endosymbiotic Theory of Green Plastids Evolution.- IV. Concluding Remarks.- Acknowledgments.- References.- Molecular Genetics of Algae.- 4 Structure and Regulation of Algal Light-Harvesting Complex Genes.- Summary.- I. Introduction.- II. Higher Plant Light-Harvesting Complexes.- III. Algal Light-Harvesting Complexes.- IV. Origin and Evolution of the Light-Harvesting Antennae.- V. Concluding Remarks.- Acknowledgments.- References.- 5 Functional Analysis of Plastid Genes through Chloroplast Reverse Genetics in Chlamydomonas.- Summary.- I. Introduction.- II. Algal Chloroplast Transformation.- III. Reverse Chloroplast Genetics of Photosynthesis.- IV. Several ycfs Encode Novel Proteins Involved in Photosynthesis.- V. Chloroplast Reverse Genetics of Essential Genes of Chlamydomonas.- VI. Conclusions and Prospects.- Acknowledgments.- References.- 6 Biochemistry and Regulation of Chlorophyll Biosynthesis.- Summary.- I. Introduction.- II. An Overview of Tetrapyrroles and Their Derivatives.- III. Chlorophyll Forms and Their Distribution in Algal Species.- IV. Early Steps in Chlorophyll Biosynthesis.- V. The Pathway from ALA to Protoporphyrin IX.- VI. The Iron Branch.- VII. The Magnesium Branch-Chlorophyll a Formation.- VIII. Biosynthesis of Chlorophyll b and Other Algal Chlorophylls.- Acknowledgments.- References.- Summary.- Biochemistry and Physiology of Algae.- 7 Oxygenic Photosynthesis in Algae and Cyanobacteria: Electron Transfer in Photosystems I and II.- Summary.- I. Introduction.- II. Overview of Photosystems I and II.- III. Mutagenesis and Genetic Engineering of the Photosystems.- IV. Photosystem II function.- V. Photosystem II Structure.- VI. Photosystem I.- VII. Conclusions.- Acknowledgment.- References.- 8 Oxygen Consumption: Photorespiration and Chlororespiration.- Summary.- I. Introduction.- II. Photorespiration.- III. Chlororespiration: A Mechanism to Maintain Thylakoid Membrane Energization in the Dark?.- Acknowledgments.- References.- 9 The Water-Water Cycle in Algae.- Summary.- I. Introduction.- II. The Water-Water Cycle in Plant Chloroplasts.- III. Operation of the Water-Water Cycle in Cyanobacteria and Eukaryotic Algae.- IV. Scavenging System of O2- and H2O2 in the Algal Water-Water Cycle.- V. Physiological Functions of the Water-Water Cycle in Cyanobacteria and Eukaryotic Algae.- VI. Concluding Remarks.- Acknowledgment.- References.- 10 Carbohydrate Metabolism and Respiration in Algae.- Summary.- I. Introduction.- II. Carbohydrate Metabolism: Low M, Compounds.- III. Carbohydrate Metabolism: Storage Polysaccharides.- IV. Carbohydrate Metabolism: Structural Polysaccharides.- V. Respiration: Carbon Pathways.- VI. Respiration: Redox Reactions and Energy Conservation.- VII. Respiration: Spatial and Temporal Aspects.- VIII. Quantifying Carbohydrate Metabolism and Respiration in Relation to Growth and Maintenance.- Acknowledgments.- References.- 11 Carbon Acquisition Mechanisms of Algae: Carbon Dioxide Diffusion and Carbon Dioxide Concentrating Mechanisms.- Summary.- I. Introduction.- II. Rubisco Kinetic Properties in Relation to the CO2 and O2 Concentrations in Cyanobacterial and Algal Habitats.- III. Lines of Evidence Used in Distinguishing Organisms Relying on Diffusive CO2 Entry from Those Using Carbon Concentrating Mechanisms (CCMs).- IV. Occurrence and Mechanism of CCMs.- V. Evolution of CCMs.- VI. Conclusions and Prospects.- Acknowledgments.- References.- Light-Harvesting Systems in Algae.- 12 Modeling the Excitation Energy Capture inThylakoid Membranes.- Summary.- I. Introduction.- II. Structural Composition of the Thylakoid Membrane.- III. Experimental Approaches.- IV. Kinetic Modeling of the Thylakoid Membrane.- V. Concluding Remarks.- Acknowledgments.- References.- 13 Light-Harvesting Systems in Algae.- Summary.- I. Introduction.- II. Chlorophylls.- III. Light-Harvesting Proteins.- IV. Optimizing Light-Harvesting Architecture.- V. Problems with Photosystem II.- VI. Off-Loading Excess Light Energy: Xanthophyll Cycle and Reaction Center Sinks.- VII. Control of Light Harvesting.- Acknowledgments.- References.- 14 Red, Cryptomonad and Glaucocystophyte Algal Phycobiliproteins.- Summary.- I. Introduction.- II. Structure and Components of Phycobilisomes.- III. Molecular Biology of Red Algal, Glaucocystophyte and Cryptomonad Phycobiliproteins.- IV. Phycobiliprotein Structure.- V. Phycobiliprotein Types.- VI. Phycobiliprotein Crystal Structure.- VII. Bilin Chromophores.- VIII. Energy Transfer.- IX. Applications/Industrial Uses.- References.- 15 Carotenoids of Light Harvesting Systems: Energy Transfer Processes from Fucoxanthin and Peridinin to Chlorophyll.- Summary.- I. Introduction.- II. Distribution of Carotenoids in Algae.- III. Optical Properties of Carotenoids in Relation to Functions.- IV. Functions.- V. Antenna Function of Carotenoids in Algae.- VI. Electronic States and Dynamic Properties of Molecules.- VII. Energy Transfer Processes and Mechanism.- References.- General Aspects of Photosynthesis in Algae.- 16 Photoinhibition, UV-B and Algal Photosynthesis.- Summary.- I. Introduction.- II. The Algal Light Climate.- II. Photoinhibition by PAR.- III. Effects of UV Radiation.- IV. Photoinhibition and UV Stress in the Field.- V. Scope for Further Research.- Acknowledgment.- References.- 17 Adaptation, Acclimation and Regulation in Algal Photosynthesis.- Summary.- I. Introduction.- II. The Range of Resource Availabilities and Other Environmental Factors within Which Algae Can Photosynthesize.- III. Adaptation of the Photosynthetic Apparatus.- V. Adaptation of Algal Photosynthesis to Environmental Extremes.- VI. Acclimation of Algal Photosynthesis.- VII. Regulation of Algal Photosynthesis.- VIII. Rates of Regulation and Acclimation.- IX. Conclusions.- Acknowledgments.- References.- 18 Photosynthesis in Marine Macroalgae.- Summary.- I. Introduction.- II. Radiation Conditions in Coastal Waters.- III. Light Absorption by Macroalgae.- IV. Determination of Photosynthetic Rates.- V. Effects of Excessive Light on Photosynthesis.- VI. Algal Photosynthesis Under Low Light Conditions.- VII. Seasonal Photosynthetic Performance of Macroalgae.- VIII. Adaptation and Acclimation of Photosynthesis and Respiration to Temperature and Salinity.- References.- 19 Photosynthesis in Symbiotic Algae.- Summary.- I. Introduction.- II. Algal Symbiotic Associations.- III. The Host-Algal Interface.- IV. Carbon Acquisition, Fixation and Secretion.- V. Photoacclimation and Photoadaptation.- VI. Coral Bleaching and Photoinhibition.- References.

Cold tolerance of C4 photosynthesis in Miscanthus x giganteus: adaptation in amounts and sequence of C4 photosynthetic enzymes.

Abstract: Field-grown Miscanthus × giganteus maintains high photosynthetic quantum yields and biomass productivity in cool temperate climates. It is related to maize ( Zea mays ) and uses the same NADP-malic enzyme C 4 pathway. This study tests the hypothesis that M. × giganteus , in contrast to maize, forms photosynthetically competent leaves at low temperatures with altered amounts of pyruvate orthophosphate dikinase (PPDK) and Rubisco or altered properties of PPDK. Both species were grown at 25°C/20°C or 14°C/11°C (day/night), and leaf photosynthesis was measured from 5°C to 38°C. Protein and steady-state transcript levels for Rubisco, PPDK, and phospho enol pyruvate carboxylase were assessed and the sequence of C 4 -PPDK from M. × giganteus was compared with other C 4 species. Low temperature growth had no effect on photosynthesis in M. × giganteus , but decreased rates by 80% at all measurement temperatures in maize. Amounts and expression of phospho enol pyruvate carboxylase were affected little by growth temperature in either species. However, PPDK and Rubisco large subunit decreased >50% and >30%, respectively, in cold-grown maize, whereas these levels remained unaffected by temperature in M. × giganteus . Differences in protein content in maize were not explained by differences in steady-state transcript levels. Several different M. × giganteus C 4 -PPDK cDNA sequences were found, but putative translated protein sequences did not show conservation of amino acids contributing to cold stability in Flaveria brownii C 4 -PPDK. The maintenance of PPDK and Rubisco large subunit amounts in M. × giganteus is consistent with the hypothesis that these proteins are critical to maintaining high rates of C 4 photosynthesis at low temperature.

Molecular engineering of c4 photosynthesis.

Abstract: The majority of terrestrial plants, including many important crops such as rice, wheat, soybean, and potato, are classified as C3 plants that assimilate atmospheric CO2 directly through the C3 photosynthetic pathway. C4 plants such as maize and sugarcane evolved from C3 plants, acquiring the C4 photosynthetic pathway to achieve high photosynthetic performance and high water- and nitrogen-use efficiencies. The recent application of recombinant DNA technology has made considerable progress in the molecular engineering of C4 photosynthesis over the past several years. It has deepened our understanding of the mechanism of C4 photosynthesis and provided valuable information as to the evolution of the C4 photosynthetic genes. It also has enabled us to express enzymes involved in the C4 pathway at high levels and in desired locations in the leaves of C3 plants for engineering of primary carbon metabolism.

Evidence for direct carotenoid involvement in the regulation of photosynthetic light harvesting

Abstract: Nonphotochemical quenching (NPQ) refers to a process that regulates photosynthetic light harvesting in plants as a response to changes in incident light intensity. By dissipating excess excitation energy of chlorophyll molecules as heat, NPQ balances the input and utilization of light energy in photosynthesis and protects the plant against photooxidative damage. To understand the physical mechanism of NPQ, we have performed femtosecond transient absorption experiments on intact thylakoid membranes isolated from spinach and transgenic Arabidopsis thaliana plants. These plants have well defined quenching capabilities and distinct contents of xanthophyll (Xan) cycle carotenoids. The kinetics probed in the spectral region of the S1 → Sn transition of Xans (530–580 nm) were found to be significantly different under the quenched and unquenched conditions, corresponding to maximum and no NPQ, respectively. The lifetime and the spectral characteristics indicate that the kinetic difference originated from the involvement of the S1 state of a specific Xan, zeaxanthin, in the quenched case.