Theoretical modelling is often overlooked in photosynthesis research even if it can significantly help with understanding of explored system. A new model of light-induced photosynthetic reactions occurring in and around thylakoid membrane is introduced here and used for theoretical modelling of not only the light-induced chlorophyll (Chl) a fluorescence rise (FLR; the O-J-I-P transient), reflecting function of photosystem II (PSII), but also of the 820 nmtransmittance signal (I820), reflecting function of photosystem I (PSI) and plastocyanin (PC), paralleling the FLR. Correctness of the model was verified by successful simulations of the FLR and I820 signal as measured with the control (no treatment) sample but also as measured with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone- (inhibits electron transport in cytochrome b 6/f) and methylviologen- (accepts electrons from iron-sulphur cluster of PSI) treated samples and with the control sample upon different intensities of excitation light. From the simulations performed for the control sample, contribution of the oxidised donor of PSI, P700, and oxidised PC to the I820 signal minimum (reflects maximal accumulations of the two components) was estimated to be 75% and 25%, respectively. Further in silico experiments showed that PC must be reduced in the dark, cyclic electron transport around PSI must be considered in the model and activation of ferredoxin-NADP+-oxidoreductase (FNR) also affects the FLR. Correct simulations of the FLR and I820 signal demonstrate robustness of the model, confirm that the electron transport reactions occurring beyond PSII affect the shape of the FLR, and show usefulness and perspective of theoretical approach in studying of the light-induced photosynthetic reactions.
To investigate the photoprotection of energy dissipation and water-water cycle, a C3 euhalophytic herb, Suaeda salsa L., was exposed either to chilling temperature (4°C) accompanied by moderate irradiance (600 μmol m-2 s-1) (CM) and/or to chilling temperature (4°C) accompanied by low irradiance (100 μmol m-2 s-1) (CL). During chilling stress, both the maximal photochemical efficiency of PSII (Fv/Fm) and the oxidizable P700 decreased in S. salsa leaves either under CM or CL, which indicated the severe photoinhibition. Relative to Fv/Fm, the oxidizable P700 decreased markedly under CL, which indicated that PSI was more sensitive to CL treatment than PSII. Initial fluorescence, number of closed PSII centers, and nonphotochemical quenching increased under CM, but more markedly under CL in S. salsa leaves. Activity of superoxide dismutase and ascorbate peroxidase was higher under CM than that under CL. The production of reactive oxygen species (ROS) decreased first and then increased under both treatments, but the content of O2.- and H2O2 was higher under CL than that under CM after 12 h of chilling stress. These results suggested that photoinhibition in S. salsa might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy. The water-water cycle could not dissipate energy efficiently under CL, which caused the great accumulation of ROS., N. Sui., and Obsahuje bibliografii
The redox interaction of exogenous cytochrome c550 (Cyt) with PSII isolated from spinach was studied. Illumination of PSII particles in the presence of Cyt led to: (1) Cyt photooxidation by PSII reaction center (demonstrated at the first time), (2) Cyt photoreduction via O2- photoproduced on the acceptor side of PSII, and (3) Cyt photoreduction by reduced electron carriers of PSII. A step-by-step removal of components of water-oxidizing complex was accompanied by the appearance of Cyt photooxidation, an increase in the superoxide dismutase (SOD)-dependent Cyt photoreduction (related to O2- formation), and a decrease in the SOD-independent Cyt photoreduction. Re-addition of PsbO protein diminished the
Cyt-induced restoration of electron transfer in PSII. Addition of diuron led to inhibition of these photoprocesses, while exogenous Mn2+ inhibited only the Cyt c photooxidation. The results can be important for correct measurements of O2- photoproduction in PSII and for elucidation of the role of cytochrome c550 in cyanobacterial PSII., A. A. Khorobrykh, D. V. Yanykin, V. V. Klimov., and Obsahuje bibliografické odkazy
The Amur Grape (Vitis amurensis Rupr.) cultivars ’shuangFeng’ and ‘ZuoShanyi’ were grown in shelter greenhouse under natural sunlight and subjected to drought. Sap flow rate, net photosynthetic rate (PN), and chlorophyll (Chl) fluorescence were measured on Amur Grape leaves subjected to different drought treatments. Significant decreases in P N were associated with increasing intercellular CO2 concentration (Ci), suggesting that the reduction in PN was caused by nonstomatal limitation. Analysis of OJIP transients according to the JIP-test protocol revealed that specific (per PSII reaction center) energy fluxes for light absorption, excitation energy trapping and electron transport have significantly changed. The appearance of a pronounced K-step and J-step in polyphasic rise of fluorescence transient suggested the oxygen-evolving complex and electron transport were inhibited. Drought stress has relatively little effect on the parameter maximal quantum yield of PSII photochemistry (Fv/Fm), but the performance index (PIABS) is more sensitive in different drought treatment. There are cultivar differences in the response of PSII activity to drought, the photosynthetic apparatus of ‘ZuoShanyi’ cultivar is more resistant to drought than that of ‘ShuangFeng’, and JIP-test could be a useful indicator for evaluation and selection to drought tolerance., Z. X. Wang ... [et al.]., and Obsahuje bibliografii
The Theobroma lethal character Luteus-Pa segregates in a 3:1 ratio, expresses in recessive homozygosis, initially inducing leaf chlorosis and finally provoking seedlings death. The objective of this work was to evaluate gas exchange, chlorophyll fluorescence emission, chemical composition and oxidative stress of wild and mutant seedlings resulting from the crosses Pa 30 × Pa 169 and its reciprocal, aiming to elucidate the seedlings death induced by Luteus-Pa. At 15 day after emergence (DAE) differences began to appear between the wild type and mutant. Mutant seedlings showed: (1) lack of photosynthesis and alterations in chloroplast morphology; (2) lower level of three abundant groups of proteins in leaves; (3) decrease in the content of chloroplastidic pigments (4) decrease in peroxidases activities and increase in leaf polyphenol oxidase activity; (5) decrease in carbohydrate and concentration of some nutrients and low dry mass in all plant parts. In leaves of mutant seedlings of both crosses damages occurred in the system responsible for the photochemical phase of photosynthesis. Variations in growth parameters and subsequent seedling death up to 60 DAE were related to exhaustion of cotyledonary reserves, inactive photosynthetic apparatus and oxidative stress. and B. C. Rehem ... [et al.].
In lichens, ribitol is known as a carbon storage compound, an osmotic agens involved effectively in cell compartments protection during dehydration of lichen thalli and as a cryoprotective compound. In our study, we investigated the effect of ribitol on photochemical processes of photosynthesis in foliose lichens [Lasallia pustulata (L.) Mérat., Umbilicaria hirsuta (Sw. ex Westr.) Hoffm.] at low temperature. The effects of three concentrations of ribitol, added externally to thalli segments on several chlorophyll (Chl) fluorescence parameters, were evaluated. The 72 h exposition to 8, 16, and 26 mM ribitol led to a concentration-dependent increase in FV/FM, decrease in non-photochemical quenching (NPQ) but no change in quantum yield of photosystem II photochemistry (ΦPSII) values at -5 °C). At higher temperature (0, +5 °C), no effect of ribitol addition on the photosynthetic parameters was apparent. and J. Hájek, P. Váczi, M. Barták.
Glaucium flavum is a biennial plant that bears a rosette of leaves, producing a flower stalk, bracteate monochasium, in its second year. The aims of this work were both to investigate the contribution of bracts to gas-exchange activities in this species and to compare this contribution to that of rosette leaves. In addition, we investigated the extent to which its responses can be explained by chloroplast ultrastructure, as well as the possible role of nutrient concentrations in the physiological responses of both leaf types. Gas exchange and plant characteristics regarding chlorophyll fluorescence were examined in a field experiment; we also determined leaf relative water content, tissue concentrations of photosynthetic pigments, chloroplast ultrastructure and nutrient contents. Although bracts indeed contributed to gas-exchange activities of G. flavum, rosette leaves showed higher values of net photosynthetic rate and stomatal conductance to CO2 for photosynthetic photon flux density above 200 μmol m-2 s-1. The incongruities in photosynthetic rates between bracts and leaves may be explained by the bigger chloroplasts of rosette leaves, which results in a larger membrane surface area. This agrees with the higher pigment concentrations and quantum efficiency of photosystem II values recorded as well for rosette leaves. On the other hand, bracts showed higher sodium concentrations, which could be a mechanism for salt tolerance of G. flavum. and S. Redondo-Gómez, E. Mateos-Naranjo, F. J. Moreno.
The study examined photosynthetic efficiency of two barley landraces (cvs. Arabi Abiad and Arabi Aswad) through a prompt fluorescence technique under influence of 14 different abiotic stress factors. The difference in the behavior of photosynthetic parameters under the same stress factor in-between cv. Arabi Abiad and cv. Arabi Aswad indicated different mechanisms of tolerance and strategies for the conversion of light energy into chemical energy for both the landraces. This study confirmed the suitability of some chlorophyll fluorescence parameters as reliable biomarkers for screening the plants at the level of photosynthetic apparatus., H. M. Kalaji, A. Rastogi, M. Živčák, M. Brestic, A. Daszkowska-Golec, K. Sitko, K. Y. Alsharafa, R. Lotfi, P. Stypiński, I. A. Samborska, M. D. Cetner., and Obsahuje bibliografii
The extrinsic proteins of photosystem II in plants (PsbO, PsbP and PsbQ) are known to be targets of stress. In previous work, differential regulation of hypothetical isoforms of these proteins was observed in Nicotiana benthamiana upon viral infection. Each of these proteins is encoded by a multigene family in this species: there are at least four genes encoding PsbO and PsbP and two encoding PsbQ. The results of structural and functional analyses suggest that PsbO and PsbP isoforms could show differences in activity, based on significant substitutions in their primary structure. Two psbQ sequences were isolated which encode identical mature proteins. and M. I. Pérez-Bueno ... [et al.].
We characterized the photosynthetic growth of wild-type (WT) and QC-site mutant cells of the cyanobacterium Synechocystis sp. PCC 6803 grown in a photobioreactor under medium-intensity [~70 μmol(photon) m-2 s-1] and high-intensity [~200 μmol(photon) m-2 s-1] light conditions. Photosynthetic growth rate (the exponential phase) increased about 1.1-1.2 fold for the A16FJ, S28Aβ, and V32Fβ mutant compared with WT cells under medium-intensity light and about 1.2-1.3 fold under high-intensity light. Biomass production increased about 17-20% for A16FJ and S28Aβ mutant cells as compared with WT cells under medium-intensity light and about 14-17% for A16FJ and V32Fβ mutant cells under high-intensity light. The greater photosynthetic growth rate and biomass production of these QC-site mutant cells could be attributed to the increased photosynthesis efficiency and decreased dissipation of wasteful energy from phycobilisomes in mutants vs. WT cells. Our results support that manipulation of photoprotection may improve photosynthesis and biomass production of photosynthetic organisms., J.-Y. Huang, N.-T. Hung, K.-M. Lin, Y.-F. Chiu, H.-A. Chu., and Obsahuje bibliografické odkazy