In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (AN), stomatal conductance (gs), substomatal CO2 concentration (Ci), transpiration rate (E), actual photochemical efficiency of PSII (ΦPSII), and maximum photochemical efficiency of PSII (Fv/Fm) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (Pr), photosynthetic electron partitioning (JC/JT), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (AN/E) was used as an indicator of water use efficiency (WUE). AN, apparent Pr, ΦPSII, Fv/Fm, qp, and gs decreased, NPQ increased, and gross Pr sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. Ci in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low Ci. and X. Guan, S. Gu.
Leafless Duvalia velutina Lavranos (Apocynaceae) is an
arido-active stem succulent common in the arid region southwest of the Arabian Peninsula. This region is characterized by a short wet season with erratic rainfall and a long dry season with high temperature and high irradiance. We investigated the survival strategy of D. velutina by studying nurse association, gas exchange, and chlorophyll fluorescence. Results showed that D. velutina exhibited the strict nurse association with shade for protection against heat and high irradiance. Results also showed that D. velutina is an obligate CAM plant with ample physiotypic plasticity involving a shift to CAM-idling under prolonged drought. Chlorophyll fluorescence measurements revealed water stress-induced reduction of PSII activity occurring in concomitance with a marked rise of nonphotochemical quenching and chlorenchyma anthocyanin content. These results reflected photoprotective capacity involving nonradiative excess energy dissipation and antioxidative attributes. We concluded that the complex survival strategy of D. velutina in its natural arid habitat includes a multifaceted interplay of nurse association, physiotypic plasticity, and photoprotective mechanisms., Y. S. Masrahi, T. A. Al-Turki, O. H. Sayed., and Obsahuje seznam literatury
Alterations in photosynthetic performance of lutein-deficient mutant lut2 and wild type (wt) of Arabidopsis thaliana were followed after treatment with low temperature and high light for 6 d. The obtained results indicated lower electrolyte leakage, lower excitation pressure, and higher actual photochemical efficiency of PSII in lut2 plants exposed to combined stress compared to wt plants. This implies that lut2 is less susceptible to the applied stress conditions. The observed lower values of quantum efficiency of nonphotochemical quenching and energy-dependent component of nonphotochemical quenching in lut2 suggest that nonphotochemical quenching mechanism(s) localized within LHCII could not be involved in the acquisition of higher stress tolerance of lut2 and alternatives to nonphotochemical quenching mechanisms are involved for dissipation of excess absorbed light. We suggest that the observed enhanced capacity for cyclic electron flow and the higher oxidation state of P700 (P700+), which suggests PSI-dependent energy quenching in lut2 plants may serve as efficient photoprotective mechanisms, thus explaining the lower susceptibility of lut2 to the combined stress treatments.
The PsbM (3.9 kDa) and PsbY (4.2 kDa) proteins are membrane-spanning, single-helix, subunits associated with the chlorophyll-binding CP47 pre-complex of photosystem II (PSII). Removal of PsbM resulted in accumulation of PSII pre-assembly complexes and impaired electron transfer between the primary (QA) and secondary (QB) plastoquinone electron acceptors of PSII indicating that the QB-binding site and bicarbonate binding to the non-heme iron were altered in this strain. Removal of PsbY alone had only a minor impact on PSII activity but deleting PsbY in the PsbM background led to additional modification of the acceptor side resulting in PsbM:PsbY cells being susceptible to photodamage and this required protein synthesis for recovery. Addition of bicarbonate was able to compensate for the light-induced damage in PsbM:PsbY cells potentially re-occupying the modified bicarbonate-binding site in the PsbM:PsbY strain and complementation of PsbM:PsbY cells with the psbY gene restored the PsbM phenotype., S. Biswas, J. J. Eaton-Rye., and Obsahuje bibliografické odkazy
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
Net photosynthetic rate of yellow upper leaves (UL) of Ligustrum vicaryi was slightly, but not significantly higher than that of green lower leaves (LL). Diurnally, maximum photochemical efficiency of photosystem 2, PS2 (Fv/Fm) of LL did not significantly decline but the UL showed fairly great daily variations. Yield of PS2 of UL showed an enantiomorphous variation to the photosynthetically active radiation and was significantly lower than in the LL. Unlike Fv/Fm, the efficiency of energy conversion in PS2 and both non-photosynthetic and photosynthetic quenching did not differ in UL and LL. Significant differences between UL and LL were found in contents of chlorophyll (Chl) a, b, and carotenoids (Car) and ratios of Chl a/b, Chl b/Chl (a+b), and Car/Chl (a+b). Leaf colour dichotocarpism in L. vicaryi was mainly caused by different photon utilization; sunflecks affected the LL. and Y. Q. Yang, X. F. Yi, P. Prasad.
Abiotic stresses induce phosphoenolpyruvate carboxylase (PEPC) expression in C3 plants which suggests PEPC function in plant adaptation to stresses. Here, we studied the response of photosynthesis to short-term drought stress in rice seedlings overexpressing C4 PEPC from maize and millet. The transgenic lines exhibited 1.2-5.5 fold of PEPC activities than the wild type before the treatment, while 1.5-8.5 fold after five or ten days of water deficit. Net photosynthetic rate (P N) declined less during the water stress and recovered more after rewatering in the transgenic lines. These changes were accompanied with changes in the stomatal conductance (g s). The lower decrease in P N and g s resulted in significantly higher intrinsic water use efficiency in the transgenic rice lines after ten days of water withdrawal. There were no significant differences between the wild type and transgenic lines in maximum photochemical efficiency of PSII and photochemical quenching. The nonphotochemical quenching and the quantum efficiency of PSII maintained both higher in transgenic lines than those in the wild type during drought stress. This indicated that the transgenic lines could dissipate more excess energy to heat to protect PSII. Our result suggested that the increased PEPC activities in rice could alleviate the decrease of photosynthesis during short-term drought stress., Z. S. Ding, X. F. Sun, S. H. Huang, B. Y. Zhou, M. Zhao., and Obsahuje seznam literatury
We analyzed the response of potted strawberry tree (Arbutus unedo L.) seedlings exposed to water stress by withholding water for 10 d (WS). Leaf water potential, net CO2 assimilation, and stomatal conductance decreased with increasing water deficit. A 30 % reduction of chlorophyll (Chl) content in the antenna complexes was observed in WS-plants. Simultaneously, a decline of photochemical efficiency (Fv/Fm) occurred as a result of an excess of solar radiation energy when carbon assimilation was limited by stomata closure due to soil water deficit. The non-photochemical quenching of Chl fluorescence (ΦNPQ) significantly increased, as well as the leaf contents of zeaxanthin (Z) and antheraxanthin (A) at the expense of violaxanthin during the WS-period. Elevated predawn contents of de-epoxidized xanthophyll cycle components were associated with a sustained lowering of predawn photosystem 2 efficiency; this suggested an engagement of Z+A in a state primed for energy dissipation. Thus, the ability of strawberry trees to maintain the functionality of the xanthophyll cycle during the Mediterranean summer is an efficient mechanism to prevent irreversible damages to the photosynthetic machinery through thermal energy dissipation in the antenna and the reduction in photochemical efficiency. and R. Baraldi ... [et al.].
Fully exposed, senescing leaves of Cornus sanguinea and Parthenocissus quinquefolia display during autumn considerable variation in both anthocyanin and chlorophyll (Chl) concentrations. They were used in this study to test the hypothesis that anthocyanins may have a photoprotective function against photosystem II (PSII) photoinhibitory damage. The hypothesis could not be confirmed with field sampled leaves since maximum photochemical efficiency (Fv/Fm) of PSII was negatively correlated to anthocyanin concentration and the possible effects of anthocyanins were also confounded by a decrease in Fv/Fm with Chl loss. However, after short-term laboratory photoinhibitory trials, the percent decrease of Fv/Fm was independent of Chl concentration. In this case, a slight alleviation of PSII damage with increasing anthocyanins was observed in P. quinquefolia, while a similar trend in C. sanguinea was not statistically significant. It is inferred that the assumed photoprotection, if addressed to PSII, may be of limited advantage and only under adverse environmental conditions. and Y. Manetas, C. Buschmann.
Kandelia candel (L.) Druce is the dominant mangrove species on the west coast of northern Taiwan. We have measured the net photosynthetic rate (PN) and chlorophyll (Chl) a fluorescence of seedlings grown at combinations of two nitrogen (0.01 and 0.1 mM) and two NaCl (250 and 430 mM NaCl) controls. With the same nitrogen level, seedlings grown at higher salinity (HS) had a significantly lower PN and stomatal conductance (gs) than those at lower salinity (LS). An increase in nitrogen availability significantly elevated PN and gs of the LS-grown seedlings. Compared to dark adapted leaves, the maximum quantum yield of photosystem 2 (PS2) (Fv/Fm) of leaves exposed to PFDs of 1200 and 1600 µmol m-2 s-1 for 2 h was significantly reduced. The degree of Fv/Fm reduction differed among leaves of the four types of treated plants. Chl fluorescence quenching analysis revealed differences among the examined plants in coefficients of non-photochemical and photochemical quenching. and Wen-Yuan Kao, Hung-Chieh Tsai.