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
LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 μmol m-2 s-1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress., T. W. Choong, J. He, L. Qin, S. K. Lee., and Obsahuje bibliografii
In this study, we presented a new approach for quantification of bicarbonate (HCO3-) molecules bound to PSII. Our method, which is based on a combination of membrane-inlet mass spectrometry (MIMS) and 18O-labelling, excludes the possibility of "non-accounted" HCO3- by avoiding (1) the employment of formate for removal of HCO3- from PSII, and (2) the extremely low concentrations of HCO3-/CO2 during online MIMS measurements. By equilibration of PSII sample to ambient CO2 concentration of dissolved CO2/HCO3-, the method ensures that all physiological binding sites are saturated before analysis. With this approach, we determined that in spinach PSII membrane fragments 1.1 ± 0.1 HCO3- are bound per PSII reaction center, while none was bound to isolated PsbO protein. Our present results confirmed that PSII binds one HCO3- molecule as ligand to the non-heme iron of PSII, while unbound HCO3- optimizes the water-splitting reactions by acting as a mobile proton shuttle., K. Tikhonov, D. Shevela, V. V. Klimov, J. Messinger., and Obsahuje bibliografické odkazy
The source-sink relationship is one of major determinants of plant performance. The influence of reproductive sink demand on light-saturated photosynthesis (Pmax), dark respiration (RD), stomatal conductance (gs), intrinsic water-use efficiency (WUEi), contents of soluble sugar (SSC), nitrogen, carbon, and photosynthetic pigments was examined in blueberry (Vaccinium corymbosum L. cv. ‘Brigitta’) during the final stage of rapid fruit growth. Measurements were performed three times per day on developed, sun-exposed leaves of girdled shoots with 0.1, 1, and 10 fruit per leaf (0.1F:L, 1F:L, and 10F:L, respectively) and nongirdled shoots bearing one fruit per leaf (NG). Girdling and lower fruit amount induced lower Pmax, gs, N, and total chlorophyll (Chl) and higher WUEi, SSC, RD, Chl a/b ratio and carotenoids-to-chlorophylls ratio (Car/Chl) for the 1F:L and 0.1F:L treatments. The impact of girdling was counterbalanced by 10F:L, with NG and 10F:L having similar values. Variables other than Pmax, RD, gs, WUEi, and SSC were unaffected throughout the course of the day. Pmax and gs decreased during the course of the day, but gs decreased more than Pmax in the afternoon, while WUEi was increasing in almost all treatments. SSC increased from the morning until afternoon, whereas RD peaked at noon regardless of the treatment. Generally, Pmax was closely and negatively correlated to SSC, indicating that sugar-sensing mechanisms played an important role in regulation of blueberry leaf photosynthesis. With respect to treatments, Pmax and N content were positively related, while RD was not associated to substrate availability. The enhanced Car/Chl ratio showed a higher photoprotection under the lower sink demand. Changes in the source-sink relationship in 'Brigitta' blueberry led to a rearrangement of physiological and structural leaf traits which allowed adjusting the daily balance between carbon assimilation and absorbed light energy., E. Jorquera-Fontena, M. Alberdi, M. Reyes-Díaz, N. Franck., and Obsahuje bibliografii
The microalga Haematococcus pluvialis is a biotechnologically important microorganism producing a ketocarotenoid astaxanthin. Haematococcus exists either as metabolically active vegetative cells with a high chlorophyll content or astaxanthin-rich haematocysts (aplanospores). This microalga featuring outstanding tolerance to a wide range of adverse conditions is a highly suitable model for studies of freezing tolerance in phototrophs. The retention of H. pluvialis cell viability after freezing-thawing is ascribed to elevated antioxidant enzyme activity and high ketocarotenoid content. However, we report that only haematocysts characterized by a lower photosynthetic activity were resistant to freezing-thawing even without cryoprotectant addition. The key factors of haematocyst freezing tolerance were assumed to be a low water content, rigid cell walls, reduction of the membranous structures, photosynthesis downregulation, and low chlorophyll content. Collectively, viability of Haematoccus after freezing-thawing can be improved by forcing the transition of vegetative cells to freeze-tolerant haematocysts before freezing., K. Chekanov, S. Vasilieva, A. Solovchenko, E. Lobakova., and Obsahuje bibliografii
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
Flavonoids are thought to participate in protection of the photosynthetic apparatus against photoinhibition under excessive light. Flavone glycoside, scutellarin, is a main active ingredient extracted from Erigeron breviscapus, the plant used in Chinese medicine. Shade-developed leaves of E. breviscapus were transferred from shade to full sunlight to quantify a relationship between the concentration of leaf scutellarin and tolerance to high radiation stress or the recovery from photoinhibition. The maximal quantum yield of PSII photochemistry showed a diurnal fluctuation in both shaded and sunlit leaves throughout the day. It indicated dynamic photoinhibition in the leaves of Erigeron, i.e., higher photoinhibition at solar noon and lower one in the morning and late afternoon. The sun-developed leaves reached the higher scutellarin content and values of nonphotochemical quenching coefficient with a lower degree of photoinhibition than the shade-developed leaves. When the shade-developed leaves were transferred to full sunlight, the content of scutellarin was declining continuously for 10 d and then was increasing for 15 d. After 50 d, all leaves became the sun-developed leaves with their scutellarin contents of about 138.5 ± 5.2 mg g-1(dry mass, DM) which was significantly higher than that of the shade-developed leaves [107.8 ± 9.8 mg g-1(DM)]. During acclimatization, the degree of photoinhibition was negatively correlated with the scutellarin content. Our results demonstrated a synchronous fluctuation between the flavonoid content and degree of protection against photoinhibition., R. Zhou, W. H. Su, G. F. Zhang, Y. N. Zhang, X. R. Guo., and Obsahuje seznam literatury
To assess the relationship between chlorophyll (Chl) fluorescence (CF) and photosynthetic pigments, soybean was grown under varying phosphorus (P) nutrition at ambient and elevated CO2 (EC). The EC stimulated, but P deficiency decreased plant height, node numbers, and leaf area concomitantly with the rates of stem elongation, node addition, and leaf area expansion. Under P deficiency, CF parameters and pigments declined except that carotenoids (Car) were relatively stable indicating its role in photoprotection. The CF parameters were strongly related with Chl concentration but not with Chl a/b or Car. However, total Chl/Car showed the strongest association with CF parameters such as quantum efficiency and yield of photosystem II. This relationship was not affected by CO2 treatment. The high correlation between CF and total Chl/Car underscores the significance of the quantification of both, Chl and Car concentrations, to understand the photochemistry and underlying processes of photoprotection and mechanisms of excess energy dissipation in a given environment., S. K. Singh, V. R. Reddy, D. H. Fleisher, D. J. Timlin., and Obsahuje bibliografii
Specific leaf area (SLA) is a key trait to screen plants for ecological performance and productivity; however, the relationship between SLA and photosynthesis is not always up-scalable to growth when comparing multiple species with different life cycles. We explored leaf anatomy in annual and perennial species of Physaria, and related it to photosynthesis and water loss. The annual Physaria gracilis had higher SLA, thinner leaves, and lower investment in protective tissues, than perennial P. mendocina. Physaria angustifolia (annual), and P. pinetorum (perennial) showed intermediate values. Both perennials had a thicker palisade and high photosynthesis, relative to annuals. The larger leaf veins of perennials should allow high water availability to the mesophyll. The thicker palisade should determine high resistance to water flow and help explain their high water-use efficiency. These leaf functions reflect the construction of long-lived leaves that efficiently use resources under environmental limitations of arid environments., L. Gonzalez-Paleo, D. A. Ravetta., and Obsahuje bibliografii
During the last century, the world soybean yield has been constantly enhancing at a remarkable rate. Factors limiting the soybean yield may be multiple. It is widely acknowledged that changes of root metabolism can influence aboveground characteristics, such as the seed yield and photosynthesis. In this study, we considered root bleeding sap mass (BSM) and root activity (RA) as indicators of the root growth vigour. We used 27 soybean cultivars, spanning from 1923 to 2009, to evaluate the contribution of root characteristic improvement to efficient photosynthesis and dry matter production. The BSM, RA, net photosynthetic rate (P N), and organ biomass were measured at different growth stages, such as the fourth leaf node, flowering, podding, and seed-filling stage. Our results showed that the soybean cultivars increased their biomass and P N thanks to genetic improvement. At the same time, BSM and RA also increased in dependence on a year of cultivar release. However, both P N and biomass were positively correlated with root characteristics only at the podding stage. Our data revealed that the improved root characteristic may have contributed to the enhanced photosynthesis, biomass, and yield of soybean cultivars during last 87 years of genetic improvement. We suggest that BSM and RA could be used as important indexes for further practice in soybean production improvement., X. Cui, Y. Dong, P. Gi, H. Wang, K. Xu, Z. Zhang., and Obsahuje seznam literatury