The transfer of light energy from phycobilisomes (PBS) to photosystem II (PSII) reaction centers is vital for photosynthesis in cyanobacteria and red algae. To investigate the relationship between PBS and PSII and to optimize the energy transfer efficiency from PBS to PSII, isolation of the PBS-PSII supercomplex is necessary. SPC (sucrose/phosphate/citrate) is a conventional buffer for isolating PBS-PSII supercomplex in cyanobacteria. However, the energy transfer occurring in the supercomplex is poor. Here, we developed a new buffer named SGB by adding 1M glycinebetaine and additional sucrose to SPC buffer. Compared to SPC, the newly developed SGB buffer greatly enhanced the associated populations of PBS with thylakoid membranes and PSII and further improved the energy transfer efficiency from PBS to PSII reaction centers in cyanobacteria in vitro. Therefore, we conclude that SGB is an excellent buffer for isolating the PBS-PSII supercomplex and for enhancing the energy transfer efficiency from PBS to PSII reaction centers in cyanobacteria in vitro., L. P. Chen, Q. X. Wang, W. M. Ma., and Obsahuje bibliografii
Photosystem II (PSII) photochemistry was examined by chlorophyll (Chl) a fluorescence analysis in high-yield rice LYPJ flag leaves during senescence. Parameters deduced from the JIP-test showed that inhibition of the donor side of PSII was greater than that of the acceptor side in hybrid rice LYPJ. The natural senescence process was accompanied by the increased inactivation of oxygen-evolving complex (OEC) and a lower total number of active reaction centers per absorption. It indicated that the inhibition of electron transport caused by natural senescence might be caused partly by uncoupling of the OEC and/or inactivation of PSII reaction centers. Chl fluorescence parameters analyzed in this study suggested that energy dissipation was enhanced in order to protect senescent leaves from photodamage. Nevertheless, considerably reduced PSI electron transport activity was observed at the later senescence. Thus, natural senescence inhibited OEC-PSII electron transport, but also significantly limited the PSII-PSI electron flow., Y. W. Wang, C. Xu, C. F. Lv, M. Wu, X. J. Cai, Z. T. Liu, X. M. Song, G. X. Chen, C. G. Lv., and Seznam literaruty
Differences in maximal yields of chlorophyll variable fluorescence (Fm) induced by single turnover (ST) and multiple turnover (MT) excitation are as great as 40%. Using mutants of Chlamydomonas reinhardtii we investigated potential mechanisms controlling Fm above and beyond the QA redox level. Fm was low when the QB binding site was occupied by PQ and high when the QB binding site was empty or occupied by a PSII herbicide. Furthermore, in mutants with impaired rates of plastoquinol reoxidation, Fm was reached rapidly during MT excitation. In PSII particles with no mobile PQ pool, Fm was virtually identical to that obtained in the presence of PSII herbicides. We have developed a model to account for the variations in maximal fluorescence yields based on the occupancy of the QB binding site. The model predicts that the variations in maximal fluorescence yields are caused by the capacity of secondary electron acceptors to reoxidize QA-., O. Prášil, Z. S. Kolber, P. G. Falkowski., and Obsahuje bibliografické odkazy
Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280-320 nm; 60 µmol m-2 s-1) exposure alone and in combination with photosynthetically active radiation (PAR; 400-800 nm; 200 µmol m-2 s-1) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O2 evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples. and M. K. Pradhan ... [et al.].
To investigate the role of glycine betaine in photosynthesis under stress, a transgenic wheat (Triticum aestivum L.) line T6 overaccumulating glycine betaine and its wild type Shi4185 were used. Seedlings were exposed to conditions of drought (30%, PEG-6000), heat (40°C) and their combination. The results revealed ultrastructural damage to the chloroplast and thylakoid lamellae with the withered phenotype by both drought and heat stress, and the damage was exacerbated by the combination of drought and heat. The appearance of a K step in the typical O-J-I-P curve and the decrease of Hill activity indicated a reduction of oxygen evolving complex function caused by stress. The greater damage was found in wild type than T6. Overaccumulation of glycine betaine in T6 could protect lipids in the thylakoid membrane from damage and stabilize the index of unsaturated fatty acids under stress. A lower ratio of monogalactosyl diacylglycerol/digalactosyl diacylglycerol and higher phosphatidylglycerol content in the thylakoid membrane of T6 were also observed under stress. These effects can promote stability of the thylakoid membrane. Otherwise, glycine betaine overaccumulation decreased photoinhibition of PSII under stress. The results also suggest that xanthophyll cycle-dependent non-radiative energy dissipation may be involved in the GB-mediated effects on PSII function under stress conditions. and G. P. Wang ... [et al.].
Chloroplast proteins of the Alb3/YidC/Oxa1p family are necessary for assembly of photosynthetic complexes in the thylakoid membranes. Alb3p in Arabidopsis thaliana is essential for posttranslational LHCII-integration into thylakoid membranes and participates in cotranslational assembly of D1. However, the pleiotropic defects of an Alb3p mutant, albino3, suggest additional functions for Alb3p. To obtain an impression of such potential further Alb3p activities from phenotypic manifestations, properties of mutants disturbed in thylakoid membrane protein transport or carotenoid biosynthesis were compared with the albino3 mutant. Specific defects observed in albino3 were similar to those in a carotenoid synthesis mutant. While this correlation did not provide tangible evidence for Alb3p being involved in the integration of carotenoids in photosynthetic complexes, it suggests a possible avenue for future investigations., M. Kugelmann, A. Fausser, F. Ossenbühl, A. Brennicke, and Obsahuje bibliografii
When cells get metals in small excess, mechanisms of avoidance occur, such as exclusion, sequestration, or compartmentation. When the excess reaches sub-lethal concentrations, the oxidative stress, that toxic metals trigger, leads to persistent active oxygen species. Biomolecules are then destroyed and metabolism is highly disturbed. At the chloroplast level, changes in pigment content and lipid peroxidation are observed. The disorganized thylakoids impair the photosynthetic efficiency. The Calvin cycle is also less efficient and the photosynthetic organism grows slowly. When an essential metal is given together with a harmful one, the damages are less severe than with the toxic element alone. Combined metals and phytochelatins may act against metal toxicity. and M. Bertrand, I. Poirier.
The distribution of rare earth elements (REEs) in the fern Dicranopteris dichotoma Bernh plants from a light rare earth elements mine (LRM) and a non-mining (NM) area in Longnan county of Jiangxi province, China were investigated by means of inductively coupled plasma-mass spectrometry, transmission electron microscopy, and energy-dispersive X-ray microanalysis. The photosynthetic characteristics of D. dichotoma were studied by chlorophyll (Chl) a fluorescence kinetics. Contents of REEs in the lamina and the root of D. dichotoma were higher than those in soils, and were mainly distributed in lamina. A part of them was found in the chloroplast. By comparing with D. dichotoma from NM area, the efficiency of photosystem 2 photochemistry and electron transport rate were significantly enhanced in lamina of the plant from LRM because most of REEs deposits were distributed along cell wall, in vacuole, and in chloroplast. High contents of REEs in lamina did not decrease the photosynthetic activities in LRM plants of D. dichotoma. Besides, D. dichotoma could change its β-carotene content to avoid the damaging effect of high REEs content. and L. F. Wang ... [et al.].