[Show abstract][Hide abstract] ABSTRACT: Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) in the thylakoid membrane (TM) has been shown to play a role in protection and regulation of photosynthesis under moderate heat stress. However, the physiological significance of RCA bound to the TM (TM-RCA) without heat stress remains unknown. In this study, it is first shown, using experiments in vivo, that the TM-RCA varies in rice leaves at different development stages, under different environmental conditions, and in a rice mutant. Furthermore, it is shown that the amount of TM-RCA always increased when the Rubisco activation state and the pH gradient across the TM (DeltapH) decreased. It was then demonstrated in vitro that the RCA bound dynamically to TM and the amount of TM-RCA increased during Rubisco activation. A high level of ATP and a high pH value promoted the dissociation of RCA from the TM. Both the RCA association with and dissociation from the TM showed conformational changes related to the ATP level or pH as indicated by the changes in fluorescence intensity of 1-anilinonaphthalene-8-sulphonic acid (ANS) binding to RCA. These results suggest that the reversible association of RCA with the TM is ATP and pH (or DeltapH) dependent; it might be involved in the RCA activation of Rubisco, in addition to the previously discovered role in the protection and regulation of photosynthesis under heat stress.
[Show abstract][Hide abstract] ABSTRACT: Besides the non-cyclic electron transport driven by the two photosystems (PSII and PSI), the cyclic electron transport pathways around PSI are also essential for efficient photosynthesis. As one of these pathways, the NAD(P)H dehydrogenase complex (NDH complex) mediated cyclic electron transport has been well studied. Along with the identification of the plastid terminal oxydase (PTOX), the functions of NDH-mediated cyclic and chlororepiratory electron transport in energy supply for photosynthesis as well as in the resistance to photooxidative stress have increasingly been brought to the researchers' attention. In the present paper, the structural characteristics of NDH complex, the regulatory mechanism, and the physiological significance of NDH mediated cyclic electron transport and chlororespiration are reviewed.
Zhi wu sheng li yu fen zi sheng wu xue xue bao = Journal of plant physiology and molecular biology 05/2007; 33(2):91-100.
[Show abstract][Hide abstract] ABSTRACT: After incubation at 42 degrees C for more than 48 h, brown damages occurred on the stems of tobacco (Nicotiana tabacum L.) ndhC-ndhK-ndhJ deletion mutant (deltandhCKJ), followed by wilt of the leaves, while less the phenotype was found in its wild type (WT). Analysis of the kinetics of post-illumination rise in chlorophyll fluorescence indicated that the PSI cyclic electron flow and the chlororespiration mediated by NAD(P)H dehydrogenase (NDH) was significantly enhanced in WT under the high temperature. After leaf disks were treated with methyl viologen (MV), photosynthetic apparatus of deltandhCKJ exhibited more severe photo-oxidative damage, even bleaching of chlorophyll. Analysis of P700 oxidation and reduction showed that the NDH mediated cyclic electron flow probably functioned as an electron competitor with Mehler reaction, to reduce the accumulation of reactive oxygen species (ROS). When leaf disks were heat stressed at 42 degrees C for 6 h, the photochemical activity declined more markedly in deltandhCKJ than in WT, accompanied with more evident decrease in the amount of soluble Rubisco activase. In addition, the slow phase of millisecond-delayed light emission (ms-DLE) of chlorophyll fluorescence indicated that NDH was involved in the building-up of transthylakoid proton gradient (deltapH), while the consumption of deltapH was highly inhibited in deltandhCKJ after heat stress. Based on the results, we supposed that the cyclic electron flow mediated by NDH could be stimulated under the heat stressed conditions, to divert excess electrons via chlororespiration pathway, and sustain CO2 assimilation by providing extra deltapH, thus reducing the photooxidative damage.
Science in China Series C Life Sciences 09/2006; 49(4):311-21. DOI:10.1007/s11427-006-2005-2 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, the function of the NAD(P)H dehydrogenase (NDH)-dependent pathway in suppressing the accumulation of reactive oxygen species in chloroplasts was investigated. Hydrogen peroxide accumulated in the leaves of tobacco (Nicotiana tabacum) defective in ndhC-ndhK-ndhJ (DeltandhCKJ) at 42 degrees C and 4 degrees C, and in that of wild-type leaves at 4 degrees C. The maximum quantum efficiency of PSII decreased to a similar extent in both strains at 42 degrees C, while it decreased more evidently in DeltandhCKJ at 4 degrees C. The parameters linked to CO(2) assimilation, such as the photochemical efficiency of PSII, the decrease of nonphotochemical quenching following the initial rise, and the photosynthetic O(2) evolution, were inhibited more significantly in DeltandhCKJ than in wild type at 42 degrees C and were seriously inhibited in both strains at 4 degrees C. While cyclic electron flow around PSI mediated by NDH was remarkably enhanced at 42 degrees C and suppressed at 4 degrees C. The proton gradient across the thylakoid membranes and light-dependent ATP synthesis were higher in wild type than in DeltandhCKJ at either 25 degrees C or 42 degrees C, but were barely formed at 4 degrees C. Based on these results, we suggest that cyclic photophosphorylation via the NDH pathway might play an important role in regulation of CO(2) assimilation under heat-stressed condition but is less important under chilling-stressed condition, thus optimizing the photosynthetic electron transport and reducing the generation of reactive oxygen species.
[Show abstract][Hide abstract] ABSTRACT: The primary mechanism of growth difference of cucumber (Cucumis sativus L.) seedlings cultured under sulfur lamp and xenon lamp in a phytotron was investigated. Compared with cucumber seedlings grown under xenon lamp, those under sulfur lamp were shorter, and the cell number in the middle hypocotyls epidermis and cortex of them were more (Fig. 1, Table 1). Endogenous hormone analysis indicates that the content of IAA and GA(3) of seedlings under sulfur lamp were 17% and 24% lower, while ABA content was 31% higher than that under xenon lamp (Fig. 2). Based on these results, it is suggested that the growth difference between cucumber seedlings grown under sulfur lamp and under xenon lamp might be related to the control of endogenous hormones.
Zhi wu sheng li yu fen zi sheng wu xue xue bao = Journal of plant physiology and molecular biology 01/2005; 30(6):687-90.