[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: Our previous study has demonstrated that both RuBP carboxylation limitation and RuBP regeneration limitation exist simultaneously in rice grown under free-air CO2 enrichment (FACE, about 200 μmol mol−1 above the ambient air CO2 concentration) conditions [G.-Y. Chen, Z.-H. Yong, Y. Liao, D.-Y. Zhang, Y. Chen, H.-B. Zhang, J. Chen, J.-G. Zhu, D.-Q. Xu, Photosynthetic acclimation in rice leaves to free-air CO2 enrichment related to both ribulose-1,5-bisphosphate carboxylase limitation and ribulose-1,5-bisphosphate regeneration limitation. Plant Cell Physiol. 46 (2005) 1036–1045]. To explore the mechanism for forming of RuBP regeneration limitation, we conducted the gas exchange measurements and some biochemical analyses in FACE-treated and ambient rice plants. Net CO2 assimilation rate (Anet) in FACE leaves was remarkably lower than that in ambient leaves when measured at the same CO2 concentration, indicating that photosynthetic acclimation to elevated CO2 occurred. In the meantime the maximum electron transport rate (ETR) (Jmax), maximum carboxylation rate (Vcmax) invivo, and RuBP contents decreased significantly in FACE leaves. The whole chain electron transport rate and photophosphorylation rate reduced significantly while ETR of photosystem II (PSII) did not significantly decrease and ETR of photosystem I (PSI) was significantly increased in the chloroplasts from FACE leaves. Further, the amount of cytochrome (Cyt) f protein, a key component localized between PSII and PSI, was remarkably declined in FACE leaves. It appears that during photosynthetic acclimation the decline in the Cyt f amount is an important cause for the decreased RuBP regeneration capacity by decreasing the whole chain electron transport in FACE leaves.
[Show abstract][Hide abstract] ABSTRACT: In order to explore the relationship between grain yield and photosynthesis, the yield composition and leaf photosynthetic rate in some super hybrid rices and ordinary hybrid rice 'Shanyou 63' as control were measured in 2000-2005. The results were as follows. (1) The yield levels of the four super hybrid rices, 'Pei'ai 64S/E32', 'P88S/0293', 'Jin23A/611' and 'GD-1S/RB207', were significantly higher, being 108%-120% of 'Shanyou 63'. (2) These super hybrid rices had a better plant type with more erect upper layer leaves and bigger panicles or more spikelets per panicle, being 125%-177% of spikelets Shanyou 63 spikelets. (3) Net photosynthetic rates of these super hybrid rices were significantly higher in the second leaf but not necessarily in the first leaf or flag leaf than those of spikelets Shanyou 63 spikelets. (4) The removal of half flag leaf led to a decline in the seed-setting rate, while the removal of half panicle induced its increase in spikelets GD-1S/RB207 spikelets. Hence, higher yield in these super hybrid rices can be attributed to their bigger panicles, better plant type and higher light use efficiency of their canopies. Raising the photosynthetic capacity of each leaf, especially flag leaf, is the key to overcome the photosynthate-source restriction on grain yield and to make a new breakthrough of yield potential in future breeding of super hybrid rice.
Zhi wu sheng li yu fen zi sheng wu xue xue bao = Journal of plant physiology and molecular biology 07/2007; 33(3):235-43.
[Show abstract][Hide abstract] ABSTRACT: Net photosynthetic rates (Pns) in leaves were compared between rice plants grown in ambient air control and free-air CO2 enrichment (FACE, about 200 micromol mol(-1) above ambient) treatment rings. When measured at the same CO2 concentration, the Pn of FACE leaves decreased significantly, indicating that photosynthetic acclimation to high CO2 occurs. Although stomatal conductance (Gs) in FACE leaves was markedly decreased, intercellular CO2 concentrations (Ci) were almost the same in FACE and ambient leaves, indicating that the photosynthetic acclimation is not caused by the decreased Gs. Furthermore, carboxylation efficiency and maximal Pn, both light and CO2-saturated Pn, were decreased in FACE leaves, as shown by the Pn-Ci curves. In addition, the soluble protein, Rubisco (ribulose-1,5-bisphosphate caboxylase/oxygenase), and its activase contents as well as the sucrose-phosphate synthase activity decreased significantly, while some soluble sugar, inorganic phosphate, chlorophyll and light-harvesting complex II (LHC II) contents increased in FACE leaves. It appears that the photosynthetic acclimation in rice leaves is related to both ribulose-1,5-bisphosphate (RuBP) carboxylation limitation and RuBP regeneration limitation.