CO_2加富对杂交稻及其亲本原初光能转化效率和激发能分配的影响

研究了ＣＯ２加富对杂交稻及其亲本叶绿素含量、ＰＳⅡ原初光能转化效率和潜在活性、以及激发能在两个光系统之间分配的影响。结果表明,在ＣＯ２加富条件下,父本和母本叶片单位面积的叶绿素含量增加,但杂交稻叶片单位面积的叶绿素含量反而下降;杂交稻、它的父本及母本的ＰＳⅡ原初光能转化效率和潜在活性分别提高８％和２４％、１８％和２９％及５％和２１％。此外,ＣＯ２加富还可提高两个光系统之间激发能分配的调节能力。     

Physiological characteristics of the primitive CO<Subscript>2</Subscript> concentrating mechanism in PEPC transgenic rice

The relationship between carbon assimilation and high-level expression of the maize PEPC in PEPC transgenic rice was studied by comparison to that in the untransformed rice, japonica kitaake. Stomatal conductance and photosynthetic rates in PEPC transgenic rice were higher than those of untransformed rice, but the increase of stomatal conductance had no statistical correlation with that of photosynthetic rate. Under high levels of light intensity, the protein contents of PEPC and CA were increased significantly. Therefore the photosynthetic capacity was increased greatly (50%) with atmospheric CO2 supply. While CO2 release in leaf was reduced and the compensation point was lowered correspondingly under CO2 free conditions. Treatment of the rice with the PEPC-specific inhibitor DCDP showed that overexpression of PEPC and enhancement of carbon assimilation were related to the stability of Fv/Fm. Labeling with 14CO2 for 20 s showed more 14C was distributed to C4 primary photosynthate asperate in PEPC transgenic rice, suggesting that there exists a limiting C4 photosynthetic mechanism in leaves. These results suggest that the primitive CO2 concentrating mechanism found in rice could be reproduced through metabolic engineering, and shed light on the physiological basis for transgenic breeding with high photosynthetic efficiency.     

The xanthophyll cycle and antioxidative defense system are enhanced in the wheat hybrid subjected to high light stress

Although the wheat hybrids have often shown higher grain yields, the physiological basis of the higher yields remains unknown. Previous studies suggest that tolerance to photoinhibition in the hybrid may be one of the physiological bases (Yang et al., 2006, Plant Sci 171:389-97). The objective of this study was to further investigate the possible mechanism responsible for tolerance to photoinhibition in the hybrid. Photosystem II (PSII) photochemistry, the xanthophyll cycle, and antioxidative defense system were compared between the hybrid and its parents subjected to high light stress (1500 μmol m⁻² s⁻¹). The analyses of oxygen-evolving activity, chlorophyll fluorescence, and protein blotting demonstrated that the higher tolerance in the hybrid than in its parents was associated with its higher tolerance of PSII to photoinhibition. High light induced an increase in non-photochemical quenching, and this increase was greater in the hybrid than in its parents. There were no differences in the pool size of the xanthophyll cycle between the hybrid and its parents. The content of violaxanthin decreased significantly, whereas the content of zeaxanthin + antherxanthin increased considerably during high light treatments. However, the decrease in violaxanthin content and the increase in zeaxanthin + antherxanthin content were greater in the hybrid than in its parents. High light resulted in a significant accumulation of H₂O₂, O₂⁻ and catalytic Fe, and this accumulation was less in the hybrid than in its parents. High light induced a significant increase in the activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, and these increases were greater in the hybrid than its parents. These results suggest that the higher tolerance to photoinhibition in the hybrid may be associated with its higher capacity for antioxidative defense metabolism and the xanthophyll cycle.     

水分胁迫对小麦叶绿素a荧光诱导动力学的影响

利用调制式荧光动力学分光光度计研究了水分胁迫对小麦叶片及叶绿体的叶绿素α荧光诱导动力学的影响.结果表明,水分胁迫对小麦光合作用的损伤是多部位的,它影响了PSⅠ活性、PSⅡ活性以及CO_2同化.对于PSⅡ的损伤部位除了它的氧化侧处,还可能损伤了PSⅡ反应中心.     

Changes in Thermostability of Photosystem Ⅱ and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll Protein Complexes

We studied the difference in thermostability of photosystem Ⅱ (PSⅡ) and leaf lipid composition between a T-DNA insertion mutant rice (Oryza sativa L.) VG28 and its wild type Zhonghua11. Native green gel and SDS-PAGE electrophoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSⅡ photochemistry (Fv/Fm) and oxygen-evolving activity of PSⅡ in leaves significantly decreased with increasing temperature. However, the PSⅡ activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of unsaturation of membrane lipids on the thermostability of PSll are discussed.     

Structural and functional analysis of the antiparallel strands in the lumenal loop of the major light-harvesting chlorophyll a/b complex of photosystem II (LHCIIb) by site-directed mutagenesis

The light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCIIb) fulfills multiple functions, such as light harvesting and energy dissipation under different illuminations. The crystal structure of LHCIIb at the near atomic resolution reveals an antiparallel strands structure in the lumenal loop between the transmembrane helices B/C. To study the structural and functional significances of this structure, three amino acids (Val-119, His-120, and Ser-123) in this region have been exchanged to Phe, Leu, and Gly, respectively, and the influence of the mutagenesis on the structure and function of LHCIIb has been investigated. The results are as follows. 1) Circular dichroism spectra of the mutations reveals that the antiparallel strands in the lumenal region are very important for adjusting pigment conformation in the neoxanthin domain of LHCIIb. Although the mutagenesis causes only a slight loss of the Neo binding in the complexes (V119F, 0.09; S123G, 0.19; and H120L, 0.27), it imparts remarkable changes to the pigment conformation. 2) Substituting Ser-123 with Gly results in a higher susceptibility to photodamage, an increased tendency to aggregate, and enhanced fluorescence quenching induced by the medium acidification. These results demonstrate that this antiparallel strands domain plays an important role in regulating the pigment conformation and in adjusting the aggregation and the fluorescence yield of LHCIIb.     

The composition and spectral properties of three different forms of light-harvesting complex II

Light-harvesting pigment-protein complexes arrayed in the thylakoid membrane serve as antenna to capture light energy and deliver it to photosynthetic reaction centers. The antenna complex of photosystem II (LHC II) is the most abundant pigment-protein complex in green plants. LHC II contains a set of polypeptides encoded by nuclear genes belonging to Lhcb family, of which, LHCB1, LHCB2 and LHCB3, encoded by Lhcb13, assemble to form heterotrimer on thylakoid membrane. The LHC II tr…     

Effect of Sodium Thiosulfate on the Depletion of Photosynthetic Apparatus in Cyanobacterium Synechocystis sp. PCC 6803 Cells Grown in the Presence of Glucose

Fluorescence spectroscopy at 77 K showed that the application of glucose lead to the depletion of phycobilisomes (PBS) and photosystems (PS) 2 and 1, and that PS2 was more sensitive to glucose than PS1. The application of sodium thiosulfate, an effective scavenger of reactive oxygen intermediates, counteracted the effects of glucose. Sodium thiosulfate effectively protected photosynthetic apparatus, PS2, PS1, and PBS against glucose-induced depletion. Sodium thiosulfate showed strong capability to inhibit the disappearance of chlorophyll induced by glucose. At a relatively low concentration of glucose, the application of sodium thiosulfate can even be helpful for the assembly of photosynthetic apparatus. Hence the reactive oxygen species might be involved in the depletion of the photosynthetic apparatus in the cyanobacterium Synechocystis sp. PCC 6803 cells grown in the presence of glucose.