We investigated the role of cyclic electron flow around photosystem 1 (CEF1) and state transition (ST) in two soybean cultivars that differed in salt tolerance. The CEF1 and maximum photochemical efficiency (Fv/Fm) were determined under control and NaCl (50 mM) stress and the NaCl-induced light-harvesting complex 2 (LHC2) phosphorylation in vitro was analysed in light and dark. NaCl induced the increase of CEF1 more greatly in wild soybean Glycine cyrtoloba (cv. ACC547) than in cultivated soybean Glycine max (cv. Melrose). The Fv/Fm was reduced less in G. cyrtoloba than in G. max after 10-d NaCl stress. In G. cyrtoloba, the increase of CEF1 was associated with enhancement of LHC2 phosphorylation in thylakoid membrane under both dark and light. However, in G. max the NaCl treatment decreased the LHC2 phosphorylation. Treatment with photosynthetic electron flow inhibitors (DCMU, DBMIB) inhibited LHC2 phosphorylation more in G. max than in G. cyrtoloba. Thus the NaCl-induced up-regulation in CEF1 and ST might contribute to salt resistance of G. cyrtoloba. and K. X. Lu ... [et al.].
The physiological response of two soybean varieties to salt stress was examined. The results showed that salt stress induced a significantly (p<0.01) lower decrease of the net photosynthetic rate (PN) in salt-tolerant S111-9 than in salt-sensitive Glycine max. PN decrease was positively related to the decrease of stomatal conductance (gs) and intercellular CO2 concentration (Ci) in S111-9, while with g s in G. max. a threshold of relative water content (RWC) was found, above which a slight decrease in RWC lead to a sharp reduction in gs. The photochemical quenching (qP), the efficiency of open PSII centers (ΦPSII) and the Rubisco activity (RA) significantly decreased with increasing salinity level in G. max. The maximum PSII quantum yield (Fv/Fm) decreased significantly under the highest NaCl in both varieties. The higher reduction of RA in G. max was attributed to Rubisco content, which was mainly regulated at LSU expression level rather than at rbcL transcript level. These findings led us to conclude that the salt-induced reduction in PN was mainly due gs and RA for S111-9 and G. max, respective. and K. X. Lu ... [et al.].
To investigate into the relationship between two Rubisco activase (RCA) isoforms and photosynthetic rate, a set of enzyme-linked immunosorbent assay (ELISA) were developed for accurate quantification of two RCA polypeptides based on two specific monoclonal antibodies against different RCA isoforms. The results showed that content of RCA small isoform (RCAS) was 5-fold more than that of RCA large isoform (RCAL) content in all leaves and the RCAL/RCAS ratio reached maximum in the leaf with the highest photosynthetic rate. Although the difference in two RCA polypeptides accumulation in leaves was caused by different transcript level of two isoforms, the decrease of RCAL/RCAS ratio during leaf aging was not attributed to transcriptional regulation. The leaves with higher photosynthetic capacity exhibited higher RCAL/RCAS ratio and the decrease in photosynthetic rate and Rubisco activation state highly correlated with the decline of RCAL/RCAS ratio during leaf aging. Our results suggest that there is a posttranscriptional mechanism regulating the RCAL/RCAS ratio, which may play as a regulator modulating photosynthetic capacity during leaf aging in rice plant. and D. Wang ... [et al.].
To investigate how excess excitation energy is dissipated in a ribulose-1,5-bisphospate carboxylase/oxygenase activase antisense transgenic rice with net photosynthetic rate (PN) half of that of wild type parent, we measured the response curve of PN to intercellular CO2 concentration (Ci), electron transport rate (ETR), quantum yield of open photosystem 2 (PS2) reaction centres under irradiation (Fv'/Fm'), efficiency of total PS2 centres (ΦPS2), photochemical (qP) and non-photochemical quenching (NPQ), post-irradiation transient increase in chlorophyll (Chl) fluorescence (PITICF), and P700+ re-reduction. Carboxylation efficiency dependence on Ci, ETR at saturation irradiance, and Fv'/Fm', ΦPS2, and qP under the irradiation were significantly lower in the mutant. However, NPQ, energy-dependent quenching (qE), PITICF, and P700+ re-reduction were significantly higher in the mutant. Hence the mutant down-regulates linear ETR and stimulates cyclic electron flow around PS1, which may generate the ΔpH to support NPQ and qE for dissipation of excess excitation energy. and S.-H. Jin ... [et al.].