The Effects of Soil Salinity on Photosystem II of Rice Seedlings

Abstract

【Objective】 Photosystem II (water-plastoquinone oxidoreductase) is a protein complex in light-dependent reactions of oxygenic photosynthesis. The purpose of this paper is to study the effect of salt stress on photosystem II of rice seedlings. 【Method】 We used the varieties of Changbai 9 and Baijing 1 as the model plants. The salt was a mixture of salts at ratios of NaCl∶Na2SO4∶Na2CO3∶NaHCO3=1∶9∶1∶9. Solution of this salt mixture at concentrations from 0 to 120 mmol/L was added to the soil with the irrigation water. In each treatment, we measured and calculated the rapid chlorophyll fluorescence induction kinetic curve using the JIP-test, from which we calculated the the change in photosystem II in the leaves of the rice seedlings. 【Result】 When salt concentration was in 0~80 mmol/L, the chlorophyll fluorescence kinetic curve of the rice seedlings of both varieties was a typical OJIP curve, and the fluorescence intensity in each treatments differed significantly from the Point J. When salt concentration was increased to 120 mmol/L, the OJIP curve of the two varieties flattened, changing from the Point J to Point P, with the fluorescence intensity at Point I and Point P decreasing remarkably compared to CK (without salinity). There were non-linear relationships between salt concentration and the index PIABS, (φEo, φRo, ψEo), donor-side index (WK) and the recipient-side index (VJ) for both varieties. With the increase in soil salinity, water content, the contents of chlorophyll a and b, maximum photochemical efficiency (FV/FM), quantum yield and efficiency (φEo, φRo, ψEo), the index PIABS of both varieties all gradually decreased, while WK, VJ, and the heat dissipation ratio (φDo) gradually increased. The change in water content, chlorophyll content and chlorophyll fluorescence parameters of the two varieties gradually increased with the increase in salt concentration. 【Conclusion】 Saline-alkali stress severely damages the donor/acceptor laterality, especially the acceptor lateral performance index VJ, hindering electron transmission and reducing the quantum yield and the performance of photosystem II. PSII performance index PIABS, VJ, WK and quantum yield are nonlinearly correlated with the salt concentration.

Keywords

• rice
• salt-alkali mixed stress
• optical system ii