Effects of High Temperature Stress on PSII Function and Its Relation to D1 Protein in Chloroplast Thylakoid in Rice Flag Leaves

Abstract

On the basis of the artificial controlled temperature treatments in growth chambers, influences of high temperature stress at rice filling stage on the expression and distribution of D1 protein in leaf chloroplast thylakoid, as well as their relations to the decline of leaf photosynthetic rate and the damage of PSII membrane system were investigated by detecting the temporal pattern of leaf photosynthetic rate and chlorophyll fluorescence parameters, with SDS-PAGE electrophoresis, western-blotting and immunogold labeling methods. The results showed that rice flag leaves exposed high temperature generally had lower net photosynthetic rate (Pn), PSII potential efficiency(Fv /Fo) and solar energy transmitting efficiency(Fv/Fm) compared with those under normal temperature, with more severe damage and remarkable function dropping in chloroplast thylakoid due to prolonging stress times and accelerating leaves senescence.The amount of D1 protein in rice leaves under high temperature stress decreased significantly. In the two types of D1 protein, the amount of non-phosphorylated D1 protein was more sensitive to high temperature stress than the phosphorylated D1 protein.The RNA transcription of psbA gene in chloroplast, controlling D1 protein synthesis, was down-regulated by high temperature stress, inhabiting mRNA transcription and protein translation in D1 protein synthesis, thereby causing the functional damage of PSII reaction centre in thylakoid and dropping leaf photosynthetic rate under high temperature stress. It could be suggested that the functional damage of PSII reaction centre under high temperature stress be caused by the combined action of D1 protein hosphorylation and psbA gene expression, resulting in the decrease of photosynthetic rate and high temperature tolerance in two rice genotypes.