Molecular mechanisms of the effects of water stress on the reduction of the rate of leaf photosynthesis during senescence

点击翻译按钮获取中文摘要

Water stress enhances the reduction of the rate of leaf photosynthesis during senescence, which results in the reduction of dry matter production in crop plants under water stress. The objective of this research was undertaken to investigate molecular mechanisms of the effects of water stress on the rate of leaf photosynthesis during senescence. The followings are obtained results in the research.(1)The reduction in leaf levels of nitrogen and ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco) was responsible for the significant reduction of the rate of leaf photosynthesis during senescence under water stress in rice plants.(2)The amount of cytokinins, especially trans-zeatin, transported from roots to shoot decreased significantly in rice plants under water stress and there were close correlations between the total amount of the cytokinins and the rate of leaf photosynthesis, the leaf levels of nitrogen and Rubisco.(3)Application of additional cytokinin increased the nitrogen partitioning and the level of Rubisco mRNA (rbcL and rbcS).(4)From the results mentioned above, it was suggested that cytokinins transported from roots to shoot might be included in the mechanisms of the enhancement of the reduction in the rate of leaf photosynthesis. The reduction in the cytokinins transport under water stress might cause the decreased portioning of nitrogen to leaves and the decreased Rubisco synthesis and/or might enhance the Rubisco decomposition.(5)In order to elucidate the mechanism of molecular responses to water stress, the protein kinase activities were analyzed in cucumber cotyledons subjected to water stress. It has been found that ABA and salt stress, which induce the water stress responsible,-amylase, activate a 38 kDa protein kinase in cucumber cotyledons. This result suggests that the 38kDa protein kinase may play an important role in responses to water stress.