高温胁迫下甜菜碱促进光系统II修复循环机理研究

Heat stress is one of the main environmental factors that limits the growth and productivity of crop plants, it seems likely that photosynthesis is most sensitive to heat stress among various physical processes. The repair of photosystem II plays an important role in enhancing tolerance of plants to environmental stress. Glycinebetaine is a compatible solute that accumulation in certain plants and microorganisms in response to various type of stress and is an effective protectant against abiotic stress. GB is synthesized from choline, and betaine aldehyde dehydrogenase(BADH) and choline oxidase(COD) are key enzymes in the synthesis of glycinebetaine. In this research, we will use BADH transgenic tomato and COD transgenic tomato plants, which can accumulate glycinebetaine in vivo, as materials to study the mechanism of glycinebetaine in accelerating the repair of photosystem II under high temperature stress. The activity of photosystem II, the D1 content, the expression of key enzyme genes that involved in the degradation and synthesis of D1 protein such as FtsH, Deg and psbA gens will be measured and analyzed to explore the mechanism of glycinebetaine accelerating the repair cycle of photsystem II. Also we will measure the CO2 assimilation, the level of reactive oxygen species (ROS), and the activities of antioxidantive enzymes to investigate the pathway that involved in the repair of photosystem II which are regulated by glycinebetaine. These researches will explore the physiological and molecular mechanism of glycinebetaine in accelerating repair of photosystem II and are important to improve the thermotolerance of crop plants by biotechnology.

高温胁迫是限制作物生长和产量的重要环境因子，光合作用对高温胁迫非常敏感。光系统II修复循环对提高植物抗逆性具有重要作用。甜菜碱是植物在逆境胁迫下重要的保护物质，甜菜碱醛脱氢酶（BADH）和胆碱氧化酶（COD）是甜菜碱合成途径中的关键酶。本项目以转BADH基因和转COD基因番茄为试材，从光系统II反应中心受损D1蛋白的降解和D1蛋白从头合成两个方面，通过测定光系统II活性、蛋白印迹检测D1蛋白含量、荧光定量PCR分析参与受损D1蛋白降解的FtsH基因、Deg基因以及D1蛋白合成的psbA基因的表达，研究甜菜碱调控PSII修复循环的作用位点和机理。通过测定CO2同化、活性氧积累、抗氧化酶活性以及基因芯片分析，探讨甜菜碱在高温胁迫下促进光系统II修复的作用途径。研究结果将阐明高温胁迫下甜菜碱促进光系统II修复的机制，同时对提高作物耐热性的基因工程具有重要指导意义。

高温胁迫是限制作物生长和产量的重要环境因子，光合作用对高温胁迫非常敏感。光系统II是高温等逆境胁迫主要伤害靶点，光系统II修复循环对提高植物抗逆性具有重要作用。甜菜碱是植物在逆境胁迫下重要的保护物质，甜菜碱醛脱氢酶（BADH）和胆碱氧化酶（COD）是甜菜碱合成途径中的关键酶。本项目以转BADH基因和转COD基因番茄为试材，从光系统II反应中心受损D1蛋白的降解和D1蛋白从头合成两个方面，通过测定光系统II活性、蛋白印迹检测D1蛋白含量、荧光定量PCR分析参与受损D1蛋白降解的FtsH基因、Deg基因以及D1蛋白合成的psbA基因的表达，研究甜菜碱调控PSII修复循环的作用位点和机理。通过测定CO2同化、活性氧积累、抗氧化酶活性以及基因芯片分析，探讨甜菜碱在高温胁迫下促进光系统II修复的作用途径。研究结果表明：转BADH基因和转COD基因番茄植株能够合成和积累累甜菜碱，增强了番茄的耐热性。高温胁迫下，番茄的光合速率下降，产生光抑制，而转基因番茄和外源喷施甜菜碱番茄植株较野生型番茄植株在高温下的光合速率较高，光抑制程度较轻，实际光化学效率较高，D1蛋白含量较高，表现出了对高温较强的耐性。甜菜碱能够减轻高温对D1蛋白的损伤，维持D1蛋白的稳定性。高温胁迫下，在D1蛋白降解方面，甜菜碱能够维持较高的FtsH和Deg的表达，及时将受损的D1蛋白降解。在D1蛋白的从头合成方面，甜菜碱能够维持较高的psbA的表达。甜菜碱能够提高高温胁迫条件下植物的抗氧化酶的活性，降低了H2O2积累和O2-的产生速率，抑制ROS的过量积累，减轻了植株的氧化胁迫程度，使可溶性蛋白的氧化水平较野生型植株低，从而使翻译延伸因子EF-G的活性受抑制程度降低，减轻ROS对D1蛋白翻译过程的抑制，从而加快D1蛋白的从头合成。研究结果初步阐明了高温胁迫下甜菜碱促进光系统II修复的机制，对对提高作物耐热性的基因工程具有重要理论指导意义。