Functional Analysis Of The LeMDAR In Tomato Under UV-B Stress

UV-B radiation is one of the factors that affect growth and development of plant. UV-B induces a big amount of reactive oxygen species (ROS), which did damage to biological big molecule including DNA and RNA in plant. The chloroplast is one of the major sites for formation of ROS in plant. To remove the ROS rapidly is essential for protecting photosynthetic apparatus and maintaining photosynthesis under environmental stress. Ascorbic acid (AsA) is a key component for ROS scavenging system in chloroplast. chlMDAR (chloroplastic monodehyedroascorbate reductase, chlMDAR) is a pivotal enzyme in AsA regeneration. It reduces DHA to AsA and maintains the chloroplast AsA pool. Therefore, to investigate the relationship between MDAR gene and UV-B stress is of great significance.We have cloned the chloroplast LeMDAR from tomato leaf in our lab previously. Overexpression of LeMDAR has shown a enhanced resistance to Methyl viologen-induced oxidative stress. In this study, we used wild type (WT) and sense lines (S-3, S-17, S-23) to measure net photosynthetic rate, chlorophyll fluorescence parameters, the production of chloroplastic ROS, lipid peroxidation and the content of Dl protein. The main results were as follows:(1) PCR and qRT-PCR showed that we had identified the sense transgenic tomato plants. Plants with overexpression of LeMDAR had significantly higher mRNA transcript than wild type.(2) The general AsA content, reducing AsA content and MDAR enzyme activity of tomato plants were investigated before and after ultraviolet stress. Under normal light, transgenic plants have higher MDAR activity and AsA level than wild type plants. After ultraviolet stress, transgenic plants could still maintain a higher level of MDAR activity and AsA level. The results showed that the ultraviolet stress could accelerate the quenching of AsA. Transgenic plants accelerated the AsA recovering. Transgenic plants had lower content of H2O2and O2-, and higher resistance.(3) After stress treatment, transgenic plants had higher photosynthetic capacity compared with wild type. Western blot of D1protein showed that transgenic plants had lower D1degradation rate than wild type after ultraviolet stress. Decrease of Pn in WT plants was more serious.The research results showed that overexpression of LeMDAR enhanced the resistance to UV-B. The enhanced MDAR activity can reduce ROS and the oxidative damage, which protected photosystem â…¡.