Effects Of Ascorbate Biosynthesis Gene Silencing On The Tolerance Of Tomato Under High Temperature And Light And Pst DC3000Stress

Plants are always subjected to various abiotic stress like high temperature and high light or biotic stress like Pst DC3000, which have negative effects on the plant growth and development. Worse than that not only the stress can kill the plants but also make the production decreased and quality debased, these problems bother people in recent years’production. As an important antioxidant, ascorbate takes part in many physiology processes, to our knowledge, it plays a role in regulating photosynthesis system, antioxidant system and cell division and expansion. Therefore, it has practical significance to study the role of ascorbate in resistance and its mechanism. In this paper, tomato (Solanum lycopersicum Mill.) is used as the material to study the response of the photosynthesis system and antioxidant system to high temperature and light stress involved in the regulation of ascorbate by virus induced gene silence (VIGS). We also investigate the resistance mechanism under biotic stress DC3000to further clarify the importance of ascorbate in regulating the tolerance of stress. The results are as follows:1.We construct three vectors by VIGS with the fragment of ascorbate biosynthesis genes:pTRV-GME1/2, pTRV-VTC2/5and pTRV-GLDH. We find that the maximal quantum yield of PSII (ΦPSⅡ) and the maximal photochemical efficiency of PSII (Fv/Fm) decreased under high temperature and light in ascorbate biosynthesis gene silenced plants, photoprotection parameters including non-photochemical quench (NPQ) and xanthophyll cycle increased to dissipate excess energy especially after high light treatment, at the same time, combined high temperature and light has the most serious effect on the plants. It is VTC2/5and GLDH gene silenced plants that their photosynthesis system damaged seriously compared with GME1/2. This maybe result from the inhibition of ascorbate biosynthesis in plants.2. The result shows that ascorbate biosynthesis gene silenced plants have less ability to resist high temperature and light stress compared with TRV plants for their electric conductivity increases and excess ROS accumulation. The excess accumulation of ROS activates the antioxidant system, gene silenced plants have lower value of AsA/DHA and no significant difference about GSH/GSSG. The antioxidant enzyme activities of SOD, GR, CAT, APX, DHAR and MDAR increase to scavenge ROS resulting form stress. The response of antioxidant system has no big difference between these gene silenced plants and this phenamenon maybe have some kind of relationship of ascorbate content in plants.3. We studied the response of ascorbate biosynthesis gene silenced plants after infection of Pst DC3000. The investigation shows that gene silenced plants can resist the Pst DC3000infection for their less bacterial cell growth and dead cells compared with TRV plants especially VTC2/5gene silenced plants. The mechanism is that pTRV-VTC2/5plants have an early H2O2burst, and it serves as secondary messenger inducing ICS gene up regulated expression. ICS is responsible for the biosynthesis of SA, which activates PRI gene’s expression, and PR1gene has positive influence on PR protein, which can deal with the pathogen infection. Furthermore, the results also reveal that pTRV-VTC2/5has strong ability in resisting pathogen implicating that VTC2/5gene is important in controlling the biosynthesis of ascorbate.