The Relationship Between Changes Of Endogenous Hormones And Reactive Oxygen Species In Tomato Seed And Fruit Ripening

Regulation mechanism of fruit ripening is a hot spot of postharvest physiology research. Recent researches suggest that endogenous hormones and reactive oxygen species act as signals regulating fruit ripening and senescence. This dissertation focused on the dynamics in postharvest ripening and differences of endogenous phytohormones and reactive oxygen metabolism between tomato expressing anti-sense LeACS2 gene and wild tomato {Lycopersicon esculentum Mill. cv. Lichun) in order to elucidate the relationship between seed and fruit ripening, and the possible role of phytohormones and metabolism of reactive oxygen in this process.During postharvest fruit ripening, endogenous phytohormones and reactive oxygen species (O₂^-and H₂O₂) in seed of anti-sense LeACS2 gene and wild tomato, were much higher and earlier than those in pericarp. It suggests that high concentration of phytohormones in seed may be closely related with triggering fruit ripening and senescence, in which H₂O₂ play an important role.During postharvest fruit ripening, ethylene biosynthesis of tomato expressing anti-sense LeACS2 gene was inhibited, as well as lower production of reactive oxygen species, However, ethylene production in seed did not reduced, although this high concentration of ethylene production in seed did not trigger fruit ripening. It suggests that decreased sensitivity of anti-sense LeACS2 tomato to ethylene and lower content of ROS are partly responsible for its delayed ripening.Great changes were found in the balance of hormones in tomato expressing anti-sense LeACS2 gene. It was revealed that peak of ratio of IAA to ABA appeared before ethylene production peak, and in tomato expressing anti-sense LeACS2 gene, this ratio reduced much slower than that in wild. It suggests that the ratio of IAA to ABA content affects fruit ripening greatly.Treatment with exogenous abscisic acid (ABA) and Fluridone (ABA biosynthesis inhibitor) indicated that abscisic acid affected ACC synthase and ACC oxidase activities, and then promoted ethylene production. It may suggest that ABA regulates fruit ripening by triggering ethylene production.