Abstract: Tomato (Lycopersicom esculentum Mill. ) pericarp and seed were used to investigate the changes of reactive oxygen and activities of antioxidant system enzymes during fruit ripening and senescence. Superoxide p roduction rate (O₂ ^·) , hydrogen peroxide (H₂O₂ ) content and the activities of superoxide dismutase ( SOD) , catalase (CAT) , ascorbate peroxidase (APX) and lutathione reductase (GR) were determined. The degrees of the oxidative damage to the membrane lip ids (MDA content) were also examined. The results showed that O₂^· production rate and H₂O₂ content in seed were significantly higher than those in pericarp at allmaturity stages, and the H₂O₂ content in the seed increased sharp ly after the p ink stage. Higher activities of SOD, CAT and GR were observed in the seeds than in the pericarp. Higher APX activities were
found from the BR stage to the RED stage in seed and that in pericarp. At the beginning of fruit ripening, an increase of CAT activity followed the ccumulation of H₂O₂ , but its activity declined quickly by the end of ripening, while that of APX and GR kep t partial activities. These patterns of enzyme activity suggest that the AsA-GSH cycle might play an important role in scavenging H₂O₂ . The maximum MDA content appeared in seeds earlier than in the pericarp, the maximum being 115 fold of that in the pericarp. High concentration of reactive oxygen in seed might be closely related with fruit ripening, and H₂O₂ might be an important factor in triggering the senescence.

Key words: Tomato, Seed, Ripening, Senescence, Reactive oxygen, Antioxidant enzymes