Abstract: Tomato (Lycopersicon esculentum Mill.) pericarp at pink stage was used to investigate the changes of NAD kinase (NADK) activity and reactive oxygen during ripening and senescence of postharvest tomato fruit at 4℃ and 20℃. Contents of NAD(H), NADP(H) and hydrogen peroxide (H₂O₂) and superoxide production rate were determined. The degree of the oxidative damage to the membrane lipids (MDA content) and ripening index (lycopene content) were also examined. The results showed that NADK activity increased sharply at early stage and declined significantly at late stage during ripening and senescence at 4℃, but its activity kept lower at 20℃ except higher activity was observed on the 5th day of storage at 20℃. The change model of NAD(H) content contrasted with one of NADK activity. Higher NADP（H）content was found at early store stage than at late store stage and at 4℃ than at 20℃. Significant increase of lycopene content was observed at late store stage at 20℃, but little change was found at the same stage at 4℃. The maximum MDA content appeared earlier at 20℃ than at 4℃. NADK might be involved in postponing ripening and senescence of postharvest tomato fruit by regulating the content and proportion of NAD(H) to NADP(H) which influenced the O₂^- production rate and H₂O₂ content.

Key words: Tomato, Ripening and senescence, NAD kinase, NAD(H), NADP(H), Active oxygen