番茄果实采后NAD激酶活性与活性氧代谢的关系

以粉红期番茄 (Lycopersicon esculentum Mill.) 果实为试材，研究了采后果实在4℃和20℃下贮藏期间成熟衰老过程中NAD激酶（NADK，nicotinamide asenine dinucleotide kinase）活性及其底物NAD（H）、产物NADP（H）以及超氧阴离子、过氧化氢（H₂O₂）、丙二醛（MDA）含量的变化，并分析了其相互关系。结果表明，番茄果实在4℃贮藏时，NADK受到激活，贮藏前期活性比后期高；在20℃贮藏时，NADK除了在贮藏后期出现一个高峰外，整个贮藏期活性比4℃的低；NAD（H）含量的变化趋势与NADK活性的变化趋势相反。4℃贮藏的NADP（H）含量高于20℃下贮藏的，贮藏前期高于贮藏后期；同时，在4℃贮藏期间果实超氧阴离子生成速率、H₂O₂含量、膜氧化产物MDA含量以及番茄红素含量均比20℃贮藏的低，说明低温在延缓果实衰老的同时激活了NADK活性，NADK可能通过影响NAD（H）、NADP（H）的含量及比例来调控超氧阴离子生成速率和H₂O₂含量，从而调控番茄果实的成熟衰老。

Relationship Between NAD Kinase and Active Oxygen During Ripening and Senescence of Postharvested Tomato Fruit

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.