The Influence Of Reactive Oxygen Species Metabolism And Related Enzymes On Peach Fruit Maturation And Softening

Peach fruits [Prumus persica (L.) Batsch, cv. Yuhuasanhao ] were used as materials to study basic physiological changes,the metabolism of reactive oxygen species (ROS) and the membrane lipid peroxidation during on-tree ripening and post-harvest storage, involving their influence on the proceeding of peach fruit senescence.(1) Firstly, changes of ethylene production, firmness and total soluble solids (TSS) content were determined in present study. During both on-tree ripening and post-harvest storage, remarkble peaks of ethylene production were presented. The firmness of fruits declined gradually. There were two parts during the firmness descender: slowly descender in the front stage of maturation and quick descender in the later stage of maturation; the ethylene production was remarkably different in the different temperature storage, the ethylene production of normal temperature was remarkably higher than that of low temperature. This indicates that low temperature could remarkably restrain the ethylene biosynthesis. The firmness of normal temperature storage descended more quickly. The firmness of low temperature was remarkable larger than that of normal temperature. These indicate that low temperature could delay peach fruit senescence.(2) Changes of O₂^-.production rate,the content of H₂O₂, GSH and ASA, the activity of catalase(CAT), superoxide dismutase (SOD), peroxidase ( POD ) glutathione peroxidase(GSH-Px), ascorbate peroxidase(APX), ascorbate oxidase(AAO) and NADP phosphatase. As shown in this work, there were both a trend of accumulation during the fruit maturation and storage.But the ROS contents of the peach fruit which was stored at the low temperature was lower.The activity of SOD might be induced by ROS contents during medium-term storage, these associated with the slighter degree of the membrane lipid peroxidation suggested that increscent contents of ROS induced the damage of cell membrane as peach fruit senescence, and promoted fruit senescence as a result.(3)The activity of allene oxide synthase and Ca²⁺-ATPase, the content of MDA were determined in the peach fruit maturation and senescence in this paper. The results indicate that LOX is an important enzyme participating in the membrane lipid peroxidation. LOX induced the number increase of free radicals which could make peach fruit senescence. The activity of AOS during normal temperature storage was remarkably higher than that during low temperature storage. This indicates that the activity of AOS is restrained during low temperature storage. There were some peaks during the change of the activity of AOS.The appearance of the AOS activity peak of normal temperature storage was 4 days ahead low temperature storage. The content increase of MDA indicated that the membrane lipid peroxidation degree got heavy during the peach fruit maturation and senescence.The decline of Ca²⁺-ATPase activity indicated the ability of cell which maintain the cytoplasmic Ca²⁺ homeostasis got down. All of theses changes could promote the peach fruit senescence.(4)The relationship among basic physiological changes, the metabolism of reactive oxygen species (ROS) and the membrane lipid peroxidation during on-tree ripening and post-harvest storage were analyzed as a whole, involving their influence on the proceeding of peach fruit senescence. The results indicated that SOD could participate the metabolization which restrains ethylene synthesization during the peach fruit maturation and softening. The reactive oxygen species eliminaters such as SOD, CAT and POD correspond to react and keep balance between reactive oxygen species creation and them in the cell. The AOS activity increased before climacteric peak of ethylene production and came to the peak prior the climacteric peak of ethylene production just like LOX. The ethylene releaseof peach fruit maybe just phenomenon but not regulator which induce maturation and softening during the peach fruit maturation and senescence. The results indicated that the content of O₂^-·and H₂O₂ increased in a whole and accumulated during the fruit senescence although the content of O₂^-· and H₂O₂ decreased sometime. The change of protection system is more complicated than that of reactive oxygen species in this experiment.