Effect Of Respiratory Metabolism Associated Enzymes In Mitochondria On Peach Fruit Ripening And Softening

Peach fruits [Prumus persica (L.) Batsch, cv. Yuhuasanhao ] were used as materials to study the metabolism of reactive oxygen species (ROS) and mitochondrial respiration 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. Obvious peaks of ethylene production lagging to the rapid change of fruit firmness could be shown, during both on-tree ripening and post-harvest storage at normal temperature (20℃). But when peach fruits were stored at low temperature (5℃), the ethylene production was relatively little, the peak of ethylene production and the change of fruit firmness were not obvious. These suggested that low temperature could delay peach fruit senescence.(2) Changes of the activity of superoxide dismutase (SOD), and the contents of ROS and malondiadehye (MDA) were studied in this paper. As shown in this work, there is a trend of accumulation in the contents of ROS and MDA with the increasing senescence of peach fruits suggested the degree of the membrane lipid peroxidation was increscent. The changes of ROS and MDA were similar between on-tree ripening and normal temperature storage. But when peach fruits were stored at 5℃, 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) Changes in the content of mitochondrial Ca²⁺ and the activities of mitochondria-localized enzymes such as succinic dehydrogenase (SDH), cytochrome C oxidase (CCO), H⁺- ATPase and Ca²⁺-ATPase were determined in this paper. The results showed that during on-tree ripening the content of Ca²⁺ increased, the activities of SDH, CCO, H⁺- ATPase and Ca²⁺-ATPase decreased varying in different degree at the later step of ripening, which were similar to those during normal temperature storage. But during low temperature storage, the activities of SDH, CCO, H⁺- ATPase and Ca²⁺-ATPase heightened, which could be attributed to the slighter degree of cell membrane lipid peroxidation. At the same time, the content of Ca²⁺ was higher at normal temperature storage than that at low temperature, which suggested that damaged mitochondria that influenced the function of fruit cell and promoted fruit senescence.(4) Then the metabolism of ROS and mitochondrial respiration were analyzed as a whole. These suggested that, during on-tree ripening and normal temperature storage, the excessive ROS and over-peroxidized membrane lipid induced damages in mitochondria that holding abundant membrane, which influenced mitochondrial respiration and promoted peach fruit senescence. But during low temperature storage, the mitochondrial function kept well because of little contents of ROS and degree of membrane lipid peroxidation, which slowed the senescence of peach fruit. These suggested a close relationship existed between ROS metabolism and mitochondrial respiration, namely, both ROS metabolism and mitochondrial respiration probably played important roles in ripening and senescing of peach fruit.