Physiological and molecular biological study on mechanism of senescence and quality changes of vegetables and investigation of keeping quality

蔬菜在收获后代谢发生迅速变化，导致衰老和品质劣化。在西兰花小花（花蕾）衰老进展迅速收获后，在环境温度。抗坏血酸含量急剧下降，叶绿素迅速损失，导致小花黄化。青花菜小花衰老过程中乙烯产生量先增加，达到最大值后下降。与乙烯产生速率平行，ACC（1-氨基环丙烷-1-羧酸）氧化酶活性增加，达到峰值后下降。从青花菜花中提取ACC氧化酶，并从转化的大肠杆菌中纯化ACC氧化酶，研究其酶学性质。茉莉酸甲酯处理青花菜小花后，ACC合成酶和ACC氧化酶活性增加，乙烯释放速率提高。茉莉酸甲酯促进青花菜小花的衰老，细胞分裂素通过抑制乙烯的产生来延缓花的衰老。因此，有可能通过控制乙烯的产生和作用来调控青花菜小花的衰老和品质变化。低温贮藏是保持青花菜品质和延缓衰老的最佳方法，可使青花菜的代谢和乙烯产生量保持在较低水平。

Rapid changes in metabolism proceed in vegetables after harvest, leading to senescence and quality detrioration. In broccoli florets (flower buds) senescence progressed rapidly after harvest at ambient temperatures. Ascorbate content declined sharply and chlorophyll loss occurred rapidly, leading to yellowing of florets. During senescence of broccoli florets ethylene production increased, reached a maximum and then declined. In parallel with ethylene production rate, ACC (1-aminocyclopropane-1-carboxylic acid) oxidase activity increased to reach a peak and declined thereafter. Enzymatic properties of ACC oxidase extracted from broccoli florets and purified from Escherichia coli transformed with broccoli ACC oxidase cDNA were investigated. Methyl jasmonate applied to broccoli florets induced and accelerated activities of ACC synthase and ACC oxidase, which resulted in enhanced rate of ethylene production. Methyl jasmonate promoted senescence, while cytokinin retarded the progress of senescence of broccoli florets by inhibiting ethylene production. Thus it will be possible to regulate senescence and quality changes of broccoli florets by controlling ethylene production and ethylene action. The best way for keeping quality and retarding senescence of broccoli florets is concluded to be low temperature storage which reduces metabolism and ethylene production at a basal low level.