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快速变化，导致衰老和品质退化。在环境温度下，西兰花小花（花蕾）在收获后迅速衰老。抗坏血酸含量急剧下降，叶绿素迅速丧失，导致小花变黄。在花椰菜衰老过程中，乙烯产量先上升，达到最大值后下降。ACC（1-氨基环丙烷-1-羧酸）氧化酶活性随乙烯产率的升高而升高，达到峰值后下降。以西兰花ACC氧化酶cDNA转化大肠杆菌为原料，从西兰花小花中提取ACC氧化酶，并对其酶学性质进行了研究。施用茉莉酸甲酯可诱导和促进花椰菜ACC合成酶和ACC氧化酶的活性，从而提高乙烯产量。茉莉酸甲酯通过抑制乙烯的产生延缓了花椰菜的衰老进程，而细胞分裂素通过抑制乙烯的产生延缓了花椰菜的衰老进程。因此，通过控制乙烯的产生和乙烯的作用来调控花椰菜小花的衰老和品质变化是可能的。低温贮藏是延缓花椰菜花期衰老和保持花期品质的最佳途径，低温贮藏在一定程度上降低了花椰菜花期代谢和乙烯产量。

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.