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

蔬菜采收后，新陈代谢发生快速变化，导致衰老和品质下降。在环境温度下，西兰花(花蕾)在采收后衰老迅速。抗坏血酸含量急剧下降，叶绿素迅速损失，导致小花变黄。在西兰花衰老过程中，乙烯生成量增加，达到最大值，然后下降。在乙烯产生速率的同时，ACC(1-氨基环丙烷-1-羧酸)氧化酶活性升高，达到峰值，然后下降。研究了从青花菜小花中提取的ACC酶和从转化青花菜ACC酶基因的大肠杆菌中纯化的ACC酶的酶学性质。茉莉酸甲酯处理青花菜诱导和加速了ACC合成酶和ACC氧化酶的活性，从而提高了乙烯的产生速率。茉莉酸甲酯促进了青花菜的衰老，而细胞分裂素通过抑制乙烯的产生延缓了青花菜的衰老进程。因此，有可能通过控制乙烯的产生和乙烯的作用来调控西兰花的衰老和品质变化。低温贮藏是保持青花菜品质和延缓其衰老的最好方法，可在较低的基础水平上减少新陈代谢和乙烯的产生。

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.