The mechanism of ethylene biosynthesis and its role in horticultural crops and regulation and function of ethylene synthesis during ripening and senescence

乙烯对植物的生长、发育起着至关重要的作用；植物的分化和衰老。在园艺作物中，乙烯与成熟和衰老的机制密切相关。另一方面，乙烯是在各种压力下迅速产生的，如由微生物感染引起的伤害和疾病。(1)花椰菜小花（花蕾）衰老过程中乙烯的生物合成及其调控：花椰菜在花蕾还未成熟时收获，花蕾上覆盖着绿色的萼片。收获后，小花在环境温度下迅速衰老，其中由于叶绿素降解而变黄。高水平的抗坏血酸（维生素C）在收获后衰老期间迅速下降。衰老过程中乙烯产量的增加与ACC氧化酶活性及其基因表达的增加是平行的。采后花椰菜小花的乙烯合成速率主要受ACC合成酶和ACC氧化酶基因表达的调控。收获花椰菜会导致水、激素、糖、氨基酸和矿物质从母体植物中运输的停止，加上切割茎的伤害可能导致触发或加速小花幼花器官的衰老。(2)黑腐菌侵染甘薯根组织中乙烯的生物合成及其机制：甘薯根受黑腐菌侵染后产生大量乙烯。乙烯生物合成途径不依赖于高等植物中广泛存在的蛋氨酸- acc途径。我们发现了甘薯根组织中乙烯合成的新途径。新途径的机制总结如下。对真菌感染的反应是磷脂酶A_2被激活，释放出亚麻酸，亚麻酸在宿主组织中被脂氧合酶加氢过氧化。然后，乙基自由基从过氧化的亚麻酸中分离出来，被铜离子氧化生成乙烯。乙烯的产生可能参与了甘薯根组织代谢的激活。少

Ethylene plays an essential role in growth, development ; differentiation, and senescence of plants. In horticultural crops ethylene is closely involved in the mechanism of ripening and senescence. On the other hand, ethylene is rapidly produced in response to various kinds of stresses such as wounding and disease caused by infection with microorganisms. (1)Ethylene biosynthesis and its regulation during senescence of broccoli florets (flower buds): Broccoli is harvested while florets are still green and immature which are covered with green sepals. After harvest senescence proceeds rapidly in florets at ambient temperatures in which yellowing progresses due to chlorophyll degradation. The high levels of ascorbic acid (vitamin C) rapidly decline after harvest during senescence. The rate of ethylene production increased during senescence which was paralleled by the increase in ACC oxidase activity and its gene expression. The rate of ethylene biosynthesis in broccoli florets was regulat … More ed by the gene expression of ACC synthase and ACC oxidase after harvest. Harvesting broccoli causes the cessation of the transport of water, hormones, sugars, amino acids, and minerals from the mother plant and together with wounding by cutting the stem may result in triggering or accelerating senescence of the young flower organ of florets. (2)Ethylene biosynthesis and its mechanism in sweet potato root tissue infected by black rot fungus (Ceratocystis fimbriata): A large amount of ethylene is produced in sweet potato roots upon infection by black rot fungus. The pathway of ethylene biosynthesis was independent on methionine-ACC pathway that is widely operating in higher plants. We have found the new pathway for the synthesis of ethylene in sweet potato root tissue infected by the pathogen. The mechanism of the novel pathway is summarized as follows. In response to infection with the fungus, phospholipase A_2 is activated, liberating linolenic acid, which is hydroperoxidized by lipoxygeriase in the host tissue. Then, ethylradical is cleaved from the peroxidized linolenic acid, which is oxidized by cupric ion to yield ethylene. Ethylene produced may be involved in the activation of metabolism in sweet potato root tissue infected by the pathogen. Less