Wisutiamonkul Apinya, Ampomah-Dwamena Charles, Allan Andrew C, Ketsa Saichol
Department of Horticulture, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand.
The New Zealand Institute for Plant & Food Research Limited (PFR), Private Bag 92169, Auckland, New Zealand.
Plant Physiol Biochem. 2017 Jun;115:308-319. doi: 10.1016/j.plaphy.2017.03.021. Epub 2017 Mar 31.
Carotenoid content in durian (Durio zibethinus) fruit is an important aspect of fruit quality, with different cultivars distinguished by differing pigmentation. We have studied the dependence of carotenogenesis on ethylene. Fruit of the cultivar 'Chanee' harvested at the mature stage were either left untreated (controls), treated with 1-methylcyclopropene (1-MCP) for 12 h, or treated with application of an aqueous ethephon solution to the stem end, or treated for 12 h with 1-MCP followed by ethephon application. Fruit were then stored for 9 d at 25 °C. Pulp color of durian became steadily yellowish as a result of accumulation of carotenoids, which were mainly beta-carotene, and alpha-carotene, with a minor amount of zeaxanthin and lutein. 1-MCP delayed the increase in the accumulation of beta-carotene, alpha-carotene, and zeaxanthin, but not lutein. In contrast, ethephon had no significant effect on carotenoid accumulation. The expression of zeta-carotene desaturase (ZDS), lycopene beta-cyclase (LCYB), chromoplast specific lycopene beta-cyclase (CYCB) and beta-carotene hydroxylase (BCH) genes was highly correlated with carotenoid content and pulp color.1-MCP resulted in significant down-regulation of ZDS, LCYB, CYCB and BCH expression. The accumulation of beta-carotene and alpha-carotene appears to be controlled by the level of expression of LCYB gene, whose function was tested in bacteria to show conversion of lycopene and delta-carotene to beta-carotene and alpha-carotene, respectively. These results suggest that ripening-induced carotenoid accumulation is regulated by endogenous ethylene controlling the expression of key genes such as LCYB.
榴莲（Durio zibethinus）果实中的类胡萝卜素含量是果实品质的一个重要方面，不同品种的色素沉着有所不同。我们研究了类胡萝卜素生成对乙烯的依赖性。在成熟阶段采收的‘Chanee’品种果实，一部分不做处理（对照），一部分用1-甲基环丙烯（1-MCP）处理12小时，一部分在果柄端涂抹乙烯利水溶液，还有一部分先用1-MCP处理12小时，然后再涂抹乙烯利。之后将果实于25℃下贮藏9天。由于类胡萝卜素的积累，榴莲果肉颜色逐渐变黄，这些类胡萝卜素主要是β-胡萝卜素和α-胡萝卜素，还有少量玉米黄质和叶黄素。1-MCP延缓了β-胡萝卜素、α-胡萝卜素和玉米黄质积累量的增加，但对叶黄素没有影响。相比之下，乙烯利对类胡萝卜素的积累没有显著影响。ζ-胡萝卜素去饱和酶（ZDS）、番茄红素β-环化酶（LCYB）、质体特异性番茄红素β-环化酶（CYCB）和β-胡萝卜素羟化酶（BCH）基因的表达与类胡萝卜素含量和果肉颜色高度相关。1-MCP导致ZDS、LCYB、CYCB和BCH的表达显著下调。β-胡萝卜素和α-胡萝卜素的积累似乎受LCYB基因表达水平的控制，该基因的功能在细菌中进行了测试，结果表明它分别将番茄红素和δ-胡萝卜素转化为β-胡萝卜素和α-胡萝卜素。这些结果表明，成熟诱导的类胡萝卜素积累受内源性乙烯调控，乙烯控制着关键基因如LCYB的表达。
