Yellowing of broccoli is a crucial limiting factor for its commercial value and consumer acceptance during postharvest. In this study, the impacts of exogenous melatonin (MEL) on chlorophyll content and fluorescence, as well as ultrastructure and membrane lipid metabolism of chloroplasts in broccoli were investigated during postharvest. The results showed that MEL treatment (200 μmol L) maintained the chlorophyll content, chloroplast autofluorescence and integral structure, and reduced the level ofserotonin in the chloroplasts in broccoli. Also, MEL treatment inhibited the membrane lipid peroxidation of chloroplasts, as indicated by low levels of superoxide anion (O), hydrogen peroxide (HO) and malondialdehyde (MDA), and high levels of endogenous MEL. In addition, the stability and fluidity of chloroplast membranes were also better maintained in the treated broccoli via increasing the contents of phosphatidylglyceroland (PG), monogalactosyldiglyceride (MGDG), digalactosyldiglyceride (DGDG) and unsaturated fatty acids as well as decreasing saturated fatty acid content and the activities of lipoxygenase (LOX) and lipase (LPS). Thus, the application of MEL facilitated the maintenance of chloroplast integrity, thus contributing to yellowing postponement and the extension of the storage life of broccoli.

中文翻译：

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外源褪黑激素通过维持叶绿体完整性来延迟收获的西兰花变黄


西兰花变黄是其商业价值和采后消费者接受度的关键限制因素。本研究研究了外源褪黑素（MEL）对西兰花采后叶绿素含量和荧光以及叶绿体超微结构和膜脂代谢的影响。结果表明，MEL处理（200μmol·L）保持了西兰花叶绿素含量、叶绿体自发荧光和整体结构，并降低了叶绿体中血清素的水平。此外，MEL 处理抑制了叶绿体的膜脂过氧化，低水平的超氧阴离子 (O)、过氧化氢 (H2O) 和丙二醛 (MDA) 以及高水平的内源性 MEL 表明了这一点。此外，通过增加磷脂酰甘油（PG）、单半乳糖甘油二酯（MGDG）、双半乳糖甘油二酯（DGDG）和不饱和脂肪酸的含量以及降低饱和脂肪酸和脂肪酸的含量，处理后的西兰花也更好地保持了叶绿体膜的稳定性和流动性。脂氧合酶（LOX）和脂肪酶（LPS）的活性。因此，MEL的应用有利于叶绿体完整性的维持，从而有助于推迟西兰花的黄变和延长保存期。