L-Phenylalanine (L-Phe) is a biologically active aromatic amino acid that improves storage quality and disease resistance in fruit and vegetables. However, the effects of preharvest L-Phe treatment on storage traits of vegetables have not been reported. This study investigated the yellowing and chlorophyll metabolism of preharvested broccoli treated with L-Phe at different concentrations during storage. The results showed that L-Phe at 2 mmol L preharvest spraying 7 d before harvest was effective in delaying the yellowing of broccoli florets during storage, and maintained higher levels in total chlorophylls, chlorophyll a and chlorophyll b and reduced the activities in broccoli florets of chlorophyllase (CLH), Mg-dechelatase (MDcase), pheophyllase (PPH) and pheophyllase a oxygenase (PAO). Further studies showed that the expression levels of genes associated with chlorophyll degradation such as chlorophyll b reductase (), chlorophyllase1 (), chlorophyllase2 (), pheophytinase () and pheophorbide a oxygenase () were significantly down-regulated by preharvest L-Phe treatment. Correlation analysis showed that total chlorophylls content was significantly and positively correlated with the H* value, hardness, chlorophylls a, b and gene expression, and significantly and negatively correlated with the L*, a*, b* values, weight loss, MDcase enzyme activity, PAO enzyme activity and gene expression ( < 0.05). The findings suggested that L-Phe preharvest treatment delayed broccoli yellowing through decreasing chlorophyll degradation.

中文翻译：

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采前喷施L-苯丙氨酸有效延缓采后西兰花叶绿素的降解

L-苯丙氨酸 (L-Phe) 是一种具有生物活性的芳香族氨基酸，可提高水果和蔬菜的储存质量和抗病性。然而，采前L-Phe处理对蔬菜贮藏性状的影响尚未见报道。本研究调查了经不同浓度 L-Phe 处理的预采西兰花在储存期间的黄化和叶绿素代谢。结果表明，采收前7 d喷施2 mmol·L L-Phe可有效延缓西兰花贮藏期间小花的黄化，保持较高的总叶绿素、叶绿素a和叶绿素b水平，降低西兰花小花的活性。叶绿素酶 (CLH)、镁脱螯合酶 (MDcase)、脱镁叶绿酶 (PPH) 和脱镁叶绿酶加氧酶 (PAO)。进一步的研究表明，采前L-Phe处理显着下调了与叶绿素降解相关的基因，如叶绿素b还原酶（）、叶绿素酶1（）、叶绿素酶2（）、脱镁叶绿素酶（）和脱镁叶绿酸加氧酶（）的表达水平。相关分析表明，叶绿素总量含量与H*值、硬度、叶绿素a、b及基因表达量呈显着正相关，与L*、a*、b*值、失重、MDcase酶呈显着负相关。活性、PAO酶活性和基因表达（<0.05）。研究结果表明，L-Phe 收获前处理通过减少叶绿素降解来延缓西兰花变黄。