Diacetyl delays postharvest leaf yellowing of pak choi (Brassica rapa subsp. Chinensis) by inhibiting ABA synthesis

Abstract

Pak choi (Brassica rapa subsp. Chinensis) is a key vegetable in daily life, however, yellowing of its leaves poses a significant challenge during postharvest storage. Diacetyl, a naturally occurring substance, was found to delay postharvest leaf yellowing of pak choi in this research. Additionally, the regulatory mechanism associated with diacetyl-mediated inhibition of leaf yellowing in pak choi was elucidated. We observed that diacetyl (7 μL L^–1) delayed the leaf yellowing and suppressed chlorophyll degradation related enzyme activities. Various chlorophyll degradation related genes were also repressed following diacetyl treatment. Transcriptome analysis identified numerous differentially expressed genes (DEGs) in diacetyl-treated group compared to control group. Analysis of DEGs revealed that diacetyl significantly regulated genes involved in abscisic acid (ABA) biosynthesis and the ABA signaling pathway. Furthermore, diacetyl treatment inhibited ABA accumulation in pak choi. Importantly, a NAC (NAM, ATAF and CUC) transcription factor (TF), BcNAC100, which was repressed by diacetyl, was associated with leaf yellowing in pak choi. BcNAC100 was localized in nuclear and had high homology to ANAC100. Significantly, BcNAC100 can bind to the promoters of BcNCED3 (nine-cis-epoxycarotenoid dioxygenase 3) and BcZEP (zeaxanthin epoxidase) genes, positively regulating their expression to enhance ABA synthesis. These results demonstrated that diacetyl repressed BcNAC100 expression, reducing ABA accumulation and delaying leaf yellowing in pak choi. Furthermore, these findings revealed a novel molecular regulatory pathway in regulating leaf yellowing of pak choi and identified diacetyl as a potential vegetable preservation agent.