Gibberellic acid and 6-benzylaminopurine delays yellowing of pak choi (Brassica rapa subsp. chinensis) by inhibiting lipid peroxidation and chlorophyll degradation

• GA+6-BA treatment extended the shelf-life of pak choi for 5 d at 20 °C. • GA and 6-BA signal was involved in chlorophyll catabolism and ROS metabolism. • GA and 6-BA treatments maintained membrane lipid stability. • Six NAC and five ERF TFs may be involved in regulating chlorophyll catabolism. Gibberellic acid (GA) and 6-benzylaminopurine (6-BA) regulate plant senescence, but the regulating effect of the two hormones in leaf yellowing of pak choi remain unclear. The study investigated the effect of 80 mg L −1 GA and 70 mg L −1 6-BA alone or in combination on leaf yellowing during pak choi storage at 20 °C. The results showed that GA, 6-BA and GA+6-BA treatments alleviated the yellowing of pak choi during 7 d of storage, and GA+6-BA was more effective than GA or 6-BA alone, extending the shelf life of pak choi for five days compared with the control. The treatments suppressed the increase in lightness (L*) value and decrease in hue angle (H) value, maintaining high chlorophyll content and low weight loss. All treatments inhibited the activity of chlorophyll catabolic enzymes chlorophyllase (CLH), Mg-de-chelatase (MDCase) and pheophytin pheophorbide hydrolase (PPH) and expression of associated genes, including BcCLH, BcPPH, BcNYC1, BcSGR and BcRCCR . GA, 6-BA and GA+6-BA treatments restrained the activity and expression of the membrane lipid degradation enzymes phospholipase (PLD), lipase and lipoxygenase (LOX). These treatments also maintained high activity and expression of antioxidase ascorbic peroxidase (APX), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD), and suppressed reactive oxygen species metabolic genes, including BcRBOHC and BcRBOHD , and correspondingly reduced superoxide anion (O 2 ·− ) , hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) accumulation. Moreover, six BcNACs (BcNAC002/055/056/082/083/090) and five BcERFs (BcERF1A/016/023/043/109) may likely be involved in chlorophyll catabolism mediated by GA and 6-BA. In conclusion, GA and 6-BA treatments delayed yellowing of pak choi by regulating chlorophyll catabolism, oxidative stress, membrane lipid metabolism, and the transcription levels of transcription factors that control chlorophyll metabolism genes.