Effect of 24-epibrassinolide on chilling injury of peach fruit in relation to phenolic and proline metabolisms

• Examined 24-epibrassinolide (EBR) treatment on peach fruit.
• EBR treatment reduced chilling injury.
• EBR activated phenolics and proline biosynthesis and led to detoxification of ROS.
• EBR lowered activities of enzymes that degrade phenolics and proline.
• Phenolic and proline metabolisms are involved in EBR-mediated chilling tolerance.

Peach fruit is cold-sensitive and vulnerable to chilling injury (CI) during cold storage, which limits its edible and market value. Brassinosteroids (BRs) have been used to alleviate CI of fruit; however, the effect of BRs on CI of peach fruit remains unknown. In this study, peach fruit were immersed in a 15 μM 24-epibrassinolide (EBR) solution for 10 min at 25 °C and then stored at 1 °C for 4 weeks and subsequently transferred to 25 °C for 3 d to investigate the effects and possible mechanisms of EBR on CI in peach fruit. EBR treatment effectively inhibited the loss of firmness and delayed the increase of CI index and levels of malondialdehyde, superoxide anion production, and hydrogen peroxide in peach fruit. EBR treatment significantly increased shikimate dehydrogenase, phenylalanine ammonia lyase, cinnamate-4-hydroxylase and 4-coumarate: coenzyme A ligase activity, but reduced polyphenol oxidase and peroxidase activity, which resulted in a higher total phenolic content that might contribute to inhibition of the CI. The treatment also significantly enhanced the accumulation of proline associated with increase in the activity of Δ1-pyrroline-5-carboxylate synthetase and decrease in proline dehydrogenase activity. These results indicate that EBR treatment may be an effective strategy to induce chilling tolerance of peach fruit, and the EBR-mediated amelioration of CI may be attributed to activation of phenolic and proline biosynthesis as well as inhibition of oxidative stress.