Effect of Rapid Heat Treatment on Wound Healing and Metabolic Mechanism in Sweet Potato

In order to explore the effect and mechanism of rapid heat treatment (RHT) on promoting callus formation in postharvest sweet potato tubers, ‘Dayehong’ sweet potatoes were artificially wounded and divided into a positive control group, a negative control group, and an RHT group. The positive control group was subjected to traditional heat treatment (35 ℃ for two days), and the negative control group was not subjected to any heat treatment. The RHT group was subjected to heat treatment at 65 ℃ for 15 min. All groups were stored at 13 ℃. The experimental period was seven days, consisting of heat treatment and storage. Lignin and suberin deposition at the wound site were observed during wound healing. The intermediate products and enzyme activities in reactive oxygen species (ROS) metabolism were determined, as well as antioxidant activity and the key enzyme activities in the phenylpropane metabolism pathway and the contents of lignin and phenols. The results showed that RHT could effectively promote lignin and suberin deposition at the wound site, and its effect was similar to that of the positive control. On the 6^th day of the experiment, the thickness of lignin and suberin deposition was significantly higher than that in the control groups (P < 0.05). RHT treatment significantly promoted the rapid accumulation of H₂O₂, hydroxyl radical and superoxide anion radical contents, induced the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and polyphenol oxidase (PPO), and significantly increased the scavenging capacity against (1,1-dipheny1-2-picryl-hydrazyl (DPPH) and 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) cation radical of sweet potato callus during wound healing (P < 0.05). RHT could also induce the increase in phenylalanine ammonia lyase (PAL), cinnamic acid-4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4CL) and cinnamyl alcohol dehydrogenase (CAD) activities and make them reach their peak earlier during wound healing, and promoted the accumulation of total phenols, flavonoids and lignin. Meanwhile, RHT significantly increased the contents of neochlorogenic acid, catechin, chlorogenic acid and epicatechin in sweet potato callus. In conclusion, RHT could not only maintain the dynamic balance of ROS in callus by stimulating the accumulation of ROS and increasing antioxidant activity, but also activate the key enzymes in the phenylpropane metabolic pathway to produce a large number of secondary metabolites and accelerate the deposition of lignin and suberin, thereby promoting rapid wound healing in sweet potato tubers.