Abstract: Objective: To investigate the effect and underlying mechanism of hot water dipping on the accumulation of suberin polyphenol and lignin at wound sites of carrots. Methods: Artificially wounded carrots were dipped in hot water at 45 ℃ for 5 min. The mass loss of wounded carrots and the disease index of inoculated carrots with Botrytis cinerea were determined. The accumulation of suberin polyphenol and lignin in wounds were observed. The activities of key enzymes of phenylpropane metabolism and peroxidase activity, and the contents of phenylpropane metabolites and H2O2 were also measured. Results: The mass loss and disease index of wounded carrots were significantly reduced by hot water dipping. The mass loss was 21% lower than that of the control group on the 5th day of healing, and the disease index of treated carrots was 22% lower than that of the control group on the 3th day. Hot water dipping accelerated the deposition of suberin polyphenol and lignin at wound sites. The thickness of suberin polyphenol (SPP) was 18% higher on the 3th day and the thickness of the lignin layer in the cells of treated carrots was 16% higher on the 5th day compared to the control group. Hot water dipping also increased the activity of phenylalanine ammonia lyase (PAL), cinnamic acid-4-hydroxylase (C4H), 4-coumaryl coenzyme A ligase (4CL) and cinnamyl alcohol dehydrogenase (CAD), promoted the synthesis of cinnamic acid, caffeic acid, ferulic acid, sinapic acid, total phenolics and flavonoids, and raised the contents of cinnamyl alcohol, coniferyl alcohol, sinapis alcohol and lignin at wound sites. Moreover, hot water dipping enhanced H2O2 content and peroxidase (POD) activity. Conclusion: Hot water dipping promotes wound healing of carrots by activating phenylpropanoid metabolism, increasing H2O2 content and POD activity, and accelerating the deposition of SSP and lignin at wound sites.

Key words: carrots; wound healing; hot water dipping; phenylpropanoid metabolism; suberin; lignin