Abstract:

【Objective】 Wound healing is a typical reaction in damaged tuber tissue of potato, which is greatly affected by external environmental factors. The effects of dark and light treatments on the wound healing of potato tubers were compared to explore its partial mechanisms. 【Method】In this study, the "Atlantic" potato seeds were selected as the test material. After being cut in half and disinfected, the tubers were healed under light (11 000 lx) and dark at ambient condition ((20±3)℃, RH (95±5)%). The determination was conducted on the basis of weight loss and disease index of tubers after inoculated with Fusarium sulphureum on 7 d during healing to evaluate the efficacy of the wound healing. The accumulation of suberin and lignin, and the chroma at wound sites of the tubers were observed. The activity of the key enzymes of phenylpropanoid metabolism and the activities of peroxidase, polyphenol oxidase and hydrogen peroxide were analyzed in order to explore the partial mechanism of light and dark at the wounded sites of potato tubers. 【Result】During healing, the weight loss of tubers under dark and light was increased gradually. Dark treatment significantly decreased the weight loss of wounded tubers and disease index of inoculated tubers, which were 54.3% and 59.0% lower than that under light after 7 d of healing, respectively. Accumulation of suberin poly phenolic, suberin poly aliphatic and lignin of tubers under dark and light were increased gradually during healing. The dark treatment comparatively improved the accumulation of suberin poly phenolic, suberin poly aliphatic and lignin at the wounded sites of potato tubers. The thickness of suberin poly phenolic, suberin poly aliphatic and lignified cell layers was increased by 38.2 %, 36.8 % and 14.7 % respectively than that under light treatment after 14 d of healing. During healing, L* and b* values of wounded tuber surface under dark and light was decreased first and then increased. The dark treatment reduced the L* and a* and elevated the b* value of the wound surface of tubers. The L* and a* values were lower than that of light by 13.51% and 32.74% on the 5th day of wound healing, respectively. The b* value was 42.11% higher than that of light on day 5 of wound healing. During healing, PAL activity at the wounded sites of tubers in dark treatment increased rapidly, while in light treatment increased slowly, C4H activity at the wounded sites of tubers under both treatments first increased and then stabilized, and 4CL activity in two treatments first increased rapidly and then decreased continuously at the wounded sites. The dark treatment significantly increased the activity of phenylalanine ammonia-lyase, cinnamic acid-4-hydroxylase and 4-coumaryl coenzyme A ligase at the wounded site of tubers, which were 79.6%, 10.7% and 72.5% higher respectively than the ones under light treatment after 7 d of healing. Moreover, the content of H₂O₂ in tuber wound under dark and light increased rapidly in the first week at the wounded sites of tubers and then flatten out. The peroxidase activity and hydrogen peroxide content at the wounded sites of tubers under dark were 49.8% and 49.9% higher than that under the light treatment after 5 d of healing, respectively. In addition, polyphenol oxidase activity was increased obviously at wound sites of tubers treated with dark on the 3rd of healing, which was 12.93% higher than that of light.【Conclusion】Dark improved the wound healing of potato tubers, while the light showed a certain extent inhibition. The improvement mechanism of the dark on wound healing involved in eliciting phenylpropanoid metabolism and the acceleration of polyphenol oxidase and peroxidase activities to promote the accumulation of suberin and lignin at wounded sites of tubers.

Key words: dark and light, potato tubers, wound healing, phenylpropanoid metabolism