Melatonin facilitates the deposition of suberin polyphenolic and lignin at wounds of potato tubers by mediating nitric oxide and reactive oxygen species

Melatonin (MT), a phytohormone, can enhance plant resistance against biotic and abiotic stresses. However, no studies have been conducted on whether MT influences suberin polyphenolic (SPP) and lignin deposition by mediating nitric oxide (NO) and reactive oxygen species (ROS). Herein, wounded tubers were treated with 50 μmol/L MT, and 25 μmol/L Nω-nitro-L-arginine (L-NNA), a specific inhibitor of nitric oxide synthase. We found that MT upregulated StNR (nitrate reductase) and StNOS (nitric oxide synthase) expression levels, and increased endogenous NO content. Additionally, MT upregulated StNOX (NADPH oxidase) expression and facilitated O2.- and H2O2 production. Moreover, MT upregulated relative expression and enhanced the activities of the main enzyme and products of the phenylpropanoid pathway, and increased peroxidase (POD) activity. MT also elevated the accumulation amount of suberin polyphenolic (SPP) and lignin at the wound tissues, resulting in less weight loss and disease index in wounded potatoes (cv. Atlantic) during healing. In contrast, L-NNA treatment suppressed the influence of MT on the generation of endogenous NO and ROS, the activity of phenylpropanoid metabolism and POD, and SPP and lignin accumulation at wounds. Taken together, MT could promote SPP and lignin deposition at wounds of potato tubers by inducing NO and ROS production and activating phenylpropanoid metabolism. However, L-NNA could eliminate the positive effect of MT.