Melatonin could promote lignin deposition at wounds of potato tubers

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 ?mol/L MT, and 25 ?mol/L N?-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.The text before is the abstract of the paper IntroductionAs a postharvest feature of potato tuber, wound healing can prevent pathogen infection, and reduce weight loss by inhibiting water transpiration and respiration rate via forming closed layer at wounds (Barros et al., 2015, Lulai, 2007). Measures are needed to accelerate wound healing due to prolonging the time required for the natural healing of potatoes. It has been shown in previous studies that several chemical elicitors could facilitate the healing of potatoes. Benzothiadiazole and ?-aminobutyric acid accelerated healing by triggering phenylpropanoid metabolism (Jiang et al., 2019, Zhu et al., 2021b). Brassinosteroids promoted wound healing by inducing reactive oxygen species (ROS) and phenylpropanoid metabolism (Han et al., 2022). Melatonin (MT) is a small molecule indoleamine compound that exists widely in animals and plants (Back et al., 2016, Kanwar et al., 2018). Not only is MT involved in the growth process of plants, but it also induces resistance against biotic stresses (Arnao and Hern?ndez-Ruiz, 2018a, Arnao and Hern?ndez-Ruiz, 2018b). MT could induce the resistance of tobacco against Phytophthora nicotianae (Arnao and Hern?ndez-Ruiz, 2018a, Arnao and Hern?ndez-Ruiz, 2018b), cotton against Verticillium dahlia, and lychee against Phytophthora litchi (Li et al., 2019a, Zhang et al., 2021). It was indicated in further studies that MT also alleviated plant diseases by triggering phytohormones generation, including salicylic acid (SA), gibberellins (GA), auxin (IAA), and abscisic acid (ABA) (Zeng et al., 2022). MT downregulated the expression of GSNOR (S-nitrosoglutathione reductase) and promoted nitric oxide (NO) synthesis in tomato seedlings (Zhang et al., 2022). MT activated phenylpropanoid metabolism by promoting H2O2 levels, which increased the content of total phenols, flavonoids and lignin, and induced resistance to B. cinerea in cherry tomato fruit (Li et al., 2019). MT promoted H2O2 accumulation in Diplocarpon mali-infected apple plants, and increased the activities of defense-related enzymes (Yin et al., 2013). MT promoted H2O2 accumulation by increasing superoxide dismutase activity and decreasing catalase and ascorbate peroxidase activity, further enhancing the resistance of strawberries against fungal infections (Aghdam and Fard, 2017). Exogenous application of MT upregulated the expression of OsWRKY45 and OsPR1b to improve resistance in rice against leaf stripes (Lu et al., 2019). MT also increased total phenolic and lignin accumulation in plums by activating phenylpropanoid metabolism (Yan et al., 2022). As a specific inhibitor of nitric oxide synthase (NOS), n?-nitro-L-arginine (L-NNA) attenuates the influence of NO by inhibiting its synthesis. SA improved the resistance of tomato plants against Fusarium wilt by promoting NO accumulation and upregulating the expression of defense genes. In contrast, L-NNA inhibited NO synthesis and attenuated the SA-induced resistance of tomato plants (Chakraborty, 2021). L-NNA also elevated the disease resistance in tomatoes against gray mold by decreasing NOS activity and NO level and suppressing the relative expression of SA and JA signaling genes (Shu et al., 2021). Although MT could induce resistance against diseases by mediating NO and ROS in crops, whether MT affects suberin polyphenolic (SPP) and lignin deposition at wounds of potato tubers by mediating NO and ROS remain unknown. In the current study, we treated wounded potato tubers with 50 ?mol/L MT and 50 ?mol/L MT+ 25 ?mol/L L-NNA treatments to (1) determine the production of NO and ROS, (2) evaluate the relative expression of genes and activities of phenylalanine ammonia-lyase (PAL), 4-coenzyme A ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD), (3) determine peroxidase (POD) activity, (4) visualize the autofluorescence of SPP and lignin at the wound tissues, (5) evaluate weight loss and disease index during the healing period. SourcesMelatonin facilitates the deposition of suberin polyphenolic and lignin at wounds of potato tubers by mediating nitric oxide and reactive oxygen speciesQihui Wang, Ye Han, Ruirui Yang, Xuejiao Zhang, Yatong Zhu, William Oyom, Yongcai Li, Dov Prusky & Yang BiPostharvest Biology and Technology, Volume 198, April 2023, 112270https://www.sciencedirect.com/science/article/abs/pii/S0925521423000315 Picture, Cornell Vegetables, Detection of Potato Tuber Diseases and Defectshttps://www.vegetables.cornell.edu/pest-management/disease-factsheets/detection-of-potato-tuber-diseases-defects/