Trehalose triggers hydrogen peroxide and nitric oxide to participate in melon seedlings oxidative stress tolerance under cold stress

Cold stress is an important environmental factor restricting the cultivation of melons in winter and spring. Exogenous trehalose (Tre) can improve the stress tolerance of crops. However, the mechanistic role of Tre in regulating crop cold tolerance is not completely clear and whether hydrogen peroxide (H2O2) and nitric oxide (NO) act as signalling molecules in Tre regulation melon cold tolerance remains unknown. Thus, this study was conducted to analyse the cold tolerance of cold-tolerant (IVF571) and cold-sensitive (IVF004) melon varieties and their H2O2 and NO levels. Then, the roles of exogenous Tre in regulating the cold tolerance of melons and the interaction of H2O2 and NO in Tre-regulated cold tolerance were investigated. Results showed that the damage to membrane lipid peroxidation in IVF571 plants was significantly slighter than that in IVF004 plants, and the levels of H2O2 and NO in IVF571 plants were significantly higher than those in IVF004 plants under cold stress. Exogenous Tre was more effective than sucrose and glucose in significantly increasing the maximal quantum yield of PSII photochemistry, reducing the relative electrical conductivity in melon leaves under cold stress by increasing the superoxide dismutase (SOD) activity under normal conditions and enhancing SOD, glutathione reductase and ascorbate peroxidase activities and GSH/GSSG ratio under cold stress. Exogenous Tre could induce the increase in H2O2 and NO levels. The removal of endogenous H2O2 with dimethylthiourea weakened the role of exogenous Tre, whereas eliminating NO with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3oxide almost abolished the effects of exogenous Tre and H2O2. In summary, the higher cold tolerance of IVF571 seedlings than that of IVF004 seedlings might be related to the increase in H2O2 and NO levels triggered by cold stress. Tre might have a unique effect on the regulation of cold-induced oxidative stress in melon. Tre could elevate endogenous H2O2 and NO levels, which stimulated the stress response system of melon. Consequently, when melon plants were exposed to cold stress, antioxidant enzyme activities improved, and the damage to membrane lipid peroxidation was reduced. In this process, H2O2 and NO participated in the roles of Tre, and NO might be located downstream of H2O2.