Exogenous melatonin alleviated growth inhibition and oxidative stress induced by drought stress in apple rootstock

Drought stress is one of the major environmental obstacles that limit the production and development of apples(Malus domestica Borkh.).The role of melatonin is well known in the protection of plants under environmental stresses.In this study,we investigated the effect of melatonin on apple rootstock M.hupehensis Rehd under drought stress.The results showed that drought inhibited the growth of M.hupehensis and dramatically reduced root surface area,root volume,the number of tips and forks,and root diameter.Drought-induced growth inhibition was significantly decreased by adding melatonin.Net photosynthetic rate(Pn),intercellular CO_(2)concentration(Ci),stomatal conductance(Gs),transpiration rate(Tr),were markedly reduced under drought stress.However,the application of melatonin could mitigate the damage to the photosynthetic apparatus and increase the quantum yield of PSII photochemistry.Additionally,generation of hydrogen peroxide(H_(2)O_(2))and superoxide radicals(O_(2)^(•–))sharply increased in apple leaves after 4 days under drought stress,and the accumulation of electrolyte leakage(EL)represented oxidative stress,while by applying melatonin under drought stress,the generation of O_(2)^(•–)and H_(2)O_(2)were significantly reduced and protected the membrane from drought damages.These results suggest that the adverse effects of drought can be minimized by applying melatonin to apples.