Regulatory Mechanism Of Melatonin On Zanthoxylum Bungeanum Under Drought Stress

Zanthoxylum bungeanum is an important economic tree species in China,which has high economic and ecological value.However,drought stress affects the production and quality of Z.bungeanum.Therefore,exploring a method that can improve the drought resistance of Z.bungeanum is important to ensure the production of Z.bungeanum.Melatonin enhances plant drought resistance by regulating plant physiological,biochemical and molecular processes under drought stress.At present,there is no report on melatonin-mediated drought resistance of Z.bungeanum.Meanwhile,potential physiological and molecular mechanism is not clear.Therefore,this study used Z.bungeanum seedlings with 200μmol L^-1 melatonin application as the test materials.By analyzing the effects of melatonin on photosynthetic parameters,chlorophyll fluorescence parameters,reactive oxygen species,antioxidant enzyme activity,osmoregulation substances and gene expression under drought stress and rehydration,this paper discussed the physiological response and possible molecular mechanism of Z.bungeanum seedlings to melatonin under drought stress.The main results are as follows.1.Melatonin alleviated the photoinhibition of Z.bungeanum under drought stress and promoted the recovery of photosynthetic capacity after rehydration.Melatonin-treated plants indicated higher water use efficiency,PSII maximum photochemical efficiency and electron transfer rate,as well as lower intercellular CO₂ concentration than those untreated plants,which reduced photosynthetic organs damage and improved photosystem II ability to use light energy.After rewatering,the net photosynthetic rate,transpiration rate and stomatal conductance of Z.bungeanum leaves treated with melatonin were 1.4,1.9 and 1.9times higher than those treated with drought stress.The parameters of Z.bungeanum leaves treated with melatonin returned to the control level or close to the control level faster than drought stress.2.Melatonin ameliorted the oxidative damage of Z.bungeanum under drought stress and accelerated plants recovery after rehydration.Superoxide anion contents,hydrogen peroxide contents and malondialdehyde contents were increased under drought stress significantly,which were 33%,26%and 27%higher than melatonin treatment.Thus,Melatonin alleviated the oxidative damage caused by drought stress.Melatonin can accelerate the recovery of various indexes and promote the restorative growth of plants after rehydration.3.Melatonin increased the antioxidant enzyme activity and soluble sugar content of Z.bungeanum under drought stress.The superoxide dismutase,peroxidase,catalase activity and soluble sugar content of Z.bungeanum were significantly increased under drought stress.Melatonin treatment further promoted the increase of antioxidant enzyme activity and the accumulation of soluble sugar,which were 18%,18%,17%and 28%than stress treatment.Melatonin improved the ability of leaves to remove excess reactive oxygen species,and reduced drought-induced damages to Z.bungeanum seedlings.After rehydration,melatonin-treated leaves can return to normal level faster.4.Melatonin can improve plants drought resistance by regulating the gene expression of Z.bungeanum under drought stress.MT up-regulated the expression of genes related to starch hydrolase in starch and sucrose metabolism pathway under drought stress,corresponding to the increase of soluble sugar content at physiological level.In addition,melatonin promoted the up-regulation of AUX1,AUX/IAA,ARF and GH3 related genes in the auxin（IAA）sub-pathway of plant hormone signal transduction.In summary,melatonin can alleviate drought-induced damages and improve drought resistance ability by regulating the gene expression of starch and sucrose metabolic pathway and coordinating plant hormone signal.