Effects Of Exogenous Melatonin On The Physiological And Biochemical Changes Of Ilex Verticillata ’oosterwijk’ Under Drought Stress

Ilex verticillata is an ornamental fruit tree species introduced into China in 2006 and has been cultivated in the provinces of Zhejiang,Shandong,Liaoning et al.To date,the drought-resistance potential of I.verticillata is little studied,which has restricted the introduction and popularization of this species to arid areas.Meanwhile,as a kind of new-found phytohormone,the roles of melatonin（MT）in drought stress has been proved in some species,but its regulatory role in I.verticillata under drought stress has not been revealed.In this paper,two-year-old cuttings of I.verticillata‘Oosterwijk’were selected as materials,and their physiological and biochemical changes in response to different levels of drought stress（80%-85%,50%-55%and 35%-40%of soil field capacity）and melatonin(100μmol·L^-1)treatment were determined to explore the drought-resistance potential and the means to increase drought-resistance of I.verticillata‘Oosterwijk’,and provide scientific evidences for introduction and popularization of this variety to arid areas.The results are as follows:1.Under drought stress,the height and basal diameter of I.verticillata‘Oosterwijk’cuttings were not significantly changed;chlorophyll content,nitrogen content,net photosynthetic rate（Pn）were significantly decreased,while transpiration rate（Tr）and non-photochemical quenching coefficient（NPQ）were significantly increased,implying that photosynthesis were restricted;the content of malondialdehyde（MDA）were significantly increased,indicating that the cell membrane were damaged;the contents of superoxyde dismutase（SOD）,peroxidase（POD）and catalase（CAT）were significantly enhanced,meaning that the antioxidant system were activated.2.Compared with single drought stress treatment,when endogenous melatonin were pretreated simultaneously,chlorophyll content and electron transport rate were increased,which indicated that the photosynthesis were revovered;the contents of SOD and CAT were significantly increased,which meant that the antioxidant system were enhanced;the contents of soluble sugars and soluble proteins,as well as the contents of abscisic acid（ABA）,indole-3-acetic acid（IAA）and gibberellin（GA）were increased,suggesting that the osmotic and hormone adjustment capacity were reinforced.3.Compared with the control group,there were no differences of physiological and biochemical indexes after 0 day of drought treatment;but more physiological and biochemical indexes were changed after 7 days of drought treatment,except for ground diameter,net photosynthetic rate,Fv/Fm,ETR and POD activity;and,most indexes were changed significantly after 30 days of drought treatment,except for stem length,ground diameter and Fv/Fm.For example,chlorophyll content,nitrogen content and Pn in N2 group were 79.42%,79.48 and 85.27%of that in CK group,respectively.Consequently,the effect of drought stress on I.verticillata‘Oosterwijk’was time-dependent.