Effects Of Exogenous Melatonin On Drought Resistance Of Oat Seedlings

In the present study,we analysed the effects of different drought stess treatments simulating with six concentration PEG-6000 solution including 0%?CK?,5%,10%,15%,20%and 25%on the main physiological and growth indexes of oat seedlings?Avena sativa L.cv.Qingyan No.1?growing in quartz sand.Moreover,the endogenous melatonin concentration,the morphological characteristics,the antioxidant system enzyme activies,the osmotic substance concentration,photosynthetic indices,chlorophyll fluorescence parameters and the endogenous hormone concentration of oat seedlings treated with the melatonin pretreatment were investigated under drought stress.The results were as follows:1.The results showed that compared to CK,the chlorophyll concentration and leaf relative water content significantly?P<0.05?reduced 50.27%and 80.64%under the drought stress of 20%and 25%PEG.and The membrane lipid was severely damaged and growth is restrained under drought stress as well.Under the drought sress of 15%PEG,oat seedlings were moderately damaged and could still survive for a long time.Oat seedlings could maintaine a relative balance of growth under the drought stress of 5%and 10%PEG,which implied oat seedlings had the resistant capability for mild drought stress.In order to carry out a further research of the resistant capability of oat seedling,oat seedlings with the melatonin pretreatment were treated under the concentration of 15%PEG.2.Melatonin pretreatment could improve antioxidant enzyme?SOD,CAT,POD,APX?activities of oat seedlings.The activities of SOD,POD and APX and the contents of ASA and GSH increased with the longer duration of drought stress.The exogenous application of melatonin could induce the contents of soluble sugar and free proline in leaves of oat seedlings under the drought stress,but had no significant effect on the contents of free total amino acids.Compared with free melatonin pretreatment,melatonin pretreatment significantly improved the RWC,root activity and biomass of oat leaves and significantly reduced plant wilting degree,relative conductivity,and the contents of MDA,H₂O₂ and O₂^-?,thereby reducing oxidative damage of drought stress.3.Under drought stress,oat leaf net photosynthetic rate and intercellular CO₂concentration dropped significantly,which showed that drought stress led to the decrease of the photosynthetic rate because of stomatal factors.The contents of chlorophyll,photosynthetic parameters?Pn,Tr,Ci,Tr?and chlorophyll fluorescence parameters?Fv/Fm,ETR,qP,qN and?PSII?of oat seedling reduced constantly under drought stress,while these changes deferred for these seedling with the melatonin pretreatment,which meant the melatonin pretreatment relieved the inhibition of drought stress on photosynthesis.4.The drought stress increased the content of endogenous melatonin and ABA,while reduced the content of GA3 and IAA and inhibited the growth of root system.The application of exogenous melatonin increased the content of endogenous melatonin contentand IAA,and GA3,while inhibited the synthesis of ABA,while implied that a certain concentration of melatonin might alleviate the damage of drought stress through regulating endogenous hormone level,and could promote the growth of root.