Mitigative Effects Of Melatonin On L.davurica Seedlings Growth Under Drought Stress

L.davurica of the genus Leguminous Lespedeza was a high-quality native forage,whose seedling stage was the key period for morphological formation,but the seedling stage was susceptible to drought stress.Therefore,it was extremely important to ensure the healthy growth of L.davurica in the seedling stage.Melatonin(MT)was an endogenous hormone widely present in animals and plants and participates in a variety of physiological processes in organisms,and many data showed that spraying melatonin could protect plant growth.However at present,there were relatively few studies on the response of melatonin to drought stress in L.davurica,and there was still a big gap.Therefore,in this experiment,the seedlings of L.davurica cv."Jinnong No.1" independently cultivated by Shanxi Agricultural University were used as the test materials spraying with 25,50,100,200 and 400 μmol·L-1 melatonin.To analyze the effects of exogenous melatonin on plant morphology,leaf water characteristics,chlorophyll content,gas exchange parameters,chlorophyll fluorescence parameters,and leaf active oxygen metabolism of seedlings of L.davurica in natural drought,exploring the effective threshold and dose effects of melatonin in regulating the seedlings of L.davurica under drought conditions,exploring the mitigation effects of melatonin on the damage of L.davurica seedlings under drought stress,hoping that melatonin could regulate L.davurica seedlings played a certain role in healthy growth in arid environment and agricultural production activities.The results were as follows:1.Foliar spraying of melatonin increased the growth of the ground part of L.davurica seedlings under drought stress,but had little effects on the growth of the underground part.100 μmol·L-1 MT has the best effect,but the lifting effect at a concentration of 400 μmol·L-1 was poor,and even inhibited the growth of L.davurica seedlings that resulting in toxic effects.2.100 μmol·L-1 melatonin significantly alleviated the leaf fresh-to-dry ratio,water content,and relative water content of L.davurica seedlings under drought stress,and significantly reduced water saturation deficit(P<0.05),and significantly enhanced free prolin,soluble sugar and soluble protein contents(P<0.05),indicating that the appropriate concentration of melatonin promoted the water transfer and absorption capacity of the seedlings of L.davurica under drought stress.3.The 100 μmol·L-1 MT treatment significantly increased the chlorophyll a content,total chlorophyll(a+b)content,chlorophyll ratio,Pn,Tr,Gs,Fo/Fm and Fo/Fv of L.davurica(P<0.05),and significantly reduced the Ci and Ls(P<0.05).It could effectively reduce the Fo,increased Fm and Fv(P>0.05).The above showed that melatonin increased the accumulation of photosynthetic pigments in L.davurica seedlings,enhanced photosynthetic efficiency,and protected the photoreaction center from drought stress.4.The exogenous application of 100 μmol·L-1 MT significantly reduced the O2.-production rate,H2O2 contents,MDA contents and cell membrane permeability of L.davurica seedling leaves(P<0.05),promoted the activity of SOD,POD,CAT and APX(P<0.05),and significantly increased the accumulation of non-enzymatic antioxidant system substances such as As A,GSH and carotenoids(P<0.05).In summary,100 μmol·L-1 MT promoted the growth of L.davurica seedlings under drought stress,increased the water accumulation in leaves,increased the content of plant chlorophyll,enhanced gas exchange parameters and fluorescence parameters,and increased the antioxidant capacity of L.davurica,enhanced its osmotic adjustment function,and relieved the damage of the seedlings of L.davurica due to drought stress.