Effects Of Exogenous Abscisic Acid And Melatonin On Carbon Metabolism And Antioxidant Metabolism Of Cotton Leaves Under Drought Stress

In order to study the effects of exogenous abscisic acid and melatonin on the physiological activity of cotton leaves under drought stress,pot experiments were conducted in 2018 and 2019 in a greenhouse of Nanjing Agricultural University.Two cotton cultivars,Yuzaomian 9110(droutht-sensitive cultivar)and Dexiamian 1(drought-tolerance cultivar)were selected and two levels of soil water regimes[soil relative water content SRWC(75±5)%,and SRWC(45±5)%]were set at the initial flowering stage.SRWC(75±5)%was set as control(CK)and SRWC(45±5)%was the drought treatment.Distilled water was spayed into the CK plants on the processing day,while distilled water,0.5 μmol/L abscisic acid(the treatment is abbreviated as D+ABA),0.2 mmol/L melatonin(the treatment is abbreviated as D+MT),0.5 μmol/L ABA+0.2 mmol/L MT(the treatment is abbreviated as D+ABA+MT)were spayed into the cotton plants under drought stress,respectively.The five treatments were abbreviated to CK,drought,D+ABA,D+MT and D+ABA+MT,respectively.The effects of exogenous ABA and MT on cotton yield,carbohydrate metabolism and antioxidant metabolism in leaves under drought stress were studied.The main findings were as follows:Boll number,boll weight,and lint percentage significantly reduced under drought stress.The application of ABA,MT,ABA+MT could all alleviate the drought-reducing effects.There were no significant differences on the boll weight and lint percentage under these three hormone treatments in the two cotton cultivars,while for the boll number,there were differed in the two cultivars.ABA+MT application had a better effect on the drought-reducing than ABA and MT treatments in Yuzaomian 9110.Drought stress reduced the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in the leaves of the two cultivars,making higher hydrogen peroxide(H2O2)and superoxide anion(O2-)contents,which finally caused the increased malondialdehyde(MDA).Exogenous MT,ABA and ABA+MT all increased the activities of SOD,POD and CAT in the cotton leaves under drought stress,and then reduced the accumulation of H2O2,O2-and MDA.There was a significant interaction of cultivar and treatment on the SOD activities.The mitigated effects of ABA on the activities of SOD were better than that of MT and ABA+MT in Yuzaomian 9110.However,the mitigated effect of ABA+MT on the activity of SOD was significantly better than that of ABA and MT treatments in Dexiamian 1.In addition,there were also significant differences in the effects of different hormone treatments on O2-content under drought stress in the two cultivars.The inhibition of D+ABA+MT treatment on the rate of O2-production was better than that of single hormone treatments under drought stress in Yuzaomian 9110,while in Dexiamian 1,the inhibition of these three hormone treatments were almost the same.The net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of cotton leaves decreased and the intercellular carbon dioxide concentration(Ci)increased under drought stress.D+ABA treatment,D+MT treatment and D+ABA+MT treatment could effectively inhibit the decrease of Pn,Gs,Tr contents,and finally decrease the Ci contents.The cultivar and treatment had a significant interaction effect on the Pn,Ci,and Tr,which mainly manifested in the effects of corresponding hormone treatments on Pn,Ci,Tr in leaves of Dexiamian 1 were much obvious than that in leaves of Yuzaomian 9110.Furthermore,drought stress also reduced the maximum photochemical efficiency(Fv/Fm),potential activity(Fv/F0)and light energy capture efficiency(ΦPSⅡ)in the two cultivar,while the application of ABA,MT,and ABA+MT all alleviated the effects of drought stress.Drought stress not only increased the sucrose contents of cotton leaves,but also increased the activities of sucrose synthase(SuSy),acid invertase(Inv),and alkaline Inv of cotton leaves,which finally increased the sucrose hydrolysis and the increase of glucose and fructose contents.Drought reduced the adenosine diphosphate glucose pyrophosphorylase(AGPase)activities and inhibited starch accumulation in cotton leaves.ABA,MT,ABA+MT could alleviate this increased or decreased effects,and the varieties and treatments had a significant interaction effect on sucrose,fructose,starch,sucrose phosphate synthase(SPS),Susy,acidic Inv activities.The effects of ABA+MT acted the most followed by MT,and ABA on the sucrose contents of leaves under drought stress in Yuzaomian 9110,while the effects of ABA+MT and MT both played significant roles in the sucrose content under stress in Dexiamian 1.The effects of corresponding hormone treatments on the fructose content in leaves were more obvious for Yuzaomian 9110 than Dexiamian 1 under drought stress.The promoting roles of ABA+MT application on the starch content were better than the single hormone application in Dexiamian 1 under stress,while for Yuzaomian 9110,there is no uniform trend across the two years.ABA+MT application was better than ABA or MT application in decreasing the activities of SPS、SuSy and acid Inv under stress in Yuzaomian 9110,while in Dexiamian 1,MT application was better than ABA or ABA+MT application in decreasing the related enzymes activities under drought.It can be concluded from the above conclusions that compound hormone spraying is superior to single hormone spraying in most cases.Yuzaomian 9110 responds to hormones more strongly than Dexiamian 1,and ultimately increase production.