Effects Of Exogenous Melatonin On Photosynthesis And Growth Of Soybean Under Drought Stress

Drought stress is one of the main abiotic stresses,which severely limits the yield of soybean.Melatonin has the effect of resisting abiotic stress.To study the effect of exogenous melatonin on photosynthesis and growth of soybean under drought stress,this experiment in 2017-2018,at the National Cereals Technology Research Center of Bayi Agricultural University of Heilongjiang Province,using Suinong 26(drought sensitive variety)as the tested variety,potted plants were used to control 50% of field water holding capacity for drought stress,with 80% of field water holding capacity.For the normal water supply control,the effects of foliar application of melatonin on photosynthesis and growth of soybean were studied under drought stress during seedling,flowering,podding and seed filiing stages.The results showed that:Exogenous melatonin promoted the growth of soybean plants at the seedling,flowering,podding and seed filing stages under drought stress.Exogenous melatonin can alleviate the inhibition of soybean seedling and flowering plant height,above-ground and below-ground fresh dry weight by drought stress,and promote the development of seed and grain stage seeds under drought stress.Exogenous melatonin promoted the growth of soybean plants at the seedling,flowering,pod-forming and granulation stages under normal water supply conditions,and increased biomass accumulation,but did not reach significant differences.Exogenous melatonin increased the number of pods per plant,number of grains per plant,100-seed weight and grain weight per plant under drought stress.Compared with drought stress,the number of pods per plant,the number of single plants and the 100-grain weight increased by 4.9%,0.8%,0.5% in the seedling stage,and the flowering period increased by 4.0% and 2.7%.5.8%,the podding period increased by 7.8%,7.1%,6.4%,the drum period increased by 4.00%,0.95%,16.4%,and the corresponding yield(single plant weight)increased by 1.2% and 7.9%,respectively.10.5% and 16.2%.Under normal water supply conditions,exogenous melatonin can increase the number of pods per plant,number of single plants,100-grain weight and grain weight per plant,but did not reach significant differences.Exogenous melatonin increased the relative water content and protective enzyme activity of soybean leaves in seedling,flowering,podding and seed fillingstages under drought stress,inhibited the production of reactive oxygen species,and protected cell membranes,thereby improving Soybean drought resistance.The drought stress caused the protective enzyme activity of soybean leaves to increase first and then decrease,the active oxygen content increased,and the cell membrane was destroyed.Exogenous melatonin can significantly increase the relative water content of soybean leaves,protective enzymes(SOD,POD,CAT,APX,MDHAR,DHAR,GR,GPX)and protective substances(ascorbic acid,glutathione),and reduce Conductivity,reactive oxygen species(O2-,H2O2)and malondialdehyde content protect the integrity of the cell membrane.Under normal water supply conditions,exogenous melatonin can increase the activity of antioxidant enzymes to a certain extent,but did not reach a significant level of difference.Exogenous melatonin increased the chlorophyll content and photosynthesis of soybean leaves in seedling,flowering,pod-forming and soaking stages under drought stress,inhibited NPQ and starch content,and improved soybean photosynthetic capacity.The drought stress caused the photosynthetic capacity of soybean leaves to decrease continuously,and the carbohydrate content increased first and then decreased.Exogenous melatonin can significantly increase Rubisco enzyme content and activity,photosynthetic parameters and chlorophyll fluorescence parameters(Pn,Tr,Ci,Gs,WUE,Fv/Fm,Fv/Fo,Fv'/Fm',?PSII,ETR,qp),carbohydrate content(sucrose,fructose,soluble sugar)and sucrose synthesis and transformation related enzyme activities(SS,SPS,AI,NI),reduced starch content and NPQ,improved photosynthetic capacity.Under normal water supply conditions,exogenous melatonin can increase photosynthetic capacity and sucrose-related enzyme activity to a certain extent,but the effect is not obvious.In summary,exogenous melatonin can increase the growth and yield of soybean seedling,flowering,pod-forming and granules under drought stress,mainly by increasing antioxidant enzyme activity and antioxidant content,promoting photosynthetic capacity and carbon metabolism.Assimilation ability,reducing membrane lipid peroxidation level.Exogenous melatonin can improve the drought resistance of soybean and can be applied to actual production as a plant growth regulator.