Physiological Responses And Proteomic Analysis Of Melatonin Treatment In Wheat Seedlings Under Drought And PEG Stress

Drought seriously affects wheat growth and yield.Studying drought resistance mechanism is the basis of drought-resistant breeding of wheat.Melatonin is a highly conserved multifunctional small molecule that is widely found in plants and has been reported to play an important role in abiotic stress.This study was designed to test the effect of melatonin on drought resistance of wheat.To this end,the drought resistance of 116 wheat germplasms from Huanghuai area and northern China was identified firstly.Then the isobaric tags for relative and absolute quantification(iTRAQ)technique combined with physiological,biochemical and cytological methods were used to analyze melatonin-induced physiological responses and proteomic differences in wheat under soil drought and PEG stress.After that we discussed the effect of melatonin on drought resistance of wheat seedlings under both two stresses and constructed protein network response to water-deficit and melatonin treatment to serve the research of drought-resistant mechanism and drought-resistant breeding in wheat.The main conclusions are as follows:1.Ten drought-resistant germplasms,three dehydration-tolerant germplasms and one melatonin-sensitive germplasm were screened.Through two-year drought-resistant identification of 116 wheat germplasms in Yangling and Yongshou County in Weibei Dryland of Shaanxi Province,wheat germplasms including Lankao Aizao8,177,98-10-30,PB1070,Pubing945,Weike2,Xiaoyan92,Xin9408,XNCW3,and XNCW4 showed good drought resistance and can be used as a germplasm for droughtresistant breeding.Wheat germplasms including Yan2801,XNTC1,and XNZK22 showed good PEG tolerance and dehydration tolerance,and can be used as important germplasms to study phyciological mechanism of drought resistance in wheat seedlings.Under PEG stress,Yan 995 is the most sensitive to melatonin and can be used to study the physiological function of melatonin in wheat.2.The applied melatonin improved the drought resistance of wheat seedlings under soil drought.Melatonin improved ROS elimination by enhancing glutathione-ascorbate(GSH-AsA)metabolism and other antioxidant enzymes,thereby alleviating cell and chloroplast damage and maintaining seedling growth under stress.Applied melatonin improved the osmotic adjustment by increasing the biosynthesis of soluble sugar,soluble protein,amino acid and polyamine,and reduced water loss by increasing epidermal cells.3.Exogenous melatonin improved seed germination and seeding growth of wheat under PEG stress.Melatonin improves water absorption of root by increasing root diameter and number of lateral roots of wheat seedlings.Melatonin improved antioxidant capacity and osmotic regulation by enhancing GSH-AsA metabolism and biosynthesis of antioxidant enzymes,soluble sugar,soluble protein and amino acid.Applied melatonin induced autophagy and ubiquitin-mediated protein degradation,and degraded the damaged biomacromolecules and organelles,thereby prolonging the survival time of seedling under stress.4.Differences of melatonin-induced protein profiles both drought and PEG were significant.Melatonin induced enzyme accumulation in antioxidant and GSH-AsA metabolism under both stresses,but the induced enzymes were different and melatonin induced more antioxidant enzymes under drought.Under soil drought,melatonin induced more up-regulated proteins which are involved in malate metabolism,citrate metabolism,degradation of glyoxylate and the biosynthesis of acetyl-CoA,proline,arginine,leucine,isoleucine,valine,glycine,and tryptophan,while PEG only induced the accumulation of enzymes related to the synthesis of tryptophan,serine,ornithine,valine and cysteine.5.Differences of protein profiles induced by drought and PEG were significant.Wheat seedlings had similar responses to two stresses,including inhibited photosynthesis and enhanced ROS levels,osmotic adjustment,and antioxidant metabolism.Drought and PEG selectively increased enzyme accumulation to enhance the metabolism of malic acid,proline,and GSH-AsA,including MDH,DHAR,P5 CS,P5CD,APX,GPX and GST.And drought induced these pathways more than PEG.PEG specifically induced the biosynthesis of spermine and spermidine and soil drought specifically induced ornithine synthesis.In conclusion,based on screening of 10 drought-resistant germplasms,3 dehydrationtolerant germplasms and one melatonin-sensitive germplasm,this study confirmed that melatonin enhanced water-deficit tolerance of wheat by selectively regulating enzymes in pathways including antioxidant metabolism and osmotic regulation under soil drought and PEG stress.These results laid the foundation for further study of the application of melatonin in wheat drought resistance.