Evaluation Of Germination Characteristics And Physiological Response Mechanism Of Wheat Seeds Under Drought Stress

Drought stress is the main abiotic stress affecting the high and stable yield of wheat.Drought stress during germination causes delayed seed germination,reduced germination percentage,and decreased seedling uniformity and robustness,which seriously affects the late growth and yield formation of wheat.There are a few studies on the response mechanisms of drought stress during seed germination of wheat.In this study,128 wheat cultivars were identified for germination characteristics under drought stress.The cultivars with significant differences of germination characteristics under drought stress were screened,and the seed germination and growth indexes,storage substance decomposing enzymes and antioxidant enzymes activities were determined under drought stress.The changes of macromolecular repair ability and seed embryo lipid metabolism ability during seed imbibition and germination were detected,in order to reveal the mechanism of drought stress affecting the quality of wheat seed germination and seedling establishment during the germination stage,and provide new ideas for the breeding of drought-tolerance wheat cultivars and the regulation of establishing and strong seedlings under drought stress.The results of the study are as follows:1.Differences in seed germination characteristics of 128 wheat cultivars under drought stressEvaluation of germination characteristics of wheat seed under drought stress by sand cultivation and water control method,and 128 wheat cultivars were classified into 5 categories according to the germination characteristics under drought stress,among which 18 wheat cultivars,such as SN28,C6878 and BN4199,had good germination characteristics under drought stress,rapid and uniformity germination,strong seedlings.26 wheat cultivars,including XM38,LX77 and LM185,had poor germination characteristics under drought stress,delayed germination,scattered germination time,low germination percentage and poor robustness of seedlings.2.Effect of drought stress on macromolecular repair ability and antioxidant ability of wheat cultivars with different germination characteristicsSix wheat cultivars(SN28,C6878,YN19,SN23,XM296 and XM38)with significant differences in germination characteristics under drought stress were selected as materials to study the effects of drought stress on macromolecular repair ability and antioxidant ability.The results showed that for SN28 and C6878 with good germination characteristics under drought stress,the radicle protruded quickly,and the TDP1 expression levels and POD activity were significantly increased at the early stage of germination under drought stress.Drought stress had no significant effect on GE,GP,VI and water absorption percentage.For XM296 and XM38,which had poor germination characteristics,the expression levels of seed embryo DNA and protein repair genes were relatively delayed under drought stress,and the SOD activity was significantly lower than that of the control at the early stage of germination.GE,GI,VI and SSDW were significantly reduction under drought stress.It showed that the macromolecule repair ability and antioxidant ability were closely related to the seed germination speed during seed imbibition and germination.3.Differences in decomposition and transformation of storage substances during seed germination and seedling establishment of wheat under drought stressThe study on the ability of storage substance decomposition and transformation with different germination characteristics of wheat cultivars under drought stress showed that drought stress had little effect on the activities of α-amylase and cysteine protease of SN28 and C6878 wtih good germination characteristics and high soluble protein content at the late stage of germination under drought stress.The soluble protein of SN28 rose earlier and mobilized substances earlier than other cultivars.Drought stress led to a significant reduction in the cysteine protease activity of XM296 and XM38,which had poor germination characteristics,but had no significant effect on the soluble protein content.In addition,the α-amylase activity in XM38 was also significantly reduction at the late stage of germination under drought stress.4.Effect of drought stress on lipid mobilization in seed embryos of wheat cultivars with different germination characteristicsThe analysis of lipid metabolism of seed embryo under drought stress showed that lipid metabolites were significantly enriched in glycerophospholipid metabolic pathway,glycerolipid metabolic pathway and autophagy-other metabolic pathway under drought stress,and the lipid metabolism of seed embryo in SN28 with good germination characteristics was stronger than that of XM296 with poor germination characteristics under drought stress.Expression testing of seed embryo lipase genes,lipid metabolism-related nsLTP genes and ABA signaling genes showed that the expression patterns of lipolytic enzyme genes,Ta LTPIg.1,MYB96 and ABI4 genes in response to drought stress were related to the germination characteristics of wheat cultivars under drought stress.SN28 and C6878 with good germination characteristics under drought stress,the expression of lipase 3 family protein gene and Ta LTPIg.1 gene during germination at 12 h under drought stress were significantly higher than the control,and the expression of ABI4 gene during germination at 12 h and MYB96 gene during germination at 24 h under drought stress were significantly lower than the control.XM296 and XM38 with poor germination characteristics under drought stress,the expression of acylhydrolase gene during germination at 12 h and Ta LTPIg.1 gene during geimination at 48 h under drought stress were significantly lower than the control,and the expression of MYB96 gene and ABI4 gene during germination at 48 h under drought stress were significantly higher than the control.In summary,drought stress during germination significantly decreased the macromolecular repair ability,antioxidant ability and lipid mobilization ability of wheat seed embryo,resulting in slower seed germination and reduced seedling strength.Improving the repair ability and lipid mobilization ability of seed embryo during imbibition and germination is an effective way to improve the quality of wheat germination and seedling establishment under drought stress.