| Pot experiment was carried out at Henan Agricultural University Experimental Station in wheat growing-season of 2015-2016 and 2016-2017.Two winter wheat cultivars with different drought resistant,Luohan 7(LH7),higher drought resistance,and low resistant cultivars Xinong 979(XN979)were planted under two different treatments(control treatment,70%~80% relative water content;moderate drought treatment,50~60% relative water content).Potosynthetic characteristics of flag leaf,antioxidant system,non-structural carbohydrate of stems and sheaths in two wheat cultivars under drought stress were tested;besides,the difference in gene expression of key enzymes involved in non structural carbohydrate synthesis and metabolism at transcriptional level was analyzed.The main results were as follows:1?Yield analysis of different wheat cultivars under drought stress Drought stress significantly reduced grain yield of XN979 and LH7.The grain yield of LH7 and XN979 under control treatment decreased by 6.8% and 26.3%,respectively,compared with control treatment.The analysis of yield components showed that there was no significant difference between the number of spikes and 1000-grain weight of LH7 between drought stress and control treatment,but the number of grains per spike under drought stress was significantly lower than that of control treatment.For XN979,there was no significant difference in 1000-grain weight between drought stress and control treatment,but drought stress significantly reduced the the grain number per spike.The results suggested that drought stress in mid-and later-growth stages had great influence on spike weight;proper cultivation measures for increasing grain number per spike would help to mitigate drought impacts on yield.2?Photosynthetic characteristics analysis of different wheat cultivars under drought stress Drought stress interfered with the protein synthesis,and would affect the synthesis of chlorophyll.Under drought stress,the SPAD of LH7 and XN979 at 20 DAS and 30 DAS under drought stress decreased by 18.8%,33%,and 11.4%,32.8%,respectively,compared with the control.SPAD value of LH7 flag leaves was higher than that of XN979.Compared with XN979,LH7 maintained a higher conversion efficiency of light energy,which may indicate that LH7 had strong photosynthesis ability helping to increase grain weight and reduce the yield lose under stress.3?Responses of antioxidant system in different wheat cultivars to drought stress The Malondialdehyde(MDA)content of flag leaves under drought stress was significantly higher than that of control,with the average increase by 20.5% of LH7,and 50% of XN979.The content of MDA in flag leaves of XN979 at 10 DAS and 20 DAS under drought stress was higher than that of LH7 under the corresponding treatment.LH7 had a higher SOD and POD enzyme activity in the flag leaves than XN979,indicating that the high resistant cultivar had higher scavenging capacity of reactive oxygen species.4?Characteristics of dry matter and non structural carbohydrate in stem and sheath of different wheat varieties under drought stress Leaves dry weight of LH7 under drought stress decreased by 10.5% and 22% than that of control treatment at 10 DAS and 40 DAS.Correspondingly,the dry weight of XN979 under drought stress decreased by 3.5%,46%,and 44.8% than that of control treatment at 20 DAS,30DAS and 40 DAS,respectively.Similar tendency was also showed in dry weight of the stem and sheath of the two wheat cultivars.At the late stage of grain filling(40DAS),the dry weight of the stem and sheath under drought stress was significantly lower than that of the control treatment.The content of non structural carbohydrates firstly increases and then decrease,and the content of NSC peak at 20 DAS.Drought stress reduced the content of non structural carbohydrates,and the maximum decrease was 3.9% and 10.9% of LH7 and XN979,respectively.The content of soluble sugar increased in the early stage of drought treatment.But,with the time of drought stress increasing,the content of sugar was significantly less than that of control treatment.This results showed that the most abundance non-structural carbohydrate was sucrose,then fructan and fructose.As temporary storage organ,there are more non structural carbohydrates in the lower stem and sheath,the sugar content of the penultimate and lower internodes were significantly higher than that of peduncle.5?Key enzyme gene expression pattern of fructan metabolism in different wheat cultivars under drought stressThe relative expression level of genes involved in fructan synthesis at different internodes decreased in general with grain filling(or the time of stress prolonging).And the relative expression reached the highest level at 10 DAS.Compared with 10 DAS,the expression level of 1-SST-A1 gene of peduncle in LH7 and XN979 under 20 DAS decreased by 58% and 80%,respectively;and the expression of corresponding penultimate genes decreased by 46% and 86%,respectively;while lower internotes increased by 183% and 79% respectively.And the expression level of most of fructan biosynthesis enzyme gene in the stem and sheath of LH7 was higher than that of XN979.The expression pattern of genes in different parts of stem and sheath were different under drought stress.The expression level of most of genes in peduncle,penultimate and lower internodes decreased compared with the control at the early stage of stress treatment,but the expression level showed an increase trend with the treating time prolonging.The genes encoding fructan hydrolase showed different expression pattern with the grain filling.Among these genes,1-FEH-W1 showed a higher expression level in the middle period of stress,while 1-FEH-W2 and 1-FEH-W3 had higher expression in the later period.The INV3 had a higher expression in the later period,while INV1 showed no obvious change with grain filling.LH7 had a higher expression at early stage of stress treatment and XN979 had a higher expression at late stage of stress.At the early stage of drought stress,the expression level of most genes in peduncle at stress was lower than that of control;while in the late stage,the expression level was higher than control.At the early stage of drought stress,the expression level of most genes in the penultimate was lower than that of control treatment;while in the late stage,most genes of penultimate showed higher expression level under stress than that of control treatment.The higher expression level of gene encoding fructan biosynthesis enzyme at early grain filling stage would benefit the accumulation of fructan in stem and sheath and improve drought resistance;while the higher expression level of gene for frctan hydrolase enzyme at late stage would benefit fructan degradation and promote the transport of storage material to grain. |
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