| Wheat,which has high nutritional value,is one of the most important food crops in the world,which is ranked behind only rice in growing area.Soil water content and nitrogen fertilizer are consist of two main factors affecting its growth and yield agriculturally.Either single factor or coupling effect has an important impact on grain yield in wheat.In this study,the spring wheat cultivar,Sptifire(S),which has high yield and protein content and Drysdale(D),which is drought tolerance and one of parent of Spitfire,were used to investigate the effects of high nitrogen(180 kg/ha)and low nitrogen(22.5 kg/ha)on the root growth physiology,root morphogenesis,upper-ground growth physiology and yield under drought stress at seedling and headingstages.The objectives of this study is to declare the physiological and molecular mechanisms of high nitrogen alleviating drought stress at seedling and heading stages in wheat.The main results are summarized as follows:1The drought stess at seedling stage:high nitrogen significantly increased chlorophyll content,GS,GDH and NR activities of both S and D cultivars but decreased soluble sugar content of leaves in S and D by 35.7%and 24.4%,respectively.Furthermore high nitrogen also dramatically reduced the expression of GS1,PEPC and NR,and the down-regulation expression of PEPC in S cultivar was lower than that in D cultivar.Moreover,the expression of GS2 and GDH in S cultivar implied markedly down-regulated but up-regulated in D cultivar,and the expression of GOGAT hardly changed in the two cultivars.Synchronously,the expression of Rubisco in S cultivar significantly demonstrated down-regulated but up-regulated in D cultivar under high nitrogen environment.High nitrogen also promoted the root morphogenesis of S culrivar and increased significantly the root activity by 58.5%.The root activity of drought-resistant cultivar D increased by 3.1%,which was much lower than that of S.However,high nitrogen reduced the dry weight of upper-ground part of S cultivar by 36.5%but D did not change much by contratst.Finally,high nitrogen reduced the dry weight of underground part of S variety by 7.0%and increased that of D variety by 12.0%.2 Under drought stress at heading stage,compared with low nitrogen,high nitrogen evidently increased chlorophyll,soluble sugar,soluble protein,free amino acids content and GS,GDH,PEPC,NR activities of S and D cultivars;high nitrogen significantly decreased the expression of GS1,GS2 and NR of S and D cultivars.GS1 expression of S cultivar was down-regulated more than that of D cultivar.high nitrogen also clearly decreased the GDH and GOGAT expression of S cultivar and increased those of D vcultivar.While the expression of Rubisco and PEPC in two cultivars added,Rubisco expression of S and D cultivars was increased by 166.1%and 473.2%while the PEPC expression was increased by 24.6%and 108.7%respectively.At the same time,high nitrogen raised the dry weight of upper-ground part of S and D cultivars by 61.5%and 33.1%,and dry matter of S cultivar raised more than D cultivar.In addition,under drought treatment,high nitrogen significantly promoted root morphogenesis of S and D cultivars,and augmented root activity of S and D varieties by 14.7%and 52.8%respectively.Also,high nitrogen increased root diameter and root volume in two varieties.However,dry weight of underground part of S variety decreased by 21.6%,while that of D cultivar increased by 40.1%.3 Under drought stress at seedling and heading stages,more nitrogen fertilizer addition increased nitrogen translocation rate in both of two wheat varieties with 39.85%and 53.63%in S and D,which showed 1.29 and 1.66 times compared to low nitrogen treatment.High nitrogen also markedly promoted wheat yield under drought stress.The grain yield of S and D cultivars reached 378.67 mg and 433.89 mg per plant,respectively,and it was 1.59 and 1.47 times than that of low nitrogen under drought treatment. |
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