Physiological and Molecular Response of Wheat Roots to Nitrate Supply in Seedling Stage

The objective of this study was to understand the morphological,physiological,and molecular responses of wheat roots to nitrate supply at seedling stage.Two wheat genotypes,Jimai 22 and Shannong 15,were grown in Hoagland＇s nutrient solution with different nitrate levels at seedling stage.Results indicated that the plant dry weight and N accumulation increased with the increase of nitrate supply.The number of axial root,total uptake area （TUA）,and active uptake area （AUA） increased with more nitrate supply.Correlation analysis indicated that significant positive correlations existed between N accumulation and dry weight,N accumulation and AUA,and N accumulation and AUA/TUA.Although,the expressions of NRT2.1,NRT2.2,and NRT2.3 decreased with nitrate supply increased,the expressions of NRT1,NRT2.1,and NRT2.3 could maintain high level at N3 treatment.The free amino acid and NO3- content in shoot also increased with the increased nitrate application,but no significant difference was found in root among the treatments.These results implied that the increase of N uptake by nitrate supply was due to the morphological and physiological responses of wheat roots and the high expression level of TaNRT genes.Similarly,the contribution of morphological,physiological,and molecular parameters was different between two genotypes of wheat.

Relation of Root Growth of Rice Seedling with Nutrition and Water Use Efficiency Under Different Water Supply Conditions

Water deficiency is one of the primary yield-limiting factors in rice. In plants, the nutrition and water use efficiency depend on root growth efficiency under different water supply conditions （WSC）. Three rice genotypes, Azucena （an upland japonica）, IR1552 （a lowland indica） and Jia 9522 （a lowland japonica）, were grown under different WSC with 0 cm （submerged）, 40 cm and 80 cm groundwater levels below the soil surface to investigate the root parameters, water use efficiency, nitrogen, phosphorous and potassium contents, net photosynthetic rate and transpiration rate of the rice plant. The relative parameters were defined as the ratio of the parameters under submerged conditions （0 cm groundwater level below soil surface） to these under upland conditions （40 cm and 80 cm groundwater levels below soil surface）. The results indicated that different genotypes showed different relative root parameters and relative nutrition content and water use efficiency under different WSC. The length and number of adventitious root are more important than seminal root length in water and nutrition uptake, and maintaining the grain yield and increasing dry matter, but the adventitious root number could not be served as an index for screening drought-resistant genotypes. Furthermore, different drought-resistant genotypes have been also found, and Azucena was resistant to drought, IR1552 sensitive to drought and Jia 9522 neither sensitive nor resistant to drought.