Genotypic Differences In Nitrogen Metabolism And The Analysis Of Physiological Mechanism

In this study, we identify the N use efficiency (NUE) of different genotype wheat under hydroponic trial and field trial. The high NUE varieties and low NUE varieties were chosen to analyze the difference in the mechanism of N metabolism. In order to definitize the difference in the mechanism of N metabolism between high and low NUE varieties, the morphology, physiology and molecular biology method were used for the study of N uptake, assimilation and transport using. The main results were as follows.1 The difference of N use efficiency among 128 wheatUnder hydroponics trial, the difference in the 128 varieties at the N content, dry weight and N accumulation was highly significant. The results showed that it was feasible to identify the NUE and choose high NUE varieties. The resultes suggested that the NUE and N uptake efficiency (NAE) had a same trend, which were the varieties with high NUE had high NAE.In the present study, it was showed that there were obvious differences among wheat varieties in the NUE. 128 wheat varieties may be classified into four categories, i.e. high NUE under high and low N trial, high NUE under high N trial, high NUE under low N trial, low NUE under high and low N trial. 10 high NUE varieties and 10 low NUE varieties were chosen to be planted in the field, and identified the NUE. Two high NUE varieties and Two low NUE varieties which with a consistent performance under hydroponic and field trial, were used for studying the difference in the mechanism of N metabolism between high and low NUE varieties.2 The difference of N demand for plant growth between two type varietiesIn the present study, under hydroponic trial, the shoot, root and total fresh weight and dry weight of high NUE varieties was higher than that of low NUE varieties. Similarly, the chlorophyll and soluble protein content in the shoot of high NUE varieties were higher than that of low NUE varieties. It was indicated that supply N could increase the biomass weight, chlorophyll and soluble protein content for both high and low NUE wheat varieties at the seedling stage. Under field trial, the grain yield, dry weight and the harvest index (HI) of dry weight of high NUE varieties were higher than that in low NUE varieties. Similarly, the soluble protein content in flag leaf and grain of high NUE varieties were higher than that of low NUE varieties at the maturity stage. The results suggested that the high NUE varieties could get more biomass. So the root would uptake more nitrogen to meet the demands imposed by plant growth.3 The difference of N uptake between two type varietiesThe form and spatial distribution of root were the important factor for N uptake. The root morphology and physiological parameters were different between the high and low NUE type wheat at seedling stage. The number of root, root max length and root volume, total uptake area, activity uptake area and root activity of high NUE varieties were higher than that of low NUE varieties. The number of root, root max length, root volume, total uptake area, activity uptake area and root activity of two type wheat were increased by supply N. With the increase of supply N, the increase of the number of root, root max length, total uptake area and activity uptake area of low NUE varieties were higher than that of high NUE varieties. Furthermore, with the increase of supply N, the increase of root volume and root activity of high NUE varieties were higher than that of low NUE varieties. The gene TaNRT expressions of high NUE varieties were higher than that of low NUE varieties. And the TaNRT expression was negatively regulated by supply N in two type wheat. The expression of TaNRT2.1 and TaNRT2.2 could keep a high level in two type varieties, while TaNRT2.3 had a low expression level.4 The difference of N assimilation between two type varietiesThe NR and GS activity of high NUE varieties were higher than that of low NUE varieties at seedling stage. And the expressions of TaGS2 and TaGS1 of high NUE varieties were higher than that of low NUE varieties. In two type varieties, the expressions of TaGS2 were higher than TaGS1, and the TaGS2 and TaGS1 gene expression were increased by supply N. With the increase of supply N, the increase of TaGS2 and TaGS1 expressions level of high NUE varieties were higher than that of low NUE varieties.In two type Varieties, the NR activity in flag leaves and GS activity in grain showed a decrease during grain filling, and that of high NUE varieties were higher than low NUE varieties. The GS activity in flag leaves of two type Varieties had a rise after anthesis and with the maximum occurring at 5 DAA. The high NUE varieties had a higher GS activity in flag leaves than low NUE varieties. The results suggested that the N assimilation of high NUE varieties were higher than that of low NUE varieties at seedling stage and maturity.5 The difference of N transport between two type varietiesTransfer amount of N amount at anthesis, transfer efficiency of N amount at anthesis and the assimilation N amount after anthesis of high NUE varieties were higher than that of low NUE varieties. The transfer amount of N amount at anthesis in flag leaves, other leaves, stem and spike of high NUE varieties showed a 22.62%, 28.78%, 28.50% and 6.94% increase than low NUE varieties. In two type wheat, transfer efficiency of N amount at anthesis manifestations were as follows: flag leaves > other leaves > stem > spike. However, the transfer N contribution to grain of high NUE varieties was lower than that of low NUE varieties.The EP and CP activity in flag leaves of two type Varieties showed a increase during grain filling and with the maximum occurring at 25 DAA. There was no difference of EP and CP activity in flag leaves between two type varieties at the beginning of grain filling, and the difference had a rise with the grain filling. High NUE varieties could get a higher EP and CP activity in flag leaves than low NUE varietie. The results suggested that the N transport ability of high NUE varieties were higher than that of low NUE varieties at maturity. However, the low NUE varieties were more depend on the assimilation N amount at anthesis than high NUE varieties.6 Effects of N supply on the N metabolism of wheat at seedling stage Seedling height, dry weight and N accumulation were significantly increased by N supply. The results suggested that supply N increase could promote the wheat growth and N demand. The number of axial root, TUA and AUA were dependent on NO3- supply increase, while supply N had an adverse effect on the root maximum length and ratio of root to shoot. The expression of NRT1 significantly increased with more N supply, while NRT2 showed quite different responses to NO3- supply. NRT2.1 and NRT2.3 expression level decreased slowly with NO3- provision increase and keep high expression level under high supply N, while NRT2.2 expression level decreased rapidly. The results suggested that supply N increased the N absorption capacity. The NR and GS activity and the expression of TaGS1 and TaGS2 were increased by supply N, and the expression level of TaGS2 was higher than TaGS1. The results suggested that supply N increased the N assimilation capacity, and there were different contributions to the N assimilation in different key enzymes of N assimilation.7 The difference of N assimilation between superior and inferior grainThe activity filling rate, mean filling rate and max filling rate of superior grain were higher than that of inferior grain. Similarly, the grain volume and grain surface area of superior grain were higher than that of inferior grain. The results suggested that superior grains usually exhibit a faster rate of increase in dry weight during development and higher final grain weight than inferior grains. The N content and N accumulation of superior grain were higher than that of inferior grain. The free amino acid content in superior grain was lower than inferior grain, while the GS activity in superior grain was higher than inferior grain. The results suggested there was enough substrate for N assimilation in inferior grain, but the activity of using the substrate was lower in inferior grain than superior grain.