| Tobacco is an important economic crop in China and has a wide range of planting area.Tobacco needs more fertilizer,so the production is often blind,resulting in a certain environmental pollution.Therefore,screening of low nitrogen and nitrogen-resistant tobacco genotypes is an effective way to improve nitrogen use efficiency and reduce nitrogen pollution.The nutrient solution with low nitrogen(0.5mmol L-1)and normal nitrogen(5 mmol L-1)with 74 genes of tobacco seedlings was determined by statistical analysis of the evaluation index,and selected low nitrogen tolerant genotypes,the expression and the typical genotypes screened the morphology,physiology and biochemistry and botany nitrogen metabolism related genes were measured to explore the nitrogen absorption and utilization of different tobacco genotypes difference reason.The main results are as follows:1.Under the condition of low nitrogen and normal nitrogen,the variation coefficients of root volume,root biomass,nitrogen accumulation and aboveground biomass of 74 tobacco genotypes were larger.The principal component analysis showed that nitrogen accumulation and aboveground biomass of stem and leaf were the main effects under different nitrogen supply conditions.The stem and leaf nitrogen accumulation and aboveground biomass as screening index,and selected 15low nitrogen tolerant genotypes,accounting for 20.3%of the tested materials,8 of which belong to the low nitrogen efficiency of normal n-inefficient type,accounting for low nitrogen tolerant genotypes 53.3%,6 belong to the low nitrogen and low normal n-inefficient type.Accounted for 40%,1 belong to the low nitrogen efficiency of normal nitrogen efficient type,accounted for 0.7%;selected 8 low nitrogen sensitive genotypes,6 of which belong to the low nitrogen and low nitrogen,normal type,accounting for 75%,2 belong to the low nitrogen and low normal n-inefficient type,accounting for 25%.It was preliminarily identified that 14P9 was a low nitrogen and nitrogen tolerant genotype,and 100 and K394 were low nitrogen sensitive and nitrogen inefficient genotypes.2.There were significant differences in nitrogen efficiency among different tobacco genotypes,and the interaction between genotypes and nitrogen levels reached a significant level.The results of path analysis showed that the direct effect of nitrogen absorption efficiency on nitrogen efficiency was greater than nitrogen use efficiency at low nitrogen or normal nitrogen levels.Taking the aboveground biomass at two nitrogen levels as an evaluation index,different tobacco genotypes can be divided into four categories:Double efficient,low nitrogen efficient,normal nitrogen efficient,double inefficient,and the double efficient genotype is G80.Under different nitrogen levels,low nitrogen efficiency genotype of aboveground plant biomass,nitrogen accumulation,nitrogen absorption efficiency,nitrogen efficiency was significantly lower than that of N efficient genotypes,nitrogen utilization efficiency was not significant difference,indicating nitrogen efficient varieties of tobacco has good nitrogen absorption ability.3.It with low nitrogen tolerance,nitrogen efficient varieties 14P9,nitrogen efficient varieties G80,low nitrogen sensitivity,low nitrogen efficiency variety Zhongyan 100 and K394 as the experimental material,through investigating the morphological and physiological indexes of Botany,results show that the nitrogen efficiency genotypes with more lateral roots than n-inefficient genotype,greater root branching area.The apical area smaller,the total root length is longer,the greater lateral root density,root tip number more,stronger root activity,total leaf area larger.The root volume and the root volume of low nitrogen genotypes 14P9 had no significant difference under different nitrogen levels,while the low nitrogen sensitive genotypes of tobacco 100 and K394 were significantly higher than those of low nitrogen conditions under normal conditions.4.Compared with normal nitrogen,the decrease of soluble protein content in14P9 leaves was lower in low nitrogen conditions,while the other 3 genotypes decreased greatly.The content of soluble protein in the stem of nitrogen efficient genotypes（G80 and 14P9）was significantly lower than that of nitrogen low efficiency genotypes at different nitrogen levels.Resistance to low nitrogen nitrate reductase genes of tobacco leaves in low nitrogen conditions of 14P9（NR）activity decreased,NR activity decline in stem was higher than the normal nitrogen level,nitrogen efficiency genotype G80 in the stem of the activity of NR was higher than the normal level of nitrogen,and n-inefficient genotype 100 and K394 in tobacco leaves and stems,the root activity of NR was lower than that of normal nitrogen level.Glutamine synthetase in leaves and roots of the（GS）activity was higher than the normal nitrogen conditions under low nitrogen condition;under low nitrogen nitrogen efficiency genotypes in stem and root activity of GS was significantly higher than n-inefficient genotype,and n-inefficient genotype normal leaf nitrogen under the condition of the activity of GS was slightly higher than that of nitrogen efficient gene type.The expression level of nitrate reductase gene（Nit）of different tobacco genotypes was all down regulated under low nitrogen,while the expression of glutamine synthetase gene（GS1-3）was upregulated,which was basically consistent with the activities of related enzymes in leaves. |
