Studies On The Physiological Mechanisms And Gene Expressions Related To Nitrogen Under Low Nitrogen Stress In Tobacco

Nitrogen plays an important role in crop yield.In order to explore the photosynthetic characteristics,agronomic traits,physiological indicators of stress resistance,key enzymes and genes of nitrogen metabolism,and nitrate transporter genes of different genotype tobaccos in response to low nitrogen stress,14P9（low nitrogen tolerate,nitrogen efficiency variety）,zhongyan100（low nitrogen sensitive,low nitrogen efficiency variety）,K394（low nitrogen sensitive,low nitrogen efficiency variety）,and G80（nitrogen efficiency variety）were used as test materials what were cultivated with low nitrogen(0.5mmol L^-1N)and normal nitrogen(5mmol L^-1N).The main results are as follows:（1）under low nitrogen stress,low nitrogen tolerant tobacco variety has higher net photosynthetic rate（Pn）,stomatal conductance（Gs）,intercellular CO₂concentration（Ci）,and transpiration rate（Tr）;low nitrogen tolerant tobacco variety have more biomass and longer root length under low nitrogen stress,and the decline in biomass is smaller than that of low nitrogen sensitive tobacco variety.（2）Under low nitrogen stress for 15 days,the superoxide dismutase（SOD）activity of low nitrogen tolerant tobacco variety were higher in leaves,stems and roots,malondialdehyde content in roots were lower than that in low nitrogen sensitive tobacco cultivars,and proline content in leaves and roots were lower than that of low nitrogen sensitive tobacco variety.Under low nitrogen stress for 30 days,there were no significant difference in SOD activity between low nitrogen tolerant variety and low nitrogen sensitive variety,the malondialdehyde content in leaves,stems,and roots were significantly lower than that of low nitrogen sensitive variety,the proline content in leaves were significantly higher than that of low nitrogen sensitive varieties,and the proline content in stems were significantly lower than that of low nitrogen sensitive variety.（3）Low nitrogen stress reduced the nitrate reductase（NR）activity in the leaves and roots of low nitrogen sensitive tobacco variety,and had less effect on the NR activity of low nitrogen tolerant tobacco cultivars;nitrite reductase（Ni R）activity in tobacco leaves were reduced due to insufficient nitrogen supply,and Ni R activity in stems and roots of low nitrogen sensitive variety were lower than that of low nitrogen tolerant variety;glutamine synthetase（GS）activity of low nitrogen tolerant variety under low nitrogen stress were higher in leaves and stems;different days of low nitrogen stress reduced the glutamate synthetase（GOGAT）activity of tobacco,and GOGAT activity in leaves of low nitrogen tolerant variety were higher than that of low nitrogen sensitive variety;The glutamate dehydrogenase（GDH）activity in the stems of low nitrogen variety increased with the increase of treatment time,but low nitrogen stress had no significant effect on the GDH activity in the leaves of low nitrogen tolerant variety.（4）Low nitrogen stress had no significant effect on the expression of nitrate reductase（Ntnia1）,nitrite reductase（Ntnii2）,glutamate synthetase（Ntgogat1）gene in leaves,stems,and roots of low nitrogen tolerant tobacco variety,but it promoted the expression of glutamine synthetase（Ntgln1-3）gene in leaves and Ntgln1-3 and glutamate dehydrogenase（Ntgdh1）genes in roots;the effects of low nitrogen stress on the two low nitrogen sensitive variety were inconsistent,increased the expression of Ntgogat1 in leaves,Ntnia1 gene in stems,and Ntgln1-3,Ntgogat1,Ntgdh1 gene in roots of zhongyan 100,promoted the expression of Ntnia1 gene in roots,Ntgdh1 gene in stems of K394;the expression of Ntgdh1 in leaves,Ntnii2 in stems of zhongyan100,and Ntgln1-3 in leaves,Ntnia1,Ntnii2in stems,and Ntnii2 genes in roots of K394 were inhibited.（5）The effects of low nitrogen stress on the expression levels of nitrate transporter genes in the roots of low nitrogen tolerant and low nitrogen sensitive tobacco cultivars are consistent.Low nitrogen stress promotes the expression of Ntnrt1.1 and Ntnrt2.1 and inhibit the expression of Ntnrt1.2.