Effects Of Ammonium And Nitrate Nutrition On Root Growth Of Flue Cured Tobacco

Nitrogen is the most important nutrient for plant uptake and utilization.Ammonium nitrogen and nitrate nitrogen are the mainly available nitrogen in the soil that can be absorbed by the plant.The ammonium nitrogen and nitrate nitrogen have different elec tric charge and the process of absorption and assimilation,the growth and development of plants under different nitrogen forms will be affected.Study on the correlation between the effect of nitrogen form on yeild and quality of flue-cured tobacco,there was less research about the effect of root morphology under different ammonium nitrate ratio.Nevertheless,it is not clear how auxin regulates the growth and development of tobacco root under different conditions of ammonium nitrate.In this paper,based on the preliminary experiment,A hydroponic experiment was carried out to study effects of the different NH₄⁺/NO₃^-ratios?0/100,50/50and 97/3?on response of tobacco different in responsivility to nitrate in root growth at the seedling stage.In this study,in order to explore the mechanism of auxin involved the different ammonium nitrate ratio on root development of tobacco seedlings,we analyzed root morphology,soluble sugar and the activities of enzymes involved in nitrogen assimilation,auxin distribution in plants and PIN genes expressions in the different ammonium nitrate ratios.We also examined the effects of the auxin polar transport inhibitor N-1-naphthylphthalamic acid?NPA?and exogenously applied auxin?NAA?on LR formation and elongation in tobacco seedlings.The results are listed as follows:1.50%NH₄⁺plus 50%NO₃^-?50/50?treatment signif icantly increased dry matter accumulation and nitrogen accumulation of ZY100?low in NO₃^-responsivity?and NC89?high in NO₃^-responsivity?,and the biomass of NC89 treatments were more significantly different.50/50 treatment significantly promoted root length of ZY100 and NC89.There was no significant difference between total and low nitrate treatments of ZY100.But treatments of NC89 were significantly different,have a stronger response to ammonium nitrate ratio.It is shown in the first lateral root initiation and elongation,as well as the initiation of second lateral roots,while the average length of the second lateral roots did not different significantly.2.There was no signif icant difference in NR activity under different treatments of ZY100.NR activity in low nitrate treatment was significantly higher than the 50/50 treatment in leaf of NC89,while root system was significantly higher in 50/50 treatment than in low nitrate treatment.The GS activity in ZY100 and NC89 increased with the increase of NH₄⁺-N.Both ZY100 and NC89 had the lowest activity of GDH in total nitrate treatment,and ZY100 had higher GDH activity to alleviate the high concentration of NH₄⁺.Compared with 50/50 treatment,the total soluble sugar content was significantly decreased in total nitrate treatment.3.Auxin content in the leaves and roots of ZY100 and NC89 were highest in the 50/50 treatment,and lowest in the low nitrate treatment.Compared with 50/50 treatment,The content of auxin in the roots of ZY100 under total nitrate treatment and low nitrate treatment were reduced the same as that of the above ground.The total nitrate treatment and low nitrate treatment were reduced more than that of the above ground of NC89.The results of Qrt-PCR showed that Compared with ZY100,NC89 has more PIN genes involved in the polar transport of auxin under different ammonium nitrate nutrition conditions.In conclusion,different ratios of ammonium and nitrate affected synthesis and auxin transport,The reason why NC89 is more responsive to the ratio of ammonium to nitrate is that there are more PIN genes play an important role in the regulation of auxin transport under different ammonium nitrate nutrition conditions.4.The application of NAA could signif icantly promote the development of root system,and the expression of DR5::GUS was signif icantly increased in different parts.Compared with ZY100,NC89under low nitrate treatment needs more NAA to reach the 50/50 level.Correspondingly,the application of NPA to 50/50 could inhibit the development of root system,which was similar to that of low nitrate treatment.Therefore,the process of lateral root response to different ratios of ammonium and nitrate was related to the change of auxin concentration in roots.