Growth Of Tobacco Seedlings Under Varying NH₄⁺/K⁺ Concentration And Bioinformatic Analysis Of The Two Relevant Ion Transporter Families

Ammonium（NH₄⁺）is essential for plant growth.High concentrations of NH₄⁺inhibit the absorption of K⁺and cause toxic symptoms in plants.Tobacco is a potassium loving crop with high tolerance to NH₄⁺.In this study,in order to explore the optimal concentration of NH₄⁺and K⁺,and the ratio of NH₄⁺to K⁺for tobacco growth at seedling stage,47 groups of different concentrations and ratios of NH₄⁺and K⁺were set up.The tobacco seedlings were cultured in nutrient solution for 15 days and the relevant physiological indexes were measured.The results showed that high NH₄⁺and low K⁺resulted in leaf yellowing or dark green,poor stem development and root growth,and inhibited K⁺absorption and accumulation.However,excessive K⁺supply had no significant effect on plant growth.At different ratios of low NH₄⁺/K⁺（combined form）,tobacco growth did not differ significantly.Under hydroponic condition,the optimal concentration of NH₄⁺and K⁺for tobacco leaf and root growth was 2 m M and 2 m M.and at ratio 1:1.The optimal concentration of NH₄⁺and K⁺for stem growth was 1 m M and 2 m M,and at ratio 1:2.Carbohydrate is the main energy for plant growth,and its distribution under different environmental stress plays an important role in plant growth and development.However,the interaction between NH₄⁺and K⁺supply,and photoassimilates is rarely reported.In order to investigate the effects of different concentrations of NH₄⁺and K⁺on the distribution of photoassimilates and growth of tobacco seedlings,9 of the 47 treatments were selected.Three different concentrations of NH₄⁺and K⁺（high,middle,low）respectively,and three different combinations of NH₄⁺/K⁺（low,middle and high）were formed.The tobacco seedlings were grown under hydroponic condition for 15 days and the relative physiological indexes were measured.The results showed that under low K⁺condition,the decrease of stem dry weight was more obvious than that of leaf and root dry weight,which resulted in the increase of root-shoot ratio and the reduction of soluble sugar and starch content.Under the medium K⁺condition,the dry weight of leaves and roots,K⁺content,activities of sucrose phosphate synthase（SPS）and sucrose synthetase（SS）,root activity and stem dry weight reached the highest value.Under the high NH₄⁺condition,the NH₄⁺content in leaves,stems and roots increased significantly,while the K⁺content decreased.The soluble sugar and starch contents decreased sharply,and the NH₄⁺content in tobacco tissues decreased gradually with the increase of K⁺concentration.Under medium concentration of NH₄⁺and K⁺,the soluble sugar and starch content of all tissues reached the maximum value.Under the condition of high NH₄⁺and low K⁺,the contents of soluble sugar and starch decreased rapidly,and the activities of SPS and SS reached the highest.Shaker K⁺channel and Ammonium transporters（Ammonium transporter;AMT）gene family are important in regulating K⁺and NH₄⁺uptake,respectively.The identification and functional analysis of related genes play an important role in elucidating the molecular mechanisms of different NH₄⁺and K⁺antagonism.Therefore,the genome-wide identification and bioinformatics analysis of tobacco Shaker and AMT families were conducted in this study.The results showed that there were 25 Shaker family K⁺channel genes and 18AMT family genes in tobacco.According to evolutionary analysis,Shaker family genes can be divided into 5subgroups（I-V）,and AMT family into 2 subgroups.The amino acid sequence size,molecular weight and isoelectric point of Shaker family members are 524-1194aa,61.82-13.70 k Da,and 6.19-9.11 respectively.The amino acid sequence size,relative molecular weight and isoelectric point of AMT family members were490-603 aa,52.68-65.42 k Da,and 5.23-8.52.The analysis of gene structure showed that each subfamily of Shaker gene had similar exon/intron structure,but the number of exons and introns was different,while the AMT gene had the similar exons/introns structure.The analysis of cis-acting elements in the promoters of Shaker family genes and AMT family genes showed that the promoter regions of both genes contained cis-elements related to hormone and drought stress.Analysis of transcriptome data showed that the expression of some Shaker family genes increased significantly in vigorous tobacco tissues or during the period of potassium cycling changes after topping.In this study,the optimal concentration and ratio of NH₄⁺and K⁺were determined for tobacco seedling growth.The effect of different concentration of NH₄⁺and K⁺on the distribution of photoassimilates and tobacco seedling was analyzed.Meanwhile,genome-wide identification and bioinformatics analysis of Shaker gene family and AMT gene family in tobacco were carried out.This study provided data to support the adjustment of nutrient balance supply and nutrient distribution in different tissues of tobacco seedlings,as well as the functional elucidation of NH₄⁺and K⁺channels.