Na~+ And K~+ Absorbtion Characteristics,Molecular Cloning Of BvAKT1 Gene And Its Expression Pattern In Sugar Beet(Beta Vulgaris L.)

Potassium is an essential macronutrient for plants growth and development,K⁺is taken up by the plant root cell K⁺channels and trasporters.However,the K⁺concentrations of the soil solution are less than 1 mmol/L,seriously affect the normal growth and development of plants.Sugar beet?Beta vulgaris L.?is known as a typical natrophilic crop that is cultivated widely in the arid and semi-arid regions of north China.While the molecular mechanism of Na⁺and K⁺uptake in sugar beet is still unclear.Therefor,in this study,we investigate Na⁺and K⁺uptake pathways in sugar beet under mild salt conditions.We proposed that the AKT1may mediate K⁺uptake,this research worked on molecular cloning of K⁺channel gene AKT1from sugar beet,also analysis expression of BvAKT1.Results are as follow:1.At different concentrations?5-50 mmol/L?NaCl treatment,The results showed that high concentration?10 or 50 mmol/L?of KCl significantly reduced Na⁺/K⁺ratios in shoot and root of sugar beet in the absence or presence of NaCl.10 or 50 mmol/L KCl also decreased Na⁺net uptake rate,or had no effects on it at 5,10,and 50 mmol/L NaCl,while enhanced K⁺net uptake rate with external NaCl concentration at 5 and 25 mmol/L.It seemed that high external K⁺levels could maintain lower Na⁺/K⁺ratio in sugar beet by enhancing K⁺uptake and restricting Na⁺uptake.2.At different concentrations?5-50 mmol/L?NaCl treatment,Both 5 and 10 mmol/L TEA⁺,which are considered to be a blocker of K⁺channels,had no significant effects on net uptake rates of Na⁺and K⁺in sugar beet in the absence or presence of NaCl.However,3 or 6mmol/L Cs⁺,which is also known to be an inhibitor of the K⁺inward-rectifying channel?AKT1?,led to significant reduction of K⁺net uptake rate but did not affect Na⁺net uptake rate in the presence of NaCl.5 or 10 mmol/L Ba²⁺which is known as another blocker of K⁺channel and transporter?HKT?,not only reduced Na⁺net uptake rate but also decreased K⁺net uptake rate?except at 25 mmol/L NaCl?in sugar beet at 5-50 mmol/L NaCl.3.A gene encoding K⁺channel was firstly isolated from sugar beet roots.The cDNA sequence of BvAKT1 is 3250 bp,which contained an open read frame of 2604 bp,71 bp 5,untranslated region,575 bp 3,untranslated region and 34 bp of poly?A?tail.BvAKT1consisted of 867 amino acid residues.We presumed molecular weight of 97.82 kDa,an isoelectric point of 6.57.The data showed that these genes have over 60%similarities with the corresponding genes previously characterized in other plants.4.Under NaCl of 5-150 mmol/L,roots BvAKT1 transcript abundance was significantly higher than in shoot.However,the transcript level was significantly higher at 150 mmol/L NaCl than that at 100 mmol/L.It was showed that salt stress can enhance BvAKT1 transcript abundance;50 mmol/L NaCl at different time points?0-72 h?,BvAKT1 transcriptional abundance weakened after 6h in root.Under KCl of 0.1-10 mmol/L,BvAKT1 transcript abundance remained unchanged,this suggested that BvAKT1 possible post-transcriptional regulation.