Study Of Sodium & Potassium Uptake Of Winter Wheat In Different Genotypes And Salt Tolerance Mechanisms

In this paper, hydroponic experiments were conducted to investigate the effects of apoplast and symplast pathways and membrane transport protein, and calcium and calmodulin activity etc.on NaCl uptake, translocation and accumulation in 4 winter wheat in different canopy temperature genotypes (include NR9405(warm), Xiaoyan6(medium incline to cold), Shan229, and RB6(cold)etc. with membrane-imperment fluorescent dye PTS (trisodium-8-hydroxy-1,3,6-pyrenesulphonate), an apoplastic tracer and the Pharmacological methods in the seeding stage. The intrinsic salt tolerance mechanisms of winter wheat in different canopy temperature genotypes were discussed. The main research results as follows:1. Effects of transpiration on sodium accumulation in the shoots of winter wheat under salt stressThere are different relationships between sodium accumulation in shoot and transpiration of winter wheat in different NaCl concentrations. Under medium salt(150 mmol/L NaCl)concentration, there is no correlation between transpiration rate and sodium accumulation in the shoots, while, under higher salt(250mmol/L NaCl)concentration, there is a significant correlation between them. The higher is transpiration rate, the more Na accumulation in shoot. There is also a significant correlation between the PTS content and sodium accumulation in shoot, especially under higher salt concentration and longer stress time. As salt concentration increased, the transpiration rate and the transpiration velocity decrease, however, the amount and the rate of sodium accumulation, and the sodium concentrations in intracellular and symplastical fluids increased. As the salt stress last, the water lost by transpiration, the sodium accumulation amount, the sodium concentration increased, but intracellular sodium concentration increase rate, sodium concentration in the symplastal fluids and Na accumulation rate in shoot decreased significantly. Whether there is salt stress or not, the transpiration velocity of warm winter wheat cultivars NR9405 and Xiaoyan 6 are smaller than that cold winter wheat genotypes of Shaan229 and RB6. These results indicate the lower canopy temperature of cold-type winter wheat is owing to the higher transpiration. Under higher salt concentration, the bypass flow has great effect on sodium accumulation in shoot. The more is the apoplastic leakage, and the more sodium accumulation in the shoot. This means that higher transpiration is an adverse characteristic of wheat under salt stress.2. Dynamics of Sodium uptake of winter wheat in different genotypes and the salt toleranceThe sodium uptake dynamics of winter wheat seedlings could be divided into two phases. Under lower salt condition, the Vmax are 0.50, 0.30, 0.58 & 0.55 Na+,mgg-1h-1,and Km are 18.50, 3.89, 70.90 & 30.68mmol/L of Xiaoyan 6, NR9405, Shaan229& RB6 respectively, and under higher salt condition, the value of Vmax are 1.81, 1.56, 2.11 & 2.11 Na+,mgg-1h-1 and Km are 107.20, 70.29, 121.06 & 102.67mmol/L respectively. Under lower salt condition, the sodium exclusion rate is almost 90%, but it is only 50%~60% under higher salt condition. The sodium absorption velocity of Xiaoyan 6 and NR9405 is 50% higher than that of Shaan229 and RB6 under lower salt condition, and there is little difference of the sodium exclusion rate among different winter wheat genotypes. On the contrary, the sodium absorption velocity of Shaan229 & RB6 is 15% higher than that of Xiaoyan 6 & NR9405, and their sodium exclusion rate is 10% lower than that of Xiaoyan 6 & NR9405 under higher salt condition, The higher sodium absorption velocity and the lower sodium exclusion rate under higher salt condition may be responsible for the salt sensitivity of Shaan229 and RB6.3. Effects of calcium ion and calmodulin on sodium uptake and accumulation of different winter wheat genotypesUnder medium salt concentration, Sodium uptake is enhanced significantly,and the potassium uptake is inhibited by 3 inhibitors: calmodulin inhibitor (chlorpromazine, CPZ), Ca2+ channels inhibitor (LaNO3) and Ca2+ chelator (EGTA). The effect of 3 inhibitors is as follow:CPZ> EGTA>> LaNO3. So the function of Ca2+ on sodium uptake maybe mainly by way of combination of Ca2+ and calmodulin (CaM); The calmodulin not only regulate Na+ efflux and Na+ annihilation in vacuole, which is critical to net Na+ influx in root cells and accumulation in the shoot, but also regulate K+ influx. Under medium salt concentration, the effect of inhibitors or chelator on the Na+ uptake of shaan229 and RB6 is higher than that of xiaoyan 6 and NR9405, but there is little difference among the different genotypes under higher salt stress concentration. So that shaan229 and RB6 are more sensitive to lower Ca2+ and CaM activity than xiaoyan 6 and NR9405, and winter wheat is more sensitive to the Ca deficiency.4. Effects of nonselective cation channels on sodium and potassium uptake of different winter wheat genotypesThe sodium content in shoots of winter wheat and the Na+ translocation from roots to shoots are significantly increased by nonselective cation channels inhibitor quinine under salt stress, while the sodium content in roots is dropped. The potassium content is decreased and the K+ uptake is inhibited by quinine simultaneously, but the K+ translocation rate from roots to shoots is significantly increased. It indicated that NSCCs play an important role on the sodium and potassium uptake and translocation from roots to shoots. There is no effect of Diethylpyrocarbonate (DEPC) on Na+ and K+ content and translocation are founded in the trials. Under medium and higher salt concentration, the sodium content increase as percentage in the shoots of xiaoyan 6 and NR9405 caused by quinine is higher than that of shaan229 and RB6. Under medium salt concentration, the sodium content drop as percentage in root of shaan229 and RB6 is higher than that of xiaoyan 6 and NR9405 in quinine treat, but it is reversed under higher salt concentration. The potassium content decrease as percentage in the root of shaan229 and RB6 are more than that of xiaoyan 6 and NR9405 in salt stress. It indicated that the function of NSCCs on sodium and potassium uptake are changed owing to different salt concentration. Under medium salt concentration, the contribution of NSCCs to xiaoyan 6 and NR9405 sodium uptake is higher than that of shaan229 and RB6, but reversed under higher salt concentration. Under salt stress, the contribution of NSCCs to shaan229 and RB6 potassium uptake is higher than that of xiaoyan 6 and NR9405.5. Functions of potassium transport protein on potassium and sodium uptake of winter wheatUnder higher potassium (3mmol/L KCl) with no salt stress, potassium uptake is inhibited by potassium competitive inhibitor (Cs+), potassium channel inhibitor (TEA) and their mixture, and the effect of Cs+ is higher than that of TEA. Under lower potassium (0.5mmol/L KCl) with no salt stress, the potassium content is significantly decreased by Cs+, but not by TEA. Under medium salt concentration, the potassium content is significantly decreased by Cs+ and TEA, and Cs+ almost has the same inhibitory effect on potassium uptake with TEA. Under higher salt concentration, no changes on potassium content are founded in Cs+ and TEA treatments. It indicated that under higher potassium with no salt stress the potassium uptake of winter is by both high affinity K+ transporters and low affinity ones, but it only by high affinity transporters under lower potassium concentration. Under medium salt concentration, both system are involved in potassium uptake; Under higher salt concentration, the regulation capacity of across-membrane way on potassium uptake is almost lost.Under higher potassium with no stress, the contribution of low affinity K+ transporter on NR9405 potassium uptake is higher than that on RB6; under lower potassium condition, potassium uptake of NR9405 mainly through the high affinity system, and RB6 uptake K+ through both ones. Under medium salt concentration, the potassium uptake system of NR9405 is more active than that of RB6, the inhibitory effect of Cs+, TEA and their mixture on NR9405 K+ uptake is higher than that on RB6. Under higher salt concentration, NR9405 can acquire a little K+ by both systems, but RB6 probably by other way.Under higher potassium with no stress, the Na+ uptake of NR9405 is not through potassium uptake systems, but RB6 can acquire some by them. Under lower potassium condition, both genotypes can absorb Na+ by potassium uptake systems. Under medium and higher salt concentration with higher potassium concentration, NR9405 can absorb Na+ by low affinity system; under lower potassium situation, both systems are involved in Na+ uptake in NR9405; while RB6 uptake Na+ through other ways in higher salt concentration. It indicated there is significant difference in K+ and Na+ uptake of two winter wheat genotypes.6. Effect of Na+/H+ antiporter or exchanger on sodium and potassium uptake of winter wheatUnder 150~250mmol/L NaCl stress there are increasing trend of sodium content in the shoots of winter wheat with the increasement of amiloride, an Na+/H+ antiporter or exchanger inhibitor, concentration, but it reversed in the roots; there are decreasing trend of potassium content both in shoots and roots. It indicated that the Na+/H+ antiporter or exchanger not only are involved in the sodium efflux and compartment in vacuoles but also in potassium uptake. In 150~250 mmol/L NaCl concentration, the sodium content in roots of NR9405, shann29 and RB6 are dropped significantly by inhibitor, but that of xiaoyan 6 is not affected. The regulation to K+ uptake by Na+/H+ antiporter or exchanger of xiaoyan 6, shann229 and RB6 is higher than that of NR9405. It indicated that there is difference the activity and function of Na+/H+ antiporter or exchanger in different winter wheat genotypes.