K+ absorption kinetics of wheat cultivars with different canopy temperature and the salt stress

The absorption kinetics and pharmacology method were employed to study the effect of Na+ on regulation of K+ transporter systems characteristics using wheat genotypes with different canopy temperature. The wheat cultivars in this study included a warm climate cultivar (cv. NR9405), a moderate climate cultivar (cv. Xiaoyan No. 6), and two cold climate cultivars (cv. RB6 and cv. Shaan229). The results indicated that the dynamics of K+ uptake by wheat seedlings in the 0 to 50 mmol/L K+ treatment could be divided into two phases. The first phase consisted of higher affinity transport (HAT) of K+ whereas the second phase consisted of lower affinity transport (LAT). The K+ absorption velocity curves of both phases were best described by Michaelich-Menten equations. The Imax and Km of higher affinity transport were higher in both cold climate cultivars than in the moderate climate and the warm climate cultivars. This indicated that the K+ affinity capacities of Xiaoyan No. 6 and NR9405 were higher than those of RB6 and Shaan229. When the LATS was inhibited, the number of K+ carriers increased in all four wheat cultivars, but the affinity capacity in the cold climate cultivars declined, but did not in other two cultivars. The Imax values of the LAT system ranged from 183 to 253 mol/(h?g), RDW and the Km values ranged from 20 to 30 mmol/L. When the HATS were inhibited, the Imax and Km of the LATS increased, indicating that number of carriers had increased but the affinity capacity of the carriers had decreased. Salt stress inhibited the absorption and transport capacity of K+ by the HAT and LAT systems in all four cultivars. The Km values of the HATS in NR9405 and Xiaoyan No. 6 were almost unaffected by Na+ stress. In contrast, Na+ stress reduced the Km values of the HATS system in the cold-climate genotypes. This indicates that the HATS of salt tolerant plants are stable. This finding has important implications for understanding the molecular mechanism of plant salt tolerance and nutrient uptake.