Effect Of Salt Stress On Kinetics Of K~+ Absorption In Wheat Seedling Genotypes With Different Canopy Temperature

In order to enrich the tempreture type theory and reveal the salt tolerance mechanism of wheat, we studied the effect of Na⁺ on K⁺ high affinity transporter systems(HATs) and low affinity transporter systems (LATs) absorption kinetic characteristics of wheat seedlings with different canopy temperatures: NR9405 (warm type),Xiaoyan NO.6(middle type),RB6 and Shan229(cold types). As well as we studied the effect of Na⁺ on shoot growth and ion accumulation of the 4 types wheat seedlings. The main research results as follows:1. In the range of 0⁵0 mmol·L^-1 K⁺, K⁺ absorption velocity of the 4 different type wheats increased with the increasing concentration. It can be divided into two phases, high affinity transport(HAT,0¹mmol·L^-1) and low affinity transport (LAT,1⁵0mmol·L^-1). both of the uptake process can be described by Michaelis-Menten equation.For K⁺-HAT, Km and Imax of warm type wheat was 0.332mmol·L^-1 and 33.57μmol·h-1·g-1RDW that less than that of the cold type, Shaan229 and RB6, which were 0.430⁰.432 mmol·L^-1 and 42.46⁴3.13μmol·h-1·g-1RDW, and that of the middle type XiaoyanNO.6 is 0.353 mmol·L^-1 and 35.38μmol·h-1·g-1RDW, which is between the two types.α[K⁺](coefficient of K⁺ influx) of the 4 types, NR9405 is 101.02, XiaoyanNO.6 is 100.36, Shaan229 and RB6 is 98.86 and 99.84. It revealed that high K⁺ affinity of warm type wheat is one reason why it had stronger K uptake capacity .For K⁺-LAT, Imax of NR9405, XiaoyanNO.6, RB6, Shaan229 wheats were 213.33,185.73,197.93 and 253.37μmol·h-1·g-1RDW, Km were 30.35,20.90,21.22 and 30.38mmol·L^-1,α[K⁺] were 7.03,8.89,9.33 and 8.31, respectively. Imax and Km of NR9405 and RB6 were higher, while XiaoyanNO.6 and Shaan229 with lower Imax and Km.α[K⁺] of Shaan229 is maximum, and NR9405 is minimum.When inhibited low affinity systems, Km was not affected and Imax andα[K⁺] increased in NR9405 and XiaoyanNO.6, while Km and Imax increased,α[K⁺] almost not changed in Shaan229 and RB6. It means that inhibited LATs not affect K⁺ affinity with HAT, but increased K⁺ absorption capacity in warm type wheat. But K⁺ affinity with HATs decreased in cold type wheat,when inhibited the LATs.When inhibited HATs,character parameters of LATs increased.Imax of 4 wheats in 314³90μmol·h-1·g-1RDW,Km in 29⁵5mmol·L^-1. Imax and Km of cold type increased more than warm type.It mean that K⁺ affinity of LATs of 4 wheats decreased and increased K⁺absorption capacity ,when inhibited HATs.2. K⁺ high affinity(0¹mmol·L^-1) absorption velocity curve could be decreased by the Michaelich-Menten under 10¹00 mmol·L^-1 Na⁺.The Imax andα[K⁺] of 4 wheats decreased by the Na⁺ exist,effect of Na⁺ on Imax andα[K⁺] of cold type wheat is relatively serious.Km of NR9405 and XiaoyanNO.6 almost uneffected by salt stress, the Km of cold type wheats decreased by 20%³0% by 100mmol·L^-1 Na⁺.The result indicated that reaction of cold type is sensitive to salt stress.Under 50¹00mmol·L^-1 Na⁺,α[K⁺] of cold type wheats lower than NR9405 and XiaoyanNO.6,it mean than K⁺ absorption capacity of cold type is lower,it is reason that salt tolerance of cold type lower than warm and middle types.3. The relationship between K⁺ low affinity absorption velocity and concentration in the solution can be described by line equation, within 1⁵0 mmol·L^-1 K⁺ concentration, and it divided into two phases , 1¹5 and 15⁵0mmol·L^-1, which described by line equation with different slopes.LATs K⁺ absorption velocity decreased as the existence of Na⁺ (100¹50 mmol·L^-1 ).Thus, the existence of Na⁺ make K⁺ flow out seriously, even with negative net absorption under lower K⁺ concentration(1³mmol·L^-1).4. K⁺ absorption capacity of NR9405 stronger than RB6.K⁺ content of shoot of the both wheat seedlings decreased with increasing Na⁺ concentration in solution.Na⁺ content of shoot not different between the both wheat genotypes seedlings.Na⁺ content and concentration of shoot of the both wheat seedlings increased with the increasing Na⁺(0¹50mmol·L^-1) concentration in the solution under every K⁺ contration,and Na⁺ accumulation content of RB6 higer than NR9405.Different cultivars and salt contration due to the effect of K⁺ on Na⁺ content of shoot were different,this effect were significant,while NR9405 under 150mmol·L^-1 Na⁺ and RB6 under 100¹50mmol·L^-1 Na⁺. The content ratio of Na⁺/K⁺ or cell concentration ratio in shoot was significantly related with the growth velocity in different treatments, thus, it was a reliable index to identify the salt resistence.