The Absorption Process Of Potassium Ions Across Cellular Membranes By Ammonium Impact Mechanism

Potassium is one of the most abundant cations in plant cells and plays an important physiologic role. Interaction between the uptake of ammonium and potassium was widely studied and inhibition of ammonium on potassium uptake is generally accepted. However, the inhibitory mechanism is a matter of controversy and lacks definite explanations. Solution culture experiments were carried out to study the inhibitory mechanism of ammonium on the potassium uptake by crop seedlings. The main results were as follows:1. 0.2 m mol/L NEM inhibited the transport ability of K⁺ carrier system greatly (above 96%). 1 mmol/L TEA inhibited the K⁺ channel protein more than 10 mmol /L. When the concentration of K⁺ was 5mmol/L, a considerable proportion of K⁺ uptake was still through the high affinity transport system composed of carrier protein. Ammonium could inhibit K⁺ carrier protein and channel protein, but the inhibition differed at different concentrations of potassium. At low K⁺ concentration, the inhibition of ammonium on channel protein was evidently further than on carrier protein. On the contrary, at elevated K⁺ concentration the inhibition of ammonium on channel protein was lower than on carrier protein. The proportions of K⁺ uptake through carrier and channel both decreased with the increase of K⁺ concentration. When the two inhibitors were appended at the same time, wheat seemed to absorb K⁺ through other transport ways, maybe through the non-selective cation channels.2. The variation of K⁺ uptake rate of three tested crops differed with the prolongation of starvation. Maize presented an upward trend, but the wheat and soybean downward. Time of starvation within 8 days had a little negative impact on the root growth of three tested crops. The total variation of each root parameter presented a rising trend, so root growth of the crops was not obviously harmed with the prolongation of starvation.3. The K⁺ uptake curve behaved by K⁺-HATS in root cells could still be described by the simple Michaelich-Menten equation. The Vmax and Km of K⁺-HATS differed greatly among crops. There was relatively little difference (below 50%) in K_m, but great in Vmax. Vmax of wheat was more than 11 times higher than that of soybean. NH₄⁺ might inhibit the expression of K⁺-HATS genes; moreover, the extent of inhibition varied among crops and...