钾离子跨细胞膜吸收过程受铵影响的机理探讨

【作者】 孙小茗；

【导师】 封克；

【作者基本信息】 扬州大学 ， 植物营养学， 2006， 硕士

【摘要】 钾是植物细胞中含量最丰富的阳离子之一,对生物体具有重要的生理功能。铵离子与钾离子的吸收之间存在拮抗作用,铵离子的存在抑制了钾离子的吸收。然而,铵离子究竟通过何种机制抑制钾离子的吸收,到目前为止还没有明确的报道。因此本试验采用水培方法对铵离子抑制作物幼苗吸收K⁺的机制进行了研究,主要研究结果如下:1. NEM的浓度选择0.2 mmol/L时即可以抑制96%以上钾载体系统对钾离子运输的能力。1mmol/L的TEA比10 mmol/L的TEA对钾离子通道的抑制效果更好。在5 mmol K⁺/L浓度下, K⁺的跨细胞膜转移过程仍有很大一部分是通过载体蛋白组成的高亲和转运系统来完成的。NH₄⁺对钾载体和钾通道均有一定的抑制作用,但对各自的抑制程度在不同外源K⁺浓度下不同。在低钾浓度下,NH₄⁺对通道的抑制作用明显高于载体,而随着外源K⁺浓度的升高,NH₄⁺对通道的抑制作用低于对载体的抑制作用。随着K⁺浓度的增加,载体通道吸收的比例下降。当两种抑制剂同时加入时,小麦仍会通过其它转移方式来吸收K⁺,这种途径很可能就是非选择性离子通道。2.随饥饿时间延长,三种作物吸收速率变化趋势不一样。玉米呈上升趋势,而小麦大豆呈下降趋势。不同植物自身的饥饿诱导能力不同。饥饿时间（<=8天时）对三种作物根系的生长的负面影响不大,各个参数总的变化趋势还是以上升为主,对三种作物根系的生长并没有造成明显伤害。3.植物根细胞K⁺高亲和系统在作用过程中所表现的K⁺吸收曲线仍可用简单的Michaelich-Menten动力学方程加以描述。不同植物K⁺高亲和系统的Vmax和Km值之间存在着明显差异:其中Km值间的差异较小,在50%以内,而Vmax值的差异很大,小麦高出大豆11倍以上。NH₄⁺可能对不同植物根表细胞膜高亲和系统K⁺载体蛋白基因表达有抑制作用,但不同植物受抑制的程度不一,NH₄⁺对豆科类植物高亲和系统K⁺载体蛋白基因表达的抑制作用最大;对高亲和系统而言,NH₄⁺的存在对K⁺和载体蛋白之间的亲和性虽有影响,但影响程度不大,由NH₄⁺所导致的K_m的降低率均在10%以内。更多还原

【Abstract】 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更多还原