Jeschke W D
Botanisches Institut I der Universität Würzburg, Würzburg, Deutschland.
Planta. 1972 Mar;106(1):73-90. doi: 10.1007/BF00385474.
Barley roots grown on a nutrient solution containing 1 mM Na(+) but no K(+) are capable of a considerable Na(+) transport via the symplasm of the root and the xylem vessels. K(+) added to the medium surrounding the root cortex severely inhibits this transport after a lag period at a high rate constant (Fig. 3).It is likely that the fluxes of Na(+) are changed drastically during this transition from low to high K(+) status. Although originally limited to steady state fluxes, the extended method of efflux analysis for excised roots (Pitman, 1971) has been applied to the non-steady fluxes which occur upon the addition of K(+) to the roots. It is shown that besides other changes the efflux of (22)Na(+) through the cortex of barley roots is stimulated instantaneously (Fig. 5) by the addition of K(+) and presumably by an influx of K(+) ions. From this a transient, K(+)-stimulated Na(+) efflux at the plasmalemma of the cortical cells can be estimated. It amounts to 10.9 μ moles/g fw · h compared to the control efflux of 3.3 μ moles/g fw · h without K(+).The stimulated efflux is attributed to a Na(+) efflux pump at the plasmalemma and is thus related to the K-Na-selectivity of barley plants. The inhibition of the Na(+) transport by K(+) is probably a consequence of this increased efflux of Na(+) from the symplasm through the root cortex.
在含有1 mM Na⁺但不含K⁺的营养液中生长的大麦根能够通过根和木质部导管的共质体进行大量的Na⁺转运。在经过一段延迟期后，以高速率常数向根皮层周围的培养基中添加K⁺会严重抑制这种转运（图3）。在从低钾状态转变为高钾状态的过程中，Na⁺的通量可能会发生剧烈变化。虽然最初仅限于稳态通量，但用于离体根的扩展流出分析方法（皮特曼，1971年）已应用于向根中添加K⁺时发生的非稳态通量。结果表明，除了其他变化外，添加K⁺并可能由于K⁺离子的流入，通过大麦根皮层的²²Na⁺流出会立即受到刺激（图5）。由此可以估计在皮层细胞质膜上存在由K⁺刺激的瞬时Na⁺流出。与无K⁺时3.3 μmol/g鲜重·小时的对照流出相比，其流出量为10.9 μmol/g鲜重·小时。受刺激的流出归因于质膜上的Na⁺流出泵，因此与大麦植株的K⁺-Na⁺选择性有关。K⁺对Na⁺转运的抑制可能是由于Na⁺从共质体通过根皮层的流出增加所致。
