Growth, contents of K+ and kinetics of K+(86Rb) uptake in barley cultured at different low supply rates of potassium

Plants of barley ( Hordeum vulgare L. cv. Salve) were grown with 6.5–35% relative increase of K⁺ supply per day (RKR) using a special computer-controlled culture unit. After a few days on the culture solution the plants adapted their relative growth rate (RGR) to the rate of nutrient supply. The roots of the plants remained in a low salt status irrespective of the rate of nutrient supply, whereas the concentration of K⁺ in shoots increased with RKR. Both V_max and K_m for K⁺(⁸⁶Rb) influx increased with RKR. It is concluded that with a continuous and stable K⁺ stress, the K⁺ uptake system is adjusted to provide an effective K⁺ uptake at each given RKR. Allosteric regulation of K⁺ influx does not occur and efflux of K⁺ is very small.