The relationship between Rb+ influx and K+-stimulated Mg2+-ATPase activity in oat roots of different K+ status flexible coupling?

The relationship between Rb+ influx and microsomal ATPase activity stimulated by K+ and Mg2++ K+ was investigated for roots of 7-day-old seedlings of oat (Avena sativa L., cv. Brighton). Different concentrations of K+ in the roots, K+root were produced by cultivating plants in complete nutrient solutions of different dilutions and dFifferent K+ concentrations at various temperatures. Experiments were performed in both light and darkness. The range of the influx/ATPase ratios was large with a factor of 5 or more between the highest and lowest values. In most cases, the highest ratios were obtained at low K+root and at high temperatures, and the lowest at high K+root and at low temperatures. At high temperatures (20 and 25°C) in the light, the influx/ATPase ratio was constant, independently of K+root, if K+ in the medium was kept constant but the bulk of the nutrient solution diluted. If K+ was varied and the other components of the medium kept constant, the normal relation of decreasing influx/ATPase ratio at increasing K+root was found; thus, Rb+ influx appears regulated by both the internal and external potassium conditions. Also in darkness, at 15°C and with K + in the medium varied, the influx/ATPase ratio was independent of K+root but in the corresponding light experiments, ratio and K+root had the normal, inverse relationship. The difference between light and dark conditions appears to indicate that growth rate is of importance for the relationship between energy input and transport. Our data lead to the concept of “flexible coupling” between transducers) of energy and ion carrier. Without excluding other possibilities, this may be one of the mechanisms for ecological adaptation to variations in the root medium.

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