Description:
<jats:p>Seedlings of spring wheat (<jats:italic>Triticum aestivum</jats:italic> L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K<jats:sup>+</jats:sup> during different periods of time to produce plants with various K<jats:sup>+</jats:sup> status. In one cultivation light‐grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 m<jats:italic>M</jats:italic> K<jats:sup>+</jats:sup> radiolabelled with <jats:sup>86</jats:sup>Rb. The uptake time was varied (5, 60 or 120 min).</jats:p><jats:p>The K<jats:sup>+</jats:sup> concentration in the roots, [K<jats:sup>+</jats:sup>]<jats:sub>root</jats:sub>, increased during the course of the uptake experiments, especially in light and at initially low [K<jats:sup>+</jats:sup>]<jats:sub>root</jats:sub>, At the same time K<jats:sup>+</jats:sup> (<jats:sup>86</jats:sup>Rb) influx in the roots decreased. The simoidal relationship obtained between K<jats:sup>+</jats:sup> (<jats:sup>86</jats:sup>Rb) influx and [K<jats:sup>+</jats:sup>]<jats:sub>root</jats:sub> was affected by these changes, and Hill plots gave various Hill coefficients, n<jats:sub>H</jats:sub>, depending on the duration of the uptake experiments. n<jats:sub>H</jats:sub> from three apparently straight line segments of the same plot, in different [K<jats:sup>+</jats:sup>]<jats:sub>root</jats:sub> ‐ intervals, indicated a falling degree of interaction between the binding sites as [K<jats:sup>+</jats:sup>]<jats:sub>root</jats:sub> increased. For the dark‐grown plants negative cooperativity could not be demonstrated.</jats:p>