The effect of Ca 2+ ‐stress on fluxes of Ca 2+ and K + in wheat and cucumber

Fluxes of Ca 2+ ( 45 Ca) and K + ( 86 Rb) were investigated in 12‐day old intact plants of cucumber ( Cucumis sativus L. var. Cilla) and 7‐day old intact plants of wheat ( Triticum aestivum L. var. Svenno) which had been cultivated in nutrient solution. The rate of K + uptake was affected by the external Ca 2+ concentration, which reduced the uptake of K + when present above and below a certain level. Pretreatment of roots in high [Ca 2+ ] during a 24 h period decreased the rate of both K + and Ca 2+ uptake. Reduced availability of Ca 2+ in the nutrient solution during 24 h reduced the uptake of K + and Ca 2+ . Separation of the Ca 1+ and K + retained in the roots from the amounts transported to the shoots in plants pretreated with low [Ca 2+ ], showed that the influx of K + retained in the roots decreased while Ca 2+ influx increased. The transport of both ions towards the shoot was, however, reduced. Reduction of available Ca 2+ in the nutrient solution was suggested to change the composition of the membranes, maintaining their permeability properties and metabolically regulated functions. Leakage of K + ( 86 Rb) from the vacuolar and cytoplasmic compartment of wheat roots increased at reduced Ca 2+ concentration in the nutrient solution.