The effect of Ca2+‐stress on fluxes of Ca2+ and K+ in wheat and cucumber

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Abstract
Fluxes of Ca2+ (45Ca) and K+ (86Rb) 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 Ca2+ concentration, which reduced the uptake of K+ when present above and below a certain level. Pretreatment of roots in high [Ca2+] during a 24 h period decreased the rate of both K+ and Ca2+ uptake. Reduced availability of Ca2+ in the nutrient solution during 24 h reduced the uptake of K+ and Ca2+. Separation of the Ca1+ and K+ retained in the roots from the amounts transported to the shoots in plants pretreated with low [Ca2+], showed that the influx of K+ retained in the roots decreased while Ca2+ influx increased. The transport of both ions towards the shoot was, however, reduced. Reduction of available Ca2+ in the nutrient solution was suggested to change the composition of the membranes, maintaining their permeability properties and metabolically regulated functions. Leakage of K+ (86Rb) from the vacuolar and cytoplasmic compartment of wheat roots increased at reduced Ca2+ concentration in the nutrient solution.