Effects of copper on active and passive Rb+ influx in roots of winter wheat

The effects of copper (CuCl2) on active and passive Rb+(86Rb+) influx in roots of winter wheat grown in water culture for 1 week were studied. External copper concentrations in the range of 10–500 μM in the uptake nutrient solution reduced active Rb+ influx by 20–70%, while passive influx was unaffected (ca 10% of the Rb+ influx in the Cu‐free solution). At external Rb+ concentrations of up to 1 mM, Cu exposure (50 μM decreased Vmax to less than half and increased Km to twice the value of the control. Short Cu exposure reduced the K+ concentration in roots of low K+ status. Pretreatment for 5 min in 50 μM CuCl2 prior to uptake experiments reduced Rb+ influx by 26%. After 60 min pretreatment with Cu, the corresponding reduction was 63%. Cu in the cultivation solution impeded growth, especially of the roots. The Cu concentration in the roots increased linearly with external Cu concentration (0–100 μM) while Cu concentration in the shoots was relatively unchanged. The K+ concentration in both roots and shoots decreased significantly with increased Cu in the cultivation solutions. Possible effects of Cu on membranes and ion transport mechanisms are discussed.