Rapid auxin- and fusicoccin-enhanced Rb(+) uptake and malate synthesis in Avena coleoptile sections

The short-term effects of auxin (indole-3-acetic acid) and fusicoccin (FC) on Rb(+) uptake and malate accumulation in Avena sativa L. coleoptile sections have been investigated. FC stimulates (86)Rb(+) uptake within 1 min while auxin-enhanced uptake begins after a 15-20-min lag period. Auxin has little or no effect on (86)Rb(+) uptake at external pHs of 6.0 or less, but substantial auxin effects can be observed in the range of pH 6.5 to 7.5. Competition studies indicate that the uptake mechanism is specific for Rb(+) and K(+). After 3 h of auxin treatment the total amount of malate in the coleoptile sections is doubled compared to control sections. FC causes a doubling of malate levels within 60 min of treatment. Auxin-induced malate accumulation exhibits a sensitivity to inhibitors and pH which is similar to that observed for the H(+)-extrusion and Rb(+)-uptake responses. Both auxin- and FC-enhanced malate accumulation are stimulated by monovalent cations but this effect is not specific for K(+).