Influence of phytohormones and other effectors on proton extrusion by isolated protoplasts from rape leaves

The roles of phytohormones and fusicoccin in H + extrusion by isolated protoplasts from rape leaves ( Brassica napus L. cv. Belinda) were investigated and compared to results obtained with leaf segments of the same plants. Net H + release by protoplasts, which was at least partly due to ATPase activity, was enhanced by 10 μ M indole‐3‐acetic acid and reduced by 20 μ M abscisic acid, whereas fusicoccin (10 μ M ), brassinosteroid (3 μ M ), kinetin (20 μ M ) and gibberellic acid (10 μ M ) had no effect. Hormone effects and H + release were not detectable with leaf segments from the same plants. However, using field‐grown plants, indole‐3‐acetic acid and especially fusicoccin stimulated the acidification of the external medium by leaf segments. Hormonecontrolled H + release by leaf cells is interpreted as the first step in acid‐triggered and turgor‐regulated cell growth.