Depolarization of tomato leaf cells by oligogalacturonide elicitors

The electrical potential difference (Em) across the plasma membrane of tomato leaf mesophyll cells consists of a cyanide‐sensitive component, presumably produced by an H+‐ATPase, and a cyanide‐insensitive component. Variation of Em between different batches of tissue is mainly caused by variation in the cyanide‐sensitive component. Oligogalacturonide elicitors that induce the synthesis of proteinase inhibitors in tomato seedlings depolarize the Em of tomato leaf mesophyll cells. This depolarization closely resembles that caused by cyanide: they are of similar magnitude and vary in a similar manner with variation in the initial Em of different batches of tissue. Treatments with cyanide and with the elicitors have similar effects on the small depolarization caused by KCl at 10 mol m−3. The results suggest that the elicitors depolarize Em by inhibiting the plasma membrane H+‐ATPase, but that the detailed mechanism of inhibition by the elicitors is different from that caused by cyanide.