Effects of 3,4-dihydroxybenzoic acid on root membrane potential in micropropagated tobacco plants

In order to understand the mechanism of action of the phenolic compound 3,4-dihydroxybenzoic acid, we tested its effect on tobacco root membrane potential. Tobacco root segments, excised from micropropagated plants grown in liquid media, were perfused with 0.1-5 mM 3,4-dihydroxybenzoic acid. Activity on the plasma membrane potential was compared with that obtained after perfusion with 0.05 mM indole-3-acetic acid, 0.05 mM kinetin and 0.05 mM gibberellic acid. Possible interactions between 3,4-dihydroxybenzoic acid and plant growth regulators were evaluated by the means of successive applications. When applied to tobacco root segments, 3,4-dihydroxybenzoic acid elicited a transient membrane depolarization. The membrane depolarization induced by 3,4-dihydroxybenzoic acid was followed by a repolarization phase, as for auxin applications. In roots preconditioned with the other growth regulators, the activity of 3,4-dihydroxybenzoic acid on membrane potential was non-specifically affected. In roots preconditioned with 3,4-dihydroxybenzoic acid, indole-3-acetic acid activity on cell membrane was altered, suggesting a specific reciprocal interaction.