Fusicoccin, an inhibitor of brassinosteroid‐induced ethylene production

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole‐3‐acetic acid (IAA) and BR + IAA‐induced ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and ACC‐synthase production by etiolated mung bean (Vigna radiata L. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μM BR started at concentrations as low as 0.05 μM. Maximum inhibition occurred at a 1 μM concentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μM) was effective in the inhibition of BR‐induced ethylene, ACC and ACC‐synthase production at low and high concentrations of BR. Fusicoccin at concentrations as high as 2 μM had no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μM). When higher concentrations (100–1000 μM) of IAA were used, fusicoccin (1 μM) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μM) had little or no effect on ACC‐synthase promoted by high concentrations of IAA (1000 μM). When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μM with maximum inhibition occurring at 0.5 μM. At a 1 μM concentration, fusicoccin was effective in inhibiting the synergistic stimulation of ACC‐synthase promoted by BR and IAA.