Inhibitors of ethylene synthesis inhibit auxin-induced stomatal opening inepidermis detached from leaves of Vicia faba L.

Using leaf epidermis from Vicia faba, we tested whether auxin-induced stoma tal opening was initiated by auxin-induced ethylene synthesis. Epidermis wa s dark-incubated in buffered KNO3 containing 0.1 mM alpha -napthalene aceti c acid or 1 mM indole-3-acetic acid. Maximum net opening was ca, 4 mum afte r 6 h. Opening was reversed by 20 muM ABA, 0.1 mM CaCl2. 1-Aminocyclopropan e carboxylic acid (ACC) synthase catalyzes synthesis of ACC, the immediate precursor to ethylene, Auxin-induced stomatal opening was fully inhibited b y 10 muM 1-aminoethoxyvinylglycine (AVG), an ACC synthase inhibitor, In sol utions containing AVG, auxin-induced opening was restored in a concentratio n-dependent manner by exogenous ACC, but not in control solutions lacking a n auxin, ACC-mediated reversal of AVG-inhibition of stomatal opening was in hibited by a-aminoisobutyric acid (AIB), an inhibitor of ACC oxidase, the l ast enzyme in the ethylene biosynthetic pathway, by 10 muM silver thiosulfa te (STS), an inhibitor of ethylene action, and by 20 muM ABA, 0.1 mM CaCl2, CoCl2, an inhibitor of ethylene synthesis, also inhibited auxin-induced op ening. Both STS and CoCl2, inhibited opening induced by light or by fusicoc cin, but neither light- nor fusicoccin-induced opening was inhibited by AVG . These results support the hypothesis that auxin-induced stomatal opening is mediated through auxin-induced ethylene production by guard cells.