Abscisic acid and ethrel abolish the inhibition of adventitious root formation of paclobutrazol-treated bean primary leaf cuttings

Abstract

Paclobutrazol (PB), a triazole growth retardant and an inhibitor of gibberellin biosynthesis, reduced at 17 μM concentration the adventitious root formation of bean primary leaf cuttings. Treatments with 5 μM ABA or 4 μM Ethrel, an ethylene-releasing compound, restored the roofing of PB- treated cuttings. Ethylene production and the content of the precursor 1- aminocyclopropane-1-carboxylic acid (ACC) were enhanced in root- forming tissues of PB-treated petioles 48 h after ABA application. The effect of ABA could be abolished by 10 μM CoCl2, an inhibitor of ACC oxidase. Thus, ABA might stimulate rooting through its effect on ethylene release. 2 mM silver thiosulphate, an inhibitor of ethylene action, decreased the rooting of PB- treated cuttings similarly to Co2+, but failed to negate the ABA effect. These data indicate that the effect of PB on rhizogenesis is not associated directly with the inhibition of the biosynthesis of gibberellins.