Inhibition of rooting of cuttings by gibberellic acid.

Gibberellic acid inhibited rooting but increased extension of pea and bean stem cuttings. Indolylacetic acid usually had a contrary effect both on extension and on root initiation. It was found possible to separate the effects of gibberellic acid on extension and rooting. Small doses of gibberellic acid applied to the bases of cuttings reduced rooting without increasing extension. Small apical doses increased extension without reducing rooting. Disbudding cuttings prevented extension, but gibberellic acid inhibited rooting of disbudded cuttings as strongly as that of normal cuttings. It has thus been found necessary to discard an earlier hypothesis that inhibition of rooting by gibberellic acid was a consequence of a diversion of essential metabolites to the extending apical regions of the cutting. The antagonism between gibberellic acid and indolylacetic acid was non-competitive. Gibberellin Aly known to occur naturally in Phaseolus , was as active a rooting inhibitor as gibberellic acid. It is now believed that inhibition of rooting of cuttings by gibberellins is a direct local effect, preventing those early cell divisions involved in transformation of mature stem tissues to a meristematic condition.