Effects of some phenolic compounds on gibberellic acid-induced shoot growth of dwarf peas

Fourteen phenolic compounds and three related nonphenolic compounds were tested for their ability to inhibit GA 3 -induced growth of dwarf pea seedlings. Test concentrations of 10:1, 100:1, and 1000:1 (phenolic or related nonphenolic to GA3 ) by weight were used. The related, nonphenolics, benzene, benzoic acid, and flavone, did not significantly reduce GA3-induced growth at any of the concentrations tested. Phenolic compounds alone did not reduce growth of dwarf peas. At a ratio of 10:1, only four of the compounds mixed with GAn reduced growth significantly from GA~ controls: quercetin (29%), phloridzin (19%), vanillic acid (18%), and tannic acid (18%). At the highest concentration (1000:1) all phenolic compounds except p-hydroxybenzoic acid reduced growth significantly from GA3 controls. Eleven of the 14 phenolics reduced growth by less than 42% while three compounds, quercetin, catechin, and tannic acid reduced growth from 70% to 82%. Catechin, a precursor to condensed tannins, was tested for reversibility of inhibition. Increasing the amount of GA3 completely reversed the inhibition so that plants treated with catechin and saturating doses of GA3 were indistinguishable from plants receiving saturating amounts of GA3 without catechin. Aspects of the chemical structure of phenolics were discussed with respect to the observed inhibition of GA3-induced growth.