Metabolism of [1,2-(3)H]gibberellin A 4 by epicotyls and cell-free preparations from Phaseolus coccineus L. seedlings.

Cell-free systems were prepared from germinating seed and seedlings of Phaseolus coccineus. Gibberellin A4 (GA4)-metabolising activity was detected in vitro using preparations from roots, shoots and cotyledons of germinating seed, but only up to 24 h after imbibition. Cell-free preparations from cotyledons converted [(3)H]GA4 to GA1, GA34, GA4-glucosyl ester and a putative O-glucoside of GA34, and, in addition converted [(3)H]GA1 to GA8. Preparations from embryo tissues contained 2β-hydroxylase activity, converting [(3)H]GA4 to GA34 and [(3)H]GA1 to GA8.The presence of GA-metabolising enzymes was also indicated by in-vivo feeds of [(3)H]GA4 to epicotyls of intact 4-d-old seedlings, which resulted in the accumulation of GA1, GA8, GA3-3-O-glucoside, GA4-glucosyl ester, GA8-2-O-glucoside and a putative O-glucoside of GA34. Gibberellin A1 was the first metabolite detected, 15 min after application of [(3)H]GA4, but after 24 h most of the label was associated with GA8-2-O-glucoside. Over 90% of the recovered radioactivity was found in the shoot. Within the shoot, movement was preferentially acropetal, and was not dependent upon metabolism of the applied [(3)H]GA4.