Metabolism of Tritiated Gibberellin A20 in Maize

After the application of 2.36 Curies per millimole [2,3-(3)H]gibberellin A(20) (GA(20)) to 21-day-old maize (Zea mays L., hybrid CM7 x CM49) plants, etiolated maize seedlings, or maturing maize cobs, a number of (3)H-metabolites were observed. The principal acidic (pH 3.0), ethyl acetate-soluble metabolite was identified as [(3)H]GA(1) on the basis of co-chromatography with standard [(3)H]GA(1) on SiO(2) partition, high resolution isocratic elution reverse phase C(18) high performance liquid chromatography and gas-liquid chromatography radiocounting. Two other acidic metabolites were identified similarly as [(3)H]GA(8) and C/D ring-rearranged [(3)H]GA(20), although gas-liquid chromatography radiocounting was not performed on these metabolites. Numerous acidic, butanol-soluble (e.g. ethyl acetate-insoluble) metabolites were observed with retention times on C(18) high performance liquid chromatography radiocounting similar to those of authentic glucosyl conjugates of GA(1) and GA(8), or with retention times where conjugates of GA(20) would be expected to elute. Conversion to [(3)H]GA(1) was greatest (23% of methanol extractable radioactivity) in 21-day-old maize plants. In etiolated maize seedlings, the C/D ring-rearranged [(3)H]GA(20)-like metabolite was the major acidic product, while conversion to [(3)H]GA(1) was low.