Metabolism of Tritiated Gibberellin A20 in Maize

Abstract

After the application of 2.36 Curies/mmol [2,3-3H]GA20 to 21-day-old maize (A. mays L., hybrid CM7 .times. CM49) plants, etiolated maize seedlings or maturing maize cobs, a number of 3H-metabolites were produced. The principal acidic (pH 3.0), ethyl acetate-soluble metabolite was identified as [3H]GA1 on the basis of co-chromatography with standard [3H]GA1 on SiO2 partition, high resolution isocratic elution reverse phase C18 high performance liquid chromatography [HPLC] and GLC radiocounting. Two other acidic metabolites were identified similarly as [3H]GA8 and C/D ring-rearranged [3H]GA20, although GLC radiocounting was not performed on these metabolites. Numerous acidic, butanol-soluble (e.g., ethyl acetate-insoluble) metabolites were obtained with retention times on C18 HPLC radiocounting similar to those of authentic glucosyl conjugates of GA1 and GA8 or with retention times where conjugates GA20 would be expected to elute. Conversion to [3H]GA1 was greatest (23% of methanol extractable radioactivity) in 21-day-old maize plants. In etiolated maize seedlings, the C/D ring-rearranged [3H]GA20-like metabolite was the major acidic product, while conversion to [3H]GA1 was low.