Heterosis and the metabolism of [3H]gibberellin A1 in maize

Abstract

Seedling growth and the metabolism of high specific activity (1.1 TBq mmol−1) [3H]gibberellin A1 were studied in two Canadian maize (Zea mays L.) inbreds, CM7 and CM49, and in their single cross F1 hybrid. As previously reported, the hybrid grew more rapidly than either parental inbred. Metabolism of the [3H]GA1 was qualitatively similar in all three genotypes and [3H]-labelled metabolites were tentatively identified through sequential, step-elution silicic acid partition chromatography followed by reversed-phase C18 high-performance liquid chromatography, relative to the retention times of authentic GAs. Although the expected 2β-hydroxylation product, [3H]GA8 was not detected, a metabolite was observed at the retention time of GA8-O(2)-glucoside. Additionally, another metabolite(s) eluted at the retention time of glucosyl conjugates of GA1, and enzymic cleavage with cellulase yielded a [3H]-labelled compound which subsequently eluted at the retention time of free GA1. While the ratio of the precursor [3H]GA1 to total [3H]GA conjugate-like metabolites was similar in the three genotypes, the hybrid contained higher levels of the [3H]GA8-glucosidelike metabolite, whereas the inbreds contained higher levels of the [3H]GA1 conjugatelike metabolite(s). Thus, there are differential rates of GA1 metabolism in a maize hybrid relative to its slower-growing inbred parents.