Metabolism of ent-Kaurene to Gibberellin A(12)-Aldehyde in Young Shoots of Normal Maize

Abstract

Young shoots of normal maize (Zea mays L.) were used to determine both the stepwise metabolism of ent-kaurene to gibberellin A(12)-aldehyde and the endogenous presence of the members in this series. Each of the five steps in the sequence was established by feeds of 17-(13)C, (3)H-labeled kauranoids to cubes from the cortex of elongating internodes, to homogenates from the cortex of elongating internodes, and/or to homogenates from dark-grown seedlings. The (13)C-metabolites were identified by Kovats retention indices (KRI) and full-scan capillary gas chromatography-mass spectrometry (GC-MS). Five substrates and the final product in this sequence were shown to be native by the isotopic dilution of 17-(13)C, (3)H-labeled substrates added as internal standards to extracts obtained from elongating internodes. Evidence for the isotopic dilution was obtained by KRI and full-scan capillary GC-MS. Thus, we document the presence in young maize shoots of the metabolic steps, ent-kaurene --> ent-kaurenol --> ent-kaurenal --> ent-kaurenoic acid --> ent-7 alpha-hydroxykaurenoic acid --> gibberellin A(12)-aldehyde.