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Metabolism and Enzymology

Metabolism of ent-Kaurene to Gibberellin A₁₂-Aldehyde in Young Shoots of Normal Maize ^1,2

Department of Biology, University of California Los Angeles, Los Angeles, California 90024-1606, School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom, Department of Agricultural Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan

Young shoots of normal maize (Zea mays L.) were used to determine both the stepwise metabolism of ent-kaurene to gibberellin A₁₂-aldehyde and the endogenous presence of the members in this series. Each of the five steps in the sequence was established by feeds of 17-¹³C, ³H-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 ¹³C-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 17-¹³C, ³H-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 -hydroxykaurenoic acid gibberellin A₁₂-aldehyde.

⁴ Present address: Department of Agricultural Sciences, University of Bristol, Long Ashton Research Station, Long Ashton, Bristol BS18 9AF, UK.

¹ Financial support is gratefully acknowledged from the National Science Foundation, grant DCB 8819809 (B.O.P.) and the Agricultural and Food Research Council (J.M.).

² These results were originally presented at the American Society of Plant Physiologists Annual Meeting held in Toronto, Canada, in August 1989.