Plant Physiol, November 1999, Vol. 121, pp. 1037-1045

Gibberellin Biosynthesis in Maize. Metabolic Studies with GA₁₅, GA₂₄, GA₂₅, GA₇, and 2,3-Dehydro-GA₉¹

Molecular, Cell and Developmental Biology, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095-1606 (G.D., B.O.P.); Tsukuba Life Science Center, The Institute of Physical and Chemical Research, 3-1-1 Koyadai Tsukuba, Ibaraki 305, Japan (M.K.); Botanisches Institut und Botanischer Garten, Brunswick University, Mendelssohnstrasse 4, D-38106 Braunschweig, Germany (T.L.); and IACR, Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Bristol BS41 9AF United Kingdom (S.J.C., P.G., J.M.)

[17-¹⁴C]-Labeled GA₁₅, GA₂₄, GA₂₅, GA₇, and 2,3-dehydro-GA₉ were separately injected into normal, dwarf-1 (d1), and dwarf-5 (d5) seedlings of maize (Zea mays L.). Purified radioactive metabolites from the plant tissues were identified by full-scan gas chromatography-mass spectrometry and Kovats retention index data. The metabolites from GA₁₅ were GA₄₄, GA₁₉, GA₂₀, GA₁₁₃, and GA₁₅-15,16-ene (artifact?). GA₂₄ was metabolized to GA₁₉, GA₂₀, and GA₁₇. The metabolites from GA₂₅ were GA₁₇, GA₂₅ 16,17-H₂-17-OH, and HO-GA₂₅ (hydroxyl position not determined). GA₇ was metabolized to GA₃₀, GA₃, isoGA₃ (artifact?), and trace amounts of GA₇-diene-diacid (artifact?). 2,3-Dehydro-GA₉ was metabolized to GA₅, GA₇ (trace amounts), 2,3-dehydro-GA₁₀ (artifact?), GA₃₁, and GA₆₂. Our results provide additional in vivo evidence of a metabolic grid in maize (i.e. pathway convergence). The grid connects members of a putative, non-early 3,13-hydroxylation branch pathway to the corresponding members of the previously documented early 13-hydroxylation branch pathway. The inability to detect the sequence GA₁₂  GA₁₅  GA₂₄  GA₉ indicates that the non-early 3,13-hydroxylation pathway probably plays a minor role in the origin of bioactive gibberellins in maize.