Gibberellins in shoots and developing capsules of Populus species

Extracts of stems of growing shoots of Populus deltoides and P. trichocarpa, and developing capsules of P. deltoides were analysed for gibberellins (GAs) by gas chromatography-mass spectrometry. The following known GAs were identified by comparison of their Kovats retention indices (KRIs) and mass spectra with those of standards: GA₁, GA₈, GA₉, GA₁₉, GA₂₀, 16β,17-dihydro-17-hydroxy GA₂₀, GA₂₃, GA₂₈, GA₂₉, GA₃₄, GA₄₄, and GA₉₇. Several of these have not been previously reported from Populus. In addition, two new GAs were identified as 12β-hydroxy GA₅₃ (GA₁₂₇) and 16β,17-dihydro-17-hydroxy GA₅₃ and their structures were confirmed by partial synthesis. Evidence was found of 16,17-dihydro-16,17-dihydroxy GA₉, 16,17-dihydro-16,17-dihydroxy GA₁₂, 12-hydroxy GA₁₄, and GA₃₄-catabolite by comparison of mass spectra and KRIs with published data. Several putative GAs (hydroxy- and dihydroxy-GA₁₂-like) were also found. The catabolites of active GAs or of key precursors, hydroxylated at C-2 in stems and either C-2, C-12, C-17, or C-16,17 in capsules, were the major proportion of the GAs.