Quantitation of gibberellins A1, A3, A4, A9 and an A9-conjugate in good- and poor-flowering clones of Sitka spruce (Picea sitchensis) during the period of flower-bud differentiation

The levels of endogenous gibberellin A₁ (GA₁), GA₃, GA₄, GA₉ and a cellulase-hydrolysable GA₉-conjugate in needles and shoot stems of Sitka spruce Picea sitchensis (Bong.) Carr.] grafts with different coning or flowering histories were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated GA₃, GA₄ and GA₉ as internal standards. The samples were taken at the approximate time of the start of flower-bud differentiation, i.e. when the shoots had elongated approx. 95% of the final length. The needles of the good-flowering clones contained 11–12 ng per g fresh weight (FW) and 15–28 ng· (g FW) ^–1 of GA₉-conjugate and GA₉, respectively. The shoot stems of the same material contained no detectable amounts of GA₉-conjugate and 11–15 ng-(g FW)^–1 of GA₉. The amounts of GA₉-conjugate and GA₉ were apparently lower in the poor-flowering clones, the needles containing 4–9 ng-(g FW)^–1 and 7–17 ng·(g FW)^–1, respectively. Also in this material the shoot stems contained no detectable amounts of GA₉-conjugate. The amounts of GA₄ were very small in both materials, ranging from 1–1.6 ng-(g FW)^–1. The good-flowering clones contained no detectable amounts of the more polar gibberellins, GA₁ and GA₃. The poor-flowering clones, on the other hand, contained high levels of GA₁₅ 17–19ng·(gFW)^–1 in the needles and 10–13 ng·(g FW) ^–1 in the shoot stems, and also smaller amounts of GA₃, 2–3 ng·(g FW)^–1 in the needles and approx. 1 ng·(g FW)^–1 in the shoot stems. The results demonstrate differences in GA-metabolism between the poor- and the good-flowering clones. The higher amounts of GA₉-conjugate and GA₉ might indicate a higher capacity for synthesizing GA₄ in the good-flowering material. This synthesis does not, however, result in a build-up of the GA₄-pool, maybe because of a high rate of turnover. Gibberellin A₄ was apparently neither hydroxylated to GA₁ nor converted to GA₃ in the goodflowering material, as was the case in the poor-flowering material. This might indicate that gibberellin metabolism in the poor-flowering material is directed towards GA₁ and GA₃, GAs preferentially used in vegetative growth.Abbreviations FW fresh weight - GA_n gibberellin A_n - HPLC high-performance liquid chromatography