Quantitation of gibberellins A1, A 3, A 4, A 9 and an A 9-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.