The control of bud development in Douglas-fir seedlings by photoperiod, flurprimidol, and endogenous gibberellins and abscisic acid Public Deposited

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  • The objective of this thesis was to evaluate the hypothesis that bud development of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings is controlled by endogenous gibberellins or abscisic acid and that cultural treatments affect bud development by altering levels of these growth regulators. To test this hypothesis, three experiments were conducted which measured bud set, bud flush, or endogenous growth regulators following treatment by photoperiod or flurprimidol, a synthetic growth regulator. In experiment I, 8 or 17 hour photoperiods were applied to actively growing, one-year-old seedlings. Bud development, foliar gibberellin activity (dwarf rice bioassay), and abscisic acid levels (gas-liquid chromatography) were measured on treatment days 0, 4, 18, and 62. Compared to seedlings under 17 hour photoperiods, seedlings under 8 hour photoperiods developed resting buds, and had elevated gibberellin-like activity. Abscisic acid levels increased under 17 hour photoperiods. In experiment II, seedlings with terminal buds that were given flurprimidol (10 mg per seedling) and held under photoperiods promotive for bud flush (15 or 17 hours) were compared with untreated controls. Bud flush was tallied periodically; foliar gibberellin activity and abscisic acid levels were measured 10 weeks after treatment; and post-dormancy shoot growth was examined. Bud flush and post-dormancy shoot growth were reduced by flurprimidol. Both gibberellin activity and abscisic acid levels were lower after flurprimidol treatment. In experiment III, flurprimidol (5 mg per seedling) was applied to seedlings with terminal buds which were then held under 17 hour photoperiods. Overwintering bud morphology, and post-dormancy shoot growth were compared with untreated seedlings grown under either 17 or 8 hour photoperiods. Overall, flurprimidol did not counteract 17 hour photoperiods for either bud morphology or postdormancy shoot growth. It was concluded that both photoperiod and flurprimidol (at 10 mg per seedling) can control bud development for Douglas-fir seedlings. Abscisic acid, a growth inhibitor, was positively correlated with shoot growth cessation and bud formation and could not be functioning as an inhibitor. However, when considering previous reports on gibberellin metabolism, gibberellin-like activity was affected in a manner which can explain treatment effects.
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