Interaction between gibberellin A_4/7 and root-pruning on the reproductive and vegetative processes in Douglas-fir. III. Effects on anatomy of shoot elongation and terminal bud development

Abstract

The relative importance of cell division and cell elongation to shoot elongation and the anatomical changes in vegetative terminal apices were assessed for 9- and 10-year-old seedlings of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) in response to two effective cone-induction treatments, gibberellin A4/7 (GA4/7) and root-pruning (RP). Root-pruning was done in mid-April at the start of vegetative bud swelling and GA treatments were begun at vegetative bud flushing in mid-May and continued until early July. Shoot elongation before flushing resulted primarily from cell divisions and was not affected by the RP treatment. Shoot elongation after flushing resulted primarily from cell expansion which was reduced by RP treatments. Root-pruning significantly slowed mitotic activity, apical growth, and development of vegetative terminal buds from mid-June through mid-July. Apical growth then resumed during leaf initiation and the final number of leaf primordia initiated was not affected. This resulted in a delay of 2 to 4 weeks in the transition from bud-scale to leaf initiation. Retarded terminal vegetative apices anatomically resembled latent axillary apices but were never completely inhibited. GA + RP had the same effect as RP. GA4/7 alone had no effect on shoot or apical development. These results show that RP and GA + RP significantly retard shoot elongation and terminal bud development but still allow normal development of vegetative terminal buds. Retardation of bud development by a few weeks shifts the critical morphogenetic phase of transition from bud scale to leaf initiation to a later time when endogenous and environmental conditions may differ from the normal.

The effect of flurprimidol on bud flush, shoot growth, and on endogenous gibberellins and abscisic acid of Douglas-fir seedlings

“…In Douglas-fir, shoots are largely preformed in the overwintering bud, with subsequent growth the result of both cell division and cell elongation (Owens et al 1985). In as much as GAs can affect elongation by stimulating both cell division and cell elongation in other plants (summarized in Jones 1973) and endogenous GA activity has been positively correlated with shoot elongation in conifers (Ross et al 1983), the results of the present study suggest that flurprimidol may inhibit GA biosynthesis.…”

Effects of exogenous gibberellin and auxin on shoot elongation and vegetative bud development in seedlings of Pinus sylvestris and Picea glauca

“…Although there is abundant evidence that GAs play a causal role in reproductive bud development in conifers (Pharis 1991, Smith 1998, scant attention has been paid to the possibility that GAs are also involved in the control of stem unit initiation in vegetative terminal buds developing at the tip of currentyear shoots. Owens et al (1985) found that applying GA 4/7 during the early period of leaf initiation in Pseudotsuga menziesii (Mirb.) Franco did not affect either the number of leaves initiated or shoot elongation the following year.…”

Location of cones in the crown and along shoots of Sitka spruce (Picea sitchensis (Bong.) Carr.) and the influence of coning intensity and shoot size

“…The proposition that the vigour of the bud meristem (or the rate of mitotic activity), rather than simply the vigour of the bearing shoot, has a major influence on the subsequent developmental pathway of the primordia has been widely considered (Anikeeva and Minina 1959;Debazac 1965;Owens et al 1985;Owens and Simpson 1988;Caron and Powell 1992). Furthermore, although there are complex relationships among apical development, elongation of the subtending shoot, and reproductive bud differentiation (Owens and Simpson 1988), this influence may be deterministic such that a particular discrete range of vigour increases the probability of specific reproductive or vegetative development (Tompsett 1978).…”