Development of Douglas-fir apices under natural and cone-inducing conditions

Abstract

The anatomy, mitotic frequenty (MF), size and total insoluble carbohydrate histochemistry were studied in axillary apices from 9- and 10-year-old Douglas-fir ( Psedotsuga menziessi (Mirb.) Franco) trees after cone induction treatments of rootpruning (RP) and (or) stem injections of a gibberellin A 4 and A 7 mixture (GA). Axillary buds were initiated at the time of RP but RP had no effect on axillary bud initiation. Axillary apices from control and GA-treated trees were similar and followed the normal sequence of bud-scale initiation, differentiation and leaf initiation described previously and no cone buds differentiated. Early development of axillary apices from RP and RP + GA treated trees was normal but development became retarded near the time of vegetative bud flush. Retarded apices were small with low MF and developed many features characteristic of latent apices. The ultrastructure of cells at the base of retarded apices sowed dense cytoplasm and some unusual features. Apical retardation continued until mid-July when normal development resumed and apices differentiated into cone or vegetative buds or became latent. The trees in which the greatest retardation of apical development occurred during lateral shoot elongation produced the most cone buds. These results are discussed in relation to hypotheses proposed to explain how cultural and GA treatments affect cone induction in the Pinaceae.