© 1988 Heron Publishing—Victoria, Canada
Control of shoot elongation in ponderosa pine: relative roles of apical and axillary meristems
Ronald M. Lanner and Kristina F. Connor
Department of Forest Resources, Utah State University, Logan, UT 84322, USA / Received May 3, 1988
Summary
Buds of ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) from which the shoot apical meristems had been surgically removed elongated normally but did not form new terminal
buds. Shoot, stem unit and needle growth were similar to those of controls. Removal of needle fascicles from buds starting
to elongate inhibited growth, whether or not the shoot apical meristem had been removed. The length of completely defoliated
shoots increased by 8.3%, the length of shoots defoliated on the upper half increased by 29.6%, and the length of those defoliated
on the lower half increased by 44.9%. The length of controls increased by 137.4% during the same period. On partially defoliated
shoots, defoliated stem units elongated less than undefoliated ones. Shoots developing from buds enclosed in light-proof,
aluminum-foil bags elongated normally but apparently lacked chlorophyll. Increases in dry weight were significantly correlated
with number of stem units (r2 = 0.53). Results suggest that shoot elongation is controlled endogenously. This control may be mediated by IAA outputs from
axillary meristems proportional to meristem number, and the importation of carbohydrates, proportional to the output of IAA.
