© 2007 Heron Publishing—Victoria, Canada
Plagiotropism and auxin in Abies nordmanniana
Bjarke Veierskov (1, 4), Hanne N. Rasmussen (2), Brian Eriksen (1) and Jens Hansen-Møller (3)
1. Royal Veterinary and Agricultural University, Department of Plant Biology, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark / 2. Royal Veterinary and Agricultural University, Department of Forestry and Forest Products, Hoersholm Kongevej 11, DK-2970 Hoersholm,
Denmark / 3. Danish Institute of Agricultural Sciences, Department of Animal Health, Welfare and Nutrition, P.O. Box 50, DK-8830 Tjele,
Denmark / 4. Corresponding author (bv@kvl.dk) / Received October 28, 2005; accepted February 26, 2006; published online October 2, 2006
Summary
Main branches of Abies nordmanniana Spach. were examined through their first growth season from subapical buds around the leader bud to fully expanded shoots.
Plagiotropism was evident in branch orientation, which was almost horizontal, as well as in the orientation of buds developing
on the branches. Auxin transport capacity was predominantly basipetal (> 90%) and consistently higher in the middle part of
the branch than in the distal and proximal ends. Auxin transport capacity was higher on the dorsal side of the branch during
the short initial hyponastic growth phase, but the difference disappeared when the branch became horizontal. No dorsal-ventral
differences could be detected in young horizontal branches in concentrations of indole acetic acid, cytokinins, gibberellins
or abscisic acid. Branch orientation was unaffected by decapitation of the leader apex or by decapitation and replacement
with exogenous auxin. However, decapitation resulted in a less plagiotropic bud arrangement on the branches, and auxin application
to the leader bud scar counteracted this effect. Thus, a signal originating in the stem seems to be involved in regulating
branch bud positioning, whereas the horizontal branch orientation must rely on a different mechanism, presumably autonomic
within the branch.
Keywords:
apical control, branching, conifer, cytokinins, hyponasty, plant growth hormones, polar auxin transport.
