© 1995 Heron Publishing—Victoria, Canada
Interaction between indole-3-acetic acid and ethylene in the control of tracheid production in detached shoots of Abies balsamea
Leif Eklund (1) and C. H. Anthony Little (2)
1. Department of Engineering and Natural Sciences, Växjö University, S-351 95 Växjö, Sweden / 2. Natural Resources Canada, Canadian Forest Service, P.O. Box 4000, Fredericton, New Brunswick E3B 5P7, Canada / Received December 16, 1993
Summary
We investigated the interaction between indole-3-acetic acid (IAA) and ethylene in the regulation of the seasonal periodicity
of tracheid production in 1-year-old balsam fir (Abies balsamea (L.) Mill.) cuttings collected at different times during the dormant period. The cuttings were left with their buds intact
or were debudded and treated either apically with IAA or 2-chloroethylphosphonic acid (Ethrel) in lanolin, laterally with
IAA or Ethrel in lanolin, or basally with Ethrel, Co2+ or Ag+ in deionized water. The treated cuttings were then cultured for up to 5 weeks under controlled environment conditions favorable
for cambial growth. No change in ethylene evolution was detected during the rest–quiescence transition, when IAA-induced tracheid
production increased. The induction of cambial reactivation by IAA was associated with a rise in ethylene evolution, but there
was no consistent relationship among IAA concentration, tracheid number and ethylene emission. Neither Ethrel, Co2+ nor Ag+ affected tracheid production when applied basally, except for 10 and 100 µM Ethrel and 100 µM Co2+, which were inhibitory. In contrast, ethylene evolution was promoted by Ethrel and inhibited by Co2+, whereas Ag+ had no effect. Similarly, applying Ethrel apically or laterally increased ethylene evolution, but did not promote tracheid
production except in the treatment in which 1 mg Ethrel g–1 lanolin was applied laterally to cuttings treated apically with 0.1 mg IAA g–1 lanolin, and in the treatment in which 10 mg Ethrel g–1 lanolin was applied laterally to budded cuttings. We conclude that (1) ethylene evolution is not specifically associated
with IAA-induced tracheid production, (2) ethylene does not mimic the promoting effect of IAA on tracheid production, and
(3) ethylene can promote tracheid production, but only when its application results in a localized unphysiologically high
concentration in the cambial region, which, in turn, induces an accumulation of IAA.
Keywords:
cambium, 2-chloroethylphosphonic acid, cobalt, dormancy, Ethrel, IAA, silver.
