© 1996 Heron Publishing—Victoria, Canada
Laterally applied Ethrel causes local increases in radial growth and indole-3-acetic acid concentration in Abies balsamea shoots
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 April 3, 1995
Summary
The terminal (1-year-old) shoot of quiescent, two-year-old balsam fir (Abies balsamea (L.) Mill.) seedlings was ringed with lanolin containing 0, 1 or 10 mg g–1 Ethrel, an ethylene-generating compound, and cultured for 6 weeks under environmental conditions favorable for growth. Bud
break and the elongation of the current-year terminal shoot were monitored, and the subjacent previous-year terminal shoot
that had been treated with Ethrel was harvested to measure stem radial growth by microscopy, shoot ethylene evolution by gas
chromatography, and cambial region indole-3-acetic acid (IAA) concentration by combined gas chromatography–mass spectrometry.
Compared with the lanolin controls, Ethrel at 1 and 10 mg g–1 did not affect bud break or longitudinal growth, but stimulated tracheid production and bark increment up to about 2-fold
at the application site, though not above or below it. In addition, the 1 and 10 mg g–1 Ethrel treatments increased the cambial region IAA concentration about 3-fold and the evolution of ethylene at least 40-fold
at the application site, compared with unwounded portions of both treated and control shoots. The 10 mg g–1 Ethrel treatment also stimulated ethylene evolution about 10-fold, both above and below the application site. However, this
stimulation was not associated with an elevation in cambial region IAA concentration. Similarly, the lanolin control treatment
increased ethylene evolution at the application site about 10-fold, without affecting the cambial region IAA concentration.
Our results suggest that the localized stimulation of radial growth in woody shoots ringed with Ethrel is mediated by an increase
in IAA concentration, which in turn is induced by a threshold, abnormally high concentration of Ethrel-derived ethylene.
Keywords:
balsam fir, bark, 2-chloroethylphosphonic acid, cortex, ethylene, tracheid, vascular cambium, xylem.
