LATERALLY APPLIED ETHREL CAUSES LOCAL INCREASES IN RADIAL GROWTH AND INDOLE-3-ACETIC-ACID CONCENTRATION IN ABIES-BALSAMEA SHOOTS

The terminal (1-year-old) shoot of quiescent, two-year-old balsam fir (Abies balsamea (L.) Mill.) seedlings was ringed with lanolin containi ng 0, 1 or 10 mg g(-1) Ethrel, an ethylene-generating compound, and cu ltured 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 be en treated with Ethrel was harvested to measure stem radial growth by microscopy, shoot ethylene evolution by gas chromatography, and cambia l region indole-3-acetic acid (IAA) concentration by combined gas chro matography-mass spectrometry. Compared with the lanolin controls, Ethr el at 1 and 10 mg g(-1) did not affect bud break or longitudinal growt h, but stimulated tracheid production and bark increment up to about 2 -fold at the application site, though not above or below it. In additi on, the 1 and 10 mg g(-1) Ethrel treatments increased the cambial regi on IAA concentration about 3-fold and the evolution of ethylene at lea st 40-fold at the application site, compared with unwounded portions o f both treated and control shoots. The 10 mg g(-1) Ethrel treatment al so stimulated ethylene evolution about 10-fold, bath above and below t he application site. However, this stimulation was not associated with an elevation in cambial region IAA concentration. Similarly, the lano lin control treatment increased ethylene evolution at the application site about 10-fold, without affecting the cambial region IAA concentra tion. Our results suggest that the localized stimulation of radial gro wth in woody shoots ringed with Ethrel is mediated by an increase in I AA concentration, which in turn is induced by a threshold, abnormally high concentration of Ethrel-derived ethylene.