Jonathan Love

The fundamental question addressed by my PhD is that of ethylene’s role in wood growth and development. Specifically, what functions does this simple two carbon gas have in the radial growth of tree stems and in the biosynthesis of the secondary cell wall? New insights into these old questions have been found by transgenically disrupting ethylene signal transduction in Populus tremula L. x tremuloides Michx. and analyzing wood development and the tension wood response. The tension wood system was chosen for its association with elevated ethylene levels and because of its interesting shift in development characterized by accelerated rates of cell proliferation, smaller and less frequent vessels, and dramatic switches in cell wall biosynthesis that leads to the formation of a cellulose rich gelatinous layer. These aspects of wood development are interesting biologically, and important ecologically and commercially.

Transgenic hybrid aspen trees with reduced sensitivity to ethylene were generated by ectopically expressing the Arabidopsis thaliana dominant mutant allele of the ethylene receptor ETR1 (Atetr1-1). Aspects of wood growth and development suppressed by Atetr1-1 were assayed by applying ethylene or its immediate metabolic precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), to independent transgenic lines and by comparing responses with wild-type. Remarkably, the rate of cell proliferation in tension wood of leaning trees with ectopic expression of Atetr1-1 was reduced. For the first time, this result provides conclusive evidence that ethylene is an endogenous regulator of wood formation.