Regulation of β-Glucan Synthetase Activity by Auxin in Pea Stem Tissue

Abstract

The 2- to 4-fold rise in particle-bound β-glucan synthetase (uridine diphosphate-glucose: β-1, 4-glucan glucosyltransferase) activity that can be induced by indoleacetic acid in pea stem tissue is not prevented by concentrations of actinomycin D or cycloheximide that inhibit growth and macromolecule synthesis. The rise is concluded to be a hormonally induced activation of previously existing, reversibly deactivated enzyme. The activation is not a direct allosteric effect of indoleacetic acid or sugars. It is blocked by inhibitors of energy metabolism, by 2-deoxyglucose, and by high osmolarity, but not by Ca2+ at concentrations that inhibit auxin-induced elongation and prevent promotion of sugar uptake by indoleacetic acid, and not by α, α′-dipyridyl at concentrations that inhibit formation of hydroxyproline. Regulation of the system could be due either to an ATP-dependent activating reaction affecting this enzyme, or to changes in levels of a primer or a lipid cofactor.