Studies on the Chemical Basis of Auxin-Induced Cell Wall Loosening

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Abstract
Chemical changes accounting for the increase in wall extensibility of tissue grown in the presence of auxin were sought on the basis of chain scission mechanisms. Incorporation of glucose-14C into the hot-water extractable constituents from cell walls of basal sections of soybean [Glycine max L. cv. Hawkeye 63] hypocotyl was increased 15 min after the addition of auxin. However, this increase represented only 1-2% of the total incorporation of radioactivity into the cell walls. With pea [Pisum sativum cv. Alaska] internode sections, both auxin-induced growth and incorporation of radioactivity from glucose-14C were inhibited at supraoptimal auxin concentrations that resulted in increased wall extensibility. No consistent correlation was found between wall loosening and rate of incorporation of glucose-14C into cell wall fractions, average length of wall polymers (based on number of free reducing groups), or the ratio of semicrystalline to amorphous wall materials (based on deuterium exchange). Wall loosening is apparently not mediated to a significant extent by mechanisms which irreversibly degrade polysaccharides.