Direct and Indirect Effects of Auxin on Cell Wall Synthesis in Oat Coleoptile Tissue

Abstract

When substrate amounts of glucose were supplied in the medium, indoleacetic acid caused an increase of 20-50% in the rate of gross cell wall synthesis in oat coleoptile segments whose elongation was inhibited by Ca++, showing that the promotive effect on synthesis is due directly to hormone action and is not simply the result of elongation. Evidence is presented to show that, in addition, elongation of coleoptile segments promoted their cell wall synthesis. This indirect effect apparently occurred because the rate of absorption of glucose from the medium was increased by elongation, and the rate of wall synthesis was strongly dependent on glucose concentration at internal sites of utilization even when high glucose concentrations were supplied in the external medium. In elongating segments treated with auxin the indirect effect on wall synthesis appeared to be of about the same magnitude as the direct effect of auxin. The data indicate that utilization of sugar for wall synthesis takes place along the route of uptake rather than from sugar already in the bulk of the alcohol-soluble fraction of the tissue.