Relation between Effects of Auxin on Cell Wall Synthesis and Cell Elongation

Abstract

Promotion by indoleacetic acid (IAA) and other auxins of cell wall synthesis in oat coleoptile tissue paralleled the effect of auxins on elongation. At concentrations supraoptimal for elongation, wall synthesis was inhibited. Among a variety of inhibitors that were tested, inhibition of elongation and the effect of IAA thereon were invariably accompanied by inhibition of the promotive effect of auxin on wall synthesis, except when elongation was inhibited by Ca++, Sr++, or osmotic concentrations of KC1. Cell wall synthesis in mature coleoptiles that had ceased elongation was not promoted by IAA. A direct promotion of wall synthesis by IAA was not observed within 1 hour even if the segments were pretreated with labeled glucose. Treatment with auxin for 4 hours resulted in a strong promotive effect on wall synthesis during a subsequent 1-hour incubation in labeled glucose. These observations show that the direct effect of auxin on rate of wall synthesis was a delayed effect compared with the effect of auxin on elongation. The data are satisfactorily explained by the hypothesis that auxin acts to promote utilization of polysaccharide precursors for a particular kind of formation or incorporation of polysaccharides that is effective in inducing cell wall expansion, while net promotion of the rate of wall synthesis follows as a response of a feedback control mechanism that regulates the pathway of wall polysaccharide synthesis.