Effects of indoleacetic acid on metabolic pathways

An approach to the study of the effects of auxins on plant tissue during auxin-induced cell elongation has been made by following the incorporation, from various suitably labeled metabolites, of isotopic carbon into the varied cellular components.Indoleacetic acid (IAA) was found to have little or no effect on the rate of incorporation of the C¹⁴ of carboxyl-labeled amino acids (glycine and leucine) into the proteins of corn and Avena coleoptiles. Protein level remains constant in excised sections of these organs over periods of 6 hr. and longer, and is independent of the presence or absence of added growth substance. IAA was found to have a promotive effect on the rate of incorporation of the carbon of carboxyl-labeled acetate into the lipides of the Avena coleoptile although this effect is small compared to the effect of IAA on growth.Chromatography and radioautography of the soluble constituents of Avena coleoptile sections which had been previously supplied with either carboxyl-labeled acetate or uniformly labeled sucrose failed to reveal any major effect of IAA although the carbon of both substrates is rapidly converted to a variety of compounds in the plant.Indoleacetic acid slightly depresses the over-all rate of incorporation of the carbon of labeled acetate or sucrose into the components of the cell wall of the Avena coleoptile. This over-all depressant effect is compounded of a considerable increase in the rate with which the noncellulosic polysaccharides become labeled and lesser effects, generally inhibitory, on other components.