Evidence against induction of protein synthesis during auxin-induced initial elongation of Avena coleoptiles

Abstract

The timing of the response of cell elongation of oat coleoptiles to auxin was studied using a flow chamber. The lag period before a steadystate rate of growth is reached is dependent on the hormone concentration. By increasing the temperature and application of high concentrations of indoleacetic acid (IAA) the lag of the growth response can be gradually shortened, down to zero. All these data indicate that auxins do not induce or promote protein synthesis, whether at the transcriptional or at the translational level. Free (nonbound) IAA seems to be the regulator of the growth response; no metabolite of the oxindole pathway could be detected. There is no indication for an induced uptake of IAA which could explain the lag. The longitudinal distribution of IAA within the coleoptile is unequal which may add to the lag. The maximal initial growth rate is constant over a concentration range of 10(-8) to 10(-3) M IAA at 21°; the dose-response curve has a sigmoid shape. Under the conditions of the standard Avena section test (conducted for 24 hr) 80-90% of the initial IAA (10(-5) to 10(-8)M) are destroyed mainly by epiphytic bacteria.