Responses of Avena Coleoptile Sections to High Concentrations of Auxin

(i) The initial elongation rate of excised coleoptile sections is shown to increase with increasing concentration of indoleacetic acid (IAA). In supra-optimal concentrations (1 X 1O-3M) this initial phase is followed by shrinkage of the sections accompanied by loss of water and solid matter; the latter is quantitatively recoverable in the solution. The respiratory rate drops rapidly while the sections elongate in 1 X 10-3M IAA.