Studies on the uptake of plant growth substances by plant tissues

Abstract

The uptake of the auxins indole-3-acetic acid (IAA) and 1-naphthylacetic acid (NAA) was investigated using fluorimetric methods of assay. Uptake by the following plant material was examined - segments of Avena coleoptile, maize mesocotyl and the hypocotyl of Phaseolus radiatus.The growth regulating substances 2,4-dichlorophenoxyacetic acid, triiodobenzoic acid (TIBA), N-l-naphthyl-phthalamic acid, (1-naphthyl-methyl-sulphide) - propionic acid, and 3:5-diiodo- and 3:5-dibromo-4-hydroxybenzonitrile were examined for their effects on the entry and accumulation of IAA and NAA. Experiments were conducted to distinguish between the initial physical phase of uptake and subsequent metabolic uptake by pretreatment of the tissue with metabolic inhibitors and poisons.As fluorescence assay can be employed, under the experimental conditions, only for measuring loss of the auxins from the external medium, C14-labelled IAA and I131-labelled TIBA were used to assay actual uptake by the plant material. As it was suspected that the effects of TIBA on the uptake of IAA were exerted through metabolic action on a sulfhydryl-enzyme system, various SH-enzyme protectors (2,3-dimercaptopropanol, cysteine) were tested in attempts towards tracing the mechanism of TIBA action.Chromatographic and fluorimetric analysis of variously treated material has been undertaken. Autoradiographic analysis to check the nature and degree of IAA metabolism and the effects of TIBA on it was conducted, and measurements made of respiratory decarboxylation of IAA - C14 under the experimental conditions.The results have been critically discussed with reference to the literature dealing with synergism and antagonism between growth regulators, uptake and transport of auxins, mechanism of auxin action in growth, general aspects of membrane permeability and solute transport, and auxin kinetics.