Studies in the auxin relationship of geotropically stimulated roots

Abstract

The effect of geotropic stimulation on auxin production in Vicia faba root tips was studied. Paper chromatography techniques were used to separate the growth substances. Three assay methods (oat first internode, oat coleoptile and pea root section tests) were used for the detection and estimation of growth substances on chromatograms. An assessment was made of a number of sources of error in the preparation of material and the extraction, purification and chromatography of extracts. Geotropic stimulation brought about an increased synthesis of an ether soluble acid auxin in root tips. The maximum amount was formed at 20 minutes stimulation and this fell to the minimum value, recorded after 40 minutes stimulation. The auxin content from longitudinally split root tips was less than the auxin content from whole root tips. This decrease was thought to be an artefact caused by longitudinal cutting of the roots. No difference was found in the auxin content between the upper and lower half of the tip. The water soluble auxins of whole and split roots were investigated. Geotropic stimulation produced a change in content of all the auxins. Colour tests and fluorimetric analyses were made on the water soluble fraction. 3,4 -dihydroxyphenylalanine and tryptophan were identified from the water soluble fraction. Substances giving a phenolic reaction coincided with areas of high growth activity. Alkaline hydrolysis revealed the presence of water soluble indole complexes.