Studies in the hormone relations of root growth

Abstract

The relationship between endogenous auxin levels and growth in roots has been studied. Paper chromatographic methods were adopted to separate the growth substances.Several assay methods (oat coleoptile and mesocotyl, wheat coleoptile and pea root section tests) were used for the detection and estimation of growth substances from chromatograms. Different patterns of endogenous auxin content could be obtained by following different purification and assay methods.Vicia faba roots acid auxins show a decline in concentration with increasing age of the seedlings. A fall in the growth rate of older roots has been correlated with the gradual disappearance or inactivation of growth substances. An increase in the concentration of IAA and total acid auxins in the early stages of growth could be related to the development of lateral meristems.Different levels of auxin concentration are maintained in different parts of the root system, the highest being in the tap root tips. Growth substances in different parts of the roots (tap root tip, root stump and laterals) show complex changes in concentrations as the organs age. The possible bearing of such changes on root growth has been discussed.The evidence indicates that synthesis of acid auxins in the lateral tips is inhibited by the presence of the tap root tips.It was further demonstrated that geotropic stimulation triggers off certain enzymatic reactions which bring about an increased synthesis of an acid auxin (occurring in the IAA zone of chromatograms) in the root apices of broad beans. The maximum amount of the substance is produced in roots stimulated for 40 minutes - the concentration being lowered in a longer period of stimulation (60 minutes). This synthesis was in no way connected with the release of free auxins from the bound state.Growth substances occurring in the water soluble fraction show spontaneous interconversion and all inhibit the growth of root sections (pea).