Studies on the stimulation of root growth by low concentration of auxins and allied compounds

Abstract

It has been reported by earlier workers in this laboratory (Bedford College) that there is a wide variation in the degree of stimulation by IAA of the growth of pea root sections. It was then suspected that effects of age, diffuse light in which sections were weighed and metallic impurities present in distilled water might modify this stimulation. Experiments were carried out to investigate the effects of these factors. The results of the experiments showed that age of the seedlings has a pronounced effect in the growth of root sections, but it does not alter the stimulatory effect of IAA.Strong light promotes the growth of root sections. It also causes a shift in the optimal concentration of IAA from one part in 10 to one part in 10. This seems to be due to IAA destruction.Metallic impurities such as Ca++, Mn++, Zn++, CU++ and Boron in dilute concentrations do not alter the response to IAA. Cobalt at 10M not only stimulates root growth but also antagonises both stimulatory and inhibitory effects of IAA.It can finally be concluded that, since the concentrations of metallic impurities likely to exist in ordinary distilled water are much lower than any of the above concentrations of metals giving interference with IAA stimulation, variations in the quantities of metallic impurities in ordinary distilled water are not likely to be the cause of the previously observed variations in sensitivity to stimulatory concentrations of IAA.The main concern of the investigations was studies on the interaction of IAA with antiauxins i.e. N.M.S.P., N.M.S.A., C.N.B. and P.C.I.B. in the stimulation of root section growth and also the interaction between antiauxins themselves. The investigations of this nature should throw some light on the hypothesis postulated by Audus and Shipton (1952) that auxin (IAA) and antiauxins stimulate the growth of root sections by antagonising the action of a natural inhibitor which holds the root growth below the possible maximum.The results of the interaction experiments with these compounds at growth stimulatory concentrations support the hypothesis that both types of compound are exerting fundamentally the same action in the growth system but suggest that the action is a direct one and not due to an antagonism of a natural endogenous growth inhibitor.