A study of the growth of coleoptile first internode and first foliage leaf of Avena sativa

Abstract

Recent evidence suggests that there may be a relationship between auxins and gibberellins in plant growth. The work described here was undertaken as an attempt to clarify the nature of the interactions between the two hormone systems. The effects of IAA, GA and other growth regulators on the growth of coleoptile, first internode, and first leaf of Avena sativa have been studied using the coleoptile, the first internode, and the first leaf base section tests. IAA and GA have a similar action in inducing elongation of the coleoptile and first internode sections, however, their log. dose-response curves are quite different. The inclusion of the coleoptilar node in the first internode sections has a pronounced effect on the GA response suggesting that GA response is associated with high endogenous growth rate. No synergism is found between IAA and GA. Synergism is observed between NAA and GA but not with 2,4-D and GA. NMSP, PCIB and 2,4,6-T all reduce the GA and IAA responses. First leaf base sections are sensitive to GA but not to IAA, kinetin adenine sulphate, certain amino acids, vitamins and growth factors. The age of seedlings from which sections are cut and the inclusion of part of the first internode have significant effects on the GA response of the first leaf base sections. The results are not in complete agreement with an auxin-mediated mechanism of GA action but suggest that the primary action of IAA and GA are not closely related and that growth factors present in the coleoptilar node and in the first internode may be involved in the growth response to GA of the first internode and of the firstleaf base sections respectively. A preliminary attempt was made to isolate the leaf growth substances in the first internodes.The effects of red and far red light on the growth of first internode sections and of intact seedlings have been investigated. The results have been discussed in the light of our present knowledge of auxin and gibberellin actions on plant growth.