THE INTERACTION BETWEEN GROWTH PROMOTERS IN APICAL DOMINANCE

Abstract

Preliminary experiments with one‐node cuttings of Solanum andigena in sterile culture indicated that residual root effects, possibly due to stored cytokinins, could obscure the effects of exogenous growth promoters on lateral bud growth in rootless cuttings. Therefore two‐node cuttings, obtained from apical cuttings that had been maintained without roots for a number of days, were used in all subsequent investigations. Application of cytokinin or gibberellin to the base of rootless, two‐node cuttings promoted the growth of lateral buds as leafy, orthotropic shoots, or diageotropic stolons, respectively; simultaneous application of both hormones completely inhibited lateral bud growth. The effects of roots, 6‐benzylammopurine (BAP) and zeatin on lateral shoot growth were similar in leading to the formation of vigorous, orthotropic, leafy shoots. Indole‐3‐acetic acid (IAA) completely inhibited lateral bud growth in rootless cuttings for at least 7 days, even when BAP was included in the nutrient medium. By using [α‐14C BAP it was demonstrated that cytokinin accumulates in the lateral buds of cuttings not treated with IAA, prior to their growth as leafy shoots; evidence of a causal relationship between cytokinin accumulation and lateral shoot growth was provided by a parallel experiment using [8‐14C]‐adenine. IAA did not appear to reduce BAP or BAP‐riboside accumulation in lateral buds by diverting these cytokinins to the point of IAA application, but did promote the formation of an unknown metabolite of BAP which accumulated in stem tissue. Copyright © 1972, Wiley Blackwell. All rights reserved