Growth regulation and phase change in some New Zealand heteroblastic plants

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Abstract
The effects of plant growth regulators on various heteroblastic New Zealand species (viz., Carpodetus serratus J.R. et G. Forst., Elaeocarpus hookerianus Raoul, Parsonsia heterophylla A. Cunn., Pennantia corymbosa J.R. et G. Forst. and Pseudopanax crassifolius (A. Cunn.) C.Koch.) were investigated. When gibberellic acid (0.4 mg per plant) was applied to rooted cuttings of adult plants, it produced a transient elongation of stems in all species and induced a juvenile habit and leafform in Carpodetus serratus and Pennantia corymbosa,a juvenile growth form with transitional leaf-form in Parsonsia heterophylla and no such changes in Elaeocarpus hookerianus. Treated adult rooted cuttings of Pseudopanax crassifolius died. Attempts to manipulate the effective internal gibberellin levels of juvenile rooted cuttings by the application of gibberellic acid (GA3), abscisic acid (ABA) and paclobutrazol (singly and in various combinations) failed to induce any adult characteristics. Concentrations of paclobutrazol (PP333) and ABA which caused a stimulation of growth in juvenile ivy produced an inhibition of growth (or even death) in the native species. The inhibition of growth caused by PP333 could often be overcome by the exogenous application of GA3, suggesting that the biosynthesis of endogenous gibberellins had been reduced.