Physiology of Bud Induction in Conifers in Vitro

Abstract

Using excised cotyledons of Pinus radiata as an experimental system, it was shown that while cytokinin was required for bud induction, both cytokinin and light were required for subsequent primordium formation. Both ethylene and carbon dioxide stimulated bud formation, and autotrophic and nonautotrophic CO2 fixation took place during shoot initiation. Using histochemical, autoradiographic, and precursor incorporation approaches, it was found that DNA, RNA, and protein synthesis was preferentially in the epidermal and subepidermal cell layers in contact with the medium. In these cell layers organized development occurred. Feeding the tissue with [14C] glucose and [14C] acetate led to the release of 14CO2 and the production of both ethanol-soluble and ethanol-insoluble fractions. Most of the label went into the ethanol-soluble fraction, which was further fractionated into lipids, amino acids, organic acids, and sugars. Further studies with [14C] glucose showed that only some amino acids and organic acids were labeled and that some turnover, particularly in glutamate and malate, occurred during bud initiation. The importance of these data in relation to bud induction is discussed.