The induction of flowering in vitro in stem segments of Plumbago indica L. : I. The production of vegetative buds.

Internode segments excised from vegetative stems of Plumbago indica, an absolute short-day plant, can be induced to form in vitro a callus, or roots, or vegetative shoots, or inflorescences and flowers. Callus formation was polarized when indolyl-3-acetic acid, L-tryptophane, naphthylacetamide, or 2,3-dichlorophenylacetic acid were incorporated into the medium, but not with isatin, phenylacetic acid or 2,4-dichlorophenoxyacetic acid (2,4-D). Roots without buds developed on cultures receiving 2,3-dichlorophenylacetic acid or 2,4-D in the presence of a cytokinin and adenine.Bud formation occurred generally when no auxin was present in the medium, although low concentrations of IAA encouraged bud formation (in the presence of a cytokinin and adenine). Various cytokinins strongly promoted bud formation, but adenine had to be present in the medium in addition. Adenine could not be replaced by adenosine, guanine, guanosine, cytosine, thymine or uracil. The presence of sugar (supplied in the form of various disaccharides) was necessary for bud formation, the concentration in the medium being critical. Long days inhibited bud formation, and so did three different gibberellins applied under short days. Several amino acids, glutamine, asparagine and riboflavine also tended to reduce budding.