The induction of flowering in vitro in stem segments of Plumbago indica L. : II. The production of reproductive buds.

Internode segments excised from vegetative Plumbago indica plants are responsive to photoperiodic treatments in vitro. Under long days, they produce vegetative buds; under short days, they develop inflorescences. These inflorescences can remain devoid of flowers ("vegetative inflorescences"), or produce normal flowers which open in the test tubes. The minimum duration of the short-day treatment capable of inducing flowering is of the order of 4 weeks.The production of inflorescences under short days is affected by various factors. An adequate level of sucrose is necessary. Sucrose can be replaced by maltose and, to a small extent, by cellobiose, but not by mannitol or lactose. Auxins and gibberellins inhibit the production of flower buds, whereas cytokinins and adenine do not. Guanine, thymine, cytosine or uracil alone are ineffective, but thymine or its precursor, orotic acid, enhance the production of floral buds when adenine and kinetin are also present in the medium. Several amino acids, as well as glutamine and asparagine, tend to reduce inflorescence formation at 3×10(-4) M or above; urea increases it slightly at the same concentrations. Both the cis- and the trans-isomer of abscisin II enhance inflorescence formation under short days, but have no such effect under long days.High concentrations of adenine re-established the red coloration of the petals which is typical of the clone used. Otherwise, the color of the flowers grown in vitro was pink, presumably because of the depressing effect of kinetin on anthocyanin synthesis.