GIBBERELLINS ARE NOT ESSENTIAL FOR PHOTOPERIODIC FLOWER INDUCTION OF PHARBITIS-NIL

The influence on photoperiodic flowering of (2-chloroethyl)trimethylam monium chloride (CCC), an inhibitor of gibberellin (GA) biosynthesis, was studied in the short-day plant Pharbitis nil cv. Violet. The cotyl edons contained high levels of endogenous bioactive gibberellins, wher eas in the plumules and first leaves the levels were low or undetectab le. The first leaf responded to a single dark treatment by inducing fl owering when it was 10 mm or wider. Similar seedlings, but without cot yledons, were used as the assay plants to study the effect of CCC on p hotoperiodic flowering. Treatment with CCC had no effect on flowering of seedlings without cotyledons, although stem elongation was inhibite d. By contrast, CCC inhibited flowering of the intact seedlings with c otyledons. Gibberellic acid applied to the shoot apex or to the first leaf promoted flowering in the CCC-treated seedlings without cotyledon s. The results indicate that gibberellins are not essential for the fl ower induction process in leaves, but that they promote flower initiat ion and/or later processes in the shoot apices.