Gibberellin and CCC Effects on Flowering and Growth in the Long-day Plant Lemna gibba G3.

The application of gibberellic acid (GA(3)) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA(3) concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A(7) was used instead of GA(3).The addition of the plant growth retardant CCC [(2-chloroethyl) trimethylammonium chloride] to the culture medium on long days resulted in almost complete inhibition of flowering at 10(-3) M. Vegetative growth was also inhibited to some extent. With CCC at 10(-3) M the simultaneous addition of GA(3) resulted in partial reversal of flower inhibition with 0.3 mg/l GA(3) being optimal. The inhibition of vegetative growth as measured by fresh and dry weight was also partially reversed by GA(3), but the threshold concentration for reversal of flower inhibition was at least 10 times lower than that for inhibition of vegetative growth.These results are interpreted as indicating that gibberellins are important for flowering in the non-rosette long-day plant L. gibba G3, but apparently are present in non-limiting concentrations on short days.