Changes in RNA levels in the shoot apex of Silene during the transition to flowering.

Changes in RNA concentration in the shoot apical meristem during induction and the transition to flowering were measured histochemically in Silene coeli-rosa (L.) Godron, a long-day plant. In the apices of plants induced by 7 long days the RNA concentration increased to about 25 per cent higher than in non-induced plants. Three long days did not induce flowering but resulted in a transient rise in RNA concentration. When plants were given long days interrupted by varying numbers of short days successful induction was accompanied by a sustained increase in RNA concentration but those treatments which were not inductive gave only transient increases in RNA. Gibberellic acid had no effect on induction or apical growth rates but increased the RNA concentration by 50 per cent or more in both induced and non-induced plants. Plants induced to flower at 13° C had the same RNA concentration and growth rate at the apex as in non-induced plants at 20° C. Since changes in RNA concentration in the apex could occur without changes in growth rate and without flowering, and induction could occur without a change in RNA concentration or growth rate, it is suggested that the increase in RNA and growth rate which normally occur at the transition to flowering might not be essential for the formation of a flower but may be more closely related to the rapid growth associated with the formation of the inflorescence.