Cyclic Mononucleotide-Gibberellin Interactions in the Flowering and Proliferation of the Long-Day Plant Lemna gibba G3

3′,5′-cAMP stimulates flowering of Lemna gibba G3 under inductive long-day conditions and enhances flower onset. 3′,5′-cAMP has no influence on frond production. 2′,3′-cGMP increases markedly the proliferation of fronds and inhibits flowering. The effect of 2′,3′-cGMP on frond multiplication is photoperiodically independent; under short-day conditions 2′,3′-cGMP replaces in fact the requirement for inductive long-day conditions. 2′,3′-cGMP increases the total amount of DNA per frond. This accumulation of DNA precedes by 2–3 days the 2′,3′-cGMP related increase in frond formation. The results are discussed in the light of the hypothesis that the active cyclic mononucleotides exert their effects on multiplication and flowering at the level of DNA.