Effect of L-Pipecolic Acid on Flowering in Lemna paucicostata and Lemna gibba

L-Pipecolic acid was found to be effective in inducing flowering of Lemna paucicostata 151, 381, 441 and 6746, and of Lemna gibba G3. When the plants were grown on half-strength Hutner's medium, L-pipecolic acid caused profuse flowering of L. paucicostata 151 maintained under 9 and 10 h of light daily. In L. paucicostata 441 and 6746, L-pipecolic acid had a strong flower-promoting effect under a near critical photoperiod. In L. paucicostata 381, by contrast, L-pipecolic acid had only a very small effect on flowering. In L. gibba G3 substantial promotion of flowering was observed under continuous light. When one-twentieth-strength Hutner's medium was used as the basic medium, L-pipecolic acid stimulated flowering in all strains of Lemna examined, even under continuous light. When L. paucicostata 151 was grown on one-tenth-strength M medium or one-twentieth-strength Hutner's medium, the flower-inducing activity of L-pipecolic acid was greatly enhanced by cytokinin under continuous light. However, when this strain was grown with 9 h of illumination daily, this synergistic effect of cytokinin was only slight. A short-term (even 1-h) treatment with L-pipecolic acid resulted in flowering, suggesting that L-pipecolic acid is involved in the induction of flowering, rather than its evocation. D-Pipecolic acid also had flower-inducing activity, but its activity was 50 times lower than that of the L-isomer.