The relationship between red and far-red light on flowering of the long-day plant, Lemna gibba

Abstract

Lemna gibba, a long-day duckweed, can be induced to flower when the 10 hr white photoperiod is extended with red or far-red light. The 10 hr red photoperiod is also effective in inducing flowering when followed by a far-red extension, but a red extension is ineffective. When 2 hr of far-red light are given immediately after the 10 hr red photoperiod, the following red as well as the far-red extension can induce flowering, indicating that the 2 hr far-red light plays an important role as a starting factor for induction. This red or far-red extension is effectively replaced by a red break given at a proper time in the darkness which follows the 2 hr far-red light as the starting factor. The effect of the red break in not cancelled by subsequent exposure to far-red, which synergistically promotes flowering. However, a red break given immediately after a proper period of far-red extension further promotes flowering. The phase sensitive to the red break coincides with that sensitive to the red break given in darkness. The effect of the red break is reversed by subsequent exposure to far-red, contrary to the effect of the red break in darkness. Using these results, relation between red and far-red light on flowering in L. gibba is discussed.