TWO LIGHT REACTIONS IN THE PHOTOPERIODIC CONTROL OF FLOWERING OF LEMNA PERPUSILLA AND L. GIBBA

Abstract

The effects of light quality on the photoperiodic control in the flowering of a SD duckweed, Lemna perpusilla strain 6746, and a LD duckweed, L. gibba strain G3, were investigated with special reference to the interaction between R and B or FR lights. In the diurnal alternation of R or G light and dark periods, L. perpusilla responded as a SDP, but in that of B or FR light it was almost daylength-indifferent. On the other hand, L. gibba responded as a LDP under B, R or FR light, although the critical light length was altered by the light quality. In the diurnal alternation of R and B or FR light periods containing no dark period, L. perpusilla flowered with the shortening of the optimal and critical R light lengths, compared with the plant exposed to that of R light and dark period. The flowering response of L. gibba to the R light length showed double peaks, that is, the first peak at the R duration less than 9 hours, and the second at the R duration longer than 9 hours. The first peak corresponds to the optimal R light length in L. perpusilla. Under the CL with a mixture of R and B or FR lights, the flowering and frond production were influenced by the intensity ratio of two light given. In both plants, the optimal ratio of B to R or FR to R for the flowering was always greater than that for the frond production. It is suggested that the B or FR light interacts with the R light in the photoperiodic process in the plants and this interaction between the R and B or FR lights should be of importance for obtaining a better understanding of photoperiodism.