EFFECTS OF PHYTOCHROME AND BLUE-NEAR ULTRAVIOLET LIGHT-ABSORBING PIGMENT ON DURATION OF COMPONENT PHASES OF THE CELL...

Single-celled protonemata of the fern Adiantum capillus-veneris, kept under continuous red light, grew with a very low rate of cell division, and the cell cycle was arrested in the early G1 phase. Cell division was induced by transferring the protonemata to the dark after various light treatments, and the duration of component phases in the cell cycle was determined by a continuous-labelling technique with 3H-thymidine. Blue light irradiation greatly reduced the duration of the G1 phase but did not affect that of other phases. The greater the fluence of blue light, the shorter was the duration of G1 phase was observed. In contrast, a brief exposure of red-light-grown protonemata to far-red light given immediately before the dark incubation showed no effect on the duration of G1 S and M phases but significantly extended that of the G2 phase. The effect of far-red light on the G2 phase was reversed by red light, and the effects of red and far-red light were repeatedly reversible. The progression in the M phase was shown by means of a time-lapse video system to be not at all influenced by any pre-irradiation described above.