PHYTOCHROME‐MEDIATED PHOTOTROPISM IN PROTONEMATA OF THE MOSS Ceratodon purpureus BRID

Abstract— Protonemata of the moss Ceratodon purpureus cultured in white light were transferred to darkness for 3 days and then used for phototropic experiments. Irradiation of the apical region of vertically position protonemata with small beams (0.2 mm) of red light induced a growth response towards the irradiated side (positive phototropism). The phototropic response showed irradiance dependence. The effect of red light was completely reversed by far‐red light following red light irradiations, demonstrating that phytochrome was the photoreceptor pigment. Far‐red light or UV‐blue light had no influence on either bulging or phototropism. Experiments with linearly polarized red or far‐red light showed a different dichroic distribution of phytochrome in its different forms, the red‐absorbing form, Pr and the far‐red‐absorbing form, Pfr. Red light with a vibration plane parallel to the long axis of the filaments was most effective. The effectiveness of far‐red light was expressed best when its vibration plane was 90° to the electrical vector of the inductive red light.