INTRACELLULAR DICHROIC ORIENTATION OF THE BLUE LIGHT-ABSORBING PIGMENT AND THE BLUE-ABSORPTION BAND OF THE RED-ABSORBING FORM OF PHYTOCHROME RESPONSIBLE FOR PHOTOTROPISM OF THE FERN Adiantum PROTONEMATA

The intracellular localization and orientation of the receptors for the blue light-induced phototropism in the fern Adianrum protonemata, phytochrome and the blue light-absorbing pigment, were investigated by combining the techniques of cell centrifugation and of microbeam irradiation with linearly polarized light. The phototropic response was induced in the cells even after they had been centrifuged basipetally to spin down the endoplasm from the apical region. When a polarized blue microbeam was given to a flank of the apical region of the protonema, the phototropic response after compensation of phytochrome effect by far-red light was most effectively induced when the polarization plane was parallel to the long axis of the cell. If protonemata were pre-irradiated with blue and far-red light, the phototropic response was mediated through phytochrome alone. If such pre-irradiated protonemata were similarly irradiated with a polarized blue microbeam, polarized light vibrating parallel to the cell axis was again most effective in inducing the response. These results indicate that both the blue light-absorbing pigment and the phytochrome responsible for the blue light-induced phototropism in Adiantum are confined to the plasma membrane and/or the ectoplasm and that the transition moments of their blue-absorption bands are nearly parallel to the cell surface.