ABSTRACT
The presence of rhodopsin-like proteins in the eyes and auricles of the freshwater planarian Dugesia japonica was confirmed using anti-frog-rhodopsin rabbit IgG. The apparent relative molecular masses of these proteins were 65×103 and 62×103, and positive reactions to IgG were localized to the microvilli of the photoreceptor cells in the eyes and to the sensory cilia, rootlets and microvilli in the auricles. Eye- or head-excised planarians showed no negative phototaxis, whereas intact or auricle-excised planarians did. During regeneration in head-excised planarians, the appearance of rhodopsin-like proteins in the regenerating eyes corresponded to the recovery of negative phototaxis behaviour. Head or auricle excision enhanced asexual fission under continuous illumination. However, eye excision had no such effect. These results suggest that the rhodopsin-like proteins in the eyes work as photoreceptors for negative phototaxis behaviour and that, in the auricles, they are involved in asexual fission originating from the circadian rhythm.
