Photoinduction of circular F-actin on chloroplast in a fern protonemal cell

Summary Circular F-actin on a photooriented chloroplast was observed by rhodamine-phalloidin staining in the fernAdiantum protonemal cells in which phytochrome- or blue light receptor-mediated intracellular photoorientation of chloroplasts was induced. The circular structure located along the edge of chloroplast on the side facing the plasma membrane but not on the opposite side. Most of the chloroplasts in protonemal cell have dumbbell-shape and the circular ring-like structure was found on each half of the dumbbell. The structure was not observed in the cells which were kept in the dark, indicating the change of F-actin organization by the light condition. Possible role of the structure on the anchorage of chloroplast in its intracellular photoorientation was discussed.