Mechanically Induced Avoidance Response of Chloroplasts in Fern Protonemal Cells

Cell response to mechanical stimulation was investigated at a subcellular level in protonemal cells of the fern Adiantum capillus-veneris L. by pressing a small part of the cell with a microcapillary. In cells receiving local stimulation, the chloroplasts moved away from the site of stimulation, whereas the nuclei failed to show such avoidance movement. Mechanical stimulation for a period as short as 0.3 min was enough to induce the avoidance response to a maximal level. The avoidance movement of chloroplasts started within 30 min and the plateau level of avoidance was attained around 2 h after stimulation. By tracing the movement of chloroplasts during the response, it was shown that the mobility of chloroplasts near the stimulation site increased transiently within 1 h after the stimulation. After 2 to 3 h, it slowed down to the control level without stimulation. The avoidance response was inhibited by 0.1 mm cytochalasin B and 25 mm 2,3-butanedione monoxime but not by 3.3 μm amiprophosmethyl or 5 mm colchicine. These findings indicate that the protonemal cells were very sensitive to mechanical stimulation and that chloroplasts moved away from the mechanically stimulated site through the actomyosin motile system.