XVI International Botanical Congess

Chloroplasts reorient within the plant cell to optimize light absorption. Previous studies using algae have implicated the actin cytoskeleton in such movements (Mineyuki et al., 1995, Protoplasma 185: 222-229). We used a modified microfilament sliding assay to demonstrate that actin strands bind to and move along isolated pea chloroplasts affixed to a nitrocellulose-coated coverslip. This movement was found to be dependent upon ATP concentration and inhibited by cytochalasin B. In addition, immunoblotting using anti-myosin antibodies was performed on isolated chloroplasts to detect the presence of myosin on the surface of the chloroplast envelope. Taken together, these data provide evidence for an actin-based mechanism in the light-induced movement of chloroplasts in leaves of Pisum sativum. This work was supported by USDA grant 96-35311-3694.