Light-Induced Changes in the Behavior of Chloroplasts under Centrifugation in Vallisneria Epidermal Cells

Using a centrifuge microscope of the stroboscopic type, effects of light irradiation and chemical applicationon the behavior of chloroplasts in epidermal cells of Vallisneria gigantea were examined. Movements of chloroplasts in the cytoplasmic layer that faces the outer periclinal wall (P side) were exclusively observed. Irradiation with blue light (451.0nm) at a high-fluence rate (24.9 μmol m -2 · sec -1) accelerated the passive gliding of chloroplasts produced by the centrifugal force of 25-40 × g. A similar acceleration was caused by application of EGTA to the dark-adapted cells in the presence of cytochalasin B. In cells preirradiated with red light (650.0nm) at a low-fluence rate (2.2 μmol m -2 · sec -1) for 3 - 4h, the minimal centrifugal force required to induce the passive gliding of chloroplasts increased to over 50 × g. The application of EGTA to these cells brought about the movement of chloroplasts in the central area of the P side, which exhibited a close resemblance to the movement induced by irradiation with blue light in the cells preirradiated with red light. Light irradiation seems to affect some mechanical properties of the cytoplasmic matrix. The significance of these findings in the light of orientation movements of chloroplasts in these cells is discussed.