Dynamic changes in the organization of microfilaments associated with the photocontrolled motility of chloroplasts in epidermal cells ofVattisneria

Summary Using time-lapse video microscopy, we performed a semiquantitative investigation of the movement of chloroplasts on the cytoplasmic layer that faces the outer periclinal wall (P side) of epidermal cells of leaves of the aquatic angiospermVallisneria gigantea Graebner. Under continuous irradiation with red light (650 nm, 0.41 W/m²), the movement of chloroplasts on the P side was transiently accelerated within 5 min. The increased movement began to decrease at around 20 min and fell below the original level after 40 to 60 min of irradiation with red light. The acceleration and deceleration of movement of chloroplasts on the P side seemed to lead directly to the increase and the subsequent decrease in the rate of migration of chloroplasts from the P side to the anticlinal layers of cytoplasm, which are responsible for the accumulation of chloroplasts on the P side, as we demonstrated previously. In the presence of inhibitors of photosynthesis, the accelerated movement of chloroplasts was maintained for as long as the chloroplasts were irradiated with red light. The rapid acceleration and deceleration of the movement of chloroplasts could be observed repeatedly with sequential irradiation with red and then far-red light (746 nm, 0.14 W/m²). Concomitantly with the loss of motility of chloroplasts on the P side, a dynamic change in the configuration of microfilaments, from a network to a honeycomb, occurred on the P side.Abbreviations APW artificial pond water - A side cytoplasmic layer that faces the anticlinal wall - ATP adenosine triphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F-actin fibrous actin - FITC fluorescein isothiocyanate - PBS phosphate-buffered saline - Pfr farred-light-absorbing form of phytochrome - Pr red-light-absorbing form of phytochrome - P side cytoplasmic layer that faces the outer periclinal wall Dedicated to Professor Eldon H. Newcomb in recognition of his contributions to cell biology