Microfilaments anchor chloroplasts along the outer periclinal wall in Vallisneria epidermal cells through cooperation of PFR and photosynthesis

In the cytoplasmic layer that faces the outer periclinal wall in epidermal cells of leaves of the aquatic angiosperm Vallisneria gigantea Graebner, we examined a possible interrelationship among the configuration of microfilaments, chloroplast motility, and anchoring of chloroplasts. In dark-adapted cells, microfilaments are arranged in a network array. During a 10-min incubation in darkness 10 to 20 min after irradiation with red light (650 nm, 0.41 W m(-2)) for 5 min, the number of cells containing a network array decreased substantially while the number of cells containing microfilaments in a honeycomb array increased. Irradiation with red light rapidly produces an increase in chloroplast motility, but chloroplast motility declined almost to initial levels during the 10-min incubation in darkness after the irradiation. Simultaneously, the chloroplasts in these cells became extremely resistant to centrifugal forces. These effects of red light were negated either by far-red light or by the presence of DCMU, and were sensitive to cytochalasin B. It appears, therefore, that microfilaments not only drive the movement of chloroplasts but also play a crucial role in accumulation of the chloroplasts along the outer periclinal wall through dynamic changes in the configuration under cooperative regulation by P-FR and photosynthesis.