A Direct Light Effect on Maintaining Photosynthetic Activity of Nitella Chloroplasts

The chloroplasts of internodal cells of Nitella are fixed to a stationary layer of cytoplasm whereas the nuclei and most of the cytoplasm stream along the longitudinal axis. Isolated internodal cells were maintained for several days with half the cell kept in the dark, the other half kept under continuous light. Photosynthetic activity of the cells was checked by placing the cell evenly illuminated in a (14)CO(2) atmosphere. Chloroplasts of the previously dark half of the cell were found to fix only half as much CO(2) as the chloroplasts which were continuously illuminated. These results are discussed in relation to the possible direct effect of light on biosynthetic reactions of mature chloroplasts.