Abstract

A marine coenocytic green alga, Bryopsis plumosa exhibited multistriate type protoplasmic streaming of a velocity less than 100 μm.min−1. When the alga was illuminated locally, chloroplasts and other cell organelles accumulated in the illuminated zone. The action spectrum for this reaction showed that blue light between 380 and 500 nm was most effective.

The velocity of chloroplast movement decreased when the cell was totally illuminated with blue light, but no comparable change was observed under red light illumination. Therefore, chloroplast accumulation probably was caused by the reduced streaming rate in the illuminated zone.

Electron microscopy showed cytoplasmic microtubules arranged parallel to the cell axis in the vicinity of the chloroplasts. Chloroplast movement was inhibited heavily by treatment with antimicrotubule agents, but was little affected by cytochalasin B at a concentration of 10 μg/ml.

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