The action of dinaction on volume changes of whole chloroplasts in light and dark.

1. Whole chloroplasts exhibit a fast and strong swelling after addition of dinactin (final concentration 10(-5) m). 2. When illuminated the partieles shrink again and reach their original volume after 15 minutes. ATP may replace the light in this energy-dependent volume reduction. 3. Both swelling and subsequent shrinking are more pronounced in a hypertonic solution of KCl than in a NaCl-medium of the same concentration. 4. These results are discussed in relation to the known ion selectivity of the macrotetralides and the possible presence of light-driven K(+) pump.