| Abstract: | The lunate cysts of Pyrocystis lunula have a bioluminescent emission spectrum with a peak intensity of 477.5 ± 1 mμ. The light originates from the protoplasm in the center of the cysts. Six to eight hr after the cysts were placed in the dark, they produced 300 to 800 times more luminescence than controls maintained under constant, illumination. Plastids contract distally when the cysts are placed in the dark. If kept in the dark, the plastids contract distally and expand with a circadian rhythm persisting several days. At intensities of 2200 μm cm-’or less, the plastids are expanded. The plastids are contracted into the central area of the cysts at light intensities of 4000 μw cm-2 and above. The Gymnodinium stage of the life cycle is not bioluminescent. |
