DISTRIBUTION OF SUBCELLULAR BIOLUMINESCENT SOURCES IN A DINOFLAGELLATE, PYROCYSTIS FUSIFORMIS

¹ Department of Biological Sciences, University of California, Santa Barbara, California 93106

Pyrocystis fusiformis exhibits rhythmic changes in the distribution and mechanical excitability of subcellular bioluminescent sources. Bioluminescence in night-phase cells can be stimulated either mechanically or by low pH and originates from microsources found throughout the cytoplasmic layer surrounding the large central vacuole. Microsources are weakly fluorescent and probably correspond to 0.5 µm or smaller cytoplasmic inclusions. With the onset of day phase, bioluminescence becomes mechanically inexcitable but responds to acid stimulation. Microsources disappear from the cell periphery during early day phase and all luminescence originates from the perinuclear region. In late day phase, bioluminescence originates both from the perinuclear region and from microsources in the periphery. However, luminescence remains mechanically inexcitable until the onset of night phase. Cells maintained in darkness exhibit the same rhythmic changes in mechanical excitability and development and disappearance of the perinuclear luminescence, except that microsources do not disappear from the periphery of early day-phase cells without a light induction period. Mechanisms which might underlie the rhythmic changes in bioluminescence distribution and mechanical excitability are proposed.

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