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Regulation of bioluminescence in the marine dinoflagellate Pyrocystis lunula Kirsten Heimann*; Matuszewski, J.; Klerks, P.L. Dept. Biology, UL at Lafayette, P.O. Box 42451, Lafayette, LA 70504, USA      *(kxh8305@louisiana.edu) Circadian rhythms control bioluminescence (BL) in phototrophic but not heterotrophic dinoflagellates. Chloroplasts and scintillons in P. lunula migrate on a day/night basis in opposite directions. During the day, the chloroplast is extended throughout the cytoplasm and the scintillons are positioned in the cell center. At night, chloroplasts appear to retract to the cell center, while scintillons move to the cell periphery. We have analyzed the chloroplast distribution in vivo and in fixed cells. None of the fixed cells exhibit the observed distribution in vivo. This indicates that night phase cells are more sensitive than illuminated cells. A membrane potential at the plasma membrane activates BL. This study investigates the response of the BL system in P. lunula to chemicals and drugs that modulate signal transduction. Preliminary data show that the PKC inhibitor BIM and PMA, which downregulates PKC, dose-dependently reduce BL. Cells incubated with A23187 display BL without mechanical activation, while the calcium chelator EGTA lessens the BL response in a dose-dependent manner. Therefore, we conclude that the mechanical stimulus may be transduced to the scintillons via calcium and/or protein kinase C-mediated processes. [Poster: heimann.kirste.40202]

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