Scintillon

Abstract: The physical identity of the bioluminescent particles (‘scintillons’) extracted from the marine dinoflagellate Gonyaulax polyedra was investigated by electron microscopy and particle counts of the active fractions from sucrose density gradients. Membranous structures are abundantly present in purified fractions, while there is a decrease, relative to activity, in the numbers of guanine crystals, which had previously been implicated as bioluminescent structures. The significance of these findings with respect to the in vivo scintillon is discussed.

Abstract: Pyrocystis lunula (Schutt) Schutt has long been a model cell system in the study of circadian rhythms of bioluminescence and photosynthesis. Despite this, relatively little is known about the cell's ultrastructure. Here we report the complete serial reconstruction of P. lunula cells during both day and night phases (the first four dimensional study of any dinoflagellate). This permitted us to track both positional and ultrastructural changes in plastids and scintillons (the organelles responsible for bioluminescence). In daytime cells, plastids extended radially from the cell center with thylakoid membranes in stacks of two. Daytime scintillons clustered in a central region of the cell surrounded by the C-shaped nucleus. During the night, plastids were closely associated in the cell center with their thylakoids stacked in a grana-like arrangement. Nighttime scintillons were spread into the cell periphery. The daily migration of plastids and scintillons may depend on these organelles' interactions with the cells' cytoskeletal framework and appears to be under control of the circadian clock.

Abstract: Two proteins,Gonyaulax luciferase and the luciferin binding protein, are involved in the bioluminescent reaction of the unicellular marine algaGonyaulax polyedra. Using antibodies raised separately against the purified proteins, their ultrastructural localizations were visualized by double immunogold labeling on sections after fast-freeze fixation, freeze-substitution and embedding in Epon or in LR White. Gold particles of two sizes attached to the secondary antibodies allowed the two primary antibodies to be distinguished. The two colocalized to cytoplasmic densifications (scintillons), which occurred in close association with the vacuolar membrane near the periphery of the cell. They also occurred in the cytoplasm of the Golgi area, either over densifications without associated membranes (prescintillons), or as very small colocalizations not associated with any evident cytoplasmic differentiation. No other site of colocalization was observed, thus unambiguously establishing the ultrastructural identity of the bioluminescent organelles.

Abstract: Publisher Summary Bioluminescence, the emission of light by living organisms, is a phenomenon that has attracted the attention of biologists from the beginning of the science. There are only a few organisms in which anything is known concerning bioluminescent organelles or intracellular sources of luminescence. The identification of subcellular light-emitting sources is not possible until photogenic tissue could be examined with the electron microscope. The photocyte must be identified among the other cells of the photophore. Even this step has been difficult to take in some luminous creatures. Fluorescence can sometimes be established as an indicator of bioluminescence. This simplifies the problem, because fluorescence is relatively long-lasting, whereas the luminescent flash is often very brief. The separation of subcellular components on sucrose density gradients or by other means may or may not be helpful. If the light-emitting fractions of the gradient are not homogeneous, an erroneous identification may be made, as for example in the case of the dinoflagellate “scintillon,” or no identification may be possible.