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It
has long been known that distinctive blue flashes—a type of
bioluminescence—that are visible at night in some marine environments
are caused by tiny, unicellular plankton known as dinoflagellates.
However, a new study has, for the first time, detailed the potential
mechanism for this bioluminesence.
The
study, which was partially funded by the National Science Foundation,
is reported by Susan Smith of Emory School of Medicine, Thomas DeCoursey
of Rush University Medical Center and colleagues in the Oct. 17, 2011
issue of the Proceedings of the National Academy of Sciences (PNAS).
A
key aspect of the potential mechanism for bioluminescence in
dinoflagellates proposed in the PNAS study involves voltage-gated proton
channels—channels in membranes that can be opened or closed by chemical
or electrical events.
J.
Woodland Hastings, a member of the Smith and DeCoursey research team
and an author of the PNAS article, suggested the presence of
voltage-gated proton channels in dinoflagellates almost forty years ago.
But the Smith and Decoursey team only recently confirmed them by the
identification and subsequent testing of dinoflagellate genes that are
similar to genes for voltage-gated proton channels that had previously
been identified in humans, mice and sea squirts.
According
to the study, here is how the light-generating process in
dinoflagellates may work: As dinoflagellates float, mechanical
stimulation generated by the movement of surrounding water sends
electrical impulses around an internal compartment within the organism,
called a vacuole–which holds an abundance of protons. (See accompanying
illustration.) These electrical impulses open so-called
voltage-sensitive proton channels that connect the vacuole to tiny
pockets dotting the vacuole membrane, known as scintillons.
Once
opened, the voltage-sensitive proton channels may funnel protons from
the vacuole into the scintillons. Protons entering the scintillons then
activate luciferase—a protein, which produces flashes of light, that is
stored in scintillons. Flashes of light produced by resulting luciferase
activation would be most visible during blooms of dinoflagellates.
This
research illuminates the novel mechanisms underlying a beautiful
natural phenomenon in our oceans, and enhances our understanding of
dinoflagellates—some of which can produce toxins that are harmful to the
environment.
