Light up your life with...
People who observe certain species of Gonyaulax in the dark are in for a treat. One understands immediately why the phylum containing dinoflagellates is termed Pyrrophyta, meaning "fireplant", or why dinoflagellates have been affectionately known as "living lanterns" of the sea. Just a jostle of a jar of dinoflagellate-laden seawater will make sparks fly. The glow they produce is sure to warm your heart. This phosphorescence is termed bioluminescence, which is light produced in an organism by means of a chemical reaction. Dinoflagellates are the only algae known to have this special eccentricity.
The genus Gonyaulax contains many bioluminescent species such as G. catenata, G. digitale, G. hyalina, polygramma, G. sphaeroidea, G. spinifera, and G. polyedra
Fluorescence microscope images .
What causes dinoflagellates to bioluminesce?
Three stimuli have been observed to cause bioluminescence in dinoflagellates:
~ mechanical stimulation - When shear forces, such as those caused by the stirring of water from the wake of a boat, a swimming fish or a breaking wave, deform the cell membrane, a short flash of approximately 1/100 of a second and 10^8 photons is produced.
~ chemical stimulation - Reducing the pH of their external medium by adding acid can cause some dinoflagellates to glow continuously.
~ temperature stimulation - Some species of dinoflagellate, such as G. polyhedra, will be induced to glow if the temperature is lowered.
What color are dinoflagellates when they bioluminesce?
Light emission from dinoflagellates is generally blue-green in color, falling in the light spectrum between 474 and 476 nanometers in wavelength. In Gonyaulax red flashes between 630 and 690 nanometers have been observed as well.
How does bioluminescence work?
The mechanism by which dinoflagellates emit light is not entirely known, but there is both a physical and a chemical component to the initiation of a flash.
The physical process - a bioluminescent flash is preceeded by an action potential during which the inside of the vaculor membrane becomes hyperpolarized ( has more negative voltage with respect to resting potential). This sets up the conditions for the chemical reaction.
The actual chemical reaction by which light is produced involves a substrate called luciferin and an enzyme called luciferase, which are sequestered in outpocketings of the vacuolar membrane. The action potential extrudes hydrogen ions into these pockets and lowering their pH. Under these acidic conditions, luciferin is released from its binding protein and is thus activated. Luciferase catalyses the oxidation of luciferin, resulting in light and an intermediate called oxyluciferin. Energy in the form of ATP must be provided to the system to regenerate luciferin.
How is bioluminescence regulated?
Bioluminescence is an expression of circadian rhythmicity, a phenomenon regulated on a daily cycle. In the absence of light, dinoflagellates exhibit peaks and valleys of bioluminescence. However, the biological clock can be 'entrained' by light exposure, shifting the peaks of luminescence to different times of day. Circadian control of cellular processes represents an adaptive advantage for dinoflagellates because they are vertical migrators in the water column. By keeping time, they can anticipate sunrise and be poised to start photosynthesizing at the surface as soon as light is available.
Why do dinoflagellates bioluminesce?
It is not known exactly why dinoflagellates bioluminesce. However, "the burglar alarm" is the leading hypothesis. It suggests that upon mechanical stimulation by potential predators, dinoflagellates light up. The light cues larger predators to the location of that predator threatening the dino. The middle predator is toast!
© 1999 Allison Arnold and Monica Draghici. All rights reserved.