Bioluminescence
Bioluminescence is the ability of living things to emit light. It is found in
- many marine animals, both invertebrate (e.g., some cnidarians, crustaceans, squid) and vertebrate (some fishes);
- some terrestrial animals (e.g., fireflies, some centipedes);
- some fungi and bacteria (photo at right)
The molecular details vary from organism to organism, but each involves
- a luciferin, a light-emitting substrate
- a luciferase, an enzyme that catalyzes the reaction
- ATP, the source of energy
- molecular oxygen, O2
The more ATP available, the brighter the light. In fact, firefly luciferin and luciferase are commercially available for measuring the amount of ATP in biological materials.
Fireflies use their flashes to attract mates. The pattern differs from species to species. In one species, the females sometimes mimic the pattern used by females of another species. When the males of the second species respond to these "femmes fatales", they are eaten!
Barry Trimmer and his colleagues at Tufts University have recently discovered how fireflies turn their luminescent organs — called lanterns — on.
- The luminescent cells of the lanterns are close to cells at the end of the tracheoles (that bring oxygen to — and take carbon dioxide away from — the insect's tissues).
- These cells contain nitric oxide synthase (NOS), the enzyme that liberates the gas nitric oxide (NO) from arginine.
- Nerve impulses activate the release of NO from these cells.
- The NO diffuses into the lantern cells and inhibits cellular respiration in the mitochondria (probably by blocking the action of cytochrome c oxidase)
- With cellular respiration inhibited, the oxygen content of the cells increases.
- This turns on light production in the peroxisomes that contain luciferase and luciferin-ATP (the ATP is generated when the lanterns are dark).
- The quick decay of NO probably contributes to the short duration of the flash.
Bioluminescence in Marine Animals
The widespread occurrence of luminescence among deep-sea animals reflects the perpetual darkness in which they live.
- At least one fish has its luminescent organ located at the tip of a protruding stalk and uses it as bait to lure prey within reach of its jaws.
- When disturbed, one species of squid emits a cloud of luminescent water instead of the ink that its shallow-water relatives use.
- Some marine animals that live near the surface have luminescent organs on their underside. These probably make it more difficult for predators beneath them to see them against the light background of the surface.
In the case of fishes, the light is emitted by luminescent bacteria that grow in luminescent organs. The photos (courtesy of Prof. J. W. Hastings) show the flashlight fish, Photoblepharon palpebratus, with the lid of its luminescent organ open (left) and closed (right). The light is produced by continuously-emitting luminescent bacteria within the organs, but its display is controlled by the fish. These animals, which were photographed along reefs in the Gulf of Elat, Israel, appear to use their luminescent organs for such varied functions as
- attracting prey;
- signaling other members of their species; and
- confusing potential predators.
17 April 2014
