from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The movement of an organism or a cell toward or away from a source of light.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The movement of an organism either towards or away from a source of light
from the GNU version of the Collaborative International Dictionary of English
- n. The influence of light on the movements of low organisms, as various infusorians, the zoöspores of certain algæ, etc.; also, the tendency to follow definite directions of motion or assume definite positions under such influence. If the migration is toward the source of light, it is termed positive phototaxis; if away from the light, negative phototaxis.
from The Century Dictionary and Cyclopedia
- n. In botany, the taking by certain organisms or organs of a definite position with reference to the direction of the incident rays of light, as when the zoöspores of various plants (Hæmatococcus, Ulothrix, etc.) place their long axes parallel to the direction of the incident rays.
- n. In biology, active migration of organisms, or of cells, in the line of rays of light affecting them — positive phototaxis if toward the source of light, and negative phototaxis if away from it. Compare photopathy.
This process, called phototaxis, was the focus of the PNAS study.
According to Sharp: Insects have a behavior phototaxis in which they tend to congregate in the vicinity of light having a wavelength in the ultraviolet range of around 350 nm.
Chlamyodomonas swim toward light (phototaxis), and Dictyostelium amoeba crawl toward a specific chemical substance (chemotaxis).
Some species possess ciliated pits in front of their cerebral ganglion that are used in phototaxis (movement towards light).
Sexual isolation caused by selection for positive and negative phototaxis and geotaxis in Drosophila pseudoobscura.
Such a generalized response to a generalized stimulus can be mediated through a nervous system, as in the case of the phototaxis of the moth, but with the development of a specialized nervous system both stimulus and response can be refined.
Pulsed light stimulation of an immobilized spheroid was used to simulate the light fluctuation experienced by a rotating spheroid during phototaxis.
Phototactic responses are essential for these flagellates because they need to orientate themselves to receive sufficient light for photosynthesis, but how does a multicellular organism accomplish phototaxis without any known direct communication among cells?
Moreover, positive phototaxis is facilitated by gravitational forces.
Under our conditions, V. rousseletii spheroids showed no negative phototaxis.