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Two photophobic responses in <italic>Volvox carteri</italic>

1979; Oxford University Press; Linguagem: Inglês

10.1093/oxfordjournals.pcp.a075885

1471-9053

Hironobu Sakaguchi, Kozo Iwasa,

Neurobiology and Insect Physiology Research

Phototaxis of Volvox carteri is the result of two photophobic responses: stop and accelerationof flagellar activity in the anterior region of the colony. These responses of a colony fixed under a microscope were analyzed quantitatively by cine-micrography. The phototactic sign of Volvox is temperature-dependent: it is positive at room temperature and negative at low temperature. When the temperature was lowered, the stop response to the on-stimulus was reduced and changed to the acceleration response, while the acceleration response to the off-stimulus changed to the stop response. Decrease in light inteasity resulted in reduction in both stop responses, i.e., the response to the on-stimulus at 24°C and that to the off-stimulus at 16°C, but scarcely affected the acceleration responses. The action spectra of the photophobic responses at 24° and 14°C are similar, with a peak at 520 nm.