Two photophobic responses in Volvox carteri

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Phototaxis of Volvox carteri is the result of two photophobic responses : stop and acceleration of 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 intensity resulted in reduction in both stop responses, i.e., the response to the on-stimulus at 24℃ and that to the off-stimulus at 16℃, but scarcely affected the acceleration responses. The action spectra of the photophobic responses at 24℃ and 14℃ are similar, with a peak at 520 nm.
日本植物生理学会の論文