Redox poise determines the sign of phototaxis in Chlamydomonas
Ken-ichi Wakabayashi, Yuka Misawa, and Ritsu Kamiya
Department of Biological Sciences, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JAPAN
Chlamydomonas cells show positive or negative phototaxis, i.e., tend to swim toward or away from the light source, depending on the light intensities, circadian rhythms, etc. Switching of the sign of phototaxis is important for the cells to stay under proper light conditions. However, the mechanism underlying this switching remains to be clarified. Here we show that the cellular redox poise is the key factor. We found that cells show positive phototaxis after treatment with reactive oxygen species (ROS), whereas they show negative phototaxis after treatment with reagents that quench ROS. These results strongly suggest that the phototactic sign in Chlamydomonas is determined by the cellular redox poise. This hypothesis readily explains the previous report that photosynthetic activities influence the phototactic sign, since photosynthesis is known to greatly affect the cellular redox poise.
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