Phototaxis inEuglena gracilis: Effect of sodium azide and triphenylmethyl phosphonium ion on the photosensory transduction chain

Phototaxis in the flagellateEuglena gracilis was studied by means of a microvideographic analysis, and the light-induced directional movement was determined by computer-based statistical treatments. Lateral white light with an illuminance of 25 lx (≙0.105 Wm−2) caused the cells to preferentially swim toward the light source (positive phototaxis), while an illuminance of 1,000 lx (≙4.2 Wm−2) induced negative phototaxis. The lipophilic membranepenetrating cation triphenylmethyl phosphonium ion (TPMP+) specifically inhibited positive phototaxis, while it hardly affected negative phototaxis. The uncoupler sodium azide, on the other hand, impaired negative phototaxis substantially.