No evidence for Ca2+ influx as an essential link in the signal transduction chains of either light-oriented chloroplast movements or Pfr-mediated chloroplast anchorage in Mougeotia

The effect of Ca2+ entry blockers on the light-induced chloroplast movements in Mougeotia was studied. The organic inhibitors diltiazem, nifedipine and ruthenium-red and the inorganic inhibitors La3+ and Co2+ do not affect the low or high fluence rate movements of chloroplasts. Only at toxic concentrations or after long-term incubations (4 – 7 days), which partially damage the cells, is chloroplast movement slightly inhibited. The Pfr-mediated increase in chloroplast anchorage and the chloroplast anchorage of dark-sensitized algae are not significantly altered by Ca2+ entry blockers within physiological concentrations. Our results contradict the hypothesis of a Pfr-controlled Ca2+ influx as an essential link in the signal transduction chain of light-oriented chloroplast movements in Mougeotia.