Effects of Calcium and Potassium Ions on Phototaxis in Cryptomonas

Effects on positive phototaxis and the cell motility of 7 cations in 5mM MOPS (morpholinopropane sulfonic acid) buffer (pH 7.0) containing 0.16 mM NaCl, 0.68 mM KCl, 0.5 mM CaCl2 and 0.16 mM MgCl2 were studied in the unicellular flagellate Cryptomonas with a photoelectrical measuring apparatus and photomicrography. When calcium ion was removed from the medium by adding 1 mM EGTA (ethylene glycol-bis-(β-amino-ethylether)-N,N′-tetraacetic acid), the phototactic response was totally inhibited, but the swimming rate was not much affected. The effect of EGTA was partially reversed by the addition of 1 mM CaCl2. When 15mM KCl or RbCl was added to the medium, phototaxis was greatly inhibited, but there was no significant influence on the swimming rate. Similar but less inhibitory effects were induced in the presence of NaCl, LiCl and CsCl. KCl-induced inhibition was partially removed by the addition of 15 mM CaCl2 or MgCl2.