CALCIUM IN THE CONTROL OF CHEMOTAXIS IN CHLAMYDOMONAS

The unicellular alga Chlamydomonas reinhardtii exhibits active orienta tion with respect to a chemical gradient. As already reported before, Chlamydomonas cells are attracted to ammonium ion and some sugars. Che motactic orientation of C. reinhardtii is Ca2+ dependent. The Ca2+ cha nnel blockers Cd2+, La3+, ruthenium red, verapamil and diltiazem compl etely inhibit chemotaxis. These data indicate that the Ca2+ currents m ediating chemotactic responses of C. reinhardtii are carried by L-type Ca2+ channels. In contrast to chemosensory signaling in eukaryotic ce lls possessed amoeboid motility (Dictyostelium discoideum amoebae, leu cocytes), chemosensory signaling in swimming cells of C. reinhardtii d oes not involve inositol 1,4,5-trisphosphate. Our results suggest that PTX2, that is a component of the signal transduction pathway for phot oshock and phototaxis, may well be involved in chemotaxis to sugars.