Gravitaxis in Chlamydomonas reinhardtii: Characterization using video microscopy and computer analysis

We characterized the gravitactic behavior of Chlamydomonas reinhardtii, a u nicellular green alga, using a computer-analysis system in order to study d irectional swimming. The effects of the calcium-channel inhibitors gadolini um and diltiazem on graviorientation and swimming speed were examined. In a ddition, we studied directional swimming in the ptx1 strain of C. reinhardt ii, a flagellar dominance mutant. Results indicate that Chlamydomonas reori ents for gravitactic swimming through a mechanism different from the calciu m-mediated pathway believed to be involved in gravity transduction in highe r plants. We suggest that calcium-mediated gravitaxis originated in an orga nism that was more evolutionarily advanced than Chlamydomonas.