CALCIUM INFLUX SIGNALS NORMAL FLAGELLAR RNA INDUCTION FOLLOWING ACID SHOCK OF CHLAMYDOMONAS-REINHARDTII

Acid shock of Chlamydomonas results in flagellar excision and inductio n of flagellar protein RNAs. The magnitude of flagellar RNA accumulati ons after flagellar excision by mechanical shear depends on the extrac ellular Ca2+ concentration. In this report, we demonstrate that the ma gnitude and duration of flagellar RNA accumulations are signaled by an acid shock-induced Ca2+ influx. RNA accumulations were greater in cel ls acid shocked in 500 mu M CaCl2 than in 200 mu M CaCl2, although the accumulation durations were similar. RNA accumulations of lower magni tude and shorter duration were observed in cells in Ca2+-containing bu ffer treated with CdCl2. RNA accumulations were of still lower magnitu de and shorter duration in cells shocked in buffer without added CaCl2 than in cells shocked in 200 or 500 mu M CaCl2 or in the presence of CdCl2. RNA accumulations similar to those in cells shocked in buffer w ithout added CaCl2 were measured in cells following acid shock in buff er containing 200 mu M CaCl2 and supplemented with neomycin, ruthenium red, or LaCl3. Acid shock of the adf-1 mutant resulted in RNA accumul ations of shorter duration and lower magnitude than those measured in adf-1 cells stimulated by mechanical shear. These results are consiste nt with an hypothesis that acid shock generates two genetically and ph armacologically distinct signals governing flagellar RNA induction; th e first signal is independent of a Ca2+ influx and flagellar excision and results in low magnitude accumulations of short duration, and the second is a consequence of a Ca2+ influx and results in accumulations of high magnitude and long duration.