STRIKINGLY DIFFERENT PROPULSIVE FORCES GENERATED BY DIFFERENT DYNEIN-DEFICIENT MUTANTS IN VISCOUS MEDIA

The propulsive force generated by Chlamydomonas mutants deficient in f lagellar dynein was estimated from their swimming velocities in viscou s media. The force produced by wild-type cells increased by 30-40% whe n viscosity was raised from 0.9 to 2 cP but decreased as viscosity was further raised above 6 cP. The biphasic dependence of force generatio n on viscosity was also observed in the mutant idal, which lacks the I 1 component of the inner-arm dynein. The mutant ida4, which lacks the inner-arm 12 component, was extremely susceptible to viscosity and sto pped swimming at 6 cP, at which other mutants could swim. In contrast, odal, which lacks the entire dynein outer arm, produced a fairly cons tant force of about one-third of the wild-type value, over a viscosity range of 0.9-11 cP. In demembranated and reactivated cell models of t he wild type, the propulsive force decreased monotonically as viscosit y increased. Thus the increase in force generation at about 2 cP obser ved in live cells may be caused by some unknown mechanism that is lost in cell models. The cell models of odal, in contrast, did not show a marked change in force generation with the change in viscosity. These results indicate that the force generation by the outer-arm dynein gre atly depends on viscosity or the velocity of movement, whereas the com plete set of inner-arm dynein present in the odal axoneme produces a f airly constant force at different viscosities. These different propert ies of inner and outer dynein arms should be important in the mechanis m that produces flagellar beating. (C) 1995 Wiley-Liss, Inc.