Ca2+-dependent waveform conversion in the flagellar axoneme of Chlamydomonas mutants lacking the central-pair/radial spoke system.

Chlamydomonas flagella undergo a striking waveform conversion from an asymmetrical ciliary type to a symmetrical flagellar type when the cell is stimulated by intense light and the Ca2+ concentration within the flagellum is increased above approximately 10(-6) M. To see whether the central-pair/radial spoke system is needed for this conversion as suggested by previous studies, we examined the effect of Ca2+ on the reactivated axonemes of the mutants lacking the central pair (pf18) or the radial spokes (pf14). Although the flagella of these mutants are paralyzed in vivo, demembranated axonemes can be reactivated to beat under certain nucleotide conditions such as in the presence of low concentrations (< 100 microM) of ATP. We examined the waveform of the axonemes reactivated at 20 microM ATP in the presence of 10(-8)-10(-4) M Ca2+ and found that these axonemes, as well as the wild-type axonemes, undergo a waveform conversion over a Ca2+ concentration range of 10(-7)-10(-5) M: a highly asymmetrical waveform at <10(-6) M Ca2+ and a symmetrical waveform at >=10(-5) M Ca2+. Although the waveform is different between the mutants and the wild type, the Ca2+ concentration at which the waveform conversion occurred was similar. These results indicate that the central pair/radial spoke system is not essential for the waveform conversion.