NUCLEUS BASAL BODY CONNECTOR OF DUNALIELLA - THRESHOLD CONCENTRATION OF CALCIUM NECESSARY FOR IN-VITRO CONTRACTION

Detergent-isolated flagellar apparatuses of the flagellate green alga Dunaliella bioculata retain remnants of the nucleus (the karyoskeleton ) which are linked to the basal bodies by the centrin-containing nucle us basal body connectors (NBBC). Such complexes were subjected to diff erent calcium concentrations (1 x 10(-9) M - 5 x 10(-4) M Ca2+) and th e distance between the basal bodies and the karyoskeleton was measured by light microscopy. The threshold concentration of Ca2+ for NBBC con traction was determined to be around 5 x 10(-8) M Ca2+. At > 10(-7) M Ca2+ NBBC were maximally contracted and the distance between the basal bodies and the karyoskeleton was only about 50 % of the initial dista nce. Using a polyclonal antibody generated against centrin (Salisbury et al., 1984), the NBBC were visualized by indirect immunofluorescence in both the extended and contracted state. Our results demonstrate th at in vitro contraction of centrin-containing filaments in green algae is initiated at about the same free Ca2+ concentration in three diffe rent centrin-containing basal apparatus components (i.e. the distal co nnecting fibre, the flagellar transitional region and the NBBC).