title: Calcium-sequestering vesicles and contractile flagellar roots.
abstract: The intracellular localization of calcium during contraction of striated flagellar roots of the green alga Tetraselmis subcordiformis was investigated using calcium pyroantimonate and calcium oxalate cytochemistry and energy-dispersive X-ray microanalysis. Vesicles (0.25 - 0.50 microns diameter) located in the anterior-most region of the cell are calcium-sequestering organelles. These vesicles exhibit a consistent and reproducible localization of electron-opaque pyroantimonate and oxalate salts of calcium. Striated contractile flagellar roots (CFR) show a periodic pattern of calcium antimonate (Ca-Sb) deposits following 'calcium shock' stimulation of contraction of this organelle. When CFRs are in a fully extended state they do not show Ca-Sb deposits. Deposits of Ca-Sb precipitate are present throughout the cytosol when CFRs are stimulated to contract. The implications of these findings with respect to the regulation of intracellular levels of 'free' Ca2+ and to the mechanism of CFR contraction are discussed.
mesh_terms: D002118:Calcium / Q000032:analysis*; D000460:Chlorophyta / Q000032:analysis / Q000648:ultrastructure*; D004577:Electron Probe Microanalysis; D005407:Flagella / Q000032:analysis / Q000502:physiology / Q000648:ultrastructure*; D008854:Microscopy, Electron
chemical_list: D002118:Calcium