Cellular localization of calcium oxalate crystals in Chaetomorpha coliformis (Cladophorales; Chlorophyta): evidence of vacuolar differentiation

Living cells of field-collected specimens of the giant-celled marine green alga Chaetomorpha coliformis (Montagne) Kutzing were found to have birefringent cellular inclusions whose composition was determined to be calcium oxalate on the basis of their reactions to diagnostic chemical solubility tests and the Yasue cytochemical staining procedure. The inclusions consisted of individual bipyramidal crystals up to 50 mu m in greatest dimension and variously sized aggregates of much smaller crystals. Some aggregates consisted of rosettes or spheres of radiating elements that resemble embryophyte druses more than any other calcium oxalate deposit yet reported in the algae. Both single crystals and aggregates occurred in the same cells with no discernible pattern to their distributions. The calcium oxalate crystals were anchored on the vacuolar face of the thin cytoplasmic layer rather than being dispersed within the voluminous central vacuole. Light and transmission electron microscopy demonstrated the presence of a nearly continuous layer of small vacuoles between the organelle-rich parietal cytoplasm and the large central vacuole, and the calcium oxalate crystals were associated with this layer of vacuoles. The occurrence of mineralization in the parietal vacuoles, but not the large central vacuole, indicates that differentiation of vacuoles according to ionic contents may be occurring.