THE BASAL APPARATUS OF THE QUADRIFLAGELLATE SPERMATOZOPSIS-EXSULTANS (CHLOROPHYCEAE) - NUMBERING OF BASAL BODY TRIPLETS REVEALS TRIPLET INDIVIDUALITY AND DEVELOPMENTAL MODIFICATIONS

Though there are no detectable structural differences between each of the axonemal doublets of Spermatozopsis exsultans Korshikov, basal body triplets do show structural peculiarities: one triplet consistently has an electron-dense patch appressed to its proximal part. This triplet is labeled No. 1, and all triplets are numbered in accordance to the numbering system used for other flagellate green algae. We present a detailed analysis of the basal apparatus (basal bodies and attached cytoskeletal elements) of S. exsultans and describe how basal apparatus elements are attached, very specifically, to particular basal body triplets. The analysis includes immunogold detection of centrin-containing structures and characterization of their sites of attachment to basal bodies. The sequence of basal body development in S. exsultans is deduced from what we know of other green algae. With this, we describe how the cytoskeletal structures associated with the separate basal bodies, particularly those attached to the right side of a basal body, undergo apparent morphological modifications from cell generation to generation. The data indicate that basal body triplets are truly different from one another and that this subsequent basal body asymmetry, combined with the developmental differences between basal bodies themselves, presumably accounts for the heterogeneity in the basal apparatus and any asymmetry in the cell as a whole.