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 bod y triplets do show structural peculiarities: one triplet consistently has an electron-dense patch appressed to its proximal part. This tripl et is labeled No. 1, and all triplets are numbered in accordance to th e numbering system used for other flagellate green algae. We present a detailed analysis of the basal apparatus (basal bodies and attached c ytoskeletal elements) of S. exsultans and describe how basal apparatus elements are attached, very specifically, to particular basal body tr iplets. The analysis includes immunogold detection of centrin-containi ng structures and characterization of their sites of attachment to bas al bodies. The sequence of basal body development in S. exsultans is d educed from what we know of other green algae. With this, we describe how the cytoskeletal structures associated with the separate basal bod ies, particularly those attached to the right side of a basal body, un dergo apparent morphological modifications from cell generation to gen eration. The data indicate that basal body triplets are truly differen t from one another and that this subsequent basal body asymmetry, comb ined with the developmental differences between basal bodies themselve s, presumably accounts for the heterogeneity in the basal apparatus an d any asymmetry in the cell as a whole.