CYTOSKELETAL DYNAMICS OF APEDINELLA-RADIANS (PEDINELLOPHYCEAE) .1. PRE-DIVISION DEVELOPMENT AND THE FORMATION OF SPINE-SCALES AND BODY SCALES

Specific events preceding cell division in the unicellular phytoflagel late Apedinella radians (Pedinellophyceae) were investigated ultrastru cturally and by immunofluorescence microscopy. These events include th e sequential formation and secretion of a duplicate set of elongate sp ine-scales, the duplication and development of basal bodies/flagella, the generation of two new dictyosomes at the future sites of spindle p oles, and the constriction (not division) of chloroplasts. Actin and m icrotubules are involved in spine-scale formation, while actin alone a ppears to play a role during body scale formation. Both scale types ar e formed intracellularly within specialized vesicles located adjacent to the posterior cell membrane. The length of spine-scales is not limi ted by cell size, as they form within cell extensions. Following secre tion, spine-scales remain attached below the equator of the cell, and are not deployed to their interphase positions until after the complet ion of cell division.