AN ULTRASTRUCTURAL-STUDY OF CELL-DIVISION IN THE CORALLINE RED ALGA BOSSIELLA-ORBIGNIANA

This investigation of Bossiella orbigniana (Decaisne) Silva ssp. orbigniana represents the first ultrastructural account of cell division in the order Corallinales. The mitotic process in this alga is differentiated from that of other red algae by a combination of characters. During prometaphase - metaphase the division poles contain unusual membrane arrangements including quantities of smooth-surfaced membranes and elongate extensions of perinuclear rough ER. At anaphase extensive remnants of nucleolar material attach to the chromosomes, trailing them to the poles. After telophase, the distal nucleus continues to move toward the apex resulting in much greater nuclear segregation than accomplished by anaphase alone. Cytokinesis is temporally displaced from mitosis and displaced distally from the metaphase plate. A reevaluation of ultrastructural patterns of red algal cell division suggests that there are two basic types of mitosis, the polar gap type and the polar fenestrations type to which B. orbigniana belongs. These two types are differentiated by a number of characters with the most important being the configuration of the prometaphase-metaphase polar region and spindle origin.