Behavior of nuclei during zoosporogenesis in Bryopsis plumosa (Bryopsidales, Chlorophyta).

The behavior of nuclei during zoosporogenesis in Bryopsis plumosa (Bryopsidales, Chlorophyta) was examined by fluorescence and electron microscopy. Each mature filamentous sporophyte had a single lenticular nucleus, which was about 25 microm in diameter and embedded in a thick cytoplasmic layer. At the commencement of multinucleation, giant nuclei with large vacuolated nucleoli, giant nuclei containing chromosomes, and dumbbell-shaped nuclei were observed. Sometimes, two small nuclei also appeared in the thick cytoplasm where the giant nucleus had presumably been present. Electron microscopy revealed the existence of ribbon-like structures resembling synaptonemal complexes within the nucleus having a large vacuolated nucleolus. Nuclei extended their distribution by repetitive divisions. A pair of centrioles was adjacent to the interphase nucleus. When the nuclei were distributed throughout the cell, they became localized nearly equidistantly from one another, each being surrounded by several chloroplasts. At this stage, many centrioles lay along the nuclear surface. The bulk of cytoplasm was then divided into many masses of protoplasm, each of which developed into a uninucleate, stephanokontic zoospore with a whorl of flagella.