Elucidation of fertilization and development in a red alga by quantitative DNA microspectrofluorometry.

Crucial nuclear events throughout the life histories of red algae have eluded researchers. Use of the DNA fluorochrome 4',6-diamidino-2-phenylindole (DAPI) and microspectrofluorometry has now resolved the problems. In the parasitic red alga Choreocolax polysiphoniae (= Leachiella pacifica), the amounts of nuclear DNA during the processes of meiosis and fertilization are documented as well as the transfer of the newly formed zygote nucleus to the adjacent accessory cell. In this organism, the G2 period predominates in the cell cycle of vegatative and reproductive cells; many nondividing vegetative cells become highly polyploid. The results indicate that the use of various fluorochromes combined with microspectrofluorometric measurements of individual nuclei is valuable for study of many developmental problems in lower eukaryotes where the relatively small nuclear DNA content has made study with conventional dyes impossible.