Disappearance of Chloroplast Nucleoids during Male Gamete Formation in Bryopsis plumosa (Hudson) C. Ag. (Chlorophyceae)

Abstract

Changes in chloroplast nucleoids accompanying chloroplast degeneration during male gamete formation in the coenocytic green alga, Bryopsis plumosa, was observed by fluorescence microscopy using the DNA-specific fluorochrome 4',6-diamidino-2-phenylindole (DAPI). The fusiform chloroplasts of vegetative cells always included numerous nucleoids, which seemed to be scattered at random throughout the chloroplast except in the pyrenoid. When gamete formation was initiated, all chloroplasts in the male gametangia turned yellowish green. At this stage, each chloroplast assumed a moniliform shape after constriction at several sites and contained many nucleoids. Subsequently, the chloroplast divided into smaller segments, each of which was then apportioned to a young male gamete. The internal structure of the chloroplast degenerated considerably with time. Nucleoids could not be discerned with DAPI staining in chloroplasts of either young or mature male gametes, but occasionally fluorescent areas could be seen within the cytoplasm of the gametes. In contrast, many nucleoids were always observed in the female gamete chloroplast. This study indicates that chloroplast nucleoids disappear during an early stage of male gamete formation. However, chloroplast DNA may be retained at a level beyond the resolution of the detection method.