LIGHT AND ELECTRON-MICROSCOPIC CHARACTERIZATION OF 2 TYPES OF PYRENOIDS IN GONIUM (GONIACEAE, CHLOROPHYTA)

The single, basal pyrenoids of Gonium quadratum Pringsheim ex Nozaki a nd G. pectorale Muller (Goniaceae, Chlorophyta) differed in appearance when vegetative colonies were cultured photoheterotrophically in medi um containing sodium acetate. Chloroplasts of G. quadratum had distinc t pyrenoids when grown in medium without major carbon compounds. Howev er, the pyrenoids degenerated and were markedly reduced in size when s uch cells were inoculated into a medium containing 400 mg.L-1 of sodiu m acetate. No pyrenoids were visible under the light microscope; howev er, with electron microscopy small pyrenoids and electron-dense bodies were visible within the degenerating chloroplasts, which had only sin gle layers of thylakoid lamellae at the periphery. The chloroplasts su bsequently developed distinct pyrenoids and several layers of thylakoi d lamellae as the culture aged. In contrast, vegetative cells of G. pe ctorale always showed distinct pyrenoids when cells were inoculated in to medium containing sodium acetate, sodium pyruvic acid, sodium lacta te, and/or yeast extract. Therefore, we propose two terms, ''unstable pyrenoids'' and ''stable pyrenoids, '' for pyrenoids of G. quadratum a nd G. pectorale, respectively. Chloroplasts of the colonial green flag ellates should thus be examined under various culture conditions in or der to determine whether their pyrenoids are unstable or stable when p yrenoids are used as taxonomic indicators. Immunogold electron microsc opy showed that the ratios of gold particle density of ribulose-1,5-bi phosphate carboxylase/oxygenase (RuBisCO) between pyrenoid matrix and chloroplast stroma in G. quadratum grown in medium with or without sod ium acetate were lower than those of G. pectorale. Heavy labeling by a nti-RuBisCO was observed in both the electron-dense bodies and pyrenoi d matrix of G. quadratum. This is the first electron microscopic demon stration of degeneration and development of both pyrenoids and thylako id lamallae in the chloroplast as a function of culture condition in g reen algae.