Fine-structural studies on three species of red algae with special emphasis on aspects of sporogenesis, spores and sporeling development

1. The introductory experiments revealed that the suitable light intensity for growth in culture of tetraspores of Palmaria palmata was 3000 lux and the paraspores of Plumaria elegans was 1000 lux. Palmaria palmata tetrasporelings attained the length of 6.7 cm at 3000 lux after twenty-one months in culture while Plumaria elegans parasporelings attained the length of 2 cm at 1000 lux after seventeen months in culture. 2. The ultrastructure of vegetative cells of the three species (Palmaria palmata, Plumaria elegans and Audouinella sagraeanum) shows (a) Presence of unusual structures within the cell walls of Audouinella sagraeanum and the cell walls of the stipes of Palmaria palmata. The cell walls of the three species are composed of microfibrils of probably random arrangement embedded in an amorphous matrix and are covered by a cuticle though it is not always clear in Audouinella sagraeanum. (b) Floridean starch lies free in the cytoplasm but small grains of similar electron density to floridean starch grains were observed within chloroplasts of Audouinella sagraeanum. (c) Each cell of the three species possesses several chloroplasts. The thylakoid arrangement within the chloroplasts of Plumaria elegans and the small chloroplasts of Audouinella sagraeanum is represented by a peripheral thylakoid enclosing several internal thylakoids, though juxtaposition of two to three thylakoids was observed in some chloroplasts within the parasporangia of Plumaria elegans and appressed thylakoids in groups of four and six were observed within a chloroplast of a newly released paraspore. The thylakoid arrangement in chloroplasts of Palmaria palmata is represented by a peripheral thylakoid enclosing one or more concentric thylakoids and several internal thylakoids. Each cell of Audouinella sagraeanum possesses a single large chloroplast in addition to several small chloroplasts. The large chloroplast has no peripheral thylakoid but a single pyrenoid (two pyrenoids on rare occasions) is present which may protrude towards the cytoplasm or be embedded within the stroma. The pyrenoid is enclosed by thylakoids which may penetrate into the matrix. Tubular structures were also observed within the matrix of some pyrenoids. There is no spatial relationship between the starch grains and the pyrenoid. (d) Pit connections of the three species are composed of a plug core and plug caps. The plug cap of Plumaria elegans and Audouinella sagraeanum is a single layer while in Palmaria palmata it is multilayered. Pit connections are also observed between immature paraspores within the parasporangium and immature tetraspores within the tetrasporangium of Plumaria elegans. (e) Mitochondria accompanied by Golgi bodies are scattered at different locations within the cytoplasm of the three species. (f) Spherical osmiophilic and crystalline bodies are present in the cytoplasm of Plumaria elegans only, and are also found in parasporeling cells growing in culture. (g) The protoplasts of the ageing cells of Audouinella sagraeanum degenerate but a new cell replaces them. The new formed cell is surrounded by two cell walls. (Abstract shortened by ProQuest.)