Electron Microscopy of Plastids of Monocilia viridis

Abstract

Abstract The Chloroplast structure of Monocilia viridis shows typical charac- teristics reported for algae and particularly the Xanthophyceae. Three thylakoids are often grouped forming lamellae, but the apposed mem- branes do not fuse; patterns involving more than three thylakoids do not occur. A gridle lamella, present in plastids of different alga groups and considered to be typical for the Xanthophyceae, was present; starch and distinctive pyrenoids could not be observed. The chloropoast envelope is also surrounded by the ER, which partly forms tubular periplastidal reticulum between the two encircling double membranes. Trans. Kans. Acad. Sci., 78 (3-4), 1975. Introduction The alga Monocilia viridis Gerneck forms freely branched filaments in culture. Monocilia normally occurs as Protococcus-like packets of globose or ellispsoidal cells. The cells contain a number of parietal discoid chloroplasts. It has been collected mainly from damp soil or tree bark. It presently is classified as a member of the Xanthophyceae sensu stricto (Hibberd and Leedale, 1970, 1972). The purpose of this paper is to give details of the chloroplast structure, thus contributing to the general information about this alga. Furthermore, the fine structure of M. viridis photosynthetic organelle is compared with that of Xanthophytes already published. Documentation of plastid ultrastructure is sparce, particularly with reference to the vegetative cell. Materials and Methods Monocilia viridis was isolated from samples collected in the vicinity of Lawrence, Kansas. Stock cultures were grown in Bold's Basal Medium (Bold, 1967), both liquid and agar. The cultures were maintained in a 12/12 light-dark regime at 22? C with illumination of approximately 1000 Ix. For electron microscopy, cells were fixed in 2% glutaraldehyde buffered with 0.2M phosphate buffer, pH 7.2, for 1 hour at room temperature. Cells were then rinsed three times with buffer for 30 minutes and postfixed with phosphate-buffered 1%