Abstract
The techniques of thin sectioning and freeze etching were employed in comparing the chloroplast structure of the wild type and photosynthetic mutant P(4) of Euglena gracilis, Z strain. The mutant chloroplasts were characterized by a lack of thylakoid pairing even under high salt conditions. In addition the mutant thylakoids were more varied in size and fewer in number than those of the wild type. No differences between the mutant and wild type were observed in the size and distribution of the particles within the chloroplast membranes seen by the freeze-etching technique.These structural abnormalities do not appear to be correlated per se with the absence of plastoquinone A in the mutant but may be related to a different lipid composition observed in the mutant.