Structural Characteristics of a Photosynthetic Mutant of Euglena gracilis Blocked in Photosystem II

The techniques of thin sectioning and freeze etching were employed in comparing the chloroplast structure of the wild type and photosynthetic mutant P₄ 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.