Comparative ultrastructure of a filamentous mutant and the wild type ofAgmenellum quadruplicatum

Abstract

A filamentous variant of the marine coccoid cyanophycean alga,Agmenellum quadruplicatum has been produced after treatment of cells with the chemical mutagen, N-methyl-N′-nitro-N-nitrosoguanidine (NTG). The mutation to the filamentous condition is stable and has been compared ultrastructurally with the unicellular wild type. The structural basis for the maintenance of the filamentous state is due to a failure of the homogeneously-structured transverse wall to differentiate into the stratified longitudinal wall. A manifestation of this condition is the continued synthesis of the investment membrane resulting in proliferations at each constriction. The wild type cells are nearly spherical while the filamentous mutant cells are smaller and elongate. An analysis of the structure and morphology of the nucleoplasmic regions is presented for both strains and a correlation between the morphology of these regions and the unicellular and filamentous conditions is made.