Periplast development in Cryptophyceae III. Development of crystalline surface plates inFalcomonas daucoides,Proteomonas sulcata [haplomorph], andKomma caudata

Summary In several cryptomonad genera the surface periplast component (SPC) is composed of discrete crystalline plates surrounded by structurally distinct borders. Freeze-etch images enable detailed investigation of surface microarchitecture in these cryptomonads, and reveal that the plates consist of precisely aligned arrays of minute subunits. The plate borders are composed of similar subunits which display marked variations in alignment. Differences in the arrangement of subunits within the plates and borders appear closely linked to the organization of the underlying plasma membrane (PM) and inner periplast component (IPC). Development of the crystalline surface plates occurs within specialized anamorphic zones located along the mid-ventral line and around the vestibular margins of cells. Examination of variations in surface microarchitecture within anamorphic zones suggests that the crystalline plates form directly on the cell surface. Development of the surface plates results from the accumulation and self-assembly of subunits, while orderly addition of subunits to plate edges facilitates subsequent growth and enlargement. The close structural relationship between the SPC, PM, and IPC in these cryptomonads suggests that self-assembly of the surface plates may be mediated by developmental changes in the underlying PM and IPC.