An in situ Freeze-Fracture Study of Spiroplasma citri and the Corn Stunt Spiroplasma

Spiroplasma citri and the corn stunt spiroplasma in sieve cells of Catharanthus roseus were investigated using freeze -fracture electron microscopy. Only the particle studded fracture faces of the plasmalemma could be exposed and not the surfaces of both the extraplasmatic and the plasmatic leaflet. The extraplasmatic fracture face (EF) shows a lower particle density than the plasmatic fracture face (PF). On the PF particle free areas could be observed, which are helically arranged in helical filaments. We suppose that the cytoplasmic fibrils, probably involved in motility processes and in maintaining the helical shape, underly the particle free area only.