Freeze-fracture study of ordered arrays of particles in the plasma membrane ofChlamydobotrys stellata Korsch. (Volvocales)

Summary Ultrarapid cyrofixation procedures revealed the existence of ordered arrays of intramembrane particles on E fracture faces and corresponding ordered imprints on P faces in freeze-fractured plasma membrane of the green algaeChlamydobotrys stellata (Korschikoff). The structure of these arrays is very sensitive to cryofixation conditions and particularly to glutaraldehyde prefixation which leads to the formation of amorphous two-dimensional aggregates. The size of the individual ordered arrays and the ratio of ordered to total surface of the membrane increase with growth temperature from 15°C to 30°C with a corresponding decrease in cell generation time. Above 30°C the size of the individual ordered arrays decreases. At high, but sublethal temperature (above 37°C) the ordered arrays become smaller. In addition to the predominant two-dimensional oblique organization (a=12.0nm, b=12.6nm, =80°), square and tetragonal arrangements are also present. The cell wall is composed of many layers, one of which displays a zipper-like structure composed of periodic ridges 25 nm distant, sandwiched between two more or less fibrillar layers. The appearance and changes of the organization of ordered arrays are discussed in relation to their eventual physiological role during the life cycle of the cells and in particular to the formation of the cell wall and the median periodic leaflet.Dedicated to our late colleague and friend Dr.Yvonne Henry.