Regular arrays of intramembranous particles in the plasmalemma of guard cell and mesophyll cell protoplasts of Vicia faba

Abstract

Freeze fractures of the plasmalemma membranes of guard-cell and mesophyll protoplasts of Vicia faba demonstrate that the inner monolayer of the plasmalemma is compartmentalized into areas with distinct, highly organized structures. Between areas of intramembranous particles dispersed randomly on a relatively smooth fracture face, membrane domains showing an extremely regular planar, hexagonal array of particles are interspersed. The dimensions of these hexagonal lattices are about 0.5 μm in diameter, the center-to-center spacing is about 22 nm, and the particle size is about 9 nm. The particle in the hexagonal arrays are accompanied by complementary pits in the opposite monolayer fracture of the plasmalemma membrane. The freeze-fracture preparation was performed by using an improved Leybold Bioetch device which provides a sufficiently high cooling rate and allows the omission of cryoprotectants, like glycerol.