Ultrastructural aspects of phytoglycogen from cryo-transmission electron microscopy and quasi-elastic light scattering data

Phytoglycogen particles extracted from the sugary maize mutant su l and dis persed in water were studied using transmission electron microscopy (TEM) a nd light scattering. Dried specimens were either negatively stained with ur anyl acetate or shadowed with W/Ta. Frozen-hydrated unstained particles emb edded in a thin film of vitreous ice were also observed using cryo-TEM. The particles exhibited a spheroidal shape, with a diameter ranging from 30 to 100 nm. Some of them presented a multilobular morphology and appeared to b e formed by smaller subunits, 20-30 nm in diameter, resembling the describe d beta-particles for animal glycogen. The diameter of stained and ice-embed ded particles was measured from electron micrographs. The corresponding siz e distribution histograms showed that the average weight diameter of ice-em bedded particles was higher than that of stained ones. In the latter case, a shrinkage of the particle was believed to occur during the drying process . Light scattering experiments confirmed the diameter of ice-embedded parti cles and indicated that they could be considered as uniformly dense spheroi dal objects. (C) 1999 Elsevier Science B.V. All rights reserved.