Protein bodies, lipid layers and amyloplasts in freeze-etched pea cotyledons.

Freeze-etching and thin-sectioning techniques have been used to study the structure of storage parenchyma cells of pea cotyledons in mature, air-dry seeds and in seeds after various periods of imbibition. Protein bodies in air-dry tissue were coated with a complex of convoluted structure, apparently rich in lipid. After brief periods of hydration this complex appeared to have expanded and to consist of a system of tubules, and after 24 h imbibition it was no longer associated with the protein bodies. Sheets of lipid bodies were associated with amyloplast surfaces and the plasmalemma. In non-imbibed tissue, the cell walls were wavy, but in imbibed tissue they were smooth. The amyloplast-envelope membranes characteristically had areas with parallel folds, and membrane particles of protein-body envelopes were occasionally aligned in orderly rows.