Fine Structure of the Membranes and Organelles in Parenchyma Cells of Poplar Shoot Observed by Freeze Etching Technique

Abstract

The cross- and surface-fractured membranes and organelles such as plasma-lemma, tonoplast, endoplasmic reticulum, Golgi bodies, mitochondria, plastids and nucleus were investigated by freeze etching technique. Particles, about 110 A in diameter, were found on both convex and concave planes of almost all the membranes and organelles. A great number of the particles were found on the convex plane of plasmalemma, while they were much less numerous on the concave plane. On the convex plane of tonoplast, and the membranes of endoplasmic reticulum and Golgi bodies, however, much less numerous particles were found than those on the concave plane. In mitochondria, plastids and nucleus which are known to have .a double membrane, particles on the convex plane of outer membrane were much less numerous than those on the convex plane of inner membrane. On the other hand, the particles on the concave plane of outer nuclear membrane were numerous than those on the concave plane of inner nuclear membrane. Similar particles as observed on the membrane surfaces were found on the fractured plane of cytoplasm, on the cross-fractured starch grain, and on the cross-fractured nuclei and nucleoli. Because of general occurrence of the particles on almost all the membranes and organelles, it is unreliable that plasmalemma particles may be involved in the synthesis and orientation of cellulose microfibrils of poplar parenchyma cells.