Membrane Systems Associated with the Plasmalemma of Plant Cells

Vesicular and membranous structures associated with the plasmalemma in both higher and lower plants have been examined using different methods of fixation; this, together with an analysis of similar structures illustrated in other published results, has led to the conclusion that such formations are not artifacts. It is suggested that all membranous or vesicular structures associated with the plasmalemma are classified under the general term—paramural body—regardless of their origin. These paramural bodies are subdivided into two classes according to their derivation. Lomasomes are derived from cytoplasmic membranes, while plasmalemmasomes are formed entirely from the plasmalemma. Paramural bodies may in some cases be involved in wall synthesis, either as a transitory stage during the incorporation of wall precursors or as the site of incorporation of enzymes for extracellular syntheses. Analysis of cell membranes using a microdensitometer lends support to the postulated derivation of paramural body membranes, as also do observations on the apparent polarity of paramural body membranes compared with the polarity of the plasmalemma.