The appearance of several malate synthase‐containing cell structures during the stage of glyoxysome biosynthesis

There is now compelling evidence that malate synthase is a membrane-bound, peripheral enzyme of glyoxysomes [l-3]. This enzyme together with two other peripheral and two matrix proteins provides the catalytic basis for the function of the glyoxylate cycle during the germination of plant seedlings. Findings such as the demonstration of morphological continuity between the endoplasmic reticulum and glyoxysome [4], the similarities in the phospholipid composition of their membranes [S], the phospholipid flow in vitro from endoplasmic reticulum to glyoxysomes [6] indicate that glyoxysome biosynthesis may take place by segmenting vesicles from the dilated cisternae of endoplasmic reticulum. Similarity in peptide pattern of microsomal and glyoxysomal membranes [7,8] also favours this model. Hence, a developmental stage characterized by the appearance of vesicles or a form of endoplasmic reticulum which contains malate synthase may be thought to precede glyoxysome formation. Here we provide evidence that, in the phase of glyoxysome biosynthesis, malate synthase is also associated with structures distinguishable from endoplasmic reticulum or glyoxysomal membranes.