Observations on the exocytosis of secretory vesicles and their products in coleoptiles of Avena

Abstract

It is shown that in the cytoplasm of the fast growing cells of Avena coleoptiles, large sacs filled with vesicles are formed. The membranes of these sacs seem to have Golgi nature because they can fuse with the plasmalemma to form anastomoses with the space outside the plasmalemma. When subsequently the boundary membrane of the sacs flattens out and becomes continuous with the plasmalemma, the contents of the sacs come to lie outside the plasmalemma so as to form part of the outer cell wall. The sacs contain at least two types of vesicles, a majority which lose their membranes and furnish the mucopolysaccharide matrix of the wall, and numerous other vesicles which stay membrane-bounded and are incorporated into the structureless, electron transparent matrix, and which may even persist in the older portions of the wall. It is thought that this latter type of vesicle represents lysosomes. This multivesicular mode of exocytosis differs from the modes described so far in which only single, individual vesicles play a part.