Endoplasmic reticulum-dictyosome interconnections in ligula cells of Isoetes lacustris.

The sub-marginal ligula cels of the water fern, Isoetes lacustris, were investigated with the electron microscope. Their most conspicuous ultrastructural elements, a well developed tubular ER and a cisternal rER, as well as numerous active dictyosomes, indicate a high activity of protein synthesis and intracellular transport. Several dictyosomes show interassociations and partly direct interconnections with each other and with the tubular ER, the latter occurring at the fenestrated regions of the Golgi cisternae. These details, demonstrated by sections parallel and perpendicular to the cisternal planes of the dictyosomes, point to the existence of a functionally homogeneous endomembrane system. The results are discussed with regard to the question whether the endomembrane concept (Morré and Mollenhauer [32]) be of general validity, or whether it needs to be restricted to the intracellular transport of secretion proteins.