The Relationships between the Dictyosomes and the Forms of Endoplasmic Reticulum in Plant Cells with Different Export Programs

The relationship between dictyosomes and the endoplasmic reticulum (ER) in a variety of plant tissues was investigated by conventional and high-voltage electron microscopy. The zinc iodide/osmium tetroxide (Z10) technique was used to stain selectively the ER and cisternal membranes. No connections were observed between either the dictyosomes and the cisternal or tubular forms of the ER in the carbohydrate-secreting cells of maize root caps, bean leaf palisade tissue, and elongating bean roots. On the other hand, in the protein-secreting gland cells of Dionaea muscipula, connections between the tubular ER and dictyosome cisternae were observed across the cisternal stack. Connections between the ER and the plasmalemma of these gland cells are also reported. The results are discussed in light of recent evidence on the endomembrane concept of plant cells.