The Morphology and Dynamics of the ER

The endoplasmic reticulum (ER) is a non-uniform compartment in plants as regards its morphologyand function. It extends as a highly anastomosing membranous network throughout the cytoplasm, isthe major compartment of membrane biogenesis, and has been verified to function as the starting site forthe secretory pathway. Early electron microscopy studies revealed three morphological ER sub-domains: thesmooth ER, the rough ER, and the nuclear envelope. In the last two decades vital staining procedures, immunologicalmethods, and green fluorescent protein technology in connection with confocal laser scanning microscopyhave extended and augmented our knowledge regarding the morphology of the different ER domains, especiallythe three-dimensional transition between the cortical tubular network, long tubular strands, and lamellarsheets during interphase and mitosis. The cytoskeleton in connection with the respective motor proteinsand cations like Ca2+ and H+play a critical role in the regulation of ER organization in dividing, differentiating, and stressedcells. Although our understanding of ER morphology in plants has improved notably, our view still remainsfounded on a rather limited number of model cells.