Cytokinesis and nodal anatomy in the charophycean green algaChara zeylanica

Summary Cell plate formation inChara zeylanica was compared with recent models of cytokinesis in higher plants in order to gain insight into the evolutionary origin of plant cytokinetic processes. Transmission electron microscopy (TEM) reveals that while cytokinesis inC. zeylanica bears many features in common with that in higher plants, there are significant differences. Unlike that in higher plants, cytokinesis inC. zeylanica begins with a congregation of smooth membrane tubules that are closely associated with endoplasmic reticulum (ER) and Golgi membranes. Mitochondria and other organelles excluded by the phragmoplast in higher plants are present as well. Unlike in higher plants, phragmoplast microtubules persist throughout cytokinesis inC. zeylanica, and the cell plate generally forms across the whole cell at once, though development is patchy, due to small regions developing at different rates; the ends of the plate form last. By identifying aspects of cytokinesis that are different inC. zeylanica and plants, our study indicates which cytokinetic features are more likely to be derived, and which are more likely to be ancestral. In addition, we demonstrated that all nodal cells ofC. zeylanica are interconnected via plasmodesmata, lending support to the idea that, whileChara spp. are generally considered to be filamentous organisms, nodal regions may be thought of as meristemlike tissues.Abbreviations HPF high-pressure freezing - KFe potassium ferricyanide - SCF stepwise chemical fixation - TEM transmission electron microscopy