CYTOKINESIS AND NODAL ANATOMY IN THE CHAROPHYCEAN GREEN-ALGA CHARA-ZEYLANICA

Cell plate formation in Chara zeylanica was compared with recent model s of cytokinesis in higher plants in order to gain insight into the ev olutionary origin of plant cytokinetic processes. Transmission electro n microscopy (TEM) reveals that while cytokinesis in C. zeylanica bear s many features in common with that in higher plants, there are signif icant differences. Unlike that in higher plants, cytokinesis in C. zey lanica 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 hi gher plants are present as well. Unlike in higher plants, phragmoplast microtubules persist throughout cytokinesis in C, zeylanica, and the cell plate generally forms across the whole cell at once, though devel opment 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 in C. zeylanica and plants, our study indicates wh ich cytokinetic features are more likely to be derived, and which are more likely to be ancestral. In addition, we demonstrated that all nod al cells of C. zeylanica are interconnected via plasmodesmata, lending support to the idea that, while Chara spp. are generally considered t o be filamentous organisms, nodal regions may be thought of as meriste m-like tissues.