Ultrastructure of cell division in Cladophora. Pregametangial cell division in the haploid generation of Cladophora flexuosa

Abstract

Cell division preceding gamete formation in the haploid generation of Cladophora flexuosa was studied with the electron microscope. Numerous, asynchronous mitotic nuclear divisions are concurrent with the progressive cleavage of the cytoplasm by invaginations of a central and peripheral vacuolar system. The spindle is enclosed by the nuclear envelope during all stages of mitosis and is associated with polar centriole pairs. The cytokinetic process is not associated with microtubules and is basically similar to that observed in other macroscopic, multinucleate green algae. Unusual mitochondria, characterized by specialized double-membrane-enclosed, presumptive DNA regions, were found during the later stages of reproductive differentiation. It is emphasized that the different types of cell divisions which can occur in plants possessing a haplodiplontic type of life history should all be thoroughly examined before the establishment of a particular mitotic sequence for any given species.