Associations between membranes and microtubules during mitosis and cytokinesis in caulonema tip cells of the mossFunaria hygrometrica

Summary The interphase nucleus in theFunaria caulonema tip cells is associated with many non-cortical microtubules (Mts). In prophase, the cortical Mts disappear in the nuclear region; in contrast to moss leaflets, a preprophase band of Mts is not formed in the caulonema. The Mts of the early spindle are associated with the fragments of the nuclear envelope. Remnants of the nucleolus remain in the form of granular bodies till interphase. The metaphase chromosomes have distinct kinetochores; the kinetochore Mts are intermingled with non-kinetochore Mts running closely along the chromatin. Each kinetochore is associated with an ER cisterna. ER cisternae also accompany the spindle fibers in metaphase and anaphase. In telophase, Golgi vesicles accumulate in the periphery of the developing cell plate where no Mts are found. The reorientation of the cell plate into an oblique position can be inhibited by colchicine. It is concluded that the ER participates in controlling the Mt system, perhaps via calcium ions (membrane-bound calcium ions have been visualized by staining with chlorotetracycline) but that, on the other hand, the Mt system also influences the distribution of the ER. The occurrence and function of the preprophase band of Mts is discussed.