Low and high voltage electron microscopy of mitosis and cytokinesis in maize roots

Abstract

The structure and distribution of cytoplasmic membranes during mitosis and cytokinesis in maize root tip meristematic cells was investigated by low and high voltage electron microscopy. The electron opacity of the nuclear envelope and endoplasmic reticulum (ER) was enhanced by staining the tissue in a mixture of zinc iodide and osmium tetroxide. Thin sections show the nuclear envelope to disassemble at prophase and become indistinguishable from the surrounding ER and polar aggregations of ER. In thick sections under the high voltage electron microscope the spindle is seen to be surrounded by a mass of tubular (TER) and cisternal (CER) endoplasmic reticulum derived from both the nuclear envelope and ER, which persists through metaphase and anaphase. At anaphase strands of TER traverse the spindle between the arms of the chromosomes. The octagonal nuclear pore complexes disappear by metaphase, but irregular-shaped pores persist in the membranes during mitosis. It is suggested that these form a template for pore-complex reformation during telophase. Phragmoplast formation is preceded by an aggregation of TER across the spindle at anaphase. Evidence is presented to suggest that the formation of the desmotubule of a plasmodesma is by the squeezing of a strand of endoplasmic reticulum between the vesicles of the cell plate.

Actin-dependent vacuolar occupancy of the cell determines auxin-induced growth repression

“…Arabidopsis seedlings roots were cut off and submerged in fixative (1% paraformaldehyde, 1% glutaraldehyde, 2% sucrose, and 2 mM CaCl in 0.1 M NaCac buffer) for 1 h at room temperature, processed using the zinc iodide osmium impregnation technique, and embedded in Spurr resin (44). Root tips then were mounted onto 3View stubs (Gatan) with conductive epoxy (Chemtronics) and were hardened for 4 h at 100°C.…”

The Establishment of the Plastid Thylakoid System

“…The chemistry of the ZIO staining reaction in plant cells is not yet fully understood (Hawes, 1981;Hawes, Juniper and Horne, 1981). However, for animal tissue it has been suggested that the electron opaque deposits between membranes are of zinc osmate and represent membrane sites with a high affinity for Ca'"+.…”

Putting the Squeeze on Plasmodesmata: A Role for Reticulons in Primary Plasmodesmata Formation

“…Primary PD form at cytokinesis during the assembly of the cell plate (Hawes et al, 1981;Hepler, 1982). Of the numerous studies devoted to the structure of the cell plate, very few have examined the behavior of the ER during cytokinesis.…”

“…During mitosis, elements of the ER are located in the spindle apparatus, separated from the cytoplasm (Hepler, 1980). Just prior to cytokinesis, there is a relative paucity of ER in the region destined to become the cell plate (Hepler, 1980;Hawes et al, 1981). The studies of Hawes et al (1981) and Hepler (1982), exploiting heavy-metal impregnation of the ER, showed that during the formation of the new cell plate, strands of cortical ER are inserted across the developing wall, between the Golgi-derived vesicles that deposit wall materials.…”

“…Just prior to cytokinesis, there is a relative paucity of ER in the region destined to become the cell plate (Hepler, 1980;Hawes et al, 1981). The studies of Hawes et al (1981) and Hepler (1982), exploiting heavy-metal impregnation of the ER, showed that during the formation of the new cell plate, strands of cortical ER are inserted across the developing wall, between the Golgi-derived vesicles that deposit wall materials. These ER strands become increasingly thinner during formation of the desmotubule, eventually excluding heavy metal stains from the ER lumen (Hepler, 1982).…”