Microtubule arrays in higher plants during meiosis and mitosis

A monoclonal antibody was raised against purified pear tubulin. This antibody was used to trace microtubule (MT) structures by indirect immunofluorescence in: mitotically dividing root tip cells of the dicot, Lycopersicon esculentum, and the monocot, Ornithogalum virens; primary and secondary microsporocytes of L. esculentum and O. virens; cells from suspension cultures of the monocot, Spartina pectinata.; Root tip cells showed stage-specific MT patterns typical of higher plant cells. These included parallel cortical interphase arrays, preprophase band (PPB) MTs in late interphase through prophase, barrel-shaped spindles, and finally phragmoplasts. Pollen mother cell divisions exhibited randomly oriented cortical MT arrays in prophase I, pointed spindles during karyokinesis, and elongate phragmoplasts. MT initiation sites were seen as broad zones associated with the nuclear envelope. A PPB was not observed in either meiotic division. The elongate phragmoplast (O. virens) or phragmoplast-like structure (L. esculentum) seen during interkinesis may serve to maintain internuclear distance and/or orient nuclei for the ensuing second meiotic division. Electron microscopy of this structure in L. esculentum revealed that MTs radiate from the nuclear envelope predominantly toward sister nuclei. Between nuclei a zone of MT overlap was observed where MTs, presumably from opposite halves of the cell, interdigitate and end in an amorphous, electron dense material.; Continuous suspension cultures of the marsh grass Spartina pectinata grow as either unorganized colonies or files of cells. Immunofluorescence of tubulin revealed that MT structures include parallel cortical arrays during interphase, cortical MT bands in some interphase cells and all prophase cells, broad barrel-shaped spindles in metaphase/anaphase, and phragmoplasts during telophase. The cortical MT bands seen in prophase and interphase were judged to be PPBs on the basis of their temporal appearance in the cell cycle and their position and orientation relative to division planes. Although PPBs are widely thought to be associated with organized tissues and polarized divisions, there are reports of PPBs in suspension cultures of four dicot species. This is the first report of a PPB in suspension cultures of a monocot species.