Formation of division spindles in higher plant meiosis

Abstract

Depolymerisation of the MT cytoskeleton during late prophase makes it impossible to follow the cytoskeleton cycle in centrosomeless plant meiocytes. This paper describes rearrangements of the MT cytoskeleton during plant meiotic spindle formation in normally dividing pollen mother cells in various higher plant species and forms in which the cytoskeleton does not depolymerise at prophase. In such variants of the wild-type, cytoskeleton rearrangements can be observed at late prophase/early prometaphase. Radial MT bundles coalesce in the meridian plane, reorientate tangentially, curve and give rise to a developed ring-shaped perinuclear cytoskeleton system at the meridian. During nuclear envelope breakdown this ring disintegrates and splits into a set of free MT bundles. Three sub-stages of prometaphase are indicated: early prometaphase (disintegration of perinuclear ring and invasion of MTs into the former nuclear area), middle prometaphase or chaotic stage (formation of bipolar spindle fibres), and late prometaphase (formation of bipolar spindle). Analysis of a range of abnormal phenotypes (disintegrated, multiple, polyarchal, chaotic spindles) reveals two previously unknown processes during late prometaphase: axial orientation and consolidation of the spindle fibres.

Meiotic behavior of wild Caricaceae species potentially suitable for papaya improvement

“…1I). Both anomalies were reported in Caricaceae species including V. goudotiana (Caetano et al 2008) and other species such as maize and intergeneric hybrids of cereals (Shamina 2005).…”

Haploid Independent Unreductional Meiosis in Hexaploid Wheat

“…Also the microtubule dynamics follows the typical Triticeae meiotic pattern (Shamina, 2005, Cai et al, 2010. During the first meiotic division prophase a perinuclear ring is formed, from which microtubules emanate into the nuclear area with progression of prophase (Figure 1 a).…”

Deformation of nuclei and abnormal spindles assembly in the second male meiosis of polyploid tobacco plants

“…The perinuclear MT band, observed in several cases in the late prophases of both the first and second meiotic divisions in dicot and monocot plants is likely to be the most controversial structure in the cytoskeleton dynamics during plant meiosis (Conicella et al, 2003;Shamina, 2005a). The functional role of this cytoskeletal structure is vague.…”

“…Among them are the disintegration of the previous cytoskeletal structure, MT elongation, projection of cytoskeleton into the former nuclear region, and straightening of the MTs previously forming the perinuclear band (Shamina, 2005a). An aberration of any of these events in the early prometaphase may lead to an abnormality in the spindle assembly (Shamina, 2005b).…”

“…Unlike the somatic cells, MMCs lack any cortical spirals and PPB while the spindle there is assembled without any intermediate structures via utilization of the MT arrays of the previous system or polymerization of new arrays (Traas et al, 1989;Chan and Cande, 1998;Franklin and Cande, 1999). However, a cytoskeletal structure specific of MMCs, namely, the prophase perinuclear MT band, which is assumed to be an intermediate for the spindle (Conicella et al, 2003;Shamina, 2005a).…”