ALPHA-TUBULIN AND F-ACTIN DISTRIBUTION DURING MICROSPOROGENESIS IN A 2N POLLEN PRODUCER OF SOLANUM

Spatial and temporal changes in configurations of microtubules (MTs) a nd microfilaments (MFs) were determined during microsporogenesis, usin g alpha-tubulin immunolocalization and rhodamine-phalloidin staining o f F-actin, in a 2n pollen producer of Solanum, to assess the anomalies in meiotic spindles and cytokinesis and their relationships to 2n pol len formation. In Solanum, MTs and MFs generally showed patterns of lo calization similar to those described in other dicotyledons with simul taneous cytokinesis. However, deviations in spatial configurations of both MTs and MFs that are related to 2n pollen were observed in meiosi s II and in cytokinesis. MTs and MFs localized in spindles in parallel orientation at meiosis II. In contrast, in the majority of normal mei ocytes, the two spindles were seen to be perpendicular to each other. The parallel spindles altered the position of the postmeiotic nuclei, causing a uniplanar instead of a tetrahedral arrangement. Subsequently , the formation of regular radial MT systems was suppressed and only t wo MT arrays, which lay parallel on one plane, formed between the nucl ei at the end of meiosis. A single cell plate formed across the two MT arrays, giving rise to a dyad containing 2n microspores.