Abstract
Accurate positioning of spindles is a critical aspect of cell division as it ensures that each daughter cell contains a single nucleus. In many flowering plants, two meiotic chromosome separations occur without intervening cytokinesis, resulting in two spindles in one cell during the second division. Here we report a detailed examination of two mutants, jason (jas) and parallel spindle1 (ps1), in which disturbed spindle position during male meiosis II results in the incorporation of previously separated chromosome groups into a single cell. Our study reveals that an organelle band provides a physical barrier between the two spindles. The loss of a single protein, JAS, from this organelle band leads to its disruption and a random movement of the spindles. JAS is largely associated with vesicles in the organelle band, revealing a role for vesicles in plant meiosis and that cytoplasmic events maintain spindle position during the chromosome division.