Apomeiotic pollen mother cell development in the apomictic Boechera species

Pollen mother cell (PMC) development in the apomictic Boechera species B. holboellii, B. gunnisoniana and B. divaricarpa were investigated by various cytological methods. In prophase I, in triploid species B. holboellii and B. gunnisoniana the individual chromosomes condensed into long strands within the nucleus. Then, in metaphase I, each PMC formed a restitutional nucleus thereby bypassing the rest of the first meiotic division. This is interpreted as representing apomeiosis. Subsequently, the restitution nuclei underwent a single cytokinesis as evidenced by the production of dyads. The cells within each dyad were separated by a callose wall. Most of the PMC in B. holboellii and B. gunnisoniana produced dyads, but a small proportion generated conspicuous tetrads. In contrast, diploid apomict B. divaricarpa produced only tetrads by simultaneous cytokinesis.