Abnormal timing of cytokinesis in microsporogenesis inBrachiaria humidicola (Poaceae: Paniceae)

Abstract

Meiosis is controlled by a large number of genes, generally dominant, whose expression is stage-specific, site-specific and time-specific (Gottschalk and Kaul 1974, 1980a,b; Baker et al. 1976; Golubovskaya 1979, 1989). Among genes acting in the meiotic process, those responsible for the partitioning of the cytoplasm after nuclear division play a very important role in the formation of viable gametes. After two rounds of chromosome segregation (karyokinesis) and one simultaneous or two successive cytoplasmic divisions (cytokinesis), the final product of male meiosis in flowering plants emerges as a tetrad of haploid microspores enclosed in a callose wall. The timing of cytokinesis varies among angiosperms. In most monocot plants, cytokinesis is successive, i.e. one partitioning of the cytoplasm occurs after telophase I and another after telophase II, so that there is a distinct dyad stage. However, in most dicots, it is simultaneous and occurs after telophase II (Peirson et al. 1996). Many meiosis mutations affecting the pattern of cytokinesis have been reported in higher plants (Peirson et al. 1996). In Brachiaria, a promising African genus of forage grass for the Brazilian savannas, absence of cytokinesis leading to 2n microspores and binucleated or tetranucleated microspores have been reported in B. brizantha (Risso-Pascotto et al. 2003) and B. nigropedata (Utsunomiya et al. 2005). The present study details meiotic and postmeiotic abnormalities related to cytokinesis observed in one accession of B. humidicola.