2n Gamete formation in the genus Brachiaria (Poaceae: Paniceae) |
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| Authors: | Patrícia Helena Gallo Pamela Lonardoni Micheletti Kellen Regina Boldrini Claudicéia Risso-Pascotto Maria Suely Pagliarini Cacilda Borges do Valle |
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| Institution: | (1) Department of Cell Biology and Genetics, State University of Maringá, 87020-900 Maringá, PR, Brazil;(2) Embrapa Beef Cattle, P.O. Box 154, 79002-970 Campo Grande, MS, Brazil |
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| Abstract: | Microsporogenesis of several Brachiaria species of the Brazilian collection at Embrapa Beef Cattle has been analyzed in detail. This paper reports abnormal cytokinesis
in three accessions of three different species (Brachiaria humidicola, 2n = 4x = 36, Brachiaria decumbens, 2n = 4x = 36, and Brachiaria dura, 2n = 6x = 54). Chromosomes paired in bi-, tri-, and quadrivalents in these accessions, whereas chromosome segregation at meiosis
I was characterized by exclusion of laggards as micronuclei. In a high number of meiocytes, the first sign of cytokinesis
appeared only in metaphase II and did not divide the meiocyte into a dyad. Total absence of cytokinesis was also detected
among meiocytes in the second division. Since in both cases the two metaphase plates were very close, they favored the rejoining
of chromosome sets after anaphase II and formed a restitutional nucleus in telophase II. Second cytokinesis occurred after
telophase II in most meiocytes. Monads, dyads, and triads with n or 2n nuclei were observed among meiotic products. The 2n gametes observed correspond to the first division restitution (FDR). The number of affected cells in each accession was variable,
but the number of microspores with restitutional nucleus, including those scored in tetrads and the released ones, did not
exceed 9%. Although polyploidy is common in the genus Brachiaria, its origin is still unclear. Current results suggest that 2n gametes may have contributed to the evolutionary history of the genus. |
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| Keywords: | Brachiaria Microsporogenesis Abnormal cytokinesis Restitutional nucleus 2n gamete Polyploidization |
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