Cytomixis in Pollen Mother Cells of Diploid Dactylis, One of the Origins of 2n Gametes

The phenomenon of cytomixis consists in the migration of chromosomes between meiocytes through cytoplasmic connections. Since cytomixis creates variation in the chromosome number of the gametes, it could be considered a mechanism of evolutionary significance. This phenomenon has been reported in numerous species of angiosperms but never in Dactylis. This article concerns the study of the meiotic behavior of a plant of Dactylis glomerata L. subsp. castellata Borrill and Parker (2n = 2x = 14) showing a pronounced phenomenon of cytomixis during microsporogenesis. The purpose of the study was to verify whether this meiotlc alteration could represent an effective mechanism for the formation of 2n pollen grains. Observation of the entire meiotic process demonstrated that cytomixis developed in such a way as to produce euploid meiocytes, rather than aneuploid meiocytes. Cytomictic pollen mother cells formed microspores with different ploidy levels among which there were certainly those of the 2n type. Pollen analysis carried out on this plant and on 10 plants with regular meiosis showed that at least 25% of the pollen of the cytomictic plant was polyploid. These results indicate that cytomixis can really be an effective mechanism for the production of 2n gametes, and so its manifestation can have consequences on the evolution of the plant.