Cell production and DNA Accumulation in the wheat endosperm, and their association with grain weight

Nuclear DNA content was measured in developing endosperm cells of two wheat varieties, Chinese Spring and Spica. 3C, 6C, 12C and 24C nuclei were detected, indicating that some form of endoreduplication and/or endopolyploidization was occurring. The total amount of DNA in the endosperm continued to increase until 24 days post anthesis. This accumulation of DNA resulted both from production of new nuclei and also from increases in the DNA content of existing nuclei. Estimates of endosperm cell numbers were made from the total DNA content per endosperm and the mean DNA content per endosperm nucleus for a range of genotypes differing in mature grain weight. Endosperm DNA content and cell number were both positively associated with mature grain weight among the genotypes examined. However, not all of the variation in grain weight could be attributed to variation in cell number because of differences in mean dry weight per endosperm cell. The large-grained variety, Spica, had a greater mean weight per endosperm cell than Chinese Spring and this difference arose after cell production in the endosperm had ceased.