Relationship of nuclear genome size, cell volume and nuclei volume in endosperm of Sorghum bicolor

Abstract

Endosperm cells of Sorghum bicolor undergo several rounds of endoreplication during seed development, resulting in somatic endopolyploidy with cells containing 3 C to 96 C nuclei (1 C represents the amount of DNA in an unreplicated haploid genome). Cells with higher DNA content are larger and contain larger nuclei. The function of large endosperm cells in Sorghum bicolor is storage of starch that will be used in germination. We analysed the ratios of nuclear genome size and volume of nuclei and cells to determine if karyoplasmic ratio is constant in cells of different endopolyploidy levels. Interestingly, the volume of cells and nuclei increases more than can be expected from the increase in genome size alone. Instead, a constant ratio was observed between genome size and surface of cells and nuclei. However, an isometric relationship was found between volume of nuclei and volume of cells, indicating that karyoplasmic ratio is constant in sense of dimensions of cellular compartments, rather than with nuclear genome size alone.