Endoreduplication in the germinating embryo and young seedling is related to the type of seedling establishment but is not coupled with superoxide radical accumulation

Abstract

During germination, the embryo axis elongates and the radicle emerges through the surrounding structures of the seed. However, this elongation is not even along the axis, and it has been suggested that the region responsible for radicle protrusion is related to the type of subsequent seedling establishment. Eleven epigeal- and five hypogeal-type species were selected to study endoreduplication, a process coupled with cell elongation, in the radicle, hypocotyl-radicle transition zone, hypocotyl, and cotyledons of dry and germinating seeds, and in seedlings after radicle protrusion. Flow cytometry was used to establish the proportions of nuclei with different DNA contents, the mean C-value, and the (Σ>2C)/2C ratio. Additionally, a nitroblue tetrazolium chloride test was applied to the embryos/seedlings in the dry state and during and after germination to localize superoxide radical (O2(•-)) accumulation, which has been suggested to play a role in cell elongation. Endoreduplication intensity varied in different species, in the embryo/seedling regions, and with the type of seedling establishment. In most of the cases, it was highest in the transition zone of epigeal species and in the hypocotyl in hypogeal species. O2(•-) was invariably produced during germination in the radicle, and additionally in the transition zone at the time of radicle protrusion; thus, it was not coupled with endoreduplication, and most probably played a role in defence against biotic and abiotic environmental stresses. These results provide information to aid in the selection of the most suitable plant material for molecular research on germination and for monitoring seed priming.

Keywords: Cell cycle; endoreduplication; epigeal; flow cytometry; hypocotyl; hypogeal; polysomaty; radicle; reactive oxygen species; transition zone..