Abstract
An increase in the ploidy level by endoreduplication is often linked with an increase in cell size but the causal relationship between these two processes still remains unclear. We have previously reported that mutations in the plant DNA topoisomerase VI (topo VI) complex lead to defects in the successive rounds of endoreduplication and cell expansion. Taking the advantage of our recent finding that endoreduplicated chromosomes in Arabidopsis form polytene rather than polyploid, we tested whether colchicine-induced polyploidisation can bypass endoreduplication in topo VI mutants and rescue their dwarf phenotype. We found that cells in the tetraploid mutant plants that derive from colchicine-treated parent lines are significantly larger than those in diploid mutant plants. This result strongly suggests that the ploidy level has a positive impact on cell size and that the topo VI complex is involved in the process of endoreduplication rather than the subsequent cell expansion.
