Increased replication in plant nuclei, whose spread chromatin contains enlarged nucleosomal linkers, is only partially due to a rise in the number of DNA elongating chains

Dormant and proliferating meristems of Allium cepa L. roots were compared. In vivo DNA synthesis was nine times higher in proliferating meristems, partially due to a 2.5 times increase in the relative number of DNA elongating chains, as estimated after the assay for 3H-TTP incorporation in permeabilized cells. Stereology done on conventional electronmicrographs showed that nucleoplasm was nearly three times larger in nuclei of proliferating meristems, while the amount of compact chromatin did not diminish but redistributed instead, resulting that the chromatin/nucleoplasm interface increased. Finally, the nucleosomal linker -as seen after the spreading of the chromatin fibres- was larger and more variable in proliferating than in dormant meristems.