REPLICATION PATTERNS OF SEX-CHROMOSOMES IN MELANDRIUM-ALBUM FEMALE CELLS

Autoradiographic analysis of chromosome replication patterns in hetero gametic male and homogametic female hairy-root cell lines of a dioecio us plant, Melandrium album, has shown an early replication of the only X and a conspicuous difference between the two X chromosomes, respect ively. This divergence could be significantly reduced by a 5-azacytidi ne treatment, thus confirming our recently published results on the di fferent degree of DNA methylation of the X chromosomes in female cells . The early replicating and aberration prone X chromosome seems to be less condensed, too. [H-3]thymidine labelling patterns as well as [H-3 ]uridine induced chromosome aberrations do not indicate any difference s between the long and short arms of the X chromosomes. The presented data support the hypothesis that one of the two X chromosomes in M. al bum female cells could be inactivated and hypermethylated as described in mammals.