Response of interphasic nucleoli to hypoxia in root meristems

Hypoxia produces structural changes in interphasic nucleoli of Allium cepa L. root meristems. Following segregation, the fibrillar portion of nucleoli seems to be extruded in masses, accessory bodies, which stay in nucleoplasm. Such bodies apparently leave the fibrillar portion in places which seem to correspond to insertion areas of the nucleolar organizers in nucleoli. Reversal of these changes is rapidly obtained when oxygenation is restored. Accessory bodies differ from prenucleolar bodies since they are compact and homogeneous and they do not display segregation under hypoxia.