NOR activity in larval and juvenile mussels (Mytilus gallopro vincialis Lmk.)

Abstract

The silver staining patterns of the nucleolus organizer regions (NORs), an indication of rDNA transcriptional activity, were studied in metaphase chromosomes from larvae and juveniles of a bivalve mussel, Mytilus galloprovincialis. Two submetacentric/subtelocentric pairs of chromosomes, out of the the total complement of 14 pairs, were characterized by the presence of silver-stained NORs. A considerable degree of inter- and intraindividual variation in NOR activity was noted. Mean NOR activity in larvae (3.27 active NORs per metaphase) was demonstrated to be higher than in the gill tissue of the juvenile mussels (1.93).