Changes in the frequency of two types of nuclear body during the interphase of meristematic plant cells

Summary After impregnating root meristems with silver nitrate two types of small (< 1 ?m diameter) body can be seen in the nuclei. These have been termed “dense body” (DB) and “nucleolus-associated body” (NAB). The number of these bodies within a nucleus varies from species to species, but in general DBs are relatively numerous and lie in the nucleoplasm, while the NAB is usually solitary and lies on the surface of the nucleolus. Using nuclear volume as an indicator of the age of the nucleus since mitosis, the numbers of DBs and NABs were related to the nuclear growth cycle. In the meristem ofPisum sativum andZea mays DBs are characteristically present in early interphase; in some regions they persist in the nucleoplasm until the next mitosis, in other regions they disappear during interphase. DBs are probably pieces of the pellicle of ribonucleoprotein that coats mitotic chromosomes which have not coalesced (as does the remainder of the pellicle) to form the nucleolus at the start of interphase. NABs grow out from the nucleolar surface during the later stages of interphase. At the end of interphase there is on average 1 NAB per nucleolus.