Multinucleate plant cells : II. Requirements for nuclear DNA synthesis

A synchronous population of multinucleate cells has been experimentally induced in Allium cepa root meristems by a chemical method that involves the induction of aneuploidy in individual nuclei. Whereas all multinucleate cells as a whole present a tetraploid chromosome complement, their aneuploid nuclei constitute compartments containing only part of the parental genetic material. We analysed the degree of synchrony in the course of S period progression in the unbalanced nuclei sharing a common cytoplasm (bi-, tri- and tetranucleate cells). In most of the multinucleate cells the nuclei entered DNA replication simultaneously, but a significant proportion of cells showed labelled and unlabelled nuclei which was due to the absence of DNA synthesis in some aneuploid nuclei. These nuclei lacked replicative capacity, but did not inhibit DNA synthesis of the replicating nuclei. Our findings confirm the existence of cytoplasmic factor(s) inducing the synchronous initiation of S period, and suggest strongly the occurrence of intranuclear factor(s)—likely gene products—as a requirement for the onset of DNA synthesis itself in every nucleus.