The Effect of Actinomycin D on Chromosome Behaviour in Delphinium

Abstract

Treatment with actinomycin D has been found to block the meiotic development in a large proportion of pollen mother cells in Delphinium. In the treated plants, the anthers on squashing are found to show two kinds of cells-those showing the expected meiotic activity and the others which show a mitotic kind of division. The latter group of cells seem to have taken a mitotic course rather than the expected meiotic sequence. The drug has the effect of blocking the differentiation of premeiotic mitotic cells along the expected meiotic pathway. This effect of actinomycin D has been interpreted as due to the action of this chemical in inactivating certain gene loci, which are thought to be involved in a meiotic development of the cell. These loci may be controlling the synthesis of protein molecules, and possibly of the DNA fraction, which is believed to be involved in meiotic development. Thus, enzymes like DNA polymerase may be affected in their synthesis and so also the repair replication enzymes, which have a role in genetic recombination.