Chromosome Endoreduplication (Endopolyploidy) in Pea Root Meristems Induced by 8-Azaguanine

Abstract

The effect of 8-azaguanine (5 × 10⁻⁴M) on the root meristems of Pisum sativum has been studied. The immediate effect of 8-azaguanine is an inhibition of interphase (G₂) nuclei to enter mitosis ending in the absence of mitosis after a 12-hour treatment. Inhibition of DNA synthesis (H³-thymidine incorporation) starts to appear after 6 hours: 8-azaguanine does not interfere with DNA synthesis once it is initiated, but it inhibits the initiation of DNA synthesis (passage from G₁ to S) at least in the majority of cells (data of the DNA cyto-photoinetry). When roots treated with 8-azaguanine for 17 hours recover in water for 24 hours, both diploid (14 monochromosomes) and endotetraploid (14 diplochromosomes = 4-chromatid chromosomes) mitoses are found in the meristem. The proportion of diplochromosome mitoses is still higher when the 24-hour water recovery follows two 8-azaguanine treatments, 17-hours each, separated by a 6-hour root immersion in 5 x 10^—4M guanine. A treatment has also been found which induces quadruplochromosomes (8-chromatid chromosomes). H³-thymidine labeling and DNA cytophotometry have shown that: Some lines of evidence are presented indicating that 8-azagnanine triggers the endoreduplication mechanism in 4C cells belonging to the differentiating cell line of the meristem (g2 cells, according to the model proposed by DEWEY and HOWARD 1963). The possible mechanism of 8-azaguanine effect on pea root meristems is discussed and attention is called on the variety of seemingly unspecific stimuli inducing endoreduplication in animal cells.