The occurrence and role of DNA synthesis during meiosis in wheat and rye

The incorporation of ³H-thymidine into the DNA of rye meiocytes at zygotene, pachytene-diplotene and metaphase I to telophase II stages has been studied. Low levels of ³H were found in highly purified DNA from meiocytes at all these stages, though there was more in the DNA from pachytene-diplotene meiocytes, and it is highly likely that the zygotene groups of anthers contained a proportion at pachytene. The buoyant density distributions of the labelled DNA from zygotene and pachytene-diplotene cells were indistinguishable, in contrast to the situation in Lilium, the only other example studied so far.The DNA synthesis inhibitor 2′-deoxyadenosine halted meiotic development of anthers in culture only at late zygotene and pachytene. It did not inhibit development at early zygotene, prevent chromosome pairing as judged by light microscopy or cause extensive chromosome fragmentation during zygotene as in Lilium. These results indicate that extensive synthesis of DNA does not occur at zygotene in cereals and does not suggest that zygotene DNA synthesis is a prerequisite for chromosome pairing as in Lilium.