Cytoplasmic DNA synthesis at meiotic prophase in Lilium henryi

Extensive cytoplasmic DNA synthesis has been discovered at meiotic prophase in Lilium henryi. Explanted microsporocytes were cultured in medium containing [³H]thymidine. Light microscope autoradiography revealed many small clusters of grains (< 3 µm) in the cytoplasm of premeiotic and pachytene cells. There were about 10 to 20 clusters per cell in each section. Most of the cytoplasmic label was extracted by hot hydrochloric acid and DNase I, but not by RNase A or pronase. Thus the grains reflect DNA synthesis, and not incorporation of products of thymidine catabolism which is extensive in this tissue. These localized centres of DNA synthesis, previously unreported, might result from mitochondrial or plastid replication, or from amplification of excised chromosomal DNA.