DYNAMICS OF NUCLEAR-DNA QUANTITIES DURING ZYGOTE DEVELOPMENT IN BARLEY

Quantities of DNA were estimated in the nuclei of mechanically isolate d egg and zygote protoplasts in two cultivars of barley using 4,'6-dia midino-2-phenylindole staining and microfluorometry. Unlike many previ ous studies on DNA amounts within the sex cells of flowering plants, w e obtained consistent and unambiguous results indicating that the egg and sperm nuclei are at the 1C DNA level (basic haploid amount) at the time of karyogamy. Karyogamy was initiated within 60 min postpollinat ion, and the male chromatin became completely integrated into the egg nucleus within 6 to 7 hr postpollination (hpp). Zygotic nuclear DNA le vels began to increase at similar to 9 to 12 hpp in cultivar Alexis an d at 12 to 15 hpp in cultivar Igri. The 4C DNA complement was reached in most zygotes by 22 to 26 hpp in cultivar Alexis and by 23 to 29 hpp in cultivar Igri. These data are fundamental to a better understandin g of fertilization and zygote maturation in flowering plants. They are also relevant to studies in which the timing of zygotic DNA replicati on is of interest, such as ongoing investigations on genetic transform ations in barley using the microinjection technique.