NUCLEAR-DNA AMOUNTS IN THE EGG AND ZYGOTE OF MAIZE (ZEA-MAYS L)

The nuclear DNA content of isolated eggs and zygotes of maize was estimated using 4',6-diamidino-2-phenylindole (DAPI) staining and microspectrofluorometry. The data indicate that egg nuclei contain the 1C level of DNA (basic haploid amount) at the time of karyogamy, and that, by inference, the sperm nuclei are also at 1C. Fertilization occurred in most ovules by 24-28 h post-pollination (hpp), and DNA synthesis was well underway by 27-31 hpp. By 30-34 hpp, 80% of the zygotes were at the 3C DNA level or above, and many were undergoing mitosis. This study provides information that is pertinent to experiments on the microinjection of exogenous DNA into isolated zygotes of maize, and it will serve as a comparative base for future determinations of the DNA content of zygotes produced and cultured in vitro.