Relation between Water Stress and DNA Synthesis during Germination of Zea mays L.

Mitotic index, percent nuclei in DNA synthesis and the relative DNA content per nucleus were determined from cells of the Zea mays radicle at various times after the beginning of germination. Nuclear DNA synthesis was initiated after 45 h and mitosis was first observed after 74 h from sowing. Most of the dormant nuclei were in the pre-synthetic or G1 phase of the mitotic cycle. By 72 h most cells were in S and 77 h after the beginning of germination, the cells of the primary root were observed in all phases of the mitotic cycle. Dehydration of karyopses after 45–74 h of imbibition progressively reduced the percent of germination to zero upon dehydration and subsequent replanting demonstrating that drought sensitivity was related to the onset of nuclear DNA synthesis and genome duplication.