THE PLANT CELL, Vol 7, Issue 4 487-494, Copyright © 1995 by American Society of Plant Biologists
Dynamics of Nuclear DNA Quantities during Zygote Development in Barley
H. L. Mogensen and P. B. Holm
Department of Biological Science, Box 5640, Northern Arizona University, Flagstaff, Arizona 86011
Quantities of DNA were estimated in the nuclei of mechanically isolated egg
and zygote protoplasts in two cultivars of barley using
4[prime],6-diamidino-2-phenylindole staining and microfluorometry. Unlike
many previous studies on DNA amounts within the sex cells of flowering
plants, we 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 postpollination,
and the male chromatin became completely integrated into the egg nucleus
within 6 to 7 hr postpollination (hpp). Zygotic nuclear DNA levels began to
increase at ~9 to 12 hpp in cultivar Alexis and 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 understanding of fertilization and zygote
maturation in flowering plants. They are also relevant to studies in which
the timing of zygotic DNA replication is of interest, such as ongoing
investigations on genetic transformations in barley using the
microinjection technique.
