TIAN, HUI-QIAO1,2, TONG YUAN1, and SCOTT D. RUSSELL1.* 1Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019 USA; 2School of Life Science, Xiamen University, Xiamen 361005, Fujian, P.R. CHINA. - Relationship between double fertilization and the cell cycle in male and female gametes of tobacco.
Cell cycle changes in the nuclear concentration of DNA were measured
in male and female gametes of tobacco (Nicotiana tabacum L.)
using 4',6-diamindino-2-phenylindole (DAPI) labeling and
microfluorimetry. Mitotic generative nuclei were used as a reference
for 2C DNA concentrations. After division of the generative nucleus,
the two sperm cells remained at a 1C DNA concentration in pollen tubes
growing in the style. Sperm cells deposited within the synergid,
however, had DNA concentrations approaching 2C. Egg nuclei are formed
at a 1C state and approach 2C at 48 h after pollination, approximately
4 h before expected karyogamy. If pollination was withheld, the onset
of DNA synthesis in the egg nucleus was delayed by 12 to 24 h. Sperm
appear to be retained within the synergid until they reach cell cycle
synchrony with the female nuclei at 2C. Zygote nuclei display a 4C
concentration of DNA soon after fusion and up to 84 h after
fertilization. These data provide evidence for gamete fusion at 2C in
dicotyledons with bicellular pollen. This differs from some modern
studies on monocotyledons and is consistent in the fusion condition
with Arabidopsis thaliana.
Key words: cell cycle, DNA microfluorimetry, egg cell, fertilization, Nicotiana, sperm