Abstract: The nuclear DNA content of male and female gametes of tobacco ( Nicotiana tabacum) was measured using DAPI stain and microspectrofluorimetric measurement. Tobacco pollen is bicellular at anthesis, containing a vegetative cell and a generative cell , which divides to form two sperm cells in a pollen tube. The nuclear DNA content of generative cell in a pollen tube was at 2C level and that of two sperm cells in a pollen tube, which elongated in the style, at 1C level. Two sperm cells began to synthesize DNA after both were released in the degenerated synergid , and the quantity of nuclear DNA
in both sperm cells approached 2C level before both fusing with egg and central cells . During this process , the nuclear DNA content of egg cell also began to increase and approached 2C level before fusing with sperm cell . After male and female gamete fused , the nuclear DNA content of zygote reached 4C level . Therefore , the fusion of male and female gametes of tobacco was at G2 of cell cycle, and this fusion of fertilization belonged to G2 type . This result displayed the fertilization multiformity in angiosperms .

Key words: Tobacco