polar nuclei
In angiosperms, the two nuclei of the central cell of the female gametophyte; they fuse with a sperm nucleus to form the triploid (3n) endosperm nucleus.
pollen ...
polar nuclei Two of the eight haploid nuclei of a megagametophyte that migrate, one from each end, to the middle of the embryo sac. These two nuclei fuse with a sperm nucleus during double fertilization.
The two central cell maternal nuclei (polar nuclei) that contribute to the endosperm arise by mitosis from a single meiotic product.
One sperm cell fuses with the egg forming the diploid zygote.
The other sperm cell fuses with the polar nuclei forming the endosperm nucleus. Most angiosperms have two polar nuclei so the endosperm is triploid (3n).
The events of "double fertilization" of the egg and polar nuclei by the two sperm cells. Image from Purves et al.
Double fertilization: The union of one male gametophyte nucleus with the ovum nucleus and another male gametophyte nucleus with the polar nuclei to form the endosperm in seed plants. See also pollen grain.
 See also: Plant, Nucleus, Tissue, Cell, Angiosperm
  
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