Question

Which cell of the female gameophyte is involved in the formation of primary endosperm nucleus (PEN) after fertilization ?

• A. Antipodals
• B. Synergids
• C. Egg cell
• D. Central cell

Answer 1

The Correct Option is D

The formation of the Primary Endosperm Nucleus (PEN) is a key event in the process of double fertilization, which is unique to angiosperms.

Let's review the structure of a typical female gametophyte (embryo sac) in angiosperms:

• It is usually a 7-celled, 8-nucleated structure. 
• It contains:
  • The egg apparatus at the micropylar end (consisting of one egg cell and two synergids).
  • Three antipodal cells at the chalazal end.
  • A large central cell containing two polar nuclei.

During double fertilization:

1. One male gamete (haploid, \(n\)) fuses with the egg cell (haploid, \(n\)) to form the diploid zygote (\(2n\)). This process is called syngamy and leads to embryo development.
2. The second male gamete (haploid, \(n\)) travels to the central cell and fuses with the two polar nuclei (each haploid, \(n\)) located within it. This fusion event, involving three haploid nuclei (\(n + n + n\)), is called triple fusion.

The product of triple fusion is the Primary Endosperm Nucleus (PEN), which is typically triploid (\(3n\)). This nucleus is formed within the large central cell, which subsequently becomes the Primary Endosperm Cell. The PEN undergoes mitotic divisions to form the endosperm, a nutritive tissue for the developing embryo.

Therefore, the cell of the female gametophyte that is involved in the formation of the PEN (by hosting the triple fusion event) is the Central cell.

Answer 2

• In angiosperms, the female gametophyte (embryo sac) contains 8 nuclei arranged into 7 cells: one egg cell, two synergids, three antipodals, and one central cell with two polar nuclei.
• During double fertilization, one male gamete fuses with the egg cell to form the zygote, and the other male gamete fuses with the two polar nuclei present in the central cell.
• This fusion results in the formation of the primary endosperm nucleus (PEN), which later develops into the endosperm — a nutritive tissue for the developing embryo.

Hence, the central cell is involved in the formation of the primary endosperm nucleus.

The correct answer is (D) : Central cell.