Question

“Pollen grains in wheat are shed at 3-celled stage while in peas they are shed at 2-celled stage.” Explain. Where are germ pores in a pollen grain?

Answer 1

Hint: In flowering plants, pollen grains contain one vegetative and one generative cell. The 3-celled and 2-celled stages of pollen grains respectively in wheat and peas depend on whether the generative cell has divided or not before shedding. Germ pores are thin areas of pollen grains that form pollen tubes.

Complete answer:
Pollen grains in wheat are shed at the 3-celled stage i.e., containing one vegetative cell and two male gametes because the generative cell in the pollen grains of wheat divide mitotically to give rise to two male gametes before pollen grains are shed while in peas, pollen grains are shed at the 2-celled stage which means that pollen grains of peas consist of only one vegetative cell and one generative cell that does not divide mitotically to give rise to two male gametes before pollen grains are shed.
Germ pores are thin areas that are present in the exine of pollen grains. Thus, they are apertures in the exine layer of pollen grains where the sporopollenin (chemically inert biological polymer that is resistant to degradation) is absent. Germ pore helps in the formation of the pollen tube and the release of pollen grains during fertilization.

Note: In pollen grains, the vegetative cell has abundant reserve food material and a large nucleus while the generative cell is spindle-shaped. The role of the vegetative cell is to produce an elongated pollen tube while the role of the generative cell is to produce two male gametes. Through the germ pores, a pollen tube emerges out and these pores are usually three in dicots and one in monocots.