Hilum vs Micropyle

The micropyle and hilum both are two distinctive markers seen on the seed coat. The seed coat develops from the integuments surrounding the embryo sac. It comprises a multi-layered tissue that includes a tough, mechanical and protective layer covered by a cuticle that is impermeable to water. The raphe, a ridge, serves as the third marker on the seed coat, which is adjacent to the hilum.

Primarily, the hilum and micropyle differ in the fact that the hilum is an elliptical scar on seeds marking the point of contact of attachment of the funicle, while the micropyle is the small opening of the hilum wherein the pollen tube passe through before fertilisation.

Hilum

  • These are scars on the seed coat which marks the place at which seeds get fastened to the tissues of the ovaries. These regulate the dynamics between the embryo and the external surroundings.
  • They form a potential route for the invasion of pathogens in seeds.
  • The permeability of seeds is based on various aspects, such as the cutin.
  • The hilum controls the content of water in seeds during the last phase of the formation of seeds.

Micropyle

  • Small pores are seen at one terminal of the hilum of seeds. It is from here that the pollen tube gets into the ovaries at the time of fertilisation.
  • At the time of germination of seeds, water passes in the seed through the micropyle, and it serves as the path for invasion of pathogens in seeds, as seen in Hilum.
  • Naturally, at times the micropyle is closed by a lid, waxy in nature which is involved in regulating the susceptibility and absorption of water in the seeds.

Key Differences between Hilum and Micropyle

The table below depicts the differences between Hilum and Micropyle.

Hilum

Micropyle

What are they?

Elliptical scars on seeds depicting the association between ovary and ovules

Pores indicating the point from which pollen tubes enter the ovary at the time of fertilisation

Regulation of water content

Water content is regulated by it in the final stages of the formation of seeds

Water enters the seed through the micropyle when seeds begin to germinate

Size

A larger region in comparison

Tiny pores

Role

Regulates absorption of water in the final stages of formation of seeds

At the time of germination of seeds, it regulates the absorption of water

Permeability control

It regulates the permeability through the cutin and the capacity to close and open based on the conditions

Water absorption in some species is regulated by the lid (waxy)

Monocot seeds

Covered by caruncle partially

Fully covered by caruncle

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