Function of Micropyle in Seed

Micropyle in Seed

Micropyle is a pore found in all seed plant ovules, which permits the transfer of sperm from the pollen tube to the ovum. Micropyle is most common in monocotyledons (such as grasses), so it may originate from plants with a grass-like evolutionary history.

A micropyle is a hole in the seed coat that allows the pollen tube to fertilise the ovule. It is an opening in the outer coat of a plant ovule. It allows pollen tubes from compatible plants to enter, thereby enabling fertilization to take place. A pollinated seed will typically have 2 or more micropyles on opposite sides of the seed coat, though one or none can also be present.

A secondary wall is present, which grows around the ovule after fertilization. The micropyle remains open as the ovule develops into a seed. It normally stays open during development, but in some cases it closes at some point after fertilization.

Function of Micropyle in Seed

A primary function of the micropyle is to allow sperm cells to enter and reach the egg cell within the ovule during pollination. The walls of the micropyle are highly elastic and resistant to drying. They are covered with a thick cuticle and are rich in lipids.

Again, at the time of germination of the seed the micropyle assists in the function of water absorption and finally the roots emerge through the micropyle during seeds germination.

When a plant sprouts from a seed with a micropyle, it emerges through this hole

The pollen enters through the micropyle in its pollen tube. This turgid structure is basically a cylinder that grows as it enters the ovule by elongation at its tip. The two nuclei contained within the pollen grain sit at opposite ends of the tube, with each nucleus producing a polar body during meiosis, which is embedded in the wall of the tube.

The nucleus of the sperm cell in the pollen tube is also covered by a cuticle, though its cuticle is thinner than that of the pollen tube. The microtubules which anchor the polar bodies in place are also located near the nuclei. These microtubules protrude from tiny pores at one end of the pollen tube. These pores allow water to enter into and leave from within the pollen tube as it grows.

At the end of the pollen tube, cells form a cap which then fuses and seals the tip. During meiosis, one of these polar bodies is ejected and is destined to become a male gametophyte while the other remains inside the ovule as a female gametophyte.

The cuticle covering the nuclei of the male gametophyte has been consumed during meiosis, removing its resistance to drying and allowing it to be exposed as a naked membrane. This allows it to absorb water and expand, pushing the synergid of the female gametophyte ahead of it.

During fertilization, the male nucleus from the pollen tube will fuse with an egg cell in the ovule. It is then known as the nucleus of the zygote.

The micropyle is a hole in the ovule which serves as a passage for pollen tubes to enter so that fertilization can take place.

In angiosperms, the micropyle is a small pore found on the outer integument (pericarp) of the ovule. Usually, one or more micropyles are present on opposite sides of the integument of most angiosperm species.

Summary

The micropyle is a small opening in the seed coat that allows water to enter and reach the embryo.  It is located at one end of the seed, opposite from where it will sprout.

In some seeds, such as peas or beans, it can be found on both ends of the seed.

When the embryo inside the seed begins to grow, it swells and pushes against the hard outer shell of the seed, which causes cracks in this shell that allow for more water and nutrients to enter