Guiding the Pollen Tube towards Egg in Embryo Sac

The process of fertilization in plants involves the growth of a pollen tube towards the embryo sac to deliver the male gametes to the egg cell. The guidance of the pollen tube towards the egg involves several mechanisms that ensure the successful fusion of the gametes. These mechanisms are discussed below:

Pollen Tube Attraction Mechanisms
The following are the mechanisms that attract the pollen tube towards the embryo sac:

• Chemical signals: The embryo sac releases several chemical signals that attract the pollen tube towards it. These signals include small peptides, lipids, and reactive oxygen species.

• Nutrient gradients: The embryo sac secretes nutrients such as sugars and amino acids that create a concentration gradient, which guides the pollen tube towards the embryo sac.

• Physical cues: The ovule and surrounding tissues provide physical cues that guide the pollen tube towards the embryo sac. These cues include mechanical pressure, gradients in hardness, and topographical features.

Rejection of Wrong Pollen Tubes
To ensure that only the right pollen tube reaches the egg cell, the following mechanisms reject any other pollen tubes:

• Recognition proteins: The stigma and style of the flower contain recognition proteins that identify the pollen grains that are compatible with the female gametes.

• Self-Incompatibility: Plants have evolved self-incompatibility mechanisms that prevent fertilization by their own pollen. This mechanism involves the recognition of self-pollen by the stigma, which triggers a response that inhibits pollen tube growth.

Conclusion
The guidance of the pollen tube towards the egg involves a complex interplay of chemical, physical, and biological factors. These mechanisms ensure that only the right pollen tube reaches the egg cell, leading to successful fertilization and seed formation.

Filiform apparatus :The synergid cell wall forming an extremely thick structure at the micropylar end is called the filiform apparatus.It bears several finger-like projections into the structure of synergid cytoplasm.The location of filiform apparatus - Micropylar end.The function of filiform apparatus is to guide entry of pollen tube and release of sperm cells.