Question

What is the function of the pollen tube? Explain it with the help of a diagram.

Answer 1

A tubular structure which is produced by the male gametophyte of seed plants when it germinates is known as a pollen tube. An integral stage in the plant life cycle is the pollen tube elongation. This tube acts as a conduit for transportation of the male gamete cells from the pollen grain which is either from the stigma to the ovules at the base of the pistil or directly through the ovule tissue in some of the gymnosperms.

Complete answer:

Pollen tubes are unique to plants and the structure of these tubes have evolved over time throughout the history of plants. For sexual reproduction to occur in seed plants, the formation of pollen tubes is important. Pollen grains are transported to the female gametophyte by the help of wind, water or pollinators.
Carrying of male gametes towards ovary through stigma and style is the main function of pollen tube. It enters the ovule by the micropylar end and then to the synergid cell which is present next to the egg cell. The entry of the pollen tube into synergids is guided by the filiform apparatus.
When a pollen grain gets implanted on a compatible stigma with the help of self-incompatibility mechanisms, the germination process gets initiated. At this process, a conformational change is undergone by the pollen grain, whereupon a given section of it begins to protrude outwards which form a tube-like structure, known as the pollen tube.

Note:
An excellent model for the understanding of plant cell behavior are pollen tubes. They can be easily cultivated in vitro and do have a very dynamic cytoskeleton which polymerizes at a very high rate. This provides the pollen tube with some interesting mechanical properties. The pollen tube extends exclusively at its apex, which has an unusual kind of growth.