The Difference Between Pollination and Fertilization in Pine Trees

About Pine Trees

• Pine trees have spores that develop into separate male and female reproductive parts. The male spore develops into pine cone-like structures with finger-like structures clustered at the tips of branches. Male cones live only a few weeks; once pollen is released, the male pine cone dies and falls off the tree. Within each pollen grain are two cells. One is called the "generative" cell and will generate two sperm while the other is a tube cell that will produce a pollen tube after pollination. The female spore grows into a pine cone or "megaspore," which produces the egg.

Pollination

• Pollination occurs only after a pollen grain, carried by wind, lands near the female pine cone's ovule opening or micropyle. Once a grain of pollen lodges in the micropyle, pollination is complete. To insure pollination, each male pine cone, on average, releases 1 to 2 million pollen grains. The pollen grains have wing-like structures or bladders that keep the grain air-bound.

Fertilization

• Once pollination occurs, a pollen tube grows until it reaches the inner structure of the female pine cone. At this stage, the female pine cone stimulates the megaspore to produce female gametophytes within the egg. In simplified terms, the pollen tube grows, ruptures, and releases sperm-carrying gametophytes that swim up the pollen tube to the egg. Each pollen tube releases two sperm, which fertilize two eggs. While one egg will develop into the fertilized egg or zygote, the other will be disintegrated by the megaspore. Unusual to the pine tree is the time delay between pollination and fertilization. While pollination occurs within one season, A full year may be required for the pollen tube to grow and for fertilization to occur.

Effectiveness

• In the pine tree, gametophytes, the chromosomal material, is enclosed in protected layers within the pollen grain. Until it comes into contact with the female ovule, it doesn't become active. Additionally, the male sperm are transferred from the pollen grain to the egg via a pollen tube. As a result, fertilization occurs within a safe, protective environment.