Pollen is the number one outdoor allergen that is involved in the sexual reproduction of the plants. Pollen grain is the male gemate of male genetic material in flower plants. Pollen is produced in the anthers, a structure within the flower. When the pollen is ready to release, the anther ruptures and exposes the pollen which is then transported to the female organ of the flower. In order for seeds to be produced, the pollen must be transferred from the male part of the flower to the female part of the flower.
Pollen is a fine to coarse grains which produce the male gametes (sperm cells). Pollen comes in a wide variety of shapes, sizes, and surface markings characteristic of the species. They have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants. When pollen lands on a compatible pistil or female cone (i.e., when pollination has occurred), it germinates and produces a pollen tube that transfers the sperm to the ovule (or female gametophyte).
During spring and fall time the air contains many types of pollen. The smallest pollen grain, the forget-me-not is around 6 µm (0.006 mm) in diameter. Wind-borne pollen grains can be as large as about 90–100 µm.
The transfer of pollen grains to the female reproductive structure is called pollination. The transfer can be mediated by the wind or insects.
Wind-pollinated plants typically produce enormous quantities of very lightweight pollen grains and the pollen is dispersed by air currents. The types of pollen that most commonly cause allergic reactions are produced by the drab, inconspicuous, plain-looking plants (trees, grasses, and weeds) that do not have showy flowers.
Common tree pollens are olive, birch, elm, oak, and walnut. Grasses generate many pollens. Examples include: blue, rye, bermuda grasses and red top. Allergy caused by grass pollen is second only to ragweed. Weeds are mostly wind-pollinating. Examples of these are ragweed, sagebrush, pigweed, and tumbleweed. Ragweed is the most important cause of seasonal allergic hay fever. There are many more trees, grasses, and weeds that generate allergy-causing pollens. Airborn pollen can be blown for long distances. Pollen has been found floating in the air 400 miles out at see and 2 miles up in the sky. Pollen even can cross continents.
Insect-pollinated plants produce pollen that is relatively heavy, sticky and protein-rich. These type of plants tend to have bright petals for flowers and are scented and exude nectar to attract insects. The main insect pollinators are bees and butterflies. The pollen will cling to the visitor as it makes the rounds of flowers to eat nectar. That’s why plants with colorful flowers generally don’t cause allergic reactions since the pollen is not usually present in the air. Many insects and some mites are specialized to feed on pollen.
For many trees the small inconspicuous flowers are produced just before the leaves develop from the buds and go unnoticed by most people. Weather has significant effects on pollen release. Warm, dry, sunny, and windy conditions favor pollen release. Cold temperature, high humidity and rain will suppress the release of pollen because the rain clean the air of pollen grains.
Tree pollen levels typically peak from late March through most of April and it last about 2-4 weeks. Another pick time is in September when ragweed pollen level begins to increase early in the month and usually peak around September 10. The levels drop slowly and are often still high in October.
A variety of producers have started selling bee pollen for human consumption, often marketed as a food (rather than a dietary supplement). The largest constituent is carbohydrates, with protein content ranging from 7 to 35 percent depending on the plant species collected by bees. The U.S. Food and Drug Administration (FDA) has not found any harmful effects of pollen consumption, except from the usual allergies, but there can be possible dangers not only from allergic reactions but also from contaminants such as pesticides and from fungi and bacteria growth related to poor storage procedures.
Every pollen has a story: http://www.ted.com/talks/jonathan_drori_every_pollen_grain_has_a_story.html
Discovery news: Massive Tree Pollen Explosion Explained: http://youtu.be/favTwuRaAgI
- Pollen (ahschoolapbio2013.wordpress.com)
- Top 5 Airborne Allergy Triggers (livingwithallergy.wordpress.com)
- Pollinator: Honey Bee (ahschoolapbio2013.wordpress.com)
- Pollen cells keep memory to control jumping genes (eurekalert.org)