How Is Pollen Produced?

Pollen does more than make you sneeze. In fact, the job of each individual pollen grain is to protect and transport male plant DNA, or genetic material, to the female part of a flower, called the stigma. Pollen evolved to allow fertilization to take place between plants that were not close to each other. By taking advantage of wind, animals brushing past and, of course, bees, pollen can travel quite a distance before it fertilizes a flower. How pollen is made can vary a little from plant to plant, but all pollen is generally produced the same way.

The formation of a pollen grain begins inside the male part of a flower called the anther, within specific tissue called sporogenic tissue. Here, the developing pollen receives nutrition and a coat of cellulose, which is a very strong plant protein. First, large pollenmothercells are produced, which eventually break into individual pollen grains through cell division. At this point, the pollen grain gets its outer coat, called the exine, which is made from another tough plant protein. The exine protects the delicate genetic material inside the pollen grain from water loss, and damage caused by UV radiation and other environmental causes. In some plants, the pollen grain also gets a sticky outer layer to help it adhere to the female part of another plant, called the stigma. The final step involves another cell division, which creates two cells within one pollen grain. After that, the pollen grains move to a drying-out phase, after which they take on their dusty appearance and are ready to go out into the world.

Once the flower has completed the pollen formation cycle, the pollen can either be carried by the wind, latch onto a passing animal, human or bumblebee, and if all goes well, find its way to a plant of the same species to fertilize. Once the pollen grain reaches the female part of another plant, called the stigma, it begins to absorb water. Once "reactivated," the pollen grain forms a tube down through the stigma and then through another female structure called the pistil. The pollen grain containing male DNA travels down this tube, where fertilization occurs in the embryo sac.