Pollen: It's not just something to sneeze at

By Gary Raham
Nature Writer and Illustrator

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Sometimes it's hard to love something that makes your eyes tear up and your nose dribble, but pollen has so much going for it that it at least deserves our respect.

Wind-borne pollen, like that produced by grasses, tweaks my allergic responses the most, but neither you nor I would want to discourage the sex life of grasses. Grasses like corn, wheat and rice feed the world. And pollen has turned out to be an amazing tool for a wide variety of scientific disciplines, including botany, paleontology, archeology, geology and climatology. All this value is wrapped up in tough little packages the size of dust grains.

Sex cells run amok

Plants practice an "overkill" method of reproduction because plant male cell producers (anthers) can't wander around looking for attractive ovaries in bars and grocery stores. Thus, a plant will produce hundreds of millions of pollen grains per flower and either coerce animals into helping them transfer that pollen or cast their fate to the winds by producing veritable clouds of particles, only a tiny fraction of which will ever surf an air current to a female flower of the right species. Here in the Rockies, pine trees often coat nearby lakes with thick films of their wind-borne, amber pollen.

Insects, birds and various mammals, tempted by pollen's rich food value, can easily be conned into helping plants. Pollen grains are 16 to 30 percent protein, 1 to 10 percent fat, 1 to 7 percent starches, low in sugar and high in vitamins. Plants that target animal messengers produce a thick, nonvolatile oil that adheres globs of pollen to each messy feeder. The animals carry that pollen to the next flower they visit, usually one of the same species.

Wind-borne pollen, light and dry, relies on blundering into the female pistil of the same species. Once at a female stigma, the male sex cell must send out a pollen tube which chemically digests its way through the neck of the ovary to the female egg cells. Two nuclei then traverse the tube. One nucleus fertilizes the egg cell, the other combines with a secondary female cell to form the endosperm that makes up most of the resulting seed--a food source to get the seedling up and growing.

Time capsule

When pollen cell nuclei reach their destination, the pollen grain has served its biological purpose. Its vacated shell holds no more value to the plant than an empty soda can has for us. But to scientists, that shell --because of its durability and uniqueness to its parent plant--is a time capsule packed with valuable information. And because pollen is so small and produced in huge quantities, it piles up in sediments everywhere.

If you drill into old lake or bog sediments and pull up a core of material, you will find a continuous record of the rain of pollen (and spores) from all the plants that ever lived near that lake for thousands--even millions--of years. Scientists have done just that ever since Axel Blytt (1843-1898), Rutger Sermander (1866-1944) and E. J. Lennart von Post (1884-1951) first came up with the idea. The ebb and flow of forests and prairies in north America and Europe have been read and recorded and used to measure the advance and retreat of glaciers as ice ages have come and gone over the past million years or so. An entire science--called palynology--has developed around all the nuances of interpreting pollen assemblages in the fossil record.

In 1954 one oil company took out a patent on a method based on the discovery that ancient ocean shorelines could be pinpointed by observing the size ratios of pollen in marine sediments. Smaller and lighter pollen grains tended to be transported farther away from shore than larger, heavier grains. Ancient shorelines thus provide geologists with clues to the location of oil deposits.

Ancient detective work

Pollen also infiltrates into some unusual places, leaving a unique signature that aids archaeologists. In late January of this year, Nature magazine reported that a French scientist, Serge Muller, is using pollen to determine exactly where certain ships lost at sea were built. It seems that pollen tends to stick to the resin used to seal a boat's hull. Pollen produced by plants near a shipyard provide a unique "birth certificate" for any boat built there.

Muller is studying the Baie-de-l'Amitie, a ship that wrecked off the south coast of France some 2,000 years ago. He believes builders sealed the boat's hull somewhere east of Italy because it contains both wood and pollen from Platanus, a tree that is restricted to the eastern Mediterranean. His conclusion is supported by pollen from weeds like Haplophyllum, most species of which are restricted to the same area. Such information helps unravel the mysteries of ancient commerce. Another researcher hopes to use Muller's technique to figure out where the Persians built the fleet they used to invade Greece in the fifth century B.C.

The human connection

Scientists have recently uncovered another interesting link between humans and pollen. An amino acid called amino butyric acid, which is an important chemical allowing human brain cells to communicate, also promotes the growth of pollen tubes necessary for plant reproduction. Perhaps the Navajos instinctively gave pollen its proper place in the scheme of things. Stephen C. Jett in "Navajo Wildlands" said, "The symbol for life and productivity, for peace and prosperity, is pollen. Pollen symbolizes light."

Gesundheit.