Pine pollen gets flight miles

Still viable after 41 kilometers of travel

Without getting even a packet of nuts during the flight, pine pollen survives air travel pretty well.

POLLEN POWER Spherical grains of pollen from loblolly pines show their vigor by sprouting elongated tubes. Floyd Bridgwater/USDA Forest Service

PRECISION PINE The reproductive parts of loblolly pines shed pollen into the wind and capture grains produced by other trees as part of a delicately timed cycle. Available via Creative Commons license on Wikimedia Commons

Loblolly pine pollen can still do its pollination job after blowing in the wind for at least 41 kilometers, or 25 miles, forest biologist Claire Williams reports in the May American Journal of Botany.  “It’s a world record,” Williams says, but she explains that for this type of real-world pollen study, it’s also the only record.

Williams’ new work is important because there’s very little information on how long pollen can remain viable, says evolutionary biologist Anna Kuparinen at the University of Helsinki. Biologists have certainly known that pollen travels far from home, but not how well it survives the trip.

The loblolly’s vigor “will probably surprise a lot of people,” says population biologist Peter Smouse of Rutgers University in New Brunswick, N.J. ”Perhaps it should not have been surprising, given that the function of pollen is to travel.”

Distance records for pollen are also a practical matter, says Williams, who works jointly with the Forest History Society and the National Evolutionary Synthesis Center, both in Durham, N.C. To understand how tree populations might cope with climate change, she says, it helps to know how far pollen could spread genes that help trees adapt to warming.

What’s more, scientists have already planted field trials of genetically modified, or transgenic, pine trees. Before commercial use, USDA regulators will need to consider how far pollen might carry engineered genes out into a wild population, Williams says.  

Distance isn’t everything, though, when talking about the possible escape of transgenes, Smouse says. What matters most is what far-flung pollen does when it reaches a wild population. Kuparinen notes that researchers will still need to know whether seedlings carrying an escaped transgene would be able to compete.

Williams has collected accounts of epic pollen travel, such as a 1937 study, sponsored in part by the Hoover vacuum cleaner company,that documented airborne pollen being sucked up aboard a ship in the middle of the Atlantic. And the south Atlantic islands of Tristan de Cunha are dusted by pollen from trees growing 4,500 kilometers away.

To add viability tests to the distance measurements, Williams took advantage of the geography of North Carolina’s Outer Banks. On the mainland grow wide swaths of loblolly pines, the most commonly planted tree in the southern United States. The barrier island of Ocracoke has no loblolly stands, and the few pines on neighboring Hatteras shed pollen early. So Williams took her collecting equipment on the ferry out to Ocracoke and collected pollen wafting from mainland trees at least 41 kilometers away. Williams caught the pollen in lab dishes and found that at least a fraction of the well-traveled grains could still sprout a pollen tube, the projection that transmits sperm cells to the female organs.

What the work does not have, Williams emphasizes, is implications for people with pollen allergies. Fewer than 5 percent of people react to pollen from pines, and she is doing her best to stamp out what she calls urban myths about allergenic pines.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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