Western Flower Absorbs Metals to Ward Off Predators, Groundbreaking Colorado State University Study Says

Note to Reporters: Photos of the Prince’s plume wildflower and the black-tailed prairie dog are available with the news release at http://www.news.colostate.edu/.

A common Western wildflower has the ability to absorb toxic levels of a naturally occurring metal so certain mammals won’t eat it – a significant finding that Colorado State University biologists say could help determine long-term ecological consequences of genetically engineered plants.

Elizabeth Pilon-Smits, a biology professor, and her doctoral student, Colin Quinn, recently completed a two-year study to investigate effects of selenium – a metal that is similar to sulfur – as a plant-defense mechanism against the black-tailed prairie dog. The study is the first of its kind with mammals, and part of a six-year project to study the ecological significance of what scientists call hyperaccumulation, which is a plant’s spongelike ability to soak up toxic elements from the soil, in the plant’s natural habitat.

The study appeared in the June issue of the American Journal of Botany in a paper co-authored by Pilon-Smits and Quinn. Also serving as a lead author on the paper was John Freeman, a former postdoctoral student of Pilon-Smits.

In the study, Pilon-Smits’ undergraduate and graduate students grew a wildflower known as Prince’s plume in laboratories, supplied the flower with various levels of selenium and transplanted them in a prairie dog colony on the university’s Foothills Campus. They then measured the degree of prairie dog-related damage to the plant and in prairie dog behavior at that site. They also studied what happened at a prairie dog colony in southwestern Fort Collins where the wildflower was already growing.

The researchers found prairie dogs preferentially ate the Prince’s plume that contained the least amount of selenium. When plants with high levels of selenium were clipped at all, they were generally not eaten but rather chopped down and left in place, so the prairie dogs could better see predators coming.

“This plant only grows in places where there is selenium in the soil, and likely benefits from the selenium, either as a nutrient but more likely because of its ecological effects,” said Quinn. “Our focus is to study how the crop affects the local ecology.”

Selenium is naturally occurring in western U.S. soils and safe in small doses where it can act as an anticarcinogen. High levels like the ones occurring in hyperaccumulator plants can be toxic and cause death in livestock. Plants like Prince’s plume and two-grooved milkvetch can accumulate selenium at levels 1,000 times greater than what’s present in the soil, and up to 1 percent of the plant’s dry weight.

“Selenium is a huge problem in the West, including Colorado,” said Pilon-Smits. “If you grow plants on selenium-rich soil, the selenium can over time accumulate in the soil and leach out into lakes and rivers, resulting in death and deformities in livestock. In addition, hyperaccumulators naturally occur on selenium-rich soils, causing substantial yearly losses in livestock. Native wildlife appears to avoid these plants, as our current study with prairie dogs show, but non-native species don’t seem to avoid them. In our earlier studies we already showed that selenium also protects plants from many invertebrate herbivores, including moths, aphids, and other pests.

“These studies are relevant for managers of selenium-rich ranch or crop land. Also, it is important to learn about the ecological effects of plant-accumulated selenium before growing selenium-accumulating plants for environmental cleanup. This is another long-term interest in our lab. We’re interested in the mechanisms behind hyperaccumulation, all the way to the molecular level, and have been able to genetically improve plant selenium accumulation nine-fold. Such plants may be used to clean up selenium from soil or water, while accumulating anticarcinogenic selenocompounds. Before growing such plants at a large scale it is vital to have insight into the ecological consequences.”

The study resulted from a six-year, $800,000 grant from the National Science Foundation.

Pilon-Smits, who joined CSU’s College of Natural Sciences in 1998, studies how plants can be used to clean up environmental pollutants, particularly how plants metabolize, accumulate and tolerate selenium.