June 30, 2009

Plants may protect themselves with metals

A U.S. biologist says the accumulation of metals in plants may be a strategy to protect the plants from predators such as prairie dogs.

Postdoctoral researcher John Freeman of Colorado State University and colleagues said certain plant species growing on soils with high metal content, such as arsenic, copper, selenium or lead, accumulate large quantities of metals in their leaves and stems. The purpose of that hyperaccumulation isn't fully known, but Freeman said it might increase a plant's ability to defend itself against bacteria, viruses and animals.

The study focused on selenium hyperaccumulation in Stanleya pinnata (prince's plume), a wildflower related to mustard plants. The researcher said just because a selenium overdose is toxic to animals doesn't mean the presence of high levels in leaves deters animals from eating the plants. Few studies have looked at whether metal hyperaccumulation acts as a deterrent.

The scientists grew two varieties of S. pinnata in soils pre-treated with low or high levels of selenium, The plants were then planted in prairie dog towns. The scientists found plants with high levels of selenium in their leaves were not as popular with prairie dogs as those with low levels of the metal.

The researchers hypothesize prairie dogs or other similar small mammals have influenced the evolution of plant selenium hyperaccumulation.

The study is reported in the American Journal of Botany.