Hot plants

Natural History, Dec, 2002 by Stephan Reebs

If you've ever visited Yellowstone National Park, you can probably still picture the sulfurous Landscape: broad, crusty, white rock terraces with their patches of ocher and canary yellow; bubbling pools of gray mud; steaming basins of jade-green and pale turquoise water. But you might not remember the scattering of plants at the water's edge. These organisms are as remarkable, in their own way, as the otherworldly landscape: the steaming soil they thrive in is hot enough to kill most other members of the plant kingdom.

For six summers and two winters Richard G. Stout and Thamir S. Al-Niemi, both biologists at Montana State University in Bozeman, have documented the distribution and microenvironment of this unusual flora. For example, the soil temperature around the roots of Dichanthelium lanuginosum, known locally as hot springs panic grass--the most common species in Yellowstone's hottest soils--is often as high as 122 degrees Fahrenheit in summer and, at some sites, seldom falls below 95 degrees even in winter.

Searing temperatures can kill organisms by unfolding their proteins, a change in shape that renders them biologically useless. Some plants counter the effect by making so-called heat-shock proteins, which probably stabilize the other proteins. Stout and At-Niemi identified a class of small heat-shock proteins (sHSPs) whose concentration in the roots of hot springs panic grass increases as the soil temperature rises. Those proteins usually do not occur in the Leaves, which are always cooler than the roots. Other kinds of heat-shock proteins are known to help plants tolerate heat for brief periods, but the work on panic grass suggests that sHSPs are important for Long-term resistance. ("Heat-tolerant flowering plants of active geothermal areas in Yellowstone National Park," Annals of Botany 90:259-67, August 2002)

Stephan Reebs is a professor of biology at the University of Moncton in New Brunswick, Canada, and the author of Fish Behavior in the Aquarium and in the Wild (Cornell University Press).