VIENNA, AUSTRIA--Whether their roots are ankle-deep in saltwater or toasting in superhot soils, grasses can tough out the weather. But they don't do it alone. According to a new study, various grass species harbor microscopic fungi that offer relief from a variety of stresses. Under the right conditions, these endophytes can help other plants, including tomatoes and watermelon, thrive in the same tough environments. The findings suggest a way to give crops a boost in unfavorable soils.
Plant physiologists have known for years that endophytes can hurt or help their plant hosts, depending on the species involved (Science, 31 October 2003). Sometimes they cause disease, other times they ward off pathogens.
Rusty Rodriguez, a microbiologist at the U.S. Geological Survey in Seattle, Washington, looked to see if endophytes protected against the geothermal heat experienced by panic grass (Dichanthelium lanuginosum) in Yellowstone Park and the salinity faced daily by coastal dune grass (Lymus mollis) in Washington state. He also wondered if endophytes would similarly protect other species.
He and his colleagues grew the grasses and other plants in the lab under various conditions, with or without endophytes. The grasses did much better when they had their endophytes. And corn, tomatoes, watermelon, and other plants became quite heat tolerant--tomatoes survived 50 degree C temperatures for several days--when they took up endophytes from panic grass, but not when they took up endophytes from grasses growing in slightly cooler soil. In addition, these species acquired salt tolerance only when they carried the fungi from grasses that grow close to saltwater, Rodriguez reported here yesterday at a meeting of the International Symbiosis Society Congress.
Plants tend to mount similar biochemical and physiological responses to any stress, be it drought, salinity, heat, or disease. But with endophytes as allies, this general response was absent. "It's as though the plants are not seeing the stress," Rodriguez says. His data suggest that the endophytes counter the production of oxygen free radicals--the first step in the stress response--thereby short-circuiting all but the specific changes needed to survive a particular condition. This should enable the plant to devote more energy to the problems at hand. "It's a much more directed response," he says.
The fact that the endophytes are so effective in both monocots--such as grasses--and dicots--such as tomatoes--shows "they have a lot of potential," says Gopi Podilla, a fungal molecular biologist at the University of Alabama in Huntsville. If these fungi could be harnessed commercially for crops, "that would be a tremendous boon, especially in marginal soils," he adds.