In a study of a coastal California lupine that harbors nitrogen-fixing bacteria in its roots, UC Berkeley researchers have shown that the roots respond differently to bacteria that efficiently produce nitrogen than they do to the slackers. Root nodules - in which bacteria share nitrogen with the plant in return for energy - grow bigger when infected with bacteria that are good at sharing nitrogen, but remain small when they house bacteria that are not.

The finding illustrates the complex symbiotic relationships that have evolved between organisms, ranging from one-sided parasitism to mutualism, a situation in which both parties benefit.

It also suggests that agricultural practices, including heavy use of nitrogen fertilizer, could disrupt these relationships and create plants with a reduced ability to choose among root bacteria.

"It's important to look at this from an evolutionary perspective and to think about plants making choices both before and after infection," said Ellen Simms, UC Berkeley professor of integrative biology and leader of the study. "We may have bred this ability out of our crops."

Simms and her colleagues, including D. Lee Taylor, a former UC Berkeley post-doctoral fellow now at the Institute of Arctic Biology in Fairbanks, Ala., current UC Berkeley graduate student Joshua Povich, and Richard P. Shefferson, now of the Forestry and Forest Products Research Institute in Tsukuba, Japan, reported their findings in October in an online publication of the Proceedings of the Royal Society B.

Simms studies mutualism between plants and bacteria, such as the classic relationship between legumes and nitrogen-fixing bacteria. As legumes such as the lupine sprout, they send out roots that enco
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Contact: Robert Sanders
rsanders@berkeley.edu
510-643-6998
University of California - Berkeley
8-Dec-2005