Smart host

Plants are hospitable to useful bacteria but have developed ways to get rid of freeloaders, according to a study by a team of biologists at the University of California in Berkeley, USA.

Led by Ellen Simms, the scientists studied a coastal California lupine (Lupinus arboreus) that harbours nitrogen-fixing bacteria in its roots. They found that the roots respond differently to bacteria that efficiently produce nitrogen than they do to those that don't. In case of the former, root nodules -- in which bacteria share nitrogen with the plant in return for energy -- grow bigger when infected. But when infected with bacteria that are not good at sharing nitrogen, the root nodules remain small.

The finding suggests that some agricultural practices, including heavy use of nitrogen fertilisers, could disrupt these relationships and create plants with a reduced ability to choose among root bacteria.

The study appeared in October in an online publication of the Proceedings of the Royal Society B.