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Impatiens prove to be ideal siblings: willing to share and not too leafy: jewelweeds hold back on competition when roots sense kin.

Jewelweeds make nice with their leaves when their roots share roots. In lab experiments, seedlings of Impatiens wildflowers react mildly when planted in pots with other offspring from the same mother plant, says ecologist Guillermo P. Murphy of McMaster University in Hamilton, Canada.

Seedlings planted among non-siblings of the same species shift extra resources into growing leaves, a plant version of elbowing out the competition to capture light. Sibling neighbors, however, grow with a few more branches than solitary seedlings but don't engage in outright leaf warfare, report Murphy and Susan Dudley, also of McMaster, in the November American Journal of Botany.

That sibling-stranger difference showed up only when the plants' roots shared soil, the researchers say.

"This is the first paper that shows that plants are responding aboveground to sibling roots," Murphy says. That's a contrast to another plant the Dudley lab has tested for kin recognition, the Great Lakes sea rocket, Cakile edentula. Only the roots of that plant grew differently with siblings. Seedlings apparently tolerated the presence of kin but strangers inspired a shift of resources to roots, as if battling to snatch water and nutrients from rivals, the team reported in 2007.


That the two species react differently makes ecological sense, Murphy says. Sea rockets sprout on beaches. Grabbing enough light there should be easy, but roots struggle for water and nutrients. Jewelweeds thrive along shady watersides, where moisture abounds but light is scarce. Easing competition among siblings takes the form most appropriate for the habitat, he says.

In both plants, though, it's the roots that seem to tell kin from strangers, Murphy says.

The new study and others suggest that "the phenomenon is quite common," says Hans de Kroon of Radboud University Nijmegen in the Netherlands. He notes, though, that kin recognition's evolutionary importance in plants is unclear.

Dudley and her colleagues have also reported that Arabidopsis seedlings grow differently in response to root secretions from their siblings versus those from strangers.

What's still uncertain is whether sharing with kin gives plants any reproductive advantage, says Ruben Milla of Universidad Rey Juan Carlos in Madrid. The power to recognize sibs could be just a by-product of an ability to recognize self from nonself in plants, he says.

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Author:Milius, Susan
Publication:Science News
Geographic Code:1USA
Date:Dec 5, 2009
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