Understanding natural crop defenses(se the presence of other plants in their...)

Date:2/27/2009

se the presence of other plants in their neighborhood by the relative increase in incoming far-red light resulting from absorption of red light by canopy leaves and reflection of far-red light from neighboring plants. "When the major photoreceptor for shade avoidance detects neighbors, plants start producing the growth hormone auxin and transport it to their stems, where it helps plants grow taller," explains Chory.

But plants also react to chemical cues in the oral secretions of herbivores and mechanical damage caused by caterpillars and their ilk nibbling on foliage. They increase the production of defense-related hormones, particularly jasmonic acid, which ramps up the concentration of chemicals that make plants unpalatable or at least less nutritious for herbivores.

"Such responses incur what is known as opportunity costs," says Chory. "Resource allocation to competition can limit investment in defense, increasing vulnerability to herbivores, while allocation to defense can reduce competitive ability against neighboring plants."

And that's exactly what first author Javier E. Moreno, a graduate student in Ballars lab, found. Fall armywormscaterpillars that prefer to chomp on corn, sorghum and other members of the grass family but won't say no to beans, potatoes, peanuts, cotton and other cropsgrew twice as fast on Arabidopsis thaliana seedling grown under crowded conditions or exposed to far-red radiation, the light signal plants use to detect the proximity of neighbors. Like many commercially grown crops, Arabidopsis the lab rat of plant biologists doesn't tolerate shade well.

But it was more than a matter of limited resources. Mutated Arabidopsis seedlings that no longer responded to far-red radiation but had normal levels of the far-red photoreceptor, still let their defenses down. At closer inspection, the researchers found that far-red radiation decreased the plants' sensitivity to jasmonates. By ignoring jasmonate sign
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Contact: Gina Kirchweger kirchweger@salk.edu 858-453-410-01340 Salk Institute Source:Eurekalert

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