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August 01, 2011
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DNA-doubling trick may help plants conquer adversity
Aug. 1, 2011
Courtesy of the University of Illinois at Urbana-Champaign
and World
Science staff
Plants may seem to just sit there
strangely passively while animals munch on them. But this appearance
is often deceptive, scientists say. Grazing can trigger various coping or defense mechanisms. These include one type of response that’s as dramatic as it is mysterious: some plants start to grow bigger and faster, and reproduce more rapidly, after being grazed. Researchers Ken Paige
(right) and Daniel Scholes (left) with their plants. (Credit: L. Brian
Stauffer)
Just how they accomplish this has been unclear. But in a new study, researchers report that one secret to this post-traumatic success is
the plants’ ability to repeatedly duplicate their chromosomes without doubling the cells that
house them. The resulting greater number of genes per cell may let
the plants boost production of proteins used for growth and reproduction, they say.
This doubling process, called “endoreduplication,” isn’t new to science. But no previous study had looked at it in relation to the seemingly miraculous burst of growth and reproductive ability seen in many plants after they have been grazed, said University of Illinois biologist Ken Paige, who conducted the study with doctoral student Daniel Scholes.
The study, published in the research journal Ecology, shows “there is a link there,” Scholes
said.
Paige and Scholes tested Arabidopsis thaliana, a flowering plant in the mustard family that repeatedly duplicates its chromosomes in some cell types. The plant begins with only 10 chromosomes – five from each parent – but after repeated duplications, some cells contain up to 320.
The researchers compared the DNA content of two cultivated varieties of
the plant. Of the 160 specimens of each variety studied, half were artificially grazed by clipping and half weren’t. One variety rebounded dramatically after clipping—quickly regrowing stems and leaves and producing more seeds—but the other didn’t, the researchers found. An examination revealed that only the first one, called Columbia, had speeded up endoreduplication in some tissues. “We think it’s that added boost that increases its reproductive success,” Paige said.
More DNA also means larger cells to fit that DNA, sometimes making the whole plant larger in turn, Scholes
said. “We tend to think that what you inherit is what you’re stuck with,” he added. “But we’re finding that plants are increasing what they have, and for the first time we’re beginning to understand how they do that, and why.”
In earlier studies over decades Paige had tracked plants through generations, “so we know that the ones that get eaten actually have up to a three-fold reproductive advantage over the ones that are never eaten,” he said. “Now we are beginning to understand the molecular mechanisms that make this possible.”
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Plants may seem to just sit there passively while animals munch on them. But this isn’t always so, scientists say. Grazing may trigger various coping or defense mechanisms. These include one type of response that’s as dramatic as it is mysterious: some plants start to grow bigger and faster, and reproduce more rapidly, after being grazed. Just how they accomplish this has been unclear. But in a new study, researchers report that one secret to this post-traumatic success is an ability to repeatedly duplicate their chromosomes without doubling the cells that contain them. The resulting greater number of genes per cell may allow the plants to increase production of proteins needed for growth and reproduction, they say. This process, called “endoreduplication,” isn’t new to science. But no previous study had looked at it in relation to the seemingly miraculous burst of growth and reproductive ability seen in many plants after they have been grazed, said University of Illinois biologist Ken Paige, who conducted the study with doctoral student Daniel Scholes. The study, published in the research journal Ecology, shows “there is a link there,” Scholes said. Paige and Scholes tested Arabidopsis thaliana, a flowering plant in the mustard family that repeatedly duplicates its chromosomes in some cell types. The plant begins with only 10 chromosomes – five from each parent – but after repeated duplications, some cells contain up to 320 chromosomes. The researchers compared the DNA content of two cultivated varieties of A. thaliana. Of the 160 specimens of each variety studied, half were artificially grazed by clipping and half weren’t. One variety rebounded dramatically after clipping—quickly regrowing stems and leaves and producing more seeds—but the other didn’t, the researchers found. An examination revealed that only the first one, called Columbia, had speeded up endoreduplication in some tissues. “We think it’s that added boost that increases its reproductive success,” Paige said. More DNA also means larger cells to fit that DNA, sometimes making the whole plant larger in turn, Scholes said. “We tend to think that what you inherit is what you’re stuck with,” he added. “But we’re finding that plants are increasing what they have, and for the first time we’re beginning to understand how they do that, and why.” In earlier studies over decades Paige had tracked plants through generations, “so we know that the ones that get eaten actually have up to a three-fold reproductive advantage over the ones that are never eaten,” he said. “Now we are beginning to understand the molecular mechanisms that make this possible.”