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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.”