Cell Biology

Mutant maize offers key to understanding plant growth – Phys.Org

February 13, 2017 From left, normal and mutant maize plants. Credit: UC Riverside

How plant cells divide and how that contributes to plant growth has been one of the longstanding unsolved mysteries of cell biology. Two conflicting ideas have fueled the mystery.

The first idea is that cells divide merely to fill space in plant tissue, and therefore the orientation of the division is unimportant to growth. In other words, the contribution of individual cell behavior to overall growth isn't very important.

The second idea is that individual cells are the basic unit of life and their individual programs eventually build an organism. In other words, each new cell created contributes to proper patterning of the tissue. In this case, the orientation of each cell's division is critical for how the plant tissue is patterned and also impacts growth.

New findings by a University of California, Riverside-led team of researchers, lend support to the second idea, that the orientation of cell division is critical for overall plant growth. The work was just published in the journal Proceedings of the National Academy of Sciences.

The researchers, led by Carolyn Rasmussen, an assistant professor of plant cell biology at UC Riverside and Pablo Martinez, a graduate student working in Rasmussen's lab, together with Anding Luo and Anne Sylvester at University of Wyoming, were working with a maize mutant, called tangled1, with known defects in growth and division plane orientation of cells. Division plane orientation refers to the positioning of new cell walls during division.

They used time-lapse live cell imaging that represented hundreds of hours of maize, (commonly called corn in the United States), cells dividing. The time-lapse of imaging allowed them to characterize a previously unknown delay during cell division stages in the maize mutant. This study clarified the relationship between growth, timely division progression and proper division plane orientation.

This study suggests that delays during division do not necessarily cause growth defects, but that improper placement of new cell walls together with delays during division causes growth defects. Therefore, division plane orientation is a critical but potentially indirect factor for growth.

The findings might have long-term implications for increasing agricultural production. For example, during the Green Revolution of the mid-20th century, researchers developed short-stature, or dwarf, wheat and rice varieties that led to higher yields and are credited with saving over a billion people from starvation. Understanding the molecular mechanisms of plant growth might contribute in the long-term to developing more suitable short-stature maize varieties.

The paper is called "Proper division plane orientation and mitotic progression together allow normal growth of maize."

Explore further: How plant cells regulate growth shown for the first time

More information: Proper division plane orientation and mitotic progression together allow normal growth of maize, PNAS, http://www.pnas.org/cgi/doi/10.1073/pnas.1619252114

Researchers have managed to show how the cells in a plant, a multicellular organism, determine their size and regulate their growth over time. The findings overturn previous theories in the field and are potentially significant ...

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A study conducted by a research team led by Michel Cayouette, Full IRCM Research Professor and Director of the Cellular Neurobiology research unit, in collaboration with a team led by Stphane Angers, Associate Professor ...

A new report from the Stowers Institute for Medical Research chronicles the embryonic origins of planaria, providing new insight into the animal's remarkable regenerative abilities.

How plant cells divide and how that contributes to plant growth has been one of the longstanding unsolved mysteries of cell biology. Two conflicting ideas have fueled the mystery.

Watching the smooth movement generated by hundreds of fish as they swim in unison is truly mesmerising. But it's not only its sheer beauty that makes it so hard to look away, for scientists, it's also the fact that its emergence ...

Recent evidence demonstrates that the origins of photosynthesis can be found in deep sea hydrothermal vents, where microbes evolved to obtain energy from ejected hydrogen sulfide and methane gases. These microbes are capable ...

A new study of songbird dehydration and survival risk during heat waves in the United States desert Southwest suggests that some birds are at risk of lethal dehydration and mass die-offs when water is scarce, and the risk ...

Scientists have discovered a new protein that likely will advance the search for new natural antibiotics, according to a study by Texas A&M AgriLife Research published Feb. 13 in the journal Nature Microbiology.

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Mutant maize offers key to understanding plant growth - Phys.Org

Biochemistry

Roses are red, violets are bluewhat gives flowers those eye … – Phys.Org

February 13, 2017 by Cheryl Dybas Knock-your-eyes-out red: A flowering plant native to Mexico called early jessamine or red cestrum. Credit: Stacey Smith

To solve the mystery of why roses are red and violets are blue, scientists are peering into the genes of plant petals.

"When you ask anyone how one flower is different from another, for most of us, color is the feature that first comes to mind," says evolutionary biologist Stacey Smith of the University of Colorado Boulder.

Most people don't think about why a flower is a particular color, but it's an important question for biologists, says Prosanta Chakrabarty, a program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funds Smith's research.

Smith and her team are "looking at the genetics of flower colors, and at changes in those colors over time," Chakrabarty says.

It all comes down to biochemistry

In nature, flowers come in hues that span the rainbow.

"On a microscopic level, the colors come from the biochemical composition of petal cells," Smith says.

Pigments are the main chemicals responsible. Plants contain thousands of pigment compounds, all of which belong to three major groups: flavonoids, carotenoids and betalains. Most flower colors come from flavonoids and carotenoids.

"In addition to giving flowers their colors, carotenoids and anthocyaninswhich are flavonoidshave antioxidant and other medicinal properties, including anti-cancer, antibacterial, antifungal and anti-inflammatory activity," says Simon Malcomber, a program director in NSF's Division of Environmental Biology.

Malcomber says the research could show how plants evolved to synthesize the carotenoids and anthocyanins that produce red flowers. "The results could be used in future drug discovery research," he says.

Much of Smith's work is focused on understanding how changes in flavonoid and carotenoid biochemistry relate to differences in flower colors. She and colleagues conduct research on the tomato family, a group of about 2,800 species that includes tomatoes, eggplants, chili peppers, tobacco and potatoes.

"These domesticated species don't have a terribly wide range of flower colors and patterns, but their wild relatives often do," Smith says. "So we study wild, or undomesticated, species, which are most diverse in South America."

Hot pursuit of red-hot color

Smith has had her share of adventures in the fieldlike the time she tried to find a plant with red flowers that lives at the base of a volcanic crater in Ecuador.

"It was my very first field trip, and I wasn't super-savvy," Smith says. "I took a bus to the outside of the crater, dragged my suitcase up to the rim then down into the crater, assuming there would be a village and a way to get out. There was neither. Thankfully, there was a park station nearby where I was able to stay overnight. I found the species in full flower in the forest the next day."

Smith is currently in hot pursuit of an answer to the question: When did red flowers first appear in the tomato family? "We thought that red flowers might have evolved many times independently of each other because red-flowered species are scattered among many branches of this family tree," she says.

Just 34 species in the entire tomato family, however, have red flowers.

"With such a small number, we can take samples of every one of these species to find out whether it represents an independent origin, and to determine the biochemistry of how it makes red flowers," Smith says.

She and other biologists traveled from Brazil to Colombia to Mexico to track down red flowers and measure their pigments. "We found surprising patterns," Smith says, "including that nearly every red-flowered species represents a new origin of the color, so red flowers have evolved at least 30 different times."

While the researchers expected that flowers would be red due to the presence of red pigments, they found that plants often combine yellow-orange carotenoids with purple anthocyanins to produce red flowers.

"Our studies are now aimed at tracing the entire genetic pathway by which plants make flower colors and identifying genetic changes to see if there are common mechanisms," Smith says.

The scientists want to know, for example, what changes have taken place since flowers first became red.

Answers in a petunia

"We're focusing on a single branch of the tomato family [petunias], creating an evolutionary history and conducting measurements of gene expression, pigment production and flower color," says Smith.

Petunias and their colorful relatives are good choices for this research, according to Smith.

"Most of us have seen the tremendous variation in petunia colors at our local nurseries, and indeed, petunias have served as models for studying flower color and biochemistry for decades."

Few people, though, are aware of the variation in petunias' wild relatives, most of which are found in Argentina and Brazil. "We're harnessing this natural diversity, as well as genetic information already available from ornamental petunias, to reconstruct the evolutionary history of flower colors," says Smith.

"If earlier studies taught us anything," she adds, "we shouldn't expect flowers to play by the rules."

Will roses always be red, and violets blue?

Explore further: Turning pretty penstemon flowers from blue to red

While roses are red, and violets are blue, how exactly do flower colors change?

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A new report from the Stowers Institute for Medical Research chronicles the embryonic origins of planaria, providing new insight into the animal's remarkable regenerative abilities.

How plant cells divide and how that contributes to plant growth has been one of the longstanding unsolved mysteries of cell biology. Two conflicting ideas have fueled the mystery.

Watching the smooth movement generated by hundreds of fish as they swim in unison is truly mesmerising. But it's not only its sheer beauty that makes it so hard to look away, for scientists, it's also the fact that its emergence ...

Recent evidence demonstrates that the origins of photosynthesis can be found in deep sea hydrothermal vents, where microbes evolved to obtain energy from ejected hydrogen sulfide and methane gases. These microbes are capable ...

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Scientists have discovered a new protein that likely will advance the search for new natural antibiotics, according to a study by Texas A&M AgriLife Research published Feb. 13 in the journal Nature Microbiology.

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Roses are red, violets are bluewhat gives flowers those eye ... - Phys.Org

Anatomy

John Oliver Details the Anatomy of Trump’s Falsehoods – Newsweek

John Oliver used the first episode of the new season of Last Week Tonight to dissect what he sees as Donald Trump's aversion to facts. Pointing out that the president "has made it clear that reality is not important to him" is nothing new; media outlets do it all the time. But Oliver wanted to delve a little deeper into the anatomy of Trump's grand pronouncementsthat are not supported by evidenceabout such things as the size of his inauguration crowd, voter fraud, the unemployment rate, the national GDP, the murder rate. Policy is being made based on such false information, and, as Oliver points out, people are getting hurt because of it.

Related: John Oliver says he is concerned about being able to stay in America

Politifact found that 25.2 percent of the statements made by President Barack Obama were false by some measure. For Trump, the number is 69.9 percent. Where do Trump's falsehoods come from?

Try Newsweek for only $1.25 per week

Oliver says Trump's worldview is reinforced primarily by cable newsor questionable websites like Breitbart or Infowars. The former routinely runs headlines like "Birth Control Makes Women Unattractive and Crazy," while the host of the latter, Alex Jones, believesthe Boston Marathon bombing and the Sandy Hook massacre were orchestrated by the government, among other conspiracy theories.Trump's reliance on cable news has been made clear through his tweets, which often reflect just-aired Fox News segments. As Oliver breaks it down, "Trump sees something that jibes with his worldview,doesnt check it, half-remembers it and then passes it on, at which point it takes on a life of its own and appears to validate itself.

Oliver uses as an example Trump's claims that millions of illegal votes were cast in the election, an idea for which there is no factual evidence.The claim originated from a Twitter user. Itwas then picked up by Infowars. It was debunked, but Trump tweeted about it. Then others talked about it on TV. This allowed theclaim to gainlegitimacy, at least for a certain section of the population.If you get your news from similar sources to him, which many people do, he doesnt look like a crank," Oliver says."He looks like the first president ever to tell you the real truth.

Trump's belief that "thousands" of New Jersey Muslims celebrated 9/11 terrorist attacks took on a similar life. When Bill O'Reilly pointed out that there was no evidence to support the claim, Trump doubled down,citing a Breitbart articlethat said he was "100% vindicated." O'Reilly said once again that there was still no real evidence and that this was never reported,but Trump said he was right because the article said people were swarming all over the place. "I don't know what that means," Trump said. "But it means a lot of people."

Oliver points out: Even if you take the kindest approach here and assume Trump made an honest, innocent mistake and passed on a news story without checking it, when he was presented with a lack of evidence, he disregarded that fact, at which point he is lying."

So how can frustrated Americans combat this problem? Oliver says it's up to the media to continue to check Trump's facts, even though the effectiveness of doing so has been diminishedas the Trump administration continuesto vilify the press. Beyond that, he says the people and organizations who oppose Trump need to stay vigilant with their protests, their lawsuitsand their diligence in double-checking the sourcing ofwhat they see on social media before they share it themselves.

Oliveralso has another solution. Because Trump loves cable news so much, Last Week Tonight bought ad space during some of the president'sfavorite morning programs. His show will use the space to airads that detailthe basics of issues about which Trump should probably be familiar, like the nuclear triad or the names of hischildren.Until we are shut down, we are prepared to educate Donald Trump one-by-one on topics were pretty sure he doesnt know about," says Oliver. Make sure you don't skip the commercials next time you tune in to Morning Joe.

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John Oliver Details the Anatomy of Trump's Falsehoods - Newsweek

Anatomy

Macabre event Anatomy Lab LIVE is really happening in Cornwall on April Fool’s Day – Cornwall Live

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It may seem like an unbelievable event and be happening on April Fool's Day but Anatomy Lab LIVE is definitely real and is definitely coming to Cornwall.

We announced last month that the intriguing tour where you have a two-course dinner before watching a "body" being dissected was coming to Cornwall and now the date and venue has been announced.

The sell-out tour Anatomy Lab LIVE will perform a live dissection of VIVIT the world's only semi-synthetic human cadaver for audiences this April.

Anatomist Samuel Piri will perform the dissection procedure to showcase health and disease on real internal organs at this unforgettable event.

VIVIT is a specially constructed synthetic human cadaver that houses real organs. During the procedure Samuel will dissect VIVIT to reveal the inside of the head and jaw demonstrating the brain and spinal cord.

READ MORE: New live show which lets you eat dinner before seeing a body dissected

Following this Samuel will open the thoracic cavity to show the trachea, lungs and heart followed by the abdominal cavity revealing the stomach, liver, gall bladder, intestines, kidneys and bladder.

All of VIVIT's organs are of swine origin due to their anatomical similarities with humans.

READ MORE: Planetariums, pirates and playfests - 23 great things to do with the kids in Cornwall this half-term

Live on stage Samuel will compare the human body in its healthy form to anatomical samples damaged by excessive alcohol consumption and smoking.

Audiences will have chance to put their questions to Samuel and to leading medics accompanying him on stage. Following the procedure the samples will be prepped for handling by those in the audience who wish to further examine the specimens.

The Cornwall tour event will be held at St Mellion International Resort on Saturday, April 1. The event begins at 6pm finishing at 11.45pm. Tickets include a two-course sit down meal before the procedure begins. Tickets are priced 60 per person or a group ticket that admits 6 is 300. All ticket holders must be over 16.

For more information visit http://www.inspiretoaspireevents.co.uk

WHAT'S ON IN CORNWALL

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Macabre event Anatomy Lab LIVE is really happening in Cornwall on April Fool's Day - Cornwall Live

Anatomy

‘Grey’s Anatomy’ Star Justin Chambers on Karev’s Fate: ‘He Just Never Seems to Catch a Break’ – Variety

Last weeks Greys Anatomy revealed the fate of Alex Karev (Justin Chambers).

After numerous episodes this season dealt with the aftermath of Karev beating up DeLuca (Giacomo Gianniotti), Alex had decided to accept a plea deal, which would put him behind bars. However, he had gone missing and no one knew what he was up to until last week when suddenly, he surprised Meredith at home.

The episode last week cut with Karevs surprise return home, begging the question, how did he get out of jail time? Tonights ep will reveal all of those details. But first,Variety chatted with Chambers aboutwhat to expect now that Alex is back.

I think having everything taken from him I think he learned a lot there, but I think he appreciates being in peace and hes very good at what he does and he thrives there, Chambers explains of how the experience will change Alex.

As for Jo (Camilla Luddington), their relationship will require a lot of work to get back on track. He was going to take a plea deal to protect his girl. Theyre not together right now, but well see where that goes, Chambers says.Hes still angry with her, but if anyone knows anything about second chances, its Alex. So he has that to think about. She messed up, but there must be a piece of him that still feels for her. Love just doesnt die like that.

Whatever happens, Chambers has a personal wish for his character: I just hope Alex finds some happiness. Crap. He just never seems to catch a break. Im thinking soon there might be some stability, he teases.

However, in real life, Chambers is ecstatic to be experiencing 13 seasons of stability

Its a blessing. Its crazy. Its so awesome, the original cast member says of Greys Anatomys flourishing in its 13th season.With a laugh, he adds, Even ER, I think theirratings dropped a lot in their 13th year.

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'Grey's Anatomy' Star Justin Chambers on Karev's Fate: 'He Just Never Seems to Catch a Break' - Variety

Anatomy

UNLV introduces virtual touch for anatomy instruction – Health Imaging

University of Las Veags (UNLV) will join a few other schools across the nation in using virtual anatomy tables in teaching programs to examine a patient without destroying vital organs.

The university's vice dean for academic affairs and education, Ellen Cosgrove, MD, said in a statement the school's committment to teaching students in a way sets the school apart from other medical programs.

This new technology displays images of the body from different perspectives and angles, 2D cross-section and 3D rotation. A few touches here and there can demonstrate different parts of the bodya simple touch can light up the veins.

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UNLV introduces virtual touch for anatomy instruction - Health Imaging

Genetics

Will Seattle Genetics’ Deal With Immunomedics Get Scuttled? – Madison.com

Last week, Seattle Genetics (NASDAQ: SGEN) announced an agreement to licenseImmunomedics'(NASDAQ: IMMU) IMMU-132, a cancer drug that's already completed midstage phase 2 trials.

The deal could be a big win for Seattle Genetics, but it doesn't have the full support of all of Immunomedics investors. After the closing market bell on Friday, venBio Select Advisors, LLC -- the beneficial owner of 9.9% of Immunomedics shares -- said Immunomedics' board of directors is "giving away its crown jewel."

IMAGE SOURCE: GETTY IMAGES.

If the deal closes, Seattle Genetics will take over development of IMMU-132, an anti-TROP-2 antibody that can target multiple tumor types. Breast cancer, lung cancer, and colorectal cancers all overexpress the TROP-2 protein and therefore could conceivably be treated by IMMU-132.

In phase 2 trials of IMMU-132 in triple negative breast cancer, there was a 29% overall objective response rate in heavily pretreated patients. Historically, the duration of response in fifth-line triple negative breast cancer patients is measured in months, but IMMU-132 delivered a 10-month duration of response and a median overall survival rate of over 18 months.

About 15% of breast cancer patients are triple negative, and patients with this type of breast cancer have a poor prognosis. According to the National Cancer Institute, 246,660 new cases of breast cancer are diagnosed annually, causing 40,450 deaths every year.

There's a big need for new treatments, and that hasSeattle Genetics thinking IMMU-132 could qualify for an accelerated FDA approval. If so, then IMMU-132 will become Seattle Genetics' second commercial-stage drug. Management didn't offer up a timeline for filing a new drug application with the FDA; however, it did say it's going to evaluate its options and update investors on a future conference call.Last fall, Immunomedics told investors it hoped to file for FDA accelerated approval in the middle of 2017.

Seattle Genetics will pay Immunomedics $250 million in cash up front, plus an additional $50 million payment related to ex-U.S., Canada, and EU rights. If it wins an FDA green light, Immunomedics has an option to co-market IMMU-132 in America. Otherwise,Seattle Genetics will pay Immunomedics a tiered double-digit royalty that's based on sales.

Seattle Genetics also agreed to pay Immunomedics up to $1.7 billion in regulatory and sales milestone payments on IMMU-132, and Seattle Genetics agreed to let Immunomedics continue negotiating with other companies on rights to IMMU-132 until Feb. 19. If a competing offer is made, Seattle Genetics can match it. If Immunomedics selects a competing offer, then it will pay Seattle Genetics a breakup fee.

Separately, Seattle Genetics acquired 3 million shares of Immunomedics at $4.90 per share that aren't tied to the closing of this deal. Seattle Genetics also secured three-year warrants that allow it to acquirean additional 8,655,804 shares at $4.90 each.

Seattle Genetics already markets the lymphoma drug Adcetris, which is FDA approved for treating Hodgkin lymphoma patientswhose disease has progressed after autologous stem-cell transplant or after two prior chemotherapy treatments, if ineligible for transplant.Adcetris is also used to treat patients with systemic anaplastic large-cell lymphomawhose disease has progressed after one prior chemotherapy treatment. A trial evaluatingAdcetris as a front-line Hodgkin lymphoma therapy is anticipated to read out data this year.

With$265.8 millionin sales last year, Adcetris is no slouch, but IMMU-132 has the potential to haul in far more in revenue than that. Immunomedics commissioned an independent analysis of IMMU-132's market potential last year, and that study estimates that IMMU-132 could generate annual sales of $3 billion in 2025, if it gets approved for use in triple negative breast cancer,urothelial cancer, and lung cancer.

That's a big opportunity, but there's no guarantee that IMMU-132 will get an early OK from the FDA, and if it doesn't, then Seattle Genetics will have to conduct a confirmatory phase 3 study. While midstage trial results were solid, investors should remember that, historically, 30% to 40% of drugs that advance into phase 3 trials fail.

Of course, for Seattle Genetics to benefit from IMMU-132 at all, this deal has to close, and based on venBio's comments, that might not be a given. Immunomedics is engaged in a proxy fight with venBio, and in its statement onFriday,venBio's Behzad Aghazadeh said, "Immunomedics' announcement of a deal with Seattle Genetics is a blatant and shameful maneuver by the current board and management to manipulate the outcome of the upcoming annual meeting and entrench themselves at the expense of stockholders' best interests, and venBio is exploring all options to hold them accountable."

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Will Seattle Genetics' Deal With Immunomedics Get Scuttled? - Madison.com

Embryology

For LI couple, in vitro fertilization procedure goes on, despite storm – Newsday

Gold Coast IVF Medical Director Steven Palter, left, and Embryology Lab Director Ed Stehlik, had to scramble to prepare to help five women who were ready to have embryos extracted during a narrow time window during the storm, Thursday, Feb. 9, 2017. (Credit: Danielle Finkelstein)

Kim Farrell had an important appointment to keep Thursday morning.

The date and time had been set for her fertility doctor in Woodbury to extract the eggs that she hopes will give her and her wife Dee their second child this year.

Nature, however, had its own designs.

A storm was brewing, snow was coming and it would be arriving, well, at about the same time as the two-hour window...

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For LI couple, in vitro fertilization procedure goes on, despite storm - Newsday

Embryology

Baby boom after fertility treatment – Independent Online

Prague - More than three million babies have been born following fertility treatment since the birth of the first IVF child nearly three decades ago, according to a report released on Wednesday.

Louise Brown made medical history when she was born in Britain after her mother had in-vitro fertilisation (IVF).

Since then the number of children conceived each year through assisted reproductive technologies (ART) has risen from 30 000 in 1989 when data was first collected to 200 000 in 2002.

"The... report covers two-thirds of the world's ART activity, so the total number of ART cycles in the world can be estimated at one million a year, and the number of ART babies produced at around 200 000 a year," said Dr Jacques de Mouzon of the International Committee for Monitoring Assisted Reproductive Technologies (ICMART).

The ICMART report shows the average pregnancy rate using fresh embryos was 25,1 percent and the delivery rate was 18,5 percent.

"However, these rates varied from 13,6 percent to 40,5 percent for pregnancy, and 9,1 percent to 37,1 percent for delivery," Dr de Mouzon said.

Fertility treatments were most available in Israel and Denmark, which also have among the highest percentage of ART babies. It was lowest in Latin America where fewer than 0.1 percent of births were due to ART.

"There is a real inequality between the different countries, and this is due to money," said Dr de Mouzon.

"Some countries provide free cycles of IVF, while in others, couples cannot have ART unless they can pay for it, for example through medical insurance."

The report released at the European Society of Human Reproduction and Embryology (ESHRE) meeting also showed that fertility clinics are moving towards transferring only one embryo during treatment to reduce the number of multiple births.

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Baby boom after fertility treatment - Independent Online

Embryology

‘Screening cuts chances for healthy babies’ – Independent Online

Lyon, France - Screening embryos for chromosomal defects, a fast-growing practice aimed at helping older women to have a baby, in fact reduces the chance of a successful pregnancy, doctors reported on Wednesday.

The process, called preimplantation genetic screening (PGS), entails taking a cell from a lab-dish embryo on its third day of development, and testing a number of its chromosomes for any abnormalities.

The goal is to filter out embryos that could develop abnormally and trigger miscarriage, leaving only the fittest for transfer to the uterus.

But Dutch fertility experts, led by the University of Amsterdam's Sebastiaan Mastenbroek, said their own large-scale investigation found PGS in fact lowers the success rate.

They looked at 408 women, aged 35 to 41 who had had three cycles of in-vitro fertilisation (IVF).

One randomly-selected group of 206 women was given PGS, while the other 202 were not given PGS, thus acting as a "control" group, or comparison.

"We found that, at 12 weeks, 52, or 25 percent, of the women in the PGS group were pregnant, whereas 74, or 37 percent, of the control group had an ongoing pregnancy," Mastenbroek said.

"And the women in the PGS group also had a significantly lower live birth rate - 49, or 24 percent, as opposed to 71, or 35 percent, of the controls."

The research was unveiled at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE), taking place in this southeastern French city. It was also published simultaneously in the New England Journal of Medicine.

PGS is a relatively new technique that is in increasing use in IVF centres around the world. But the process also has stirred concerns that it encourages eugenics, and some countries ban it or restrict its use to embryos from parents who have an inherited disease.

Mastenbroek said there could be several explanations why PGS had failed in these older women.

One was that the taking of the sample cell, a process called a biopsy, could somehow affect the embryo's potential to develop normally, he said.

Another possible cause was that the number of chromosomes which are analysed was too small. This meant that embryos which had been certified as normal were in fact abnormal, because they carried one or more flawed chromosomes that had not been tested.

A third explanation could be that the biopsied cell may be an odd-one-out - it may not be representative of the chromosomal composition of the whole embryo.

Mastenbroek said further work was needed to see whether PGS was effective or not in other groups of women, such as those who suffer recurrent miscarriage.

But, he said, the results of his research suggest PGS should not be carried routinely for older would-be mothers.

Meanwhile, British and Danish researchers said infertile women who turn to so-called complementary therapies such as reflexology and nutritional supplements to support their IVF treatment also have a lower chance of pregnancy.

Their study of 818 Danish women in the 12 months following the start of IVF found that those who used complementary therapies had a 20-percent lower pregnancy success rate.

"It may be that complementary therapies diminish the effectiveness of medical interventions, as has been shown in previous research," said Jacky Boivin of Cardiff University, Wales.

"Or it may simply be that persistent treatment failure encourages women to seek out CATs because they are more willing to try anything to get pregnant."

The next step is to study the same group over five years to get a longer-term view of the pregnancy rate.

"It is important to do this because we are concerned that, with persistent treatment failure, women might become more and more susceptible to deceptive advertising about ineffective CATs or other unproven treatments," Boivin said.

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'Screening cuts chances for healthy babies' - Independent Online