From: Subject: UT Knoxville Professor Finds Unexpected Key to Flowering Plants' Diversity Date: Fri, 1 Aug 2008 14:21:01 -0300 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01C8F3E1.D30EC1D0" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01C8F3E1.D30EC1D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://www.utk.edu/news/article.php?id=4677 UT Knoxville = Professor Finds Unexpected Key to Flowering Plants' Diversity

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UT Knoxville Professor Finds Unexpected Key to Flowering Plants'=20 Diversity

July 29, 2008

KNOXVILLE -- What began with an off-the-cuff curiosity eventually led = Joe=20 Williams to hang from the limbs of a tree 80 feet above the soil of = northeastern=20 Australia.

Austrobaileya=20 flowerThe things Williams, a University of Tennessee, Knoxville,=20 researcher found there may help explain the amazing diversity in the = world's=20 flowering plants, a question that has puzzled scientists from the time = of=20 Charles Darwin to today.

Williams' findings, published online = this week=20 by the Proceedings of the National Academy of Sciences, show that the = ability of=20 flowering plants -- known as angiosperms -- to quickly and efficiently = move=20 sperm from pollen to egg through a part of the plant was the key to = their=20 evolutionary diversity.

His curiosity was based in the time it = takes from=20 when pollen lands on a plant to the time that its seed is fertilized. = Williams=20 noticed a recurring theme in the research papers he read:

"They = would=20 usually describe how fertilization was occurring, but they never tell = you much=20 about timing," said Williams, an assistant professor of ecology and = evolutionary=20 biology at UT Knoxville.

For a seeded plant to fertilize, pollen = that=20 lands on the flower must grow a tube to carry sperm to the egg. In = non-flowering=20 plants, the pathway is usually short, because the pollen tube must = destroy cells=20 in its path, which is a time-consuming process. In flowering plants, = though,=20 pollen tubes are able to cover longer distances to the egg by = essentially=20 "squeezing" between cells. It is a trait that Williams says is vital to = their=20 diversification.

"The longer a plant takes to fertilize, for the = pollen=20 to reach the egg," said Williams, "the more chance there is for it to=20 die."

When he studied the data he had collected through the = years,=20 Williams found that older lineages of flowering plants -- those on lower = branches of the angiosperms' evolutionary family tree -- grew shorter = tubes of=20 pollen than those that went on to evolve into the diverse array of = flowering=20 plants that exist today.

That's what brought Williams to a = harness in the=20 rainforest of Australia. To confirm what he found in the data analysis, = he=20 pollinated -- by hand -- an ancient vine known as Austrobaileya that = grows high=20 in the canopy. He chose that plant, along with another plant found only = on the=20 Pacific island of New Caledonia and a water lily that grows high in the = Colorado=20 mountains, to test because they developed as species early in flowering = plants'=20 evolution.

He found that, when compared to more recently evolved = species=20 of angiosperms, the older plants grew shorter pollen tubes and took = longer to do=20 so than more diverse modern species. According to Williams, this = indicates that=20 these pollen tubes likely played a previously unknown role in spurring = the=20 evolution of the roughly 250,000 species of flowering plants we see=20 today.

"As these plants gained the ability to grow pollen tubes = faster=20 and over longer distances," said Williams, "It gave them the ability to = develop=20 the much larger and more complex flowers as well as deeper ovaries with = more=20 seeds -- that is to say, larger fruits -- that we see around us=20 today."

Williams' work was funded by UT Knoxville and the = National=20 Science Foundation.

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Contacts:

Jay Mayfield = (865-974-9409,=20 jay.mayfield@tennessee.edu)
Joe Williams (865-974-6202,=20 joewill@utk.edu)

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UT Knoxville Professor Finds Unexpected Key to Flowering Plants'=20 Diversity

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