Subscribe free to our newsletters via your
. Earth Science News .




FLORA AND FAUNA
How some leaves got fat: It's the veins
by Staff Writers
Providence RI (SPX) Apr 18, 2013


Veins, housed within the purple-stained mucilage deposits of this cross-section of a succulent Phemeranthus teretifolius leaf, are arranged in a ring shape that reduces the distance between veins and photosynthetic cells. Credit: Matt Ogburn.

A "garden variety" leaf is a broad, flat structure, but if the garden happens to be somewhere arid, it probably includes succulent plants with plump leaves full of precious water. Fat leaves did not emerge in the plant world easily.

A new Brown University study published in Current Biology reports that to sustain efficient photosynthesis, they required the evolution of a fundamental remodeling of leaf vein structure: the addition of a third dimension.

Leaves, after all, are food factories complete with plumbing to transport water and sugar. The farther those veins are from cells performing photosynthesis, the less efficient the process will be.

Researchers Erika Edwards, a professor at Brown, and former graduate student Matt Ogburn, wondered how plants managed to evolve fat leaves, given the hydraulic challenges of gaining girth.

Of all plants, Edwards said, maybe succulents could sustain photosynthesis in fat leaves with sparse venation because they store so much water right where it's needed. But she and Ogburn found that even succulents were constrained by 2D veins.

"There must be some kind of a tradeoff in a fat leaf that's really different from most flat leaves," said lead author Ogburn, who is now a postdoctoral fellow at Yale. "There's a benefit to that in storing water in the leaf, but it's going to have a cost to it in terms of the other things the leaf has to do."

To do their study, Ogburn and Edwards looked deep into the catalog of two dry-climate plant groups, Portulacineae and Molluginaceae. They pieced together their evolutionary history, measured the water storage of 83 species, and the vein structure of 42.

Up to a certain level of thickness, leaves retained the planar vein structure of flat leaves. As a consequence, their vein structure was sparser and path lengths were longer - but only up to a point.

The researchers discovered that after a certain threshold of thickness, vein structure had evolved to become three dimensional, abandoning the single plane layout of flatter leaves for either an oval or circular orientation in cross-section.

That 3D vein structures independently evolved more than 10 times, in two ways, in just this limited sample of two lineages, suggests that the different vein structure is no coincidence, Ogburn and Edwards said. Instead it seems conclusively to be a functional trait that emerged to allow leaves to become thicker.

"If you had just a 2D-veined pile of species and a 3D-veined pile of species and you didn't know how they were related to each other, you might say, maybe 3D venation just evolved once a long time ago, and had absolutely nothing to do with succulence," Edwards said.

"But when you can lay them out on a phylogeny and reconstruct how many times this transition happened- the more times you see this repeated correlation between these two traits the more power you have to say that this is actually adaptive."

The researchers wrote that 2D arrangements of veins, because they produce a low density of veins in thicker leaves, likely imposed a hard limit on leaf thickness. Evolution of 3D veins allowed them to burst through those constraints.

"Increased leaf thickness [when veins are planar] negates the hydraulic benefits of dense leaf venation," Edwards and Ogburn wrote in Current Biology.

"It also predicts an upper limit to leaf thickness that would be set by the minimal functional vein density... However, the repeated evolution of 3D venation allowed for further increases in succulence while maintaining moderate hydraulic path lengths."

In other words, leaves became free to be fat, in an evolutionary vein.

.


Related Links
Brown University
Darwin Today At TerraDaily.com






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








FLORA AND FAUNA
Secrets of bacterial slime revealed
Newcastle, UK (SPX) Apr 18, 2013
Newcastle University scientists have revealed the mechanism that causes a slime to form, making bacteria hard to shift and resistant to antibiotics. When under threat, some bacteria can shield themselves in a slimy protective layer, known as a biofilm. It is made up of communities of bacteria held together to protect themselves from attack. Biofilms cause dental plaque and sinusitis; in he ... read more


FLORA AND FAUNA
Fukushima leaking radioactive water

IAEA begins fresh probe into Japan's Fukushima

Fukushima plant springs another radioactive leak

Hong Kong ferry crash captains face manslaughter charges

FLORA AND FAUNA
Softening steel problem expands computer model applications

New material gets itself into shape

For the very first time, two spacecraft will fly in formation with millimeter precision

High pressure gold nanocrystal structure revealed

FLORA AND FAUNA
Study reveals seasonal patterns of tropical rainfall changes from global warming

Liverpool Bay sediment discovery could save millions

Mass sea lion strandings baffle California

Cutting specific pollutants would slow sea level rise

FLORA AND FAUNA
New insight into accelerating summer ice melt on the Antarctic Peninsula

Recent climate, glacier changes in Antarctica at the 'upper bound' of normal

Austria's glaciers shrank in 2012: study

New chart shows the entire topography of the Antarctic seafloor in detail

FLORA AND FAUNA
Virginia Tech research team creates potential food source from non-food plants

Egypt faces food crisis over wheat shortage

Chickens with bigger gizzards are more efficient

Hundreds of pigs, dogs die in Chinese city: officials

FLORA AND FAUNA
Research aims to settle debate over origin of Yellowstone volcano

'Thousands' of Pakistanis affected by Iran quake

US offers aid as Iran quake kills 34 in Pakistan

Japan island rocked by 30 quakes

FLORA AND FAUNA
Radical Nigeria cleric rejects place on amnesty panel

Zimbabwe deputy PM tells Africa to be tough on China

Nigeria moves closer to amnesty offer for Islamists

Chad quits Mali war, French stick it out

FLORA AND FAUNA
New Research Reveals How Human Ancestor Walked, Chewed, and Moved

Pottery reveals Ice Age hunter-gatherers' taste for fish

Google adds 'digital estate planning' to its services

Better Understanding of Human Brain Supports National Security




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement