Thursday, November 1, 2007

Leaves' Fall Colors Have "Dirty" Secret, Study Finds


New Englanders are blaming this year's lackluster fall-color season on drought, but if you don't like the colors in your own backyard, you might blame the dirt, a new study says.

In an undergraduate research project, Emily Habinck, who has since graduated from the University of North Carolina at Charlotte, found that autumn leaf color is related to the richness of the soil.

She determined that on a North Carolina floodplain that was rich in nitrate—a nitrogen-containing nutrient—yellow-leafed trees dominated. But in the poorer soils of the hillside behind it, there were more reds.

Even among the trees that typically bear red leaves no matter the conditions, poorer soils made for redder hues.

Habinck based her study on her faculty advisor's observation that floodplain trees tended to be yellow and that soil nutrients might have something to do with it.

While Habinck was at work on the project, William Hoch, a plant physiologist at Montana State University, wrote a paper suggesting an additional link between the red-leaf pigment anthocyanin and autumn sunlight.

"It wasn't until I read his paper that it became a full story," Habinck said.

Leaf Protection

Leaves turn color in the fall as trees start shutting down their energy production and withdrawing nutrients into their roots.

"[The tree] pulls as many of these in as it can, then tries to drop just a skeleton of a leaf when it's done," Hoch said in a telephone interview.

But nutrient withdrawal takes time, and the process leaves the leaves vulnerable to damage from sunlight.

Anthocyanins protect leaves by "shading" them from excessive sunlight during the plant's relatively vulnerable autumn season, Hoch explained.

In a study of plants that had been genetically modified not to be produce anthocyanins, Hoch found that the modified plants were unable to send as many nutrients to their roots for winter storage.

"So the bottom line is that the plants that were able to produce red pigments were able to squeeze more of the nutrients out of their leaves than the ones that couldn't," he said.

Thus, Hoch says, plants living in nutrient-poor soils benefit more from anthocyanin than those living on better soils.

Scientists only recently made these connections, Habnick said, because when most other leaf-peepers are taking their fall-color tours, biologists are busy with academics.

"Most people's field season is in the summer," she said.

"Brainbows" Illuminate the Mind's Wiring


Genetically engineered mice furnished with fluorescent proteins are providing the most detailed pictures yet of the brain's intricate circuitry.
The innovation offers an intimate peek into the development and inner workings of the nervous system at the level of individual neurons, researchers say.

"Imagine the brain as a radio for which we never had a good wiring diagram," said Jeff Lichtman, a neurobiologist at Harvard University and a co-author of the study.

"The aim of this work is to tag the individual wires with their own color" to get a better idea of their connections, he added.

If every cell in the brain were imaged using a single color, Lichtman explained, numerous wires bunched together would be indistinguishable.

But the various fluorescent proteins used in the new research make the multitudes of strands that comprise the complex tissue of the nervous system stand out from each other.

In their effort to tease out the details of connections in the nervous system, Lichtman and his colleagues developed about 30 lines of mice.

The team incorporated a chain of three different fluorescent protein genes—which they call a brainbow—into these mice.

The researchers then crossed the genetically engineered mice with mice that expressed an Cre, an enzyme in their brains.

In the offspring of this cross, Cre randomly snipped off or rearranged the brainbow sequence. This process caused just one of the brainbow colors to turn on at any given point.

Since each cell contains multiple copies of the brainbow, the end result is a unique mixture of red, green, and blue colors in each cell—and a random riot of color in the brain overall.

"It is like a television monitor where three basic colors—red, blue, and green—mix together and form various other colors," said Lichtman, whose findings will appear tomorrow in the journal Nature.

Shape Matters

Ed Lein is director of neuroscience at the Allen Institute for Brain Science in Seattle, Washington.

The Harvard researchers, he said, have essentially developed a novel technique that allows one to look at the shape of many different neurons simultaneously.

"The shape of the neuron is a pretty powerful piece of information. It allows you to infer, and in some cases demonstrate, who that cell is connected to," Lein said. " It lets you look at detailed microcircuitry in the brain."

The technique, he explained, will help researchers look at the shape of cells during embryo development and postnatal development in real time—and perhaps understand the progression of disease.

"It is too difficult to trace the 'wires' of the brain, because they are so thin and it is easy to make mistakes," said Sebastian Seung, a computational neuroscientist at MIT.

"The brainbow technique makes it easier to trace them."