Is your leaf left-handed? Previously overlooked asymmetry in Arabidopsis and tomato leaves

Jun 22, 2012
This is a model of developing leaves. Credit: Richard Smith

Research published in the Plant Cell shows that the spiral pattern of leaf formation from the point of growth affects the developing leaf's exposure to the plant hormone auxin; This exposure leads to measurable left-right asymmetry in leaf development, in species previously assumed to have symmetric leaves.

The front of a leaf is different from the back of a leaf and the tip is different from the base. However, a leaf from a tomato or an Arabidopsis plant superficially appears to be bilaterally symmetrical, or the same on the left and right sides. Don't let its appearance fool you; there is an underlying between the left and right sides of such leaves—it just took a while for scientists to discover it. The story begins with the mechanism by which leaves form along a stem. In broad-leafed , dicots, leaves form from the meristem, an actively dividing tissue at the top of the plant, so that as you look down the stem, the oldest leaves are at the bottom. Leaves don't just become arranged by random chance either—phyllotaxis, the arrangement of leaves or flowers along a stem, affects key plant characteristics, such as how much light can filter through to lower leaves. Leaves can form opposite each other, or in alternation, or in whorls; often leaves form in spirals where the next leaf is offset by roughly 137 degrees, known as the "golden angle", which is related to the Fibonacci sequence.

Recent research has shown that leaf initiation in the meristem is specified by locally high concentrations of the . In a study published in The , an international group coordinated by Neelima R. Sinha, Ph.D., of the University of California at Davis, examined how the pattern of auxin concentrations might affect the symmetry of the leaf. She explains, "As leaves are initiated within a spiral context, we might expect that they would be asymmetric and exhibit the same handedness of the spiral, like propeller blades. Yet, superficially many leaves appear symmetrical." To examine whether the spiral pattern of leaves affected symmetry, her team first modeled the anatomy of the forming leaves and the location of the highest concentrations of auxin, finding that the two were not perfectly aligned. Following up, they found that this difference caused asymmetry at both the molecular level, altering gene expression, and the anatomical level, altering leaf shape, in tomato and Arabidopsis thaliana leaves. Indeed, the authors found measurable anatomical differences between the left and right sides of both young and mature leaves, identifying a previously overlooked axis of asymmetry.

Dr. Sinha summarizes: "Our results show that asymmetry is indeed very much present in the leaves around us and that the spiral, within which they are initiated, influences their development from the earliest stages. Quite literally, the handedness of the spiral in plants transmits its asymmetry to leaves. By studying these asymmetries, we can begin to understand the mechanisms by which plants produce such a staggering array of shapes in such regular arrangements."

Explore further: A step into the unmown creates a 'win-win' for wildlife and humans

More information: www.plantcell.org/content/earl… 98798.full.pdf+html/

Related Stories

Can a single layer of cells control a leaf's size?

Feb 25, 2010

Ever looked carefully at the leaves on a plant and noticed their various sizes and shapes? Why are they different? What controls the size and shape of each individual leaf? Very little is known about the developmental ...

Why do dew drops do what they do on leaves?

Jan 11, 2012

Nobel laureate poet Rabindranath Tagore once wrote, "Let your life lightly dance on the edges of time like dew on the tip of a leaf." Now, a new study is finally offering an explanation for why small dew drops ...

How size matters: The beauty of nature explained

Dec 12, 2007

The beauty of nature is partly due to the uniformity of leaf and flower size in individual plants, and scientists have discovered how plants arrive at these aesthetic proportions.

Recommended for you

Dogs can be pessimists too

5 hours ago

Dogs generally seem to be cheerful, happy-go-lucky characters, so you might expect that most would have an optimistic outlook on life.

Transparent larvae hide opaque eyes behind reflections

19 hours ago

Becoming invisible is probably the ultimate form of camouflage: you don't just blend in, the background shows through you. And this strategy is not as uncommon as you might think. Kathryn Feller, from the University of Maryland ...

Peacock's train is not such a drag

20 hours ago

The magnificent plumage of the peacock may not be quite the sacrifice to love that it appears to be, University of Leeds researchers have discovered.

User comments : 0