May 1, 2013
Genetic And Hormonal Signals Responsible For Shape, Function Of Leaves
Brett Smith for redOrbit.com - Your Universe Online
As the spring flowers (finally) begin to bloom across the United States, take a closer look and you may find a whole host of genetic and hormonal signaling that is responsible for the shape and function of various aspects of the leaves of plants.In the latest edition of the open access journal PLoS Biology, a group of UK biologists has detailed new insights into the differences and similarities between flowering plants´ petal and leaf formation.
Roses are the perfect example of how the same plant can grow pointed leaves, but fan-shaped petals use a similar signaling process, according to the researchers.
The group, led by Enrico Coen from the John Innes Centre (JIC) in Norwich, performed previous research on the leaf development in Arabidopsis, a mustard plant that is popular in laboratories. The team found that leaf shape is created partially by a hormone known as auxin, which is transported from cell to cell in a particular direction. This type of transport creates a polarity that drives auxin toward the tip of the leaf.
Leaf shape in Arabidopsis is also controlled by certain patterns of cell growth that occur relative to the auxin polarity field. For example, if cell growth rates are parallel with the polarity field near the tip of the leaf, they begin to slow — giving the leaf its shape.
For the new study, Coen´s group decided to see if these same mechanisms were responsible for flower petal growth. First the team analyzed the shape and growth patterns of the Arabidopsis flower petals. Then they used a series of computer models to see which would most correctly predict the petal´s growth patterns and shape.
Instead of examining the convergent model found to give leaves their narrowing shape, the UK team looked at a divergent model, in which the polarity field spread outward. This model was found to coincide with the researchers´ experimental data.
"The discovery of these hidden polarity maps was a real surprise and provides a simple explanation for how different shapes can be generated," Coen said in a statement.
To confirm their hypothesis surrounding the divergent model, Coen and his colleagues searched for signaling markers in the petals and found an auxin response marker known as DR5. They speculated that the convergent model would show more DR5 at the tip of the petal, while the divergent model would have the marker more broadly throughout the petal.
Using microscopic imaging, the researchers found that DR5 appeared at the tip of the petal in the early stages of petal development, but after one to three days of growth, it was broadly spread across the petal epidermal cells.
In the final part of their study, the team looked for a gene that might be responsible for petal development in Arabidopsis. The unique shape of petals in one mutant plant called JAGGED led the researchers to take a closer look at the JAG gene. They found that JAG is indeed involved in establishing the extent of the divergent polarity field, in part by regulating another gene known as PETAL LOSS, or PTL.