Different plants exhibit leaves with very diverse shapes, and scientists studying a carnivorous plant called Utricularia gibba (bladderwort) have learned how nature creates all the various leaf forms we see in the world. The bladderwort generates cup-shaped leaves that can catch prey with trap doors, and the researchers used the aquatic plant as a model in their study of leaf production. They learned how gene expression is manipulated in the leaf bud to produce leaves of all shapes and sizes. The findings have been reported in Science.
"We've discovered a general principle by which leaves from flat sheets to needle-like and curved shapes are formed," said Professor Enrico Coen of the John Innes Centre. "We found that the complex leaf shapes of carnivorous plants evolved from species with flat leaves through simple shifts in gene activity in the leaf bud. What surprised us is that such a simple mechanism could underlie such a wide diversity of leaf shapes."
Previous work by the Coen lab identified a type of intrinsic cellular compass called a polarity field that orients cells as they grow and form leaves. In this new research, they studied gene expression and computer modeling to assess the formation of cellular sheets. This revealed a second polarity field and the gene activity that controls it. Their work reveals the biological mechanism behind the formation of different leaf shapes, and how cup-shapes can evolve from flat leaves.
The leaves of the bladderwort have needle-like leaflets that are coupled with a trap. The traps are triggered and develop based on gene activity that is contained within a small area. If the gene expression is not restricted to this area, the traps don't form, only the leaflets do.
Flat leaves can use light in photosynthesis, and the cup-shaped leaves are exceptions to the rule. Their unusual forms have helped researchers learn more about the basic principles of leaf generation.
"If you want to understand why water boils at 100 degrees Celsius, look for situations in which it doesn't, like the top of Mount Everest where it boils at 70 degrees Celsius. From that we learn the general principle that boiling point depends on air pressure. Similarly, if you want to understand why most leaves are flat, you might study exceptions, like the leaves of some carnivorous plants which form pitchers to trap prey," explained Professor Coen.
This work may now help plant breeders and scientists create crops that are more sustainable in a changing environment.