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Fresh insights into the Venus flytrap

08.09.2011
Trap closes, insect dies: the plant known as the Venus flytrap relies on an ingenious mechanism for capturing tiny creatures. Researchers from the University of Würzburg are now providing new insights into how this insect trap works in the magazine PNAS.

In the wild, the Venus flytrap only grows in wetlands deficient in nutrients in the USA. The insects that it captures and digests with its leaves provide it with valuable additional nutrition. If a fly or ant crawls around on the plant’s two-lobed leaves, the plant registers this contact and snaps its leaves shut in a fraction of a second, trapping its prey. In a kind of little “green stomach”, gland secretions then cause the fly or ant to be digested. The nutrients released mainly from the proteins in the prey are absorbed by the Venus flytrap so that it can expand its arsenal of traps.



Open Venus flytrap (A): The sensory hairs are clearly visible; their nature is made clear in the sectional enlargement (B) using scanning electron microscopy. If potential prey touches a hair, the hair’s cells are squeezed so that it bends. This creates an electrical signal that travels over the surface of the trap. If a second signal follows shortly after, the trap snaps shut. From its rosette-like gland complexes (visible in B) the plant then secretes digestive enzymes. There are 60 glands for every square millimeter, so around 37,000 per trap.
Images: Christian Wiese (A), Benjamin Hedrich (B)


Electrical, chemical, and mechanical signals

“Ever since the days of Charles Darwin, biologists have been trying to find out how sensors and biomechanics function in the Venus flytrap", says Professor Rainer Hedrich. This biophysicist and his team from the University of Würzburg have now made new discoveries. In the US journal PNAS (Proceedings of the National Academy of Sciences) they describe how the Venus flytrap couples electrical, chemical, and mechanical signals in order to capture and digest insects.

The Würzburg scientists were assisted in their work by Nobel Prize winner Erwin Neher from Göttingen, an expert in secretion processes in animal cells, and by plant hormone specialist Bettina Hauser from Halle.

“Touch” hormone stimulates digestion

Once an insect is caught in the trap, it tries desperately to escape. But these mechanical stimuli activate the trap more and more: it produces the touch hormone OPDA, which in turn triggers the glands in the trap to secrete digestive enzymes. This can be demonstrated using an experiment: if a compound resembling OPDA is administered to the traps, they shut and form a stomach in which the glands become active – without any contact stimuli from prey whatsoever.

Stimulation puts other traps on high alert

The researchers have made another finding: if a trap is stimulated by the OPDA hormone, it forwards this chemical signal to the other traps, putting them on higher alert of a catch. This makes perfect sense as insects rarely arrive on their own: where one ant appears, there are likely to be others following closely behind.

Stimulated traps also respond with a series of action potentials, i.e. a temporary change in the electrical conductivity of their cell membranes. “From action potential to action potential, the trap closes ever more tightly. By struggling to survive, the victims keep on making their situation worse", says Hedrich.

Going without food during times of drought

The secretion of digestive fluid also means a loss of water for the Venus flytrap. So, how does it react during times of drought? What happens is that the water stress hormone abscisic acid makes the plant less sensitive to touch and suppresses the production of watery secretion, as the scientists have established. In the event of a shortage of water, the flytrap goes without food – it starves itself so it does not die of thirst.

Deciphering the genetic make-up of the Venus flytrap

Hedrich’s conclusions: “The closing of the traps and the secretion of digestive liquid appear to be controlled via different signal paths. The task is to nail the genes responsible. That is why we are now working on deciphering the genetic make-up of the Venus flytrap.” The scientists also want to discover how this carnivorous plant puts together a fluid that will digest its prey.

Millions from the European Research Council

Hedrich is pressing ahead with his research into the Venus flytrap and other carnivorous plants thanks to top-level funding. The European Research Council has given him a grant of EUR 2.5 million for his work. Hedrich’s team consists of ten bioinformaticians, molecular biologists, chemists, and biophysicists. The researchers are planning to analyze the genetic material of the main types of trap as well as the genes that are only active in the traps. By comparing different plant species, they want to find clues as to the evolution of this special diet.

María Escalante-Pérez, Elzbieta Krol, Annette Stange, Dietmar Geiger, Khaled A. S. Al-Rasheid, Bettina Hause, Erwin Neher, and Rainer Hedrich: „A special pair of phytohormones controls excitability, slow closure, and external stomach formation in the Venus flytrap”, PNAS 2011, published online on 06-11-2011, doi:10.1073/pnas.1112535108

Contact

Prof. Dr. Rainer Hedrich, T +49 (0)931 31-86100,
hedrich@botanik.uni-wuerzburg.de

Robert Emmerich | Uni Würzburg
Further information:
http://www.uni-wuerzburg.de
http://www.pnas.org/content/early/2011/08/29/1112535108.full.pdf+html?sid=e066daaa-7d91-4817-a04c-a27b4c9645a6

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