A young scientist from Comenius University presents a study on the recognition of prey by a carnivorous plant
How is it possible that a carnivorous plant is able to recognize what has fallen into its “trap” even though it has no sensory organs or nervous system? Where does this ability come from? These questions were asked by Comenius University doctoral student Miroslav Krausko, who is working under the supervision of Associate Professor Andrej Pavlovič. Krausko’s research, which saw him awarded a prize by the Dean of the Faculty of Natural Sciences, has been published in the prominent academic journal New Phytologist. The world-renowned molecular ecologist Dr Axel Mithöfer, who works at the Max Planck Institute, has also responded positively to Krausko’s work.
In their natural environment, carnivorous plants do not get enough nutrition from the soil, which is why they have had to “think” of a way to make up for this lack of nutrients. Carnivorous sundew plants catch prey by excreting a sticky secretion which becomes a sticky trap. This secretion is formed at the end of elongated protrusions (tentacles) and gives the impression of dew. It is exactly for this appearance that the sundew has acquired its name. Sundews react to the catching of prey by moving their tentacles, which wrap around the prey from all sides before the whole leaf wraps itself around it, thus creating an “external stomach”. “In our research we focused on the method of signals (touch and various chemical substances) sensed and processed by the plant which it uses to evaluate whether it has caught some prey that it can “eat” or whether it is a false alarm which would make digestion a waste of precious energy and nutrients,” Krausko said.
The Comenius University doctoral student looked for the answers to the question of how it was possible that the plant could recognize what it has caught even though it has no sensory organs or nervous system. First of all, it was necessary to understand the regular reactions of plants, which have to do daily battle with pests such as herbivores and insects. Damage to the plant creates the spreading of an electric signal throughout its whole body, which triggers a synthesis of plant hormones and defensive substances. These defensive substances can be various forms of enzymes which attack pests by decomposing the complex molecules which make up their bodies. This defensive mechanism is reliant on a quick signal transmission and a subsequent answer by the whole plant organism, not just its damaged part. Animals transmit signals to the whole body through a nervous system, which plants obviously do not have. However, plants do have a system of mutually interconnected cells which form a branched-out network which has the role of transporting water and nutrients to the whole body. These arterial bundles are used by plants as a nervous system for the quick transfer of information which resembles the electric signals present in animals. “We found out that contact with the tentacles creates the spreading of electric signals, the formation of plant hormones, and digestive enzymes, whose activity would quickly quieten down. However, when we added chemical substances which are released by prey to this mechanical irritation, we could see a ten times greater reaction. The plant can therefore sense the ‘taste’ of prey and react with greater digestive activity,” surmised Krausko.
The observed events, spreading of electric signals, and the formation of plant hormones and digestive enzymes of carnivorous plants have the same progression as when plants are attacked by pathogens. This is what led the research team to the hypothesis that the carnivorous nature of plants is a result of evolution through the gradual modification of defensive mechanisms with the aim of using them to gain nutrients from prey. In order to test the validity of this hypothesis, the team simulated an attack on the plant by repeatedly pricking it with a needle which was supposed to resemble the effect of the mandibles of insects. “We discovered that this sort of injury also produces a cascade of processes leading to the movements of the tentacles and the production of digestive hormones. The difference was that when attacked, all the plant’s traps produce digestive enzymes, whereas with the capture of prey only the trap which was successful in capture releases them. This is an interesting discovery, because there is no reason for the plant to produce digestive enzymes if there is no captured prey in a trap. This is a remnant of evolution and a confirmation of the theory on the development of carnivorousness from the defensive reactions of plants. Even the digestive enzymes of the sundew plant which we identified conspicuously resemble those enzymes produced by the plant when it is attacked by pathogens,” said Krausko. Evolution thus relies on existing mechanisms which are able to adjust and perform a new function over time.
Information about the research: http://onlinelibrary.wiley.com/wol1/doi/10.1111/nph.14352/abstract