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Plants serve themselves as food to various herbivores, insects and larvae. Earlier, they didn’t have a way to defend themselves. However, after millions of years of evolution, they have in-built a defensive system to ensure their survival for the next generation.
A recent study by the University of Copenhagen, Denmark, proposed that plants use substances that taste similar to wasabi and mustard sauce that stimulate a burning sensation in their predators’ mouths, thereby preventing themselves from getting eaten up. Instead of serving plants as food, these pungent-smelling chemicals repel insects and herbivores to defend them.
Glucosinolates are naturally occurring substances in plants that play an important role in their defensive mechanisms. When herbivores start eating plant leaves, the plant tissues are crushed, and an enzyme is released called Myrosinase. This enzyme gets mixed with glucosinolates to produce toxic metabolites that inhibit most insects to eat leaves. Interestingly, plants can self-adjust the amount of these toxic substances in each leaf, which is evident when new seeds are produced.
“When a plant goes to flower, everything revolves around the next generation. At this point, it is more important to defend the young leaves that supply future seeds than to protect the older ones. As such, the concentration of glucosinolates in younger leaves increases, which is what we have scientifically proven for the first time,” said Alexander Schulz, professor at the University of Copenhagen.
How did the researchers find this mechanism?
During the experiment, scientists created a genetically engineered thale cress plant (a flowering weed), Arabidopsis thaliana by changing its genetic features. The plant was reprogrammed to produce defensive toxins equally in old and new leaves. On the contrary, older leaves redirected large doses of the toxins in the younger leaves of the plant.
When the insect larva was set to feed the leaves, researchers found that they ate both young and old leaves of the mutant Arabidopsis thaliana plant. But, they avoided eating young leaves of the normal plant due to the excess presence of defensive toxins.
“In the study, we prove that the old leaves of a plant selflessly sacrifice themselves by redirecting their defenses to younger leaves, for the sole purpose of scaring larvae and other herbivores away and off to the old leaves instead. By doing so, the plant ensures for the survival of its next generation,” said Barbara Ann Halkier, a professor at the University of Copenhagen and study lead author.
How are the study findings useful?
According to the researchers, the study findings provided evidence of how plants use their defensive mechanisms to protect their next generations from predators. Also, the discovery suggested new knowledge to develop ways to control agricultural pests like the African cotton leafworm (Spodoptera littoralis), one of the most devastating moth larvae for crops. Agriculturists and biotechnologists can use the study results to in-built plants’ defensive mechanisms.
“The new knowledge could be used in other studies where one is trying to strengthen a plant’s own defenses against pests, so as to limit agricultural pesticides use,” said Halkier.
The study has been published in the journal Proceedings of the National Academy of Sciences.