Plants Respond To Being Wounded

Many of us omnivores like to eat our steak or chicken drumsticks, but get rather squeamish when it comes getting it from the field to our plate. Prepackaged from the grocery store seems a much nicer option than chasing a chicken round the yard even if it means that we have less exercise that we will eventually have to make up on the treadmill in the gym.

Plants on the other hand induce no sign of squeamishness at all. We happily pick leaves off “pick and come again” lettuce plants. Many different species of herbivores will also munch on our plants, but we should remember that the plants are going to do their best to combat this.

The problem of how a plant recognizes that it is wounded has been studied recently by Heil et al of CINEVESTAV in Mexico and published in the Public Library of Science (1). Their study was mainly on lima beans, but addressed a variety of other plants too. Plants had their leaves wounded mechanically with a wire brush and by a lighter flame.

Wounding was found to cause the release of the plant hormone Jasmonic acid. The application of sucrose or adenosine triphosphate (cellular metabolites) were found to trigger the release of Jasmonic acid as well. Jasmonic acid is the frontline defense for the plants.

As Jasmonic acid is released, the extrafloral nectaries of the plant start secreting nectar. The strategy here is to attract insects such as ants and recruit them into a plant defense force.

This is an excellent strategy against small herbivores such as caterpillars, but it won’t work quite as well with you or I damaging the leaves as we start to harvest the beans. Although, perhaps if there are a lot of plants and we are being slow, we may get put off if a large number of angry ants start patrolling the leaves.

The paper makes the interesting comparison that we also recognize the presence adenosine triphosphate outside our skin cells as a signal of wounded skin. So it seems that we have more in common with that tomato plant than we might have thought, so talk to them nicely as you tend them in your greenhouses before stealing their fruit. Pinching out their growing tips is likely to upset them.


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