How Plants Deal With Stress

 

    Plants have a range of defense mechanisms against herbivores or omnivores. No, they won’t pull out boxing gloves and fight off a caterpillar, but they do have other ways to keep from being eaten. Plants have a fairly simple anatomical structure, they have an epidermis on the outside, cortex (tissue right after the epidermis), medulla (inner tissue), cambium (separates the xylem/phloem), and the xylem/phloem which regulate transport within the plant. 

    The layout of these structures help us to get a better understanding of exactly how these defense mechanisms defend the plant. A study suggests all of the mechanisms of plant defense and explains how each of them help the plant to survive. One mechanism that actually changes the epidermis is called lignin which is a type of polymer, or cluster of cells. Lignin provides structural support to the epidermis and limits the entry of diseases into the plant and provides less nutritional value to the consumer. Another mechanism that provides the plant with more structural support is called ethylene. Ethylene is actually a very important mechanism for plants, primarily because of its triple response when it undergoes stress: the plant stops growing, becomes thicker, and turns away from the obstacle (if there is one). Both of these mechanisms help the plant not to get eaten, but what happens if something already tries to eat it? 

Plants have numerous enzymes that can cause the insect currently eating it to rethink its decision. One enzyme called Polyphenol oxidases, or PPO for short, this mechanism can cause the plant to lose its nutritional value. The way it works is when an herbivore takes a bite out of the plant's epidermis there is a signaling molecule that tells the plant that there is a wound. The plant retaliates by causing the cortex tissue to lose the nutritional value. Another enzyme that helps the plant when an insect attacks is called Peroxidases (POD). When a herbivore eats the plant, a signal is sent throughout its tissue telling the plant that it needs to act fast. The plant produces molecules that reduce its digestibility, causing it to be toxic to the consumer. Furthermore, POD’s have been reported to, “have direct toxicity in the guts of herbivores.” So, it keeps working even after it loses some of its tissue. 

Like humans, plants need to have defense mechanisms in place for when they are under attack. These mechanisms can be useful when a herbivore eats it or when there are stressful conditions in general. Learning more about plants can help us to understand our relationship to them and how there’s more to them than we think. 

Here's a cool video of a plant reacting to a person touching it.