Thursday, November 6, 2014

I Am Groot! Plants Are More “Alive” Than We Think

So who saw Guardians of the Galaxy this summer? Awesome, wasn’t it? How could a movie with a talking raccoon and a 1970s-based soundtrack go wrong? Oh, and then there’s Groot, the beloved walking, talking tree-like creature who sprouted the catch phrase, “I AM GROOT!” Until Groot, the only sentient plants children probably knew of were the Evil Trees hurling apples at Dorothy in The Wizard of Oz. But Groot was a “Giving Tree” incarnate.    

Groot shatters the evil living plant stereotype and saves the day in Guardians of the Galaxy.
Groot was so endearing, he has given my kids a new reason not to eat their veggies – they don’t like the idea of slaughtering plants. When I reminded the kids that plants are only sentient in the movies, they gave me the look of skepticism. I know it well…I taught it to them. This inspired me to leaf through some botany literature. Much to my surprise, my kids might have a point! Plants are more “alive” than we ever imagined.

Exhibit A.  Plants know when they are being eaten alive! And they fight back…

There is a plant that scientists typically use as a model to study in the lab called Arabidopsis (thale cress, similar to broccoli but tastes even worse). Researchers recently discovered that when they expose these plants to vibrations that mimic those produced by a hungry caterpillar, the plants increase production of glucosinolate and anthocyanin defenses. These are mustard oils that don’t sit well with caterpillars. In other words, the plants can tell when they are being chewed on and release oils to deter the predator.

Another sophisticated defense system used by plants comes from studies on tobacco. When caterpillars attack, these tobacco plants produce “green leaf volatiles”, compounds that act as a distress call by attracting insects that devour caterpillars!
The Hungry Caterpillar: Adorable children's tale or a horror story of gruesome predation?
Exhibit B. Plants have a memory and can be trained.

Everyone is familiar with the story of Pavlov’s dog, the famous experiment that demonstrated classical conditioning. Dogs salivate when presented with meat. If you ring a bell before presenting the meat, the dogs become conditioned to salivate at just the sound of a bell. Plants do a similar thing when exposed to light. Researchers have shown that when a plant is exposed to a certain wavelength of light, and then infected with a plant pathogen, the plant “learns” to build up resistance to that pathogen when it “sees” that particular wavelength of light once again. Plants that were infected and then exposed to the light developed no protective response. Plants must possess some sort of biochemical nervous system and memory in order to execute this kind of behavior.

Plants don’t have a brain, but they do behave as if they can think.
Exhibit C. Plants protect their young.

Seeds are the equivalent of a plant’s babies and plants have evolved a variety of fascinating ways to take care of their young. Consider serotinous plants, which keep some of their seeds inside the plant body instead of releasing them into the environment where they can be eaten or destroyed by weather. These plants can hold onto their seeds and release them when the time is most favorable for them to survive.

In the 1986 film, “Little Shop of Horrors”, the carnivorous plant Audrey II demonstrated a terrifying new way plants could protect their kin.
In another striking example, scientists studying a plant called sea rocket (Cakile edentula) noticed that when grown in a pot with a different member of its species, its roots grew wildly so to soak up more water and nutrients from its competitor. However, if the sea rocket was put into the same pot as its offspring, this competition did not take place!

Still not convinced that plants are more alive than we give them credit for? Check out this video by Michael Pollan.


While the evidence above isn’t sufficient to conclude that plants on Earth are like Groot, it is clear they are capable of some level of feeling and response. But don’t tell your vegetarian friends…what else would they eat?

Contributed by:  Bill Sullivan
Appel HM, & Cocroft RB (2014). Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia, 175 (4), 1257-66 PMID: 24985883

Allmann, S., & Baldwin, I. (2010). Insects Betray Themselves in Nature to Predators by Rapid Isomerization of Green Leaf Volatiles Science, 329 (5995), 1075-1078 DOI: 10.1126/science.1191634

Karpiński S, & Szechyńska-Hebda M (2010). Secret life of plants: from memory to intelligence. Plant signaling & behavior, 5 (11), 1391-4 PMID: 21051941

Dudley SA, & File AL (2007). Kin recognition in an annual plant. Biology letters, 3 (4), 435-8 PMID: 17567552

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