19-25 December 2014 #737

Plant intelligence

New findings show that plants do, in fact, process information and communicate with each other intelligently
Science bytes by Roshan Karki

So you thought turning vegetarian absolved you from the guilt of killing a sentient being? Think again. 

The moral high ground people associate with vegetarians is based on the premise that plants are sessile, inanimate, and unresponsive organisms. But recent research into plants has unraveled surprising and sophisticated modes of communication by which they engage dynamically with one another conveying seemingly ‘intelligent’ responses much like animals.

Plants under stress emit a scent, comprised of volatile organic compounds, like the smell of freshly cut grass. Scientists call this the ‘silent scream’ of plants. When a plant is under attack, like a caterpillar chomping on its leaves, the leaf releases a chemical and when other plants pick up this distress signal, they ramp up their own chemical defenses specific to the invader. More interestingly, the scent also alerts neighbouring plants about invading caterpillars.

The chemicals that deter caterpillar pests may also attract nearby predators like wasps inviting them to a juicy caterpillar meal. Wasps inadvertently become plant bodyguards in this mutually beneficial partnership. Chemicals like caffeine found in the nectar of many plants act not only as a predator repellent, but also attract insects like bees to visit the same plant and facilitate pollination. All plants have elaborate modes of chemical communication. 

Plants can ‘listen’ for specific cues and tease out dangers. In a first study of its kind, a recording of a caterpillar’s nibbling on leaves triggered an increase in defense chemicals when played back to certain plants. But sounds of wind or insects harmless to plants did not elicit such responses. Scientists believe that plants are responding to specific chewing vibrations of caterpillars. More studies are needed, but plants are definitely listening. 

Plant communication via roots is even more fascinating. Roots of same kind of trees form an underground network so as not to hinder access to nutrients and water but compete with non-kin trees. The tips of roots behave like animals and race (at plant speed) towards nutrients but slow down once reaching them. Roots of many plants laden with fungi are more resistant to pests than those that are not. In a dense forest where competition for light and nutrients is fierce, a 1000- year-old mother tree spanning a huge area provides necessary nutrients to many younger cousins through its inter-connected root system. This concept of a mother tree was depicted in the movie Avatar.

How do plants process information without a brain, sensory organs, or the central nervous system? That is a million dollar question. Some scientists contend that there is an analogous nervous system in plants that is yet to be discovered. This may not be far-fetched considering the discovery in plants of neurotransmitters such as serotonin, dopamine and glutamate that are found in brains of animals, but their functional roles in plants is unknown. Other scientists dismiss this, and suggest that the very sessile nature of plant has allowed complex evolution to account for all their perceived intelligent functions. Both sides do agree that plants are much more than just ornaments, food-source, or furniture pieces.

The destiny of the human race is deeply rooted in plants that provide us resources, along with the essential oxygen for survival. Our ancient texts talk of sages meditating in forests feeling interconnected with nature. With recent evidence of plant communication and ensuing scientific development, we may do that literally someday.

We may even decipher the messages plants may be sharing with us– perhaps the message of how to live together in harmony as a single community.

Read also:

Saving a botanists’ paradise, Sampreethi Aipanjiguly

Godavari green, Alok Tumbahangphey

Vegetarianism for vegetables, Indu Nepal