What Plants Talk About

It says in Tehillim (96:12), “Then the trees of the forest will sing out.” Rav Avigdor Miller explains that in Yemos HaMoshiach, the Messianic Era, the trees of the forest will begin to sing in the sense that everyone will see the wonders of Hashem in nature like never before. It will be as if a veil was removed from our eyes.

The infinite wisdom of the Creator is reflected in the natural world, but the limitations of science and the potential biases of scientists can numb or blind us to that wisdom. Popular science tends to invest nature with intelligence – it “selects” or “adapts” or otherwise acts in an ingenious and complex way. (This is like how ancient pagans invested inanimate objects with divinity.) They use language in a way that blunts the idea that everything in the world reflects the unfathomable and infinite intelligence of a Creator, of one G-d.

Despite that, some researchers are more open-minded to the idea that the old way science views the world is limiting. New discoveries can be so astounding that it becomes almost impossible to deny the intelligence inherent in the creation. The world of plants and trees is one such area. For instance, scientists have discovered that plants actually communicate with each other and exhibit social behavior.

This reaffirms something said long ago: “The heavens declare the glory of Hashem; the sky proclaims His handiwork. Day to day makes utterance, night to night speaks out. There is no utterance, there are no words, whose sound goes unheard. Their voice carries throughout the earth, their words to the end of the world” (Tehillim 19:3-5).

 

Listening to Plants

They don’t have eyes or ears, but they can find their own food. They lack a brain, but some scientists think they can communicate, cooperate and even wage war…

Plants lead anything but solitaire sedentary lives. They actively respond to the nutrients, predators and the herbivores around them. From nurturing their young to eavesdropping on their neighbors ,it seems plants are doing and saying quite a bit.

Plant ecologist J. C. Cahill has crisscrossed the continent researching a book that focuses on one central question: Do plants behave like animals? It’s an idea that seems a little far out to a lot of people, including scientists. “You can understand the skepticism,” Cahill admits. “Out in the field, observing plant behavior is a little bit like watching paint dry. They may not swing from branches or gallop across the Savannah, but plants do move, and they do behave and one of the ways they behave is through growth.”

But does all this growth really constitute behavior? Are the movements of plants in any way comparable to a fox hunting for mice using every weapon in his arsenal to find a meal?

“Everyone knows that a Venus Fly Trap catches unsuspecting insects that roam into its claw-like leaves. All it takes is a brush with two of the plant trip-hairs and the trap is sprung. The bug is then slowly digested, providing the plant with much needed nutrients. “For years,” Cahill goes on, “we just assumed that the Flytrap was the exception that proved the rule. Plants don’t ‘behave.’ It turns out we were wrong.”

Plants aren’t necessarily eating living organisms, but they’re engaging in elaborate behaviors above ground and below ground. They’re slower than the snapping of the flytrap, but all plants have complex feeding behaviors. In fact, every plant on Earth is on a constant hunt for food, including the light they need to photosynthesize.

But plants don’t just need light to thrive. They also need nutrients – food that lies in a hidden world below our feet. As much as 80% of a plant’s total mass lives below the ground in a secret world that scientists once called the “black box.” However, with the aid of new technology, science is now exploring that world and discovering that when it comes to finding food, plant roots are a lot more animal-like than we ever imagined.

“They’re not unlike a grizzly bear family,” Cahill explains, “who are busy foraging for berries and other edible plants. When they find a berry pouch, they will spend time there. Plants do something roughly like that.”

In his lab at the University of Alberta, Cahill has been using high-tech cameras to explore the underground world of foraging plant roots. He and his students have taken thousands of pictures documenting how long it takes the roots to reach the nutrients and how they behave once they find them. “It takes long hours to review those images,” he relates, “but the surprises are worth the wait.”

For example, they may photograph a plan with “sudden root growth” of almost three centimeters over three days. “The growth rate of one root suddenly accelerates as it homes in on a nutrient patch. Then just as suddenly, growth slows down, while the root, like the Grizzlies, eats its fill.”

 

The Vampire Plant

Roaming legs or multiplying growth cells, the mechanism may differ, but the foraging behavior is the same. The question is how they do it. How do plants find the food they’re looking for both above the ground and below it when they have no eyes and no ears, let alone no brain?

The feeding habits of a strange snake-like vine called the dodder vine may hold the answer. “It’s the Count Dracula of the plant world,” Cahill explains. “The vine has no roots and can’t produce its own food, so it lives entirely off a host plant and it has just 72 hours to find that host or it dies. Its tiny teeth-like probes pierce the stem of another plant and grow into it, draining the victim of its life-giving sap. This botanical vampire seems to prefer some plants over others. Tomatoes are among its favorite victims.”

How does it find its host and how does it choose between one plant and another? Dr. Cahill went to Pennsylvania to meet Consuelo De Moraes and Mark Mescher, the scientists who solved that mystery.

Dodder vines, Mescher explains, “are completely dependent on the host plant. If they don’t find a host plant within a few days, they’ll exhaust their energy resources and die. So there’s a really intense pressure to be good at foraging and identifying their host.”

But while the dodder vine may be good at finding a victim, could it actually choose between two different host plants? De Moraes and Mescher made it their mission to find out in a series of experiments.

They placed wheat and tomato seedlings in the same pot and planted a newly sprouted dodder vine between them. Then they set up a time-lapse camera to see if the seedling was actually making a choice. For hours, it circled the air like a snake as if sniffing out its victims. Remarkably, nine times out of ten, its preferred victim was the juicy tomato, a tender plant that’s easier to attach to.

But how did the little stem make its choice? The team decided to play a hunch. They knew that all plants produce green leaf “volatiles” – chemical scents released by their leaves as they breathe. Maybe this predatory plant was sniffing out its victim.

To test that theory, the team devised another experiment. First, they captured the scent of a tomato: essentially condensing the chemical odor released by the plant. Once distilled, they presented the tomato “perfume” to the vine along with a real tomato encased in glass; it couldn’t possibly smell it. Time after time, the dodder homed in on the chemical language that said, “Yes I’m a tomato.”

“There’s no doubt with the dodder that there’s choice,” Cahill explains. “There’s choice involving the suitable host or non-suitable host. This is a very familiar thing in animal foraging behavior that we’re seeing in this plant foraging behavior.”

 

Free Choice in Plants

But the dodder isn’t the only plant exhibiting animal-like behavior. Once it’s under a full-scale dodder attack, the tomato releases the chemical equivalent of a scream. In fact, many plants emit a chemical “SOS” when they’re under attack – and we’ve all caught a whiff of it. It’s the smell of freshly cut grass. We all love the smell of freshly cut grass. We all love the smell of flowers that we put into a vase. We all love the smells of plants. But those smells mean one thing to us and another thing to the plants.

“We are causing stress,” Cahill explains. “We are causing trauma to these plants. It’s the plants’ way of calling out for help.”

If it’s a cry for help, who or what are plants calling out to? Well, if an unassuming desert plant is any indication, they may be calling in some pretty effective reinforcements: insects that eat the insects that eat them.

 

Calling Reinforcements!

The desert isn’t the most welcoming place for people, but it can be an ecological nightmare for some plants. Unlike us, plants can’t escape the heat or walk for miles to find water. Nor can they run and hide when attacked by insects. But it’s precisely because they can’t move that plants need some nifty methods of self-defense.

“We used to think or view plants as just sitting there and ‘whatever happens, happens,’” Cahill says. “They make their seeds and go on, but we’re realizing it’s much more complex. They’re actively engaging with the environment in which they live. They actively communicate. They actively respond to the nutrients as well as the predators and herbivores around them. It’s a really dynamic system. If you were to rip off a leaf, from the plant’s point of view, you ate some of its body. This plant is likely to start changing its defensive chemistry. It can start communicating with its neighbors or insects…”

In the Utah desert, there’s a wild species that shows us just how dynamic plants are when it comes to self-defense. It’s called Nicotiana Attenuate, the wild tobacco plant.

For more than a decade, Dr. Ian Baldwin has been studying the wild tobacco and the amazing ways it responds to threats in its environment. “This plant has probably more genes involved in environmental perception than most animals do. Most plants have to because they sit still, and they have to really tune their physiology and biochemistry to what’s going on. They need a very sophisticated system of perception and response.”

Being able to respond quickly is essential for wild tobacco, because its seeds need wildfire to kick-start their growth. They can wait for hundreds of years for that to happen, so when they finally do emerge, they may face enemies they’ve never seen before.

“It has no idea,” Baldwin elaborates, “what it’s going to face when it germinates out of that seedbank and has to cope with whatever’s there. There are all these other organisms that close in on this habitat that’s just been cleared out by a fire. Just about every part of the plant is attacked in a different way by a specialist that feeds on that particular part. It’s a very complex problem they have to solve.”

And it’s not just one problem. This plant’s enemies are as plentiful as desert sunlight. But it turns out that the wild tobacco has a secret chemical weapon to deploy. As soon as an herbivore attacks, it ramps up a toxin – one that some of us are all too familiar with. This toxin will poison any organism with a muscle. It’s called nicotine – the one that human beings have such a relationship with. Any insects that eat this plant are going to be poisoned.

But while its nicotine cocktail poisons some bugs, it has absolutely no impact on one. The hornworm caterpillar can mow down a tobacco plant in a matter of days. But this cunning little plant has a few more defensive tricks up its leaves.

Once the caterpillar starts feeding, the plant’s leaves release an “SOS” – chemical messages that drift up into the air, where they’re picked up by the enemies of their enemies: predators that just love feasting on caterpillars. If you find it hard to believe that plants can call in insect mercenaries, Baldwin has proof.

In one experiment, he captured the chemical signals released by the leaves of plants that were under attack. Then he glued caterpillar eggs onto a leaf, smeared them with the chemical scent, and waited to see if anyone would show up. Within hours, an insect commonly known the big-eyed bug (Geocoris) responded to the plant’s call for help. A big-eyed bug is a pint-sized predator that devours eggs and larvae alike. In fact, it’s even been known to take a bite out of a full-size caterpillar.

But, wait a minute. How does the plant even know who’s attacking it, let alone which predator to call? The answer lies in yet another chemical message, this one delivered by the caterpillar itself.

“When the caterpillar chews a plant,” Baldwin says, “it has to have saliva in its mouth. In that saliva, there are these various compounds that provide information to the plant, which the plant uses to say, ‘Ah, it is the hawk moth and not a Negro bug that’s feeding on me.’ So, it adjusts and tunes its responses to that particular herbivore.”

Baldwin has discovered that this plant has another secret weapon specifically designed to rid itself of caterpillars. This is the trichome, a sweet little treat deposited by the plant and irresistible to caterpillars. Beautiful, yes, but it’s as lethal as a landmine. “When a caterpillar chews on a trichome,” Baldwin explains, “it gets a very bad case of body odor. About 20 minutes after eating the trichome, they exude a unique smell that inform predators, particularly ground-foraging predators. The plant is offering this nice little sugary meal for the caterpillars, but it’s an ‘evil lollipop,’ because the caterpillar gets tagged for predation. Plants, after all, can’t run away, so they must solve their environmental problems by changing who they are.”

Being able to change who they are is critical to the tobacco plant’s survival, because it turns out that the mother of these voracious caterpillars is also the plant’s best friend. Its main pollinator is the hawk moth. Tobacco flowers bloom at dusk, the perfect draw for a nocturnal pollinator like the hawk moth. As the moth sips nectar, it gathers pollen, spreading it from one plant to the next. But while the moth happily does so, it has its own agenda. A single moth can lay as many as 200 eggs – eggs that grow into plant-munching caterpillars.

Therefore, sometimes, despite its best defenses, the wild tobacco can still get infested with caterpillars. Even then, the plant has another card to play. It simply switches pollinators.

 

Switching Pollinators

Baldwin’s colleague, Danny Kessler, was the first to observe this astonishing behavior. He was out photographing tobacco plants in the early hours before dawn. Most were infested with caterpillars. As he worked, he noticed something odd. Instead of blooming at night, some of the flowers were opening at dawn, and the daytime flowers didn’t look or smell the way they should. They differed completely from the night opening flowers in terms of nectar volume sugar concentration and didn’t emit floral volatiles.

The oddness continued. Not only had the bloom’s nectar and perfume changed, but the shape of the flower itself had completely transformed. Essentially, by changing its flowers and bloom time, the plant had stopped talking to its nocturnal pollinator, the hawk moth, and struck up a conversation with a daytime pollinator, the hummingbird.

The eggs that hummingbirds lay don’t hatch into caterpillars. They hatch into little baby hummingbirds, which don’t eat plants. By switching its pollinator, the plant avoids a whole group of herbivores that it would normally get. No one knows why the plant doesn’t permanently switched pollinators, but the switch can happen in less than eight days.

“The ability to change the shape, smell and quality of nectar and flowers almost immediately is incredible,” Dr. Baldwin says. “It’s incredibly complex! And we have no idea how common this is across species. It’s a very novel, new finding.”

 

Can Plants Talk to Each Other?

So can plants talk to each other? Superficially, we would say it certainly doesn’t seem that way. Plants don’t have complex sensory or nervous systems like animals do. They look passive, basking in the sun, and responding instinctively to inputs like light and water. Nevertheless, plants can communicate with each other. Just like animals, plants produce all kinds of chemical signals in response to their environments, and they can share those signals with each other, especially when they’re under attack.

If you think of communication as an exchange of information, then plants seem to be active communicators. They’re sending, receiving, and responding to signals without making a sound, and without brains, noses, dictionaries or the internet.