Maybe a more important question is: what can we learn from what plants sense and how they adapt? No one was around to collect data three billion years ago on Earth, but geologic evidence suggests that cyanobacteria, single-cell organisms that photosynthesize, were there and producing enough oxygen to reach the crucial level that supported the development of life on Earth. About 750 million years ago, while oxygen was available, carbon dioxide was excessive, and the planet was very warm (tropics in the Arctic), a tiny water fern called azolla, with cyanobacteria inside its cells, showed up in the Arctic. Azolla reproduced very quickly and consumed tons of carbon dioxide, died, and dropped, with the carbon dioxide safely sequestered, to the ocean floor. Azolla is still found in temperate climates today. Over hundreds of thousands of years, this tiny fern sequestered so much carbon dioxide that some scientists believe it triggered the Ice Age. Now that is what I call adapting to one’s environment! The Azolla Event, as it is hypothesized, led to the atmosphere as we know it.
The thing for humans to take away from this story is that we are absolutely dependent on plants in order to breathe, to eat, and to support all life on Earth. Because plants are sessile (immobile), observers centuries ago relegated them to the category of lower life forms. Yet luckily, in spite of us, drought, and climate change, they adapt and endure. What are their secrets? What allows them to survive and adapt to the changing environment? What can we do to understand how they sense and respond, so that we can support their existence or at least get out of their way?
In the last decades of botany research, scientists learned that plants are “smarter” than we know. They don’t have brains or neurons, but anyone who has observed a field of sunflowers turn their bright faces as the sun moves understands that plants sense light. If a plant gets tall and “leggy,” it isn’t getting enough light; plants respond to a lack of light by growing taller, bending, or turning to find the sun. Research shows that plants sense they are being shaded and respond by increasing the production of auxin, a plant hormone, to help them bend or grow towards light.
From personal experience, I know that pruning, instead of irreparably damaging plants, causes new growth and healthier-looking plants. Those of you familiar with California native and many other flowering plants are familiar with the lovely scents that float in the air when these plants are brushed against or stepped on. Pruning, brushing, or stepping on leaves signals “damage” to the plant and causes a response. In scientific jargon, those lovely scents are called volatile organic compounds (VOCs), and they are not there for our pleasure, but rather as a warning signal to plant neighbors, believe it or not. Recent research has demonstrated that brushing against plants for a few seconds on a daily basis may actually make the individual plant hardier over time compared to undisturbed plants, and that is a direct response by the plant to damage.
Several experiments have shown that flowering plants respond to sound. Nope, no ears and they don’t get Bach. However, the buzzing of pollinators (frequency range of 100-500 Hz) can temporarily increase the level of sugars in nectar. It is hypothesized that the ability of plants to temporarily respond to pollinator sounds saves plants the energy that would be required to constantly maintain elevated sugar in nectar.
The question that remains is: how does this work? We know plants don’t have neurons or brains, so how does the information move within the plant to cause a response? Plants are equipped with a vascular system that carries water, minerals, nutrients, and other compounds. Could this system be part of plant sensing and response?
Fortunately, three scientists became interested in green fluorescent protein (GFP) several decades ago and won the Nobel Prize for their work. Other scientists learned how to introduce the simple gene that makes GFP, found in Aequorea victoria, a jellyfish, into plants. When the studied plants are visualized with a fluorescence microscope, botanists can detect changes in calcium ions, voltage, pH, and enzyme activity and watch the fluorescence move through the vascular system. This has been the fascinating key to literally seeing how plants sense and respond to their world.
Gilroy, Simon. “Are my Plants Listening to Me?” University of Wisconsin, Madison on YouTube
Karban, Richard. The Ecology and Evolution of Induced Resistance Against Herbivores, Functional Ecology 25, 339–347,2011.
Schlanger, Zoe. The Light Eaters, 2024, HarperCollins Publishers, New York, NY