Exploring science

Plants need space, the right temperature, light, water, carbon dioxide, and nutrients to grow. In return, they provide us with clean air, food, shelter, fiber, medicines, and many other resources. However, we don’t treat plants the same way we treat humans or animals. Besides using their resources, we often pluck and play with their leaves, flowers, and branches. If you were to relate these actions to human or animal body parts, it’s akin to pulling out hairs, limbs, and gametes. This might sound absurd, but it’s a fact. We do this with the strong belief that plants are not sentient.

It’s logical to think that plants don’t possess a central nervous system to control thoughts, actions, and emotions in response to stimuli. However, the truth is that, even though plants don’t possess sentience in the same way as animals or humans, they use physiological signals and environmental cues through electrical signals. Just like the neuron network in mammals, plants have a vascular system that acts as a conduit to transmit signals throughout their systems. This vascular system includes Xylem and Phloem. In this context, the Phloem plays a crucial role in delivering information by transporting molecules to distant plant organs.

In this discussion, we’ll explore various ways in which plants use signals or processes that could be likened to emotions to communicate and respond to stimuli.

Chemical Signals

When a cabbage or cauliflower plant is attacked by pests like Pieris rapae, a cabbage-eating caterpillar, these plants release chemical signals initiated through volatile organic compounds (VOCs). These signals trigger defense responses in other parts of the plant. Methyl jasmonate (MeJa) is one of the most common VOCs. This defense response acts as an alarm, releasing gases into the air to alert neighboring plants of an impending threat. Simultaneously, it informs the predators of the insects, such as parasitic wasps, that prey on the cabbage-eating caterpillar. This mechanism is referred to as “plant communication,” serving to protect the plants from their enemies.

Memory and Learning

Some studies suggest that plants can retain information about past environmental conditions and adjust their responses accordingly. For example, a plant can remember its previous responses to environmental stimuli like wind, light, rain, salt, drought, or insect bites. This memory remains inactive until a similar stimulus recalls it, allowing the plant to use its previous experiences to adapt to similar situations. This way, plants acquire knowledge about their environment and learn to adapt as needed.

Response to Environmental Stimuli

Plants can respond to various environmental stimuli, such as light, gravity, and touch. When plants respond to touch and grow in the direction of the stimulus, it’s called tropism. Different types of tropisms include phototropism (growth towards light), hydrotropism (root growth towards higher water concentration), and chemotropism (movement of plant parts towards specific chemicals). Plants also respond to physical touch, as seen in the closing of leaves in “touch-me-not” plants. These responses to stimuli are driven by plant hormones, which control various aspects of a plant’s life, from flowering to fruit setting and even the shedding of leaves in autumn. Unlike mammals, which produce hormones through specialized glands, plants produce hormones through nearly all of their cells.

Root Communication

Just as humans have social connections, trees in forests also have intricate relationships. Mycorrhizal fungi play a significant role in this interaction. These fungi can grow on tree roots or within the soil, forming a symbiotic relationship with both the roots and the soil. They spread their fungal filaments through the soil, connecting neighboring trees in a system known as a Common Mycorrhizal Network (CMN). Despite these interactions, understanding how trees interact with CMNs remains a complex challenge, and further studies are needed to confirm the extent of plant communication through these networks.

Overall, while plants may not experience sentience in the same way animals or humans do, they exhibit complex and fascinating ways of responding to their environment and communicating with each other. The core of the story is that plants are excellent communicators. Scientists are still working to unravel the complete mystery of plant communication. Nevertheless, the next time you walk over the grass or pluck the flowers or leaves, just remember that the wounded plant might be crying out to its neighbors.