The Secrets of The Forest World: How Plants Communicate?
I have always believed that the forest holds a lots of secrets and have always been curious about the mysteries of the life entangled in that dense green foliage. And the one that has always fascinated me is the communication between the living entities within it. We humans communicate through words and sign languages, birds through their melodious tunes and the animals through their alarming roars. How do plants communicate? As a child, I often wondered looking at the trees, whether they have their own language? How does one tree alerts its neighbors to danger? I used to feel sorry for them, thinking they had no means to warn each other.
I further delved into the research of renowned biologists like Charles Darwin and uncovered the astonishing ways in which plants interact with each other.
Early Discoveries in Plant Communication:
Charles Darwin, the renowned biologist was among the first to explore communication in plants. He discovered that the root tips respond to light, gravity, sound, water and chemicals, much like human sensory organs. Darwin performed a series of experiments, and concluded that “root tip acts like the brain of plant”. Although his theory was not entirely accurate, it proved the importance of root tips in plant signaling via chemicals.
How Plants Communicate?
Plants belong to the Kingdom Plantae and Domain Eukarya. The plant cell is enclosed by both a cell wall and cell membrane. The cytoplasm is the body of the cell. The chloroplasts within contain chlorophyll for photosynthesis. Plasmodesmata connect neighboring cells facilitating material transport through the cytoplasm.
Plants communicate through a process called signal transduction which involves 3 steps:
1)Reception: Plants detect chemical signals or environmental stimuli through receptors usually located in the plasma membrane.
2)Transduction: The signals activate proteins inside the cell, and the signaling molecule changes the receptor protein
3) Response: When signal is received to proteins they produce a physiological and cellular response.
Communication via Roots:
The primary way of communication between plants is through roots, as suggested by Darwin. They secrete root exudates(organic compounds secreted by plants) into the soil, which interact with the rhizosphere, or root zone. These exudates facilitate symbiotic relationships with mycorrhizal fungi.
Symbiotic relationships are the ones based on mutual benefit. The mycorrhizal fungi contain big mycelial networks that are efficient in transmitting signals between the roots of plants, and also help the plant’s root to acquire water and minerals from the soil. For example, if a tomato plant is damaged, it can signal neighboring tomato plants through its roots to prepare defenses against herbivore attacks. When a plant detects an attack by herbivores or pathogens, it initiates a chain of defensive responses, one of which involves the production and release of Jasmonic acid. The fungi transports these chemical signals to neighboring plants connected by the same mycorrhizal network and the fungi are provided carbohydrates and minerals from the plant signifying a symbiotic relationship.
Allelopathy and Volatile Organic Compounds (VOCs):
Inter plant communication occurs also through Allelopathy, a process where plants release allelochemicals to influence another plants. For example, Juglone, an allelochemical released from all parts of the black walnut tree — leaves, roots, and nuts, is highly toxic to plant species, like tomatoes and potatoes. Similarly, Eucalyptus trees release Cineole and other volatile oils that can inhibit the germination and growth of shrubs and tall grasses, hence reducing competition for water and nutrients.
Another way of communication in plants is through VOC’s (Volatile Organic Compounds). VOCs are the organic chemicals that plants release into the air to alert their neighbors about threats. One of the most common plant VOCs is Methyl Jasmonate (MeJA), which is produced and released by plants that are under attack. MeJA is produced within wounded plants, such as when an animal attempts to feed on them. It then spreads through the air to nearby plants, triggering defense mechanisms in undamaged areas. Plants detect VOCs and start making anti-fungal compounds or anti-insect toxins to protect themselves.
For instance, in forests, herbivore attacks are frequent occurrences. When giraffes consume Acacia leaves, the trees emit ethylene gas as a signal. This gas triggers the production of tannins and other defensive chemicals not only in the attacked tree but also in neighboring acacia trees. So when the giraffe attacks the neighboring acacia tree, the leaves seem less palatable to them and further attacks are prevented.
Similar example is of corn (maize) plants. When corn plants face caterpillar attacks, they emit a mixture of VOCs like terpenoids, methyl salicylate, and GLVs. These airborne signals are detected by neighboring corn plants, which then increase the production of the defensive chemicals, such as benzoxazinoids, making them less palatable to herbivores. Additionally, they release β-caryophyllene, attracting parasitic wasps, enemies of caterpillars. These wasps lay their eggs in the caterpillars, leading to the caterpillar’s eventual death. So, next time, if you spot a caterpillar on a maize plant, take note if another caterpillar is present on neighboring plants.
Acoustic Communication:
Plants also use sound waves for communication. In 1970, renowned biologist and musician, Dorothy Retallack performed an experiment on plants exposed to different music genres. Her findings suggested that plants exposed to classical and jazz music showed healthier and vigorus growth, than those exposed to rock music or no music. Although her studies faced criticism, other research supports the idea that sound waves can influence plant growth. For instance, studies in South Korea showed that rice plants exposed to specific sound frequencies exhibited increased growth and yield.
It is true that plants can communicate via sound waves just as humans. But not all sound waves are detectable by human ears. We can only hear sound waves in the frequency range 20–20000 Hz. Plants produce sounds at frequencies often inaudible to humans, but they can be heard by other plants and animals.These sounds can influence root growth direction. In a research, it was discovered that young maize roots produce faint clicking noises within the lower range of human hearing. When these roots were suspended in water to facilitate movement, they exhibited a tendency to bend towards these sounds. Other sounds, such as those from the xylem network transporting water and minerals, are ultrasonic and detectable by insects and some animals.
Additionally, a research conducted in 2013, clearly showed the positive impacts of basil plants on the growth of Chili plants. However, Chili plants showed stunted growth in the presence of fennel plants. The researchers suggest that subtle vibrations within plant cells may generate signals that inform neighboring plants about their proximity to favorable or unfavorable companions.
Plants, although immobile, have developed numerous sophisticated ways of communication. These secrets of plant communication hidden in the forest world are quite fascinating and there might be innumerable ones that we are still unaware of!
So the next time you walk through a garden, remember that the plants around you are actively communicating, warning each other of danger, and coordinating their growth and defenses, and before plucking a flower think for a second, that the poor wounded plant might be screaming out to its neighbors — but sadly we cannot hear them!
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