Plant intelligence

In botany, plant intelligence is the ability of plants to sense the environment and adjust their morphology, physiology and phenotype accordingly.^[1] Research draws on the fields of plant physiology, ecology and molecular biology.

Intelligence is an umbrella term describing abilities such as the capacities for abstract thought, understanding, communication, reasoning, learning, learning from past experiences, planning, and problem solving. Studies indicate plants are capable of problem solving and communication.

Contents 1 Problem solving 2 Communication 3 Mechanisms 4 Plant perception 4.1 Alarm signals 4.2 Light 4.3 Contact Stimuli 5 Plant adaptation vs plant intelligence 6 History 7 See also 8 References

Problem solving

Plants adapt their behaviour in a variety of ways:

• Active foraging for light and nutrients. They do this by changing their architecture, physiology and phenotype.^[2][3][4]
• Leaves and branches are positioned and oriented in response to light source.^[2][5]
• Ability to detect soil volume and adapt growth accordingly independently of nutrient availability.^[6][7][8]
• Adaptively defend against herbivores.

Communication

Plants respond to volatile signals produced by other plants.^[9][10]

Mechanisms

In plants, the mechanism responsible for adaptation is signal transduction.^{[11][12][13][14]} Plants do not have a brain or neuronal network, but reactions within signalling pathways may provide a biochemical basis for learning and memory.^[15] Controversially, the brain is used as a metaphor in plant intelligence to provide an integrated view of signalling,^[16] (see plant neurobiology).

Plant cells can be electrically excitable and can display rapid electrical responses (action potentials) to environmental stimuli. These action potentials can influence processes such as actin-based cytoplasmic streaming, plant organ movements, wound responses, respiration, photosynthesis and flowering.^{[17][18][19][20]}

Plant perception

Plants have many strategies to fight off pests. For example, they can produce different toxins (phytoalexins) against invaders or they can induce rapid cell death in invading cells to hinder the pests from spreading out. These strategies depend on quick and reliable recognition-systems.

Alarm signals

Wounded tomatoes are known to produce the volatile odour methyl-jasmonate as an alarm-signal.^[21] Plants in the neighbourhood can then detect the chemical and prepare for the attack by producing chemicals that defend against insects or attract predators.^[21]

Light

Many plant-organs contain photo-sensitive compounds (phototropins, cryptochromes and phytochromes) each reacting very specifically to certain wavelengths of light. These light-sensors tell the plant if it's day or night, how long the day is (photoperiodism), how much light is available and from where the light comes. Plants also can detect harmful ultraviolet B-rays and then start producing pigments which filter out these rays.^[22]

Contact Stimuli

The mimosa plant (Mimosa pudica) makes its thin leaves point down at the slightest touch and carnivorous plants such as the Venus flytrap snap shut by the touch of insects.

Mechanical perturbation can also be detected by plants.^[23] Jasmonate levels also increase rapidly in response to mechanical perturbations such as tendril coiling.^[24]

Poplar stems can detect reorientation and inclination (equilibrioception).^[25]

Plant adaptation vs plant intelligence

It has been argued that although plants are capable of adaptation, it should not be called intelligence. "A bacterium can monitor its environment and instigate developmental processes appropriate to the prevailing circumstances, but is that intelligence? Such simple adaptation behaviour might be bacterial intelligence but is clearly not animal intelligence."^[26] However, plant intelligence fits with the definition of intelligence proposed by David Stenhouse in a book he wrote about evolution where he described it as "adaptively variable behaviour during the lifetime of the individual".^[27]

It is also argued that a plant cannot have goals because operational control of the plant's organs is devolved.^[26]

History

Charles Darwin studied the movement of plants and in 1880 published a book The Power of Movement in Plants. In the book he concludes:

It is hardly an exaggeration to say that the tip of the radicle thus endowed [..] acts like the brain of one of the lower animals; the brain being situated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.

Indian scientist Sir Jagdish Chandra Bose began to conduct experiments on plants in the year 1900. He found that every plant and every part of a plant appeared to have a sensitive nervous system and responded to shock by a spasm just as an animal muscle does.^[28][29]

Bose's experiments stopped at this conclusion, but American polygraph expert Cleve Backster conducted research that led him to believe that plants can communicate with other lifeforms.^[30][31] Backster's interest in the subject began in February 1966, when Backster wondered if he could measure the rate at which water rises from a philodendron's root area into its leaves. Because a polygraph or "lie detector" can measure electrical resistance, and water would alter the resistance of the leaf, he decided that this was the correct instrument to use. After attaching a polygraph to one of the plant's leaves, Backster claimed that, to his immense surprise, "the tracing began to show a pattern typical of the response you get when you subject a human to emotional stimulation of short duration".

See also

• Plant neurobiology
• The Secret Life of Plants

References