By Claire Laurant, ethnobotanist
These days we hear a lot about the intelligence, memory and sensitivity of plants. Recent scientific research reveals the astonishing properties of certain species.
Let’s not forget that the fundamental characteristics of plants are already quite extraordinary… Using the intermediary of the sun’s energy, they are able to transform CO2 into absorbable substances which are necessary to their vitality (sugars). Certain species do the same with gaseous nitrogen – plants of the Fabaceae family are capable of enriching the soils with nitrogen. If they can’t find nitrogen in a deficient soil, they transform the gaseous nitrogen present in the air into substances useful for their growth.
In his recent book A quoi pensent les plantes ? (Editions Odile Jacob), Jacques Tassin, a researcher in plant ecology, refers to plants as ‘the daughters of light and the sun’. They also draw their energy from the soil via their root system and transform the minerals into substances that can be assimilated by not only the plants, but by animals and by human beings. The root system associates with bacteria and fungus to produce mycelium, which provides the roots of the plant the minerals they need to survive. In exchange, the fungus draws its energy from the plants, because it contains no chlorophyll.
Plants concentrate their energy on three main activities – undefined growth, reproduction, and adaptation to their environment.
They are capable of perceiving their environment, adapting to it, and communicating these perceptions to other plants.
Plants communicate with each other, and
Since they are not mobile, plants need to communicate information. First of all via the air - Luc Jacquet’s film Il etait une foret details the chemical emissions which are transmitted from one tree to another, from one plant to another. They can be activated if a predator should appear. For example, kudus, a species of antelope from Southern Africa, feed on acacia leaves. The leaves that have been wounded by these predators liberate ethylene and phytohormones which inform the neighbouring acacias, causing them to become uneatable.
Information can also spread underground, via mycelium. An experiment performed in the 2000’s showed that when a tobacco plant is stressed (ultraviolet rays), the plants nearby produce more polyphenols in order to protect themselves. These plants were informed of the stress experienced by the neighbouring plant via their shared underground network.
There is talk of memory in plants - Les plantes ont-elles une memoire ? asks Michel Thellier (Editions Quae, 2015). Plants are able to store information, to retain it for a certain time and reuse it if the situation demands. Plants know which information they need to conserve, a form of « memory » whose mechanism we don’t yet understand.
The experiments by Barbara Hohn’s team, published in 2006 in Nature magazine, explores the epigenetic regulation of plants, which is connected to the environmental effect on genes. Hohn shocked one plant with ultraviolet lights. The seeds which developed from this plant presented the same alteration in their genome as the plant which had suffered the initial shock.
Apart from this, plants react to numerous stimuli. They perceive vibrations – Indian music or hard rock increase the production of certain enzymes in hibiscus plants. When tomato plants are beaten, they develop tannins to defend themselves. Some plants go as far as retracting if the person who beat them should pass by…
Plants are capable of mimicry and manipulation
A parasite liana, Cuscuta pentagona, has only a few days to find its host, failing which it dies. The seedling of the liana has receptors which perceive the phytohormones emitted by its potential host, and grows in that direction. Once it has found its target, it deploys its sinkers to draw out the nutritive substances.
Another parasitic plant takes the form of its host plant – its leaves begin to resemble those of its host. Is this due to an exchange of genetic material or simply mimicry by chemical transmission?
Another example of mimicry is provided by the wild rice that invades the rice paddies of South-East Asia – its resemblance to cultivated rice is astonishing, but it does not produce seeds.
The Ophrys orchid takes on the form and the colour of the insect which will pollinate it – but produces no nectar – a real manipulator!
Plants have the same mineral, cellular and enzymatic constitution as humans and animals – they are part of the Vivant, ‘the living’. It’s worth noting that chlorophyll has the same molecular structure as haemoglobin – the only distinction is that chlorophyll has one atom of copper, where haemoglobin has an atom of iron.
But plants are still very different from us, and we can’t look at them from our anthropocentric standpoint. Let’s allow them to have their own particularities! It would be inaccurate to interpret the intriguing plant characteristics mentioned above represent intentionality or "feelings"…