Plants warn each other via electrical signals transmitted on the surface of their leaves. A new mechanism of plant communication has been described and explained by a team led by a Polish scientist.
A team of scientists led by Prof Stanisław Karpiński from the Warsaw University of Life Sciences in collaboration with researchers from the University of Missouri (the USA) has for the first time described the quantum-molecular and physiological basis of a previously unknown form of communication between plants and the mechanism it triggers, called Network Acquired Acclimation (NAA). The findings are presented in The Plant Cell, the most prestigious journal publishing articles on plant cell biology.
“Imagine a meadow full of milkweed (common dandelions). It’s not just a plethora of beautiful yellow flowers, but also a thicket of leaves from different plant species coming into contact with each other,” describes team leader Prof. S. Karpiński of the Warsaw University of Life Sciences in an interview with PAP. “When a single dandelion leaf is injured, the information quickly spreads in the form of an electrical signal throughout the plant and is passed on to the leaves of other plants. One dandelion ‘speaks’ to its neighbour with a coded electrical signal: ‘I’m hurt, watch out!’ The whole meadow is buzzing with information sent between the plants.”
In one experiment, the leaves of two dandelions were brought together. One of them was connected by an electrical circuit to the leaves of a mimosa plant, which is known to rapidly drop its leaves in response to touch. A video recording recorded that when the first dandelion was gently touched with a wire, after a few seconds… the mimosa leaves folded. An electrical signal was transmitted from the touched dandelion leaf to the second leaf, which in turn came into contact with the second dandelion leaf, and then – from the second dandelion – the signal travelled in an electrical circuit to the mimosa.
“Such an electrical signal is transmitted quite quickly in terms of plant response. It has a speed of a few millimetres to a few centimetres per second. The condition is a moist environment to close the electrical circuit,” Prof. S. Karpinski says.
Humans or animals, when they experience danger, can, for example, run away, reduce the threat or take informative action. A plant cannot escape, it has other strategies to defend itself, but it also effectively transmits information about danger. It has already been known that plants can send chemical signals to each other – for example, when leaves from African acacias are eaten by giraffes, they synthesise volatile chemicals (e.g. methylated jasmonates). This signals neighbouring plants and leaves to produce bitter alkaloids, substances that alter taste – and thus make them less attractive as food. It was also known that the roots of neighbouring plants communicate signals to their neighbours about the availability of water and minerals via soil fungal hyphae…
A video of an experiment which shows that electrical information flows between leaves of different plants.
Source: The Plant Cell, M.Szechyńska-Hebda et all.
“Now an electrical signal carried on the surface of leaves has been added to the list of communication mechanisms. The ability to detect the danger early undoubtedly enables an individual plant to survive, and rapid communication between plants can facilitate the preparation of an entire plant population for danger,” emphasises the leading co-author of the published research, Magdalena Szechyńska-Hebda, PhD, from the Plant Breeding and Acclimatisation Institute – National Research Institute. She adds that this hitherto unknown mechanism of transmitting information in electrical signals across the leaf surface may be prioritised when chemical or root signals are too slow or when it is difficult for a plant to define a specific receiver of its signal – for example, in a damp thicket of plants.
“Plants are not as primitive organisms as they seem to be. A great multitude of stimuli can be received, processed and physiologically remembered. The level of communication between plant cells is just as complex as in the nervous tissue of animals,” Prof. S. Karpinski specifies.
“Our research confirms that surface electrical signals function as a communication link between plants, which are organised as a global network (community) of plants – just as James Cameron depicted in the film ‘Avatar’. So, they work a bit like Facebook or Twitter,” says the scientist from the Warsaw University of Life Sciences.
“It is conceivable soon to connect an amplifier of electrical signals to plants and to use the discovered mechanisms as part of an early warning system against plant infestation by necrotrophic pathogens, pests, or other plant damage in precision agriculture,” said the authors of the publication.
For now, it is not known whether only binary information about danger is transmitted between leaves, or whether the communication is more advanced in terms of intensity, frequency, and multiple signals. It is also unknown whether plants only transmit an ‘honest’ signal to their neighbours, or whether they can transmit signals to mislead competitors. “This is a whole new area of research. One discovery leads to a whole series of further discoveries, which we are already working on,” says Prof. S. Karpinski.
The scientist explains that the NAA mechanism that allows plants to communicate must be evolutionarily very old – since the electrical signal is generated via chloroplasts, responsible for the process of photosynthesis, which are the key cell organelles for plants life. It can therefore be assumed that all green plant species, trees, perennials, ferns, or mosses and seaweeds can produce surface electrical signals.
“It is fascinating that plants can transmit information so precisely in the aboveground system – because this means that the same system can be used to ‘communicate’ with other organisms, such as pollinating insects,” the study authors add.
Prof. Karpiński points out that the discovery and description of the mechanism of Network Acquired Acclimatisation (NAA) were supported by two earlier important discoveries. One concerns Systemic Acquired Acclimatisation (SAA, more in: Science, 1999), the other – Light Cell Memory within a single plant (CLM – more in: The Plant Cell, 2010). Integrated electrical signals, a mechanism for non-photochemical quenching of excess absorbed energy in photosystems (Non-Photochemical Quenching, NPQ), and Reactive Oxygen Species (ROS) play key roles in both of these physiological processes.
“We have now found that electrical signals and reactive oxygen species can be directly transmitted between two different plants and can regulate NPQ changes in neighbouring plants, which was previously unknown. We have discovered a new type of direct terrestrial communication between plants involving: electrical signalling at the leaf surface, reactive oxygen species and a photosystem network. An electrical signal induced by injury or severe light stress in a single leaf of a dandelion can be transmitted by our team’s previously described SAA and CLM mechanisms to all leaves of the dandelion and to a plant that is in direct contact with one leaf of the stimulated plant. In contrast, the newly described NAA mechanism causes changes in both plants. Moreover, similar changes can be induced in a network of plants connected in series with each other solely by leaf contact,” describes Prof. Stanislaw Karpinski. He adds that in an average tree with a thousand leaves we have trillions of possible virtual communication links between individual photosystems.