Fundamental Science: Do plants have memory?

Plants are not passive victims, unprepared and always taken by surprise at every change in the environment. They can learn, remember and even predict change.

Generally speaking, memory is the ability to store information, but each area of ​​science has a definition. In medicine and psychology, it is the faculty of remembering and retaining information in the mind. In computing, it is related to storing data on computer chips and the like. In botany, it exists when a plant is able to store information from a stimulus, allowing its response to changes in the environment to be more efficient.

There are certain heat stimuli, for example, that can be lethal in some plants – exposing a young heat-sensitive rice plant that was growing in a 25°C environment to 47°C for one hour. The plant will most likely die. Surprisingly, if even two days earlier this young plant had been exposed for two hours to a sublethal heat stimulus, i.e. not capable of causing death, say 42°C, it could have survived the temperature experienced for two days. later. Heat tolerance was acquired by remembering the first stimulus.

In nature, keeping information about a very high temperature episode is very advantageous for plants that grow in the summer, as this way they will protect themselves better and faster from the next heat wave that will most likely come and be devastating. An important aspect throughout the evolution of plants, the advantage of memory for their survival can be applied to various stimuli and different species.

Memory in plants occurs in each cell and has molecular bases, involving complex networks of genetic and metabolic interaction. Drought, for example, leaves molecular marks on the weather response machinery that can remain even when the plant is irrigated again. These are marks that can last for hours, days or stay forever, enabling greater efficiency in responses to subsequent stimuli.

The circadian clock of plants is a very important component of the process, as it allows the prediction of cyclical changes in the environment, such as day and night. During the day, the inflorescence of a young sunflower, for example, follows the sun until it sets in the west, while at night it reorients itself to the east in preparation for the rising sun. This is possible because the circadian clock measures time and coordinates the most appropriate responses for each hour of the day, often just before the stimuli occur, allowing the plant to organize itself.

The memory in plants has also been explored by biotechnology. There are pre-treatments of seeds and seedlings that increase the vigor of the plants before they are taken to the final planting site. The hardening process, for example, has been used to assist in the adaptation of nursery seedlings to adverse environmental factors in the field. In this process, stimuli such as drought, high sun exposure and low soil nutrition are introduced gradually, allowing a progressive learning that results in plants better adapted to the field.

On the other hand, memory does not always offer an agricultural advantage, as is the case with onion bulbs (small bulbs formed from the germination of onion seeds), whose memory of a cold period leads to early flowering, unwanted for some. horticulturists. Companies that sell these cloves stored in the cold (to avoid deterioration) manage to circumvent the problem by exposing them to high temperatures two or three weeks before planting. This treatment undoes the memory of cold storage, preventing unwanted early flowering.

The molecular mechanisms involved in the formation, maintenance and effects of memory in plants are still not fully understood, despite the advanced stage of current knowledge on the subject. Recent molecular biology technologies, such as next-generation sequencing, have enabled more systemic analyzes of the complex molecular networks involved in the process, offering great promise to expand our understanding of this phenomenon. This understanding is especially important against the backdrop of global climate change. Maybe this way we will be able to develop plants with more efficient memories and capable of growing more easily on a planet with increasingly extreme climatic variations?

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Cristiane Calixto has a PhD in plant biology and is a professor at USP.

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