Stress Memory in Plants: Can Plants ‘Remember’ Drought, Heat or Salt?

Plants cannot move away when their environment becomes hostile. A wheat plant cannot search for shade during a heatwave, and a crop growing in drying soil cannot simply move closer to water. Instead, plants survive environmental fluctuations by continuously adjusting their physiology, metabolism and gene expression.

One of the most fascinating outcomes of this ability is plant stress memory.

When a plant experiences drought, heat, salinity or another environmental stress, the effects of that experience do not necessarily disappear as soon as favourable conditions return. In some situations, the first exposure leaves behind molecular, biochemical or physiological changes that influence how the plant responds when stress occurs again.

In simple terms, a plant that has experienced stress once may respond differently the second time.

This phenomenon is commonly described as stress memory, stress priming or stress imprinting, although these terms are not completely interchangeable. It does not mean that plants remember events consciously as animals do. Plants have no brain or nervous system capable of storing memories in the neurological sense. Instead, information about previous environmental conditions can persist through changes in gene regulation, chromatin, proteins, metabolites, hormones and cellular physiology.

Understanding this phenomenon has become particularly important as crops increasingly experience repeated droughts, heatwaves and episodes of soil salinity. If scientists can understand how plants retain information about previous stress, it may eventually help us develop crops that recover faster and tolerate increasingly unpredictable environments.

What Is Stress Memory in Plants?

Plant stress memory can be described as the ability of a previous environmental experience to modify the plant’s response to a later challenge.

Imagine two genetically similar plants.

One has grown continuously under favourable conditions. The second experiences a moderate period of drought, recovers after watering and is later exposed to drought again.

During the second drought, the previously stressed plant may activate certain protective genes more rapidly or strongly, accumulate protective metabolites differently, regulate stomata differently or maintain aspects of cellular protection established during the first stress.

The plant’s second response is therefore not necessarily identical to its first response.

Researchers often describe the initial mild or non-lethal exposure that prepares the plant for a later challenge as priming. The biological information that persists after the original stimulus has disappeared can contribute to what is called stress memory.

However, priming does not guarantee improved performance in every situation. The outcome depends on the plant species and genotype, developmental stage, intensity and duration of the first stress, recovery period, type of subsequent stress and environmental conditions.

Stress memory should therefore be viewed as a dynamic biological state rather than a permanent switch that simply makes a plant “stress resistant.”

What Happens During the First Stress?

The first encounter with stress triggers a large signalling network inside the plant.

Consider drought.

As soil water availability decreases, changes in cellular water status are detected throughout the plant. The hormone abscisic acid (ABA) becomes particularly important, contributing to stomatal regulation and the expression of many drought-responsive genes.

At the same time, calcium signalling, reactive oxygen species (ROS), protein phosphorylation cascades and other signalling pathways help transmit information from stress perception to cellular responses.

Transcription factors activate or repress large groups of genes. Proteins involved in cellular protection accumulate. Osmotically active compounds can increase. Antioxidant systems are adjusted, membrane properties may change, and growth can slow as resources are redirected towards survival.

If favourable conditions return, many of these responses gradually decline.

But importantly, not everything necessarily returns immediately to the exact pre-stress state.

Some transcriptional, metabolic or chromatin-associated changes can persist during the recovery period. These persistent changes may influence how the plant behaves during the next stress event.

This residual biological state provides one possible foundation for stress memory.

Memory Genes: Why the Second Response Can Be Different

One of the clearest ways scientists investigate stress memory is by examining gene expression during repeated stress cycles.

Not every stress-responsive gene behaves in the same way.

Some genes are activated during the first stress and respond similarly when the stress returns. Others show a different pattern during subsequent exposure.

A transcriptional memory gene, for example, may be strongly induced during drought, decline after rewatering and then become activated more strongly or differently during another dehydration episode.

Other genes can show the opposite pattern and become less responsive after repeated exposure.

This distinction is important because stress memory is not simply a situation in which all defence genes remain permanently activated.

Keeping the entire stress-response machinery switched on would consume energy and potentially interfere with growth and reproduction.

Instead, plants can retain a more selective molecular state in which particular genes or pathways remain more easily inducible.

The genome has not necessarily changed. Rather, the way specific parts of that genome are regulated can remain altered for some time after the initial stress.

Epigenetics and the Molecular Basis of Stress Memory

Epigenetic regulation is one of the most intensely studied components of plant stress memory.

DNA inside the nucleus is packaged with histone proteins into chromatin. Chromatin is not simply packaging material; its organisation strongly influences whether particular genes are accessible to the transcriptional machinery.

Environmental stress can alter this regulatory landscape.

Several mechanisms have been associated with stress responses and memory, including DNA methylation, histone modifications, nucleosome positioning, chromatin remodelling and regulatory non-coding RNAs.

These mechanisms can change how easily particular genes are expressed without changing the underlying DNA sequence.

This provides plants with a potentially flexible system: the genetic information remains largely unchanged, while its accessibility and activity can be adjusted according to environmental experience.

However, an important scientific distinction must be made. Finding an epigenetic change after stress does not automatically prove that the change stores the memory. In many cases, researchers have identified strong correlations between particular chromatin modifications and stress memory, but establishing direct causation remains an active area of research.

Histone Modifications Can Leave Genes in a Prepared State

Histone proteins can undergo numerous chemical modifications that influence chromatin structure and transcription.

One modification frequently discussed in plant stress memory research is methylation of lysine 4 on histone H3, particularly H3K4me3.

This histone modification is generally associated with transcriptionally active or transcriptionally competent regions.

During dehydration and other stresses, altered H3K4 methylation has been observed at certain stress-responsive genes. In some experimental systems, elevated H3K4me3 can persist during recovery even after transcription has decreased.

This creates an intriguing possibility.

The gene is no longer producing large amounts of RNA, but part of its previous transcriptional state remains reflected in its chromatin environment. When stress returns, that locus may therefore be positioned differently for renewed transcription.

Other histone modifications are also involved. Changes involving H3K27 methylation, histone acetylation and chromatin remodelling have been associated with different stress-memory systems.

Rather than one universal “memory mark,” current evidence points towards a network of chromatin states whose importance varies between genes, tissues, stresses and species.

Drought Memory: Preparing for the Next Dry Period

Drought provides one of the best studied examples of plant stress memory.

Plants exposed to repeated dehydration and rehydration cycles can develop responses that differ from those of plants encountering drought for the first time.

These differences have been observed at transcriptional, physiological, biochemical and metabolic levels.

During drought, ABA signalling contributes to stomatal closure and large-scale changes in gene expression. Plants can also accumulate compatible solutes such as proline and soluble sugars, modify antioxidant metabolism and adjust root and shoot growth.

Following rewatering, visible symptoms may disappear relatively quickly, but some molecular changes can persist longer.

Repeated drought can subsequently alter the expression of dehydration-responsive genes compared with the initial stress exposure.

This does not mean that a previously drought-stressed plant will always outperform an unstressed plant during another drought. Severe initial stress can damage photosynthetic tissues, reproductive structures, membranes and cellular machinery. In such cases, the cost of the first stress may exceed any benefit associated with priming.

The most useful stress memory is therefore generally associated with an initial experience that prepares rather than irreversibly injures the plant.

Heat-Stress Memory: Surviving a Second Heatwave

Heat stress provides an especially well-characterised example of plant acclimation and memory.

A plant exposed to moderately elevated temperature can sometimes become more tolerant of a later, more severe heat episode. This process is associated with acquired thermotolerance.

Heat activates a sophisticated network involving heat-shock transcription factors and heat-shock proteins (HSPs).

Heat-shock proteins help maintain protein homeostasis by assisting protein folding, preventing harmful protein aggregation and supporting the recovery of damaged proteins.

Importantly, some components of the heat-response system persist after the temperature has returned to normal.

In Arabidopsis thaliana, the transcription factor HEAT SHOCK FACTOR A2 (HSFA2) is a major component of heat-stress memory. HSFA2 participates in maintaining prolonged expression or enhanced reactivation of specific heat-memory genes.

Research has also identified roles for chromatin regulation and histone modifications in maintaining heat-stress memory. Heat-responsive loci such as HSP22 and HSP17.6C have become useful experimental systems for studying how chromatin states change during the period between initial heat exposure and subsequent stress.

Heat memory therefore illustrates an important feature of plant adaptation: surviving the first heatwave can temporarily change the molecular state of the plant in ways that influence its response to the next one.

But this memory does not last forever.

As plants continue growing under normal temperatures, heat-memory-associated molecular states can gradually disappear.

Salt-Stress Memory: Remembering an Ionic and Osmotic Challenge

Salinity creates a particularly complex challenge because salt stress has both osmotic and ionic components.

When salts accumulate around roots, plants initially experience difficulty taking up water because soil water potential becomes more negative. Over longer periods, excessive accumulation of ions such as sodium can disturb cellular ion balance, enzyme activity, membrane function and nutrient acquisition.

Plants respond by adjusting ion transport, osmotic balance, antioxidant metabolism, hormonal signalling and gene expression.

Repeated exposure to salinity can also produce transcriptional memory.

One gene frequently discussed in this context is P5CS1, which encodes an enzyme involved in proline biosynthesis. Proline can contribute to osmotic adjustment and cellular protection during environmental stress.

Changes in transcriptional behaviour and chromatin modifications have been associated with repeated salt exposure at stress-responsive loci.

As with drought and heat, however, salt memory should not be interpreted as a permanent upgrade to the plant. Its strength and duration vary greatly, and prolonged or severe salinity can simply overwhelm the protective capacity of the plant.

Stress Memory Is More Than Epigenetics

It is tempting to describe plant stress memory entirely as an epigenetic phenomenon, but that would oversimplify the biology.

Memory can exist at several interconnected levels.

Proteins produced during the first stress may remain in cells after the stress ends. Metabolites can remain elevated. Antioxidant capacity can change. Hormonal sensitivity may be altered. Membrane composition can shift. Transcription factors can persist, and signalling pathways may remain modified.

Changes in root architecture or leaf development can also influence future responses.

A plant that develops a deeper or differently distributed root system during water limitation may respond differently to another drought simply because its physical structure has changed.

Similarly, accumulated osmoprotectants or antioxidant compounds may allow cells to respond more effectively to another episode of stress.

Stress memory is therefore better understood as an integrated physiological and molecular state rather than a single molecular mark.

Reactive Oxygen Species: Damage Signals and Information Carriers

Reactive oxygen species are another important part of this network.

Drought, heat and salinity can all increase the production of molecules such as hydrogen peroxide and superoxide.

At excessive concentrations, ROS can damage lipids, proteins, pigments and nucleic acids. Plants therefore maintain sophisticated antioxidant systems involving enzymes such as superoxide dismutase, catalase, ascorbate peroxidase and other components of redox metabolism.

But ROS are not simply toxic by-products.

At controlled concentrations, they also act as signalling molecules.

ROS signals interact with calcium signalling, protein kinases, hormones and transcription factors, helping cells translate environmental stress into changes in gene expression and metabolism.

Previous stress exposure can modify these redox and antioxidant networks, potentially changing how rapidly or strongly the plant responds when stress occurs again.

The same molecules that can cause damage at high concentrations can therefore participate in signalling at controlled concentrations—an excellent example of the complexity of plant stress biology.

Hormones Connect Environmental Experience With Future Responses

Plant hormones provide another layer connecting environmental conditions with stress memory.

ABA is especially important during drought and salinity, but it works alongside jasmonates, ethylene, salicylic acid, auxins, cytokinins, gibberellins and other signalling molecules.

Stress changes not only hormone concentrations but also hormone synthesis, transport, degradation, perception and downstream signalling.

Consequently, a previously stressed plant may enter a later stress event with a different hormonal or signalling state.

This altered state can influence stomatal behaviour, root growth, leaf expansion, senescence, antioxidant activity and stress-responsive transcription.

Stress memory therefore emerges from interactions among signalling networks rather than from one isolated pathway.

Can One Stress Prepare a Plant for Another?

An especially interesting phenomenon is cross-stress priming.

A previous environmental challenge does not always affect only the response to the same stress. In some situations, exposure to one type of stress can modify tolerance to another.

This is biologically plausible because drought, salinity, heat, cold and pathogen attack share parts of their signalling networks.

ROS, calcium, mitogen-activated protein kinase pathways, hormones, transcription factors and antioxidant systems are used repeatedly across different environmental responses.

For example, drought and salinity both impose osmotic stress, while drought and heat can both increase oxidative pressure and disrupt photosynthesis.

Consequently, priming one signalling network can sometimes influence the response to another challenge.

However, cross-stress effects are highly context dependent. One stress can improve tolerance to another in one species or treatment regime but increase susceptibility under different conditions.

Plant stress responses involve trade-offs rather than universally beneficial protection.

How Long Does a Plant Remember?

There is no single duration for plant stress memory.

Some molecular changes last only hours. Others persist for days or weeks, and certain effects may remain throughout significant portions of the plant’s life.

Duration depends on the stress, genotype, developmental stage, tissue, severity of exposure and molecular mechanism involved.

This raises an important concept: forgetting is biologically useful too.

Permanent activation of stress defences would be expensive.

A plant continuously behaving as though it were experiencing drought might keep stomata more closed, reduce carbon dioxide uptake, suppress growth and divert resources into protective metabolism even when water is abundant.

Plants therefore face a fundamental trade-off between growth and defence.

Stress memory must persist long enough to provide an advantage if stress returns, but in many cases it should eventually fade when environmental conditions remain favourable.

Memory decay is therefore not necessarily failure. It may be an essential component of efficient plant growth.

Can Stress Memory Be Passed to the Next Generation?

This is one of the most fascinating—and most easily overstated—areas of plant stress-memory research.

Some experiments have reported that parental exposure to environmental stress can influence the phenotype or stress responses of offspring. DNA methylation, small RNAs and chromatin modifications have all been proposed as possible contributors.

This raises the possibility of intergenerational or transgenerational stress memory.

However, the terminology matters.

If a parental plant is exposed to stress while reproductive tissues or developing seeds are also directly exposed, effects detected in the immediate offspring do not automatically demonstrate stable transgenerational epigenetic inheritance.

Strong evidence for transgenerational memory requires effects to persist into generations that were not themselves directly exposed to the original stress and requires careful separation of epigenetic inheritance from genetic variation, seed provisioning and maternal environmental effects.

Plants also possess mechanisms that can reset epigenetic states between generations.

For these reasons, although transgenerational stress effects are well documented in particular experimental systems, it would be inaccurate to claim that plants universally transmit drought, heat or salt memories permanently to their descendants.

The stability, mechanisms and adaptive importance of such inheritance remain active areas of research.

Stress Memory Comes With a Cost

Memory sounds entirely beneficial, but maintaining a primed state can require resources.

Producing protective proteins, antioxidants and metabolites consumes carbon, nitrogen and energy. Maintaining altered signalling or transcriptional states may also influence growth and reproduction.

This creates what researchers often describe as a priming cost or growth–defence trade-off.

If another stress occurs soon, maintaining preparedness may be advantageous.

If the environment remains favourable for a long period, however, investing heavily in defence may reduce competitiveness compared with a plant allocating those resources to leaf growth, roots, flowers or seeds.

This trade-off probably helps explain why many forms of stress memory are reversible rather than permanent.

Plants must continually balance the probability of future stress against the energetic cost of remaining prepared.

Can We Train Crops to Handle Climate Stress?

The agricultural implications of stress memory are substantial.

Modern crops increasingly experience environmental stress as repeated episodes rather than isolated events. A field may experience drought followed by irrigation and another drought, or several heatwaves separated by cooler periods.

If controlled priming can prepare plants for later stress without imposing unacceptable growth penalties, it could potentially become part of climate-resilient crop management.

Seed priming is already widely studied as one approach. Seeds can be exposed to controlled hydration or other treatments before sowing to influence germination and subsequent stress performance.

Researchers are also investigating chemical priming, temperature conditioning and controlled stress exposure.

Another possibility is breeding.

Genotypes differ in their capacity to establish, maintain and erase stress-associated states. Identifying genes and regulatory networks controlling these differences could allow breeders to select crops that respond more efficiently to repeated environmental challenges.

Epigenome engineering is an even more experimental possibility. If researchers establish that a particular chromatin modification directly produces a useful memory phenotype, targeted manipulation of that state could eventually offer new approaches to crop improvement.

But this requires caution.

Agricultural environments contain combinations of drought, heat, nutrient limitation, salinity, pathogens and fluctuating weather. A molecular response that improves survival under controlled laboratory conditions does not automatically improve yield in a farmer’s field.

The ultimate target is not simply a plant that survives stress. It is a plant that maintains useful productivity despite stress.

Stress Memory Changes How We Think About Plant Adaptation

For many years, environmental stress research largely focused on the immediate question: What happens to a plant when stress begins?

Stress-memory research adds another question:

How does what happened yesterday change what the plant does tomorrow?

That shift is important.

Plants are not repeatedly returning to a perfectly blank physiological state after every environmental event. Their previous experiences can influence their current molecular and physiological condition.

A drought can alter transcription and chromatin. Heat can leave components of the heat-response network in a prolonged state of readiness. Salinity can modify ion regulation, metabolism and transcriptional responses. Some of these changes disappear rapidly, while others persist long enough to influence another environmental challenge.

This does not mean that plants possess memory in the neurological sense. Instead, their cells can retain biological information about previous environmental conditions.

That information may reside in chromatin, transcriptional machinery, proteins, metabolites, hormones, redox networks or developmental changes—and often in interactions among several of these systems.

Perhaps the most remarkable aspect of plant stress memory is not that a plant can simply “remember” drought, heat or salt. It is that a stationary organism has evolved multiple ways to use its environmental history to continually recalibrate its future response.

As climate change increases the frequency of heatwaves, irregular rainfall and soil salinisation, understanding these mechanisms is becoming more than an interesting question in plant biology. It may become an important part of designing the next generation of climate-resilient crops.

References

Avramova, Z. (2015). Transcriptional ‘memory’ of a stress: transient chromatin and memory (epigenetic) marks at stress-response genes. The Plant Journal, 83, 149–159.

Crisp, P. A., Ganguly, D., Eichten, S. R., Borevitz, J. O., & Pogson, B. J. (2016). Reconsidering plant memory: intersections between stress recovery, RNA turnover, and epigenetics. Science Advances, 2, e1501340.

Ding, Y., Fromm, M., & Avramova, Z. (2012). Multiple exposures to drought ‘train’ transcriptional responses in Arabidopsis. Nature Communications, 3, 740.

Fleta-Soriano, E., & Munné-Bosch, S. (2016). Stress memory and the inevitable effects of drought: a physiological perspective. Frontiers in Plant Science, 7, 143.

Hilker, M., & Schmülling, T. (2019). Stress priming, memory, and signalling in plants. Plant, Cell & Environment, 42, 753–761.

Kambona, C. M., Koua, P. A., Léon, J., et al. (2023). Stress memory and its regulation in plants experiencing recurrent drought conditions. Theoretical and Applied Genetics, 136, 26.

Lämke, J., & Bäurle, I. (2017). Epigenetic and chromatin-based mechanisms in environmental stress adaptation and stress memory in plants. Genome Biology, 18, 124.

Molinier, J., Ries, G., Zipfel, C., & Hohn, B. (2006). Transgeneration memory of stress in plants. Nature, 442, 1046–1049.

Harris, C. J., Amtmann, A., & Ton, J. (2023). Epigenetic processes in plant stress priming: Open questions and new approaches. Current Opinion in Plant Biology, 75, 102432.

Kovalchuk, I. (2023). Role of epigenetic factors in response to stress and establishment of somatic memory of stress exposure in plants. Plants, 12, 3667.