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Review

Hormesis as a Particular Type of Plant Stress Response

by
Agnieszka Siemieniuk
,
Małgorzata Rudnicka
*,
Gabriela Jemioła
and
Eugeniusz Małkowski
Plant Ecophysiology Team, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, 40-007 Katowice, Poland
*
Author to whom correspondence should be addressed.
Plants 2025, 14(24), 3815; https://doi.org/10.3390/plants14243815
Submission received: 9 October 2025 / Revised: 11 December 2025 / Accepted: 11 December 2025 / Published: 15 December 2025
(This article belongs to the Section Plant Response to Abiotic Stress and Climate Change)
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Abstract

Plants are continuously exposed to various abiotic and biotic stress factors, which influence their growth, productivity, and ecological fitness. This paper clarifies the concept of hormesis as a distinct low-dose stress response to toxic substances and presents its relationships with other plant stress phenomena. Based on evidence from the published literature, hormesis can be considered a particular type of acclimation because it involves temporary, non-heritable physiological adjustments to mild toxic stress. It is induced by low doses of toxic substances (e.g., cadmium (Cd), lead (Pb), and chromium (Cr)) and characterised by stimulated growth resulting from the moderate activation of defence mechanisms, including antioxidant activity, reactive oxygen species regulation and/or enhanced photosynthetic efficiency, as well as increased auxin content. We propose that the fundamental parameter for identifying hormetic responses should be plant growth, expressed as shoot biomass or elongation, as analyses of single physiological traits alone are insufficient. Furthermore, growth stimulation caused by factors with physiological functions (physiological factors) such as light, temperature or mineral nutrients should be regarded as forms of acclimation rather than hormesis. These assumptions provide a clearer framework for future studies on plant stress physiology.

1. Introduction

In natural conditions, plants are constantly exposed to a variety of stress factors. The resulting stress, as a state of deviation from homeostasis, represents the crucial factor of selective pressure and underlies such important plant processes as growth, yield, reproduction or the occupation of environmental niches. The phenomenon of plant stress is also associated with processes such as adaptation, acclimation and hormesis [1].
Hormesis is a phenomenon that has been known and studied in humans and animals for many years [2,3,4,5,6,7,8,9]. Studies in which hormesis has been observed in plants have also been conducted for many years. However, this specific plant response to any toxic agent initially did not attract widespread interest among plant biologists [10]. Over the past 25 years, interest in hormesis in plants has increased significantly. Many new experimental studies have been published, with authors describing hormesis induced by different toxic agents in many plant species [11,12,13,14,15,16,17,18,19,20,21]. A significant review paper that tried to describe the terminology and precisely define hormesis in plants was the article by Poschenrieder et al. [10]. They recommended that the term hormesis can be used for the stimulation of plant growth in response to treatment with low concentrations of toxic metals in cases where the underlying mechanisms remain to be elucidated. If the mechanism responsible for growth stimulation is identified, such terms as amelioration, defence gene activation, priming or acclimation should be used. More recently, the term priming has been assigned to biotic factors, which are not the subject of this review [22]. Although Poschenrieder et al. [10] demonstrated that the phenomenon of hormesis could be classified as one of the well-known processes (acclimation, amelioration), these terms are not used in papers investigating hormesis, e.g., [14,16,19,21], even if a hormetic stimulation mechanism is proposed. In our opinion, this classification is partially true; however, the mechanism of hormesis may constitute a distinct type of one of the aforementioned processes. In addition, it seems that the terms “adaptation”, “adaptive mechanism” or “adaptive traits” in papers on hormesis are used too frequently or attributed to an inappropriate meaning [14,23,24].
In recent years, several new review papers on hormesis have been published [8,23,25,26,27,28,29,30,31,32,33]. In some of these papers, hormesis is defined as the stimulating action of any factor, including factors with physiological functions, such as light, water, CO2, or mineral nutrients [28,33,34]. This approach does not seem to be fully justified. For many years, the plant response to changes in the intensity or concentration of factors with physiological functions has been called acclimation [35,36,37,38,39]. Furthermore, Poschenrieder et al. [10] showed that the concentration–growth response curve for mineral nutrients (e.g., N, Fe, Zn) has an entirely different course than for toxic trace elements (e.g., Cd, Cr, Pb). This indicates that the linking of factors with physiological functions to hormesis is based on erroneous assumptions. As a result, the aim of our review article is to highlight the erroneous assumptions about the phenomenon of hormesis that have recently appeared in the literature, as well as to present the relationships among hormesis, acclimation, and adaptation. We hope that our article will open up a wide scientific discussion on the phenomenon of hormesis. The reviewed literature was collected from the scientific databases, covering publications from 2000–2025.

2. Plant Responses to Stress Factors

Physiological factors (factors with physiological functions), in their optimal range, are essential for plant metabolism and developmental processes. However, the occurrence of these factors outside the physiological range contributes to a phenomenon known as stress [40]. Stress factors can be divided into abiotic (i.e., drought, flooding, fluctuations in oxygen and carbon dioxide levels, excess light or inadequate temperature) and biotic (i.e., microorganisms), or in terms of the influence they have on the plant: positive effects (eustress) and adverse effects that may even lead to the death of the plant (distress) [40,41,42]. The relationships between eustress and distress are shown in Figure 1.
Four main phases of the stress response can be distinguished: the alarm phase, the recovery phase, the hardening phase, and the stabilisation phase (Figure 1) [40,41,43]. In the alarm phase, a series of events occurs at the molecular level, e.g., signal perception and transduction or the activation of transcription factors. In the recovery and hardening phases, the plant responds to the stress factors through repair mechanisms (i.e., changes in gene expression or the proteome). During the stabilisation phase, all changes at the molecular level result in the establishment of a new physiological state optimal for the stress conditions. If the plant is under hard/high stress (distress), it enters an exhaustion phase, leading to severe damage and, ultimately, death [40,41,42,43,44,45]. However, a lower-intensity stressor may not be destructive, but may instead trigger plant tolerance to stress. Sometimes, it can even lead to the phenomenon of temporary enhanced plant growth and productivity, known as hormesis.

3. The Phenomenon of Hormesis

Hormesis was defined many years ago as a beneficial response, in plants, to a low dose of a toxic substance [10,46]. In recent years, this concept has been expanded to include the action of other factors, not just toxic ones. Currently, hormesis is defined as the action of all factors, including physiological ones, such as light, water, or macro- or micronutrients ([47,48,49] and literature herein). Meanwhile, the model of response describing a plant’s reaction to physiological factors differs significantly from the typical hormesis curve of response (Figure 2). A comparison of the two curves clearly shows that the plant response to a physiological factor is different from the hormetic response to a toxic factor. Thus, the positive response of plants to physiological factors should not be considered a hormesis phenomenon. Moreover, numerous authors define hormesis by limiting it to only two phases of this process, which depend on the intensity of the stress factor: low-dose stimulation and high-dose inhibition [31,32,50]; on the other hand, the common and widely accepted scientific model describing the phases of hormesis takes into account the phase of the sub-hormetic level or even the absence of the stress factor [30,51]. This pattern only fits stressors originally considered hormetic, such as non-essential ones (Figure 2).
As mentioned above, the primary assumption of the hormesis model is that responses are amplified/stimulated (i.e., upregulated) to allow adjustment to low doses of a toxic factor. For example, this could involve increasing biological resistance, in contrast to the detrimental, irreversible effects of high doses [52,53]. In accordance with recent hypotheses, hormesis is the consequence of moderate defence activation, which results in the elimination of damage and the enhancement of photosynthesis and dark respiration efficiency. Consequently, the assimilation of energy by the plant exceeds its dissimilation (leading to a positive energy budget), which promotes plant growth and productivity [32]. Nevertheless, it should be stressed that photosynthesis stimulation is not always necessary for hormetic growth stimulation, as demonstrated by Małkowski et al. [16] in maize treated with low Cd concentrations.
However, reviewing the scientific literature, it can be concluded that hormesis no longer has its original meaning of a dose–response relationship and now comprises a wide range of different concepts and mechanisms, such as amelioration, acclimation, eliciting stress responses, crosstalk in stress signalling, and epigenetic effects [10]. Firstly, it should be emphasised that the hormesis phenomenon should be defined as the temporary beneficial effect of mild stress (eustress) caused by toxic substances on the growth response and fitness of plants [10,40]. Additionally, when analysing the beneficial effects of low concentrations of a stress factor on plants, a thorough assessment of the probable mechanism of action of a given stressor is necessary. The hormetic action of a stress factor should include direct and beneficial interactions and indirect actions, or both of them, through the induction of defence mechanisms. Defence mechanisms include signal perception, signal transduction and the activation of defence mechanisms at the transcriptional and/or post-transcriptional level, leading to increased stress resistance or tolerance [10,54,55,56]. Among these mechanisms are primarily the production of reactive oxygen species (ROS), an increase in antioxidant enzyme activity, changes in nutrient uptake and translocation and associated changes in enzyme activity. In addition, these mechanisms should include increases in photosynthetic pigments, changes in the expression levels of specific genes, modifications to metabolic pathways and increases in the efficiency of the photosynthetic process [10,23,27,57]. On the other hand, all mechanisms that do not occur in planta, such as the interaction between the stress factor and metal ion out of the plant organism (known as the ion amelioration phenomenon), must be excluded. When investigating the hormesis phenomenon, the aspect of time should also not be excluded, as the hormetic response observed after a few minutes of exposure may differ markedly from that occurring after hours, days or even weeks [58]. Observing several time points is worthwhile to understand the dynamics of the changes accompanying hormesis [10,59,60].
Defence mechanisms induced in the hormetic response include the alleviation of oxidative stress by increasing the activity of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and catalase [12,61,62] and increasing the production of glutathione, metallothioneins and phytochelatins (PCs) [63]. In addition, low concentrations of stress hormones such as ABA accompanying this phenomenon promote an increase in photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids) and photosynthetic efficiency [64,65,66,67,68].
To date, we do not know the exact mechanism determining the stimulation of plant growth during hormesis. We suggest that this is probably related to the energy costs of the plant. In the case of typical acclimation, in order to adjust to the presence of a stress factor in the environment, additional metabolic pathways which are distinct from the existing metabolic processes are activated, with a significant energy cost associated with this. In order to reduce energy costs, the plant first inhibits growth (Figure 3, top row). In contrast, during hormesis, only the already functioning metabolic pathways are stimulated. As a result, energy costs are low and the enhanced metabolism enables the plant to increase biomass despite the stressor (Figure 3, bottom row). Nevertheless, the hormetic responses described in the literature, i.e., the direct and indirect reactions and the metabolic pathways activated, correspond to processes characteristic of the classical response to a stress factor, i.e., acclimation. Therefore, the present study proposes to classify hormesis as a particular type of this typical plant adjustment process.

4. Other Stress-Related Processes

Variable environmental conditions and stress factors can induce transient individual responses or fixed changes in the plant genotype (Table 1). Adaptive changes are heritable and irreversible and underpin the natural evolution of organisms according to the principle that the better-adapted organism wins (‘survival of the fittest’ notion) [69]. While genotype changes resulting from mutation or gene transfer are relatively rapid, their fixation through natural selection and maintenance in the population is slow and lengthy [70].
Adaptations, as permanent changes in the plant genotype, should be distinguished from changes in the life of individuals in response to a new unfavourable changes in the environment caused by a stress factor. Such changes, part of a process called acclimation, are generally transient, non-heritable, and mainly disappear when the stress factor no longer exists. Although epigenetic mechanisms typical for acclimation (DNA and histone methylation or acetylation) can extend the duration of acclimation and make it heritable by mitotic and meiotic divisions [71], this is a relatively rare phenomenon. Much more common in plants is the resetting of epigenetic mechanisms and a return to the state prior to the action of the stressor, with an evolutionary advantage for plants living often under highly variable environmental conditions [72].
Acclimation mechanisms are activated in plants primarily in response to an excess or deficiency of a factor necessary for the plant to function correctly. Factors activating the acclimation response are, for example, elevated CO2 [35], reduced oxygen levels, flooding [73,74], drought [75], high or low temperatures [76,77], and excess or insufficient light [78,79]. Also widely reported by many authors is acclimation in response to macro- and micronutrient imbalances [80,81,82,83,84]. Acclimation has also been described as a response to toxic nonessential factors such as heavy metals (Cd, Pb) [85,86,87].
Based on the literature reviewed, it is clear that the hormesis phenomenon described by many authors so far relates to the life of the individual, and the hormetic response they observed was certainly not related to sustained changes at the genome level [14,15,16,17,18,19,20]. It can thus be concluded that the hormesis phenomenon cannot be linked with adaptation mechanisms. Consequently, the terms ‘adaptation’ and ‘adaptive traits’ should not be used to describe this process.
Hence, if hormesis is not an adaptive process, it raises the question of whether it is somehow related to the process of acclimation. The preceding discussion on stress and acclimation indicates that analogous processes are triggered in plants during both acclimation and hormesis [26,27,28,88]. In accordance with the foregoing, the hormesis phenomenon should be regarded as a distinct form of acclimation. Figure 4A shows a typical growth response during the acclimation of a plant to stress conditions (eustress).
Perception of a stress stimulus (alarm phase) at a low or moderate dose usually decreases the plant growth response. Then, as a result of the activation of repair processes during acclimation, the growth returns to the initial rate (Figure 4A, resistance phase) when the plant has adjusted to the stress conditions. Ultimately, the plant produces a smaller biomass than the control plants. In the case of hormesis (very low or low doses of the toxic factor), presented in Figure 4B, no significant decrease in growth response is observed during the alarm phase. Moreover, the growth rate increases during the acclimation phase compared to the growth response before the stressor is applied. Once acclimation is completed and the plant has adjusted to the new environmental conditions, the growth response decreases to the optimum rate for the plant, probably the rate observed in control plants. The effect of faster plant growth during acclimation is ultimately increased biomass relative to that of control plants.
Accepting that the hormesis phenomenon is an example of acclimation has many implications. Since acclimation is related to the adjustment of plants to changed environmental conditions [89], only the terms “adjustment”, “adjustment traits”, etc., should be used in relation to hormesis. By contrast, such terms as “adaptation”, “adaptation mechanisms”, and “adaptation traits” should not be used. Acclimation is the response of a plant to changes in the environment. Therefore, the response of plants to changes in physiological factors, such as temperature, light, soil moisture, and macro- and micronutrients, should be considered a typical acclimation response and not hormesis, even when growth stimulation is observed. In contrast, growth stimulation under the influence of low doses of toxic substances, for example cadmium (Cd), chromium (Cr), mercury (Hg) or lead (Pb), should be considered hormesis. This assumption of hormesis is also proposed by other authors [10,29,90]. In view of the aforementioned points, environmental hormesis also should be re-defined and re-described, as the study revealed that this topic often includes considerations of physiological factors such as light, temperature, soil moisture, or nitrogen [24,49].

5. Experimental Assessment of Hormesis

Currently, a holistic approach to various issues in plant biology is becoming increasingly important [91,92,93]. In our opinion, such a holistic approach should also apply to research on hormesis in plants. Therefore, we propose that the parameter determining the occurrence of hormesis should be the growth of whole plants or shoots, determined by elongation growth, or fresh or dry weight. At the same time, measuring root growth alone seems unjustified. Root biomass accounts for 15 to 30% of shoot biomass, so studying roots alone to observe hormesis seems unreliable. For example, Szopiński et al. [94] observed in hydroponic cultures in Arabidopsis arenosa a 5.5-fold lower dry biomass of roots compared to shoots. In turn, Rusinowski et al. [95] found in pot studies on maize that the dry weight of shoots was 3.0 to 4.8 times greater than that of roots, depending on the soil type. Moreover, shoot biomass is used to determine the yield of various plant species, mainly grasses but also dicotyledons [96,97,98]. These results confirm that shoot biomass is the most important factor in determining plant growth. Furthermore, examining individual parameters, such as chlorophyll content, or only one process, for example photosynthesis, is not sufficient to conclude that hormesis has occurred. Therefore, the results of studies on hormesis that present findings concerning only roots [11,99] or individual processes, such as photosynthesis [17,29,100], or one parameter, such as chlorophyll content [31], should be regarded with great caution. In the case of the aforementioned studies, it would be valuable to repeat them and supplement them with the growth response of shoots or whole plants in order to be sure that hormesis actually occurred.
If a single physiological process is considered, it is easy to overlook actual hormesis, that is, the stimulation of plant growth. For example, Małkowski et al. [16] showed in maize treated with 10 µM Cd that photosynthetic rate and PSII activity were significantly lower compared to the control, while at the same time, stimulation of the elongation growth of Cd-treated seedlings, i.e., a hormesis phenomenon, was observed. If only PSII activity or photosynthetic rate was studied in this case, it would have been concluded that Cd at this concentration and in this experimental setup did not induce hormesis, which would have been a mistake. The same authors also studied Pb-induced hormesis in the same experimental setup [16]. The strongest stimulation of maize shoot growth occurred in the presence of 5 µM Pb. However, unlike with Cd, hormetic growth stimulation was accompanied by an increased photosynthetic rate and chlorophyll content. These results indicate that, depending on the metal, hormetic growth stimulation may result from changes in different metabolic pathways of the plant. A typical response for both metals during hormesis was an increase in auxin content and flavonols. However, no increase in H2O2 content was observed, suggesting the absence of oxidative stress [16]. This does not indicate that Cd did not stimulate ROS generation. Indeed, it must be remembered that an increase in ROS formation alone does not cause oxidative stress. As long as the antioxidant system of the plant is able to maintain the ROS content at a safe level for the plant, no oxidative stress occurs despite the increase in ROS production. It is only when the antioxidant system fails to cope with the removal of ROS formed in the plant that the accumulation of ROS and oxidative stress occur [101]. In turn, an increase in auxin levels may be the main cause of the elevated plant growth response during hormesis, since auxin primarily stimulates cell elongation growth, particularly in the above-ground parts of plants. A similar correlation of the hormetic growth response with a higher content of auxin in plant tissues or the activation of auxin synthesis pathways has been reported [102,103].
On the basis of the examples given above, it must be concluded that hormesis in plants must be studied at the organismal level and not at the level of individual organs or tissues; particularly, it should not be studied at the level of individual physiological processes, such as photosynthesis. The primary parameter that must always be measured is plant growth. Growth measurement can consist of measuring the fresh or dry weight or the elongation growth of the shoots. Of course, whole-plant biomass is also a suitable parameter, although in many cases, it is difficult to measure. Since the shoot biomass is generally 2–4 times greater than the root biomass, the biomass of the aboveground parts is the best parameter for the observation of hormesis.
According to the assumptions given above, we cannot talk about hormesis on the grounds of a root-only response. For example, during drought stress, an increase in the ABA concentration in the plant stimulates root growth relative to that of shoots, the growth of which is strongly inhibited [104]. Based on root biomass alone, one could speak of hormesis. At the same time, however, shoot biomass is sometimes significantly reduced, resulting in the lower biomass of the whole plant so that hormesis does not occur in such a case. Also, other authors consider the organismal level to be the basis when studying hormesis (Table 2) and that for plants, growth is the primary and most important parameter [10]. To conclude, stress can modify plant growth by increasing the growth of certain parts in response to specific stresses, but this usually involves the sacrifice of other parts. The overall effect of stress is better reflected by the accumulation of whole-plant biomass [105].

6. Conclusions

Hormesis refers to the stimulation of plant growth under the influence of low concentrations or doses of toxic substances. It is proposed that growth stimulation should be the primary parameter without which one should not speak of hormesis. Measurements of other parameters, for example chlorophyll content, oxidative stress, and photosynthetic rate, are intended to help determine the mechanisms of hormetic growth stimulation. However, they cannot be the only parameters based on which hormesis is established. Since toxic substances induce hormesis, it is not correct to speak of hormesis due to physiological factors such as light, temperature, soil moisture, or micro- or macronutrients. It seems that hormesis can be regarded as specific type of acclimation.
There is a need for more experiments on the role of auxins in hormetic growth stimulation.

Author Contributions

A.S., M.R. and E.M.: Conceptualization; A.S.: Investigation; A.S., M.R. and E.M.: Writing—Original draft preparation; A.S. and G.J.: Visualisation; A.S., M.R. and E.M.: Writing—Reviewing and Editing; E.M.: Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study.

Acknowledgments

We would like to express our gratitude to Julia Salachna from the Academy of Fine Arts in Katowice, Poland, who prepared Figure 1, Figure 3 and Figure 4 in this article. In addition, we would like to express our deepest gratitude to Agata Korzeńska from the Academy of Fine Arts in Katowice, Poland, for her invaluable assistance and recommendations regarding all the Figures included in this document. Finally, we would like to sincerely thank Krzysztof Sitko for his valuable suggestions, which greatly improved the quality of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Stress response phases (on the basis of [40]; modified). The green line illustrates the behaviour of the plant in the absence of the stress factor. The blue line illustrates the effect of a stress factor at low intensity, causing eustress. Eustress is associated with an increase in the resistance of the plant to stressors. The red line illustrates the action of the stress factor at a high intensity, causing the occurrence of distress. Distress results in damage to the plant or death.
Figure 1. Stress response phases (on the basis of [40]; modified). The green line illustrates the behaviour of the plant in the absence of the stress factor. The blue line illustrates the effect of a stress factor at low intensity, causing eustress. Eustress is associated with an increase in the resistance of the plant to stressors. The red line illustrates the action of the stress factor at a high intensity, causing the occurrence of distress. Distress results in damage to the plant or death.
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Figure 2. Model of plant growth response to various factors. The black solid line shows the reaction of the plant to physiological factors such as macro- and micronutrients, light or water. The shape of the response curve to physiological factors indicates a reduction in growth when a deficiency or an excess of essential factor occurs. However, when the levels of physiological factors are within the optimal range, a maximum growth response (100%) is recorded. The green dashed line shows a typical hormesis curve of the response to toxic factors. The inverted “J” shape is characteristic and can be divided into three phases: 1—when no changes in growth response are observed with increasing dose; 2—when beneficial effects of stress factors are observed; and 3—when the growth response of plant is inhibited. The dotted line symbolises the maximum growth response (100%) when optimal growth conditions occur, and there is no interaction with the stress factor.
Figure 2. Model of plant growth response to various factors. The black solid line shows the reaction of the plant to physiological factors such as macro- and micronutrients, light or water. The shape of the response curve to physiological factors indicates a reduction in growth when a deficiency or an excess of essential factor occurs. However, when the levels of physiological factors are within the optimal range, a maximum growth response (100%) is recorded. The green dashed line shows a typical hormesis curve of the response to toxic factors. The inverted “J” shape is characteristic and can be divided into three phases: 1—when no changes in growth response are observed with increasing dose; 2—when beneficial effects of stress factors are observed; and 3—when the growth response of plant is inhibited. The dotted line symbolises the maximum growth response (100%) when optimal growth conditions occur, and there is no interaction with the stress factor.
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Figure 3. Probable mechanism of plant growth stimulation during hormesis. Upper row: additional metabolic pathways are activated during typical acclimation, with a significant metabolic cost due to the higher level of oxidative stress, the effects of which must be alleviated through new pathways (dark respiration, secondary metabolites synthesis, and other defence processes), resulting in restricted plant growth. Lower row: during acclimation with hormesis, when oxidative stress only reaches the signalling level, the already functioning metabolic pathways are enhanced. The energy cost is low, and the increased metabolic activity and auxin content stimulate growth. The hypothetic hormesis-related processes are as follows: IAA biosynthesis and signalling, sugar metabolic pathways, and photosynthesis-related processes.
Figure 3. Probable mechanism of plant growth stimulation during hormesis. Upper row: additional metabolic pathways are activated during typical acclimation, with a significant metabolic cost due to the higher level of oxidative stress, the effects of which must be alleviated through new pathways (dark respiration, secondary metabolites synthesis, and other defence processes), resulting in restricted plant growth. Lower row: during acclimation with hormesis, when oxidative stress only reaches the signalling level, the already functioning metabolic pathways are enhanced. The energy cost is low, and the increased metabolic activity and auxin content stimulate growth. The hypothetic hormesis-related processes are as follows: IAA biosynthesis and signalling, sugar metabolic pathways, and photosynthesis-related processes.
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Figure 4. Comparison of the typical acclimation response (A) with a particular type of acclimation, which is hormesis (B).
Figure 4. Comparison of the typical acclimation response (A) with a particular type of acclimation, which is hormesis (B).
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Table 1. Concise definitions of processes highlight the fundamental differences between them.
Table 1. Concise definitions of processes highlight the fundamental differences between them.
ProcessDefinition
AcclimationA facultative physiological modification during the individual life of a plant in response to changes in environmental factor(s) necessary for the plant to function correctly, e.g., fluctuations in water, light, macro- and micronutrients, and concentrations of CO2 and O2, as well as toxic factors as toxic trace elements or toxic organic substances.
AdaptationA genetically conserved, heritable modification in the genome of plants to survive and reproduce in a hostile environment. Examples of adaptation include photosynthetic processes in CAM and C4 plants or hyperaccumulation of Zn and Cd in Arabidopsis halleri.
HormesisA beneficial effect of low doses of toxic factor(s), e.g., Cd, Hg, Pb, ozone, and herbicides, on plant growth response and fitness.
PrimingThe capacity of plants to memorise environmental stresses, thereby improving their responses to recurrent stress.
Table 2. Examples of plant hormetic response based on whole-plant growth parameters.
Table 2. Examples of plant hormetic response based on whole-plant growth parameters.
No. Hormesis-Inducing FactorPlant SpeciesParameters Analysed FindingsPublication Details
1CadmiumPolygonatum sibiricumplant biomass, photosynthetic efficiency, and polysaccharide content, as well as CAT, SOD and POD activity and MDA content were measured. Moreover, the polysaccharide contents (PCP1, PCP2 and PCP3) were determined.A hormetic increase in plant biomass was observed, accompanied by enhanced photosynthetic efficiency, increased antioxidant activity, and a higher polysaccharide content.[19]
2 Glyphosate Solanum lycopersicum The plant growth reaction (height), photosynthetic pigment content, photosynthetic efficiency, antioxidant enzyme activity (CAT, SOD and POD) and non-photochemical quenching and expression of genes related to NPQ were analysed. In the case of low doses of glyphosate, an increase in photosynthetic pigment content and photosynthesis efficiency, enhanced antioxidant enzyme activity, and increased plant growth were observed. [106]
3CadmiumTriticum aestivumThe plant biomass, root morphology and development, photosynthetic rate, stomatal conductance, intercellular carbon dioxide concentration, and transpiration rate, along with MDA,
non-protein thiol (NPT), phytochelatin,
and glutathione content, were determined. Moreover, antioxidant enzymes activity was also analysed. 		An increase in whole-plant biomass, improved root development and enhanced photosynthetic rate were observed in the presence of a low cadmium concentration. This hormetic response is connected with the enhancement of the photosynthetic and antioxidant system. [107]
4Cerium oxide nanoparticles Allium sativumGrowth parameters such as the length and fresh and dry mass of roots and shoots, together with the mitotic index, levels of MDA and ROS, photosynthetic pigment content, and soluble sugar and protein content, were measured.Hormesis was observed in the presence of cerium oxide nanoparticles, with increased growth, decreased levels of ROS and MDA, increased carbohydrate and protein content, increased photosynthetic pigment levels, and a higher mitotic index.[108]
5CadmiumLonicera japonica Thunb. The net photosynthesis rate,
stomatal conductance, intercellular CO2 concentration and transpiration rate, as well as photosynthetic pigment contents, photosynthetic efficiency and total plant biomass were measured. 		Increased levels of net photosynthesis rate, photosynthetic pigments, enhanced photosynthetic efficiency, and higher total plant biomass were detected in the case of low cadmium concentration. [109]
6AcephateSolanum lycopersicum L.The shoot height, root length, and dry weight (DW) of shoots and roots, as well as chlorophyll a fluorescence, photosynthesis pigment content, and CAT, SOD and POT activity, were measured. Moreover, the expression levels of genes involved in the photosynthesis antenna were also analysed.An increase in plant biomass and photosynthetic rate, as well as increased photosynthetic pigment content, was observed in the presence of low doses of acephate. A similar effect was recorded for genes participating in photosynthesis.[110]
7Cadmium, Chromium, LeadCardamine hirsuta, Poa annua, Stellaria mediaThe root and shoot dry biomass, number of nodes, leaf area, and photosynthetic pigment content were analysed.In the presence of chromium for all species tested, the dry biomass of both the roots and shoots increased, as did the number of nodes. However, in the presence of cadmium, a similar hormetic reaction to that described above was observed only for C. hirsuta and P. annua. Furthermore, in the case of the latter species, this reaction was also accompanied by an increase in leaf area and in the content of photosynthetic pigments.[111]
8CadmiumBrassica chinensis L.Phenotyping of the whole plant, leaf cell anatomy, shoot fresh biomass, and CAT, SOD and POD activity, as well as H2O2, O2˙, and MDA content, were measured. Moreover, analysis of the level of soluble sugars and sequencing of the transcriptome and metabolome were performed.Brassica chinensis showed an increase in shoot biomass and enhanced he antioxidant system when treated with low levels of cadmium. Moreover, enhanced IAA biosynthesis signalling and the plants’ sugar metabolic pathways were observed.[103]
9CadmiumBrassica oleraceaThe fresh plant biomass, as well as levels of IAA, GSH, GSSG, glucosinolate and MDA, were measured. Additionally, differences in gene expression were analysed in order to identify hormesis-related ones. Treatment of Brassica oleracea with low cadmium doses resulted in an increase in plant biomass, enhanced auxin biosynthesis and an increase in the ratio of reduced to oxidised glutathione. Moreover, up-regulated genes under low Cd concentrations were identified as potentially related to hormesis, such as a transcription
factor regulating the Fe deficiency response; an enzyme catalysing the degradation of GSLs; enzymes modulating the structure of the cell wall; and proteins involved in the photosystem II unit.		[102]
10GlyphosateCoffea arabicaPlant height, leaf number, leaf area, total dry biomass, CO2 assimilation, transpiration and stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, rate of electron transport, photosynthetic efficiency, and content of shikimic acid pathway compounds were analysed. Treatment with low concentrations of glyphosate increased plant biomass, improved photosynthetic efficiency and caused beneficial changes in morphology and biochemistry (shikimic acid pathway compounds).[112]
11GlyphosateToona ciliataPlant height and stem diameter, chlorophyll a fluorescence, net carbon assimilation rate, stomatal conductance, transpiration rate, internal CO2 concentration and ratio of internal to external CO2 were measured. Moreover, morphoanatomical characterisation and visible leaf symptom analyses were performed.Toone ciliata exhibited increased plant height and photochemical yield (photosynthetic rate and carboxylation efficiency) in response to lower doses of glyphosate.[113]
12CadmiumCelosia argentea, Celosia cristata, Malva crispa and Malva rotundifoliaThe shoot length, leaf area, shoot and root dry biomass, Cd bioaccumulation (BCF) and translocation (TF) coefficients, as well as the tolerance index (TI), were measured.The introduction of a low cadmium concentration resulted in an increase in both shoot and root biomass in the case of Celosia argentea, Celosia cristata, Malva crispa and Malva rotundifolia.[114]
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Siemieniuk, A.; Rudnicka, M.; Jemioła, G.; Małkowski, E. Hormesis as a Particular Type of Plant Stress Response. Plants 2025, 14, 3815. https://doi.org/10.3390/plants14243815

AMA Style

Siemieniuk A, Rudnicka M, Jemioła G, Małkowski E. Hormesis as a Particular Type of Plant Stress Response. Plants. 2025; 14(24):3815. https://doi.org/10.3390/plants14243815

Chicago/Turabian Style

Siemieniuk, Agnieszka, Małgorzata Rudnicka, Gabriela Jemioła, and Eugeniusz Małkowski. 2025. "Hormesis as a Particular Type of Plant Stress Response" Plants 14, no. 24: 3815. https://doi.org/10.3390/plants14243815

APA Style

Siemieniuk, A., Rudnicka, M., Jemioła, G., & Małkowski, E. (2025). Hormesis as a Particular Type of Plant Stress Response. Plants, 14(24), 3815. https://doi.org/10.3390/plants14243815

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