Hormetic effects of glyphosate on plants

Rhizosphere Bacteria Help to Compensate for Pesticide-Induced Stress in Plants

Although exogenous chemicals frequently exhibit a biphasic response in regulating plant growth, characterized by low-dose stimulation and high-dose inhibition, the underlying mechanisms remain elusive. This study demonstrates, for the first time, the compensatory function of rhizosphere microbiota in assisting plants to withstand pesticide stress. It was observed that pak choi plants, in response to foliar-spraying imidacloprid at both low and high doses, could increase the total number of rhizosphere bacteria and enrich numerous beneficial bacteria. These bacteria have capabilities for promoting plant growth and degrading the pesticide, such as Nocardioides, Brevundimonas, and Sphingomonas. The beneficial bacterial communities were recruited by stressed plants through increasing the release of primary metabolites in root exudates, such as amino acids, fatty acids, and lysophosphatidylcholines. At low doses of pesticide application, the microbial compensatory effect overcame pesticide stress, leading to plant growth promotion. However, with high doses of pesticide application, the microbial compensatory effect was insufficient to counteract pesticide stress, resulting in plant growth inhibition. These findings pave the way for designing improved pesticide application strategies and contribute to a better understanding of how rhizosphere microbiota can be used as an eco-friendly approach to mitigate chemical-induced stress in crops.

Glyphosate hormesis stimulates tomato (Solanum lycopersicum L.) plant growth and enhances tolerance against environmental abiotic stress by triggering nonphotochemical quenching

BACKGROUND

Glyphosate is the most widely applied herbicide in the world. Hormesis caused by low glyphosate doses has been widely documented in many plant species. However, the specific adaptative mechanism of plants responding to glyphosate hormesis stimulation remains unclear. This study focused on the biphasic relationship between glyphosate dose and tomato plant growth, and how glyphosate hormesis stimulates plant growth and enhances tolerance to environmental stress.

RESULTS

We constructed a hormesis model to describe the biphasic relationship with a maximal stimulation (MAX) of 162% above control by glyphosate at 0.063 g ha-1. Low-dose glyphosate increased photosynthetic pigment contents and improve photosynthetic efficiency, leading to plant growth stimulation. We also found that glyphosate hormesis enhanced plant tolerance to diuron (DCMU; a representative photosynthesis inhibitor) by triggering the nonphotochemical chlorophyll fluorescence quenching (NPQ) reaction to dissipate excess energy stress from photosystem II (PSII). Transcriptomic analysis and quantitative real-time polymerase chain reaction results revealed that the photosynthesis-antenna proteins pathway was the most sensitive to glyphosate hormesis, and PsbS (encoding photosystem II subunit S), ZEP (encoding zeaxanthin epoxidase) and VDE (encoding violaxanthin de-epoxidase) involved in NPQ played crucial roles in the plant response to glyphosate hormesis.

CONCLUSION

These results provide novel insights into the mechanisms of plant hormesis and is meaningful to the application of glyphosate hormesis in agriculture. © 2024 Society of Chemical Industry.

Application of confocal microscopy and flow cytometry to identify physiological responses of Prorocentrum micans to the herbicide glyphosate

The physiological response of the dinoflagellate P. micans to the effect of the herbicide glyphosate at a concentration of 25-200 μg L-1 was evaluated. It has been shown that P. micans is able to grow due to the consumption of dissolved organic phosphorus formed as a result of the mineralization of glyphosate by bacteria. The addition of glyphosate to the medium inhibits the photosynthetic activity of cells; there is a pronounced inhibition of the relative electron transfer rate along the electron transport chain and the maximum quantum efficiency of the use of light energy. Morphological and ultrastructural changes in P. micans cells were evaluated at sublethal (150 μg L-1) and lethal (200 μg L-1) glyphosate concentrations. It has been shown that at a herbicide concentration of 150 μg L-1, the first signs of apoptosis appear in most P. micans cells: a decrease in lateral light scattering, cytoplasmic retraction, partial destruction of cytoplasmic organelles, a change in the morphology of nuclei, mitochondria, a change in the potential of mitochondrial membranes, and a decrease in the autofluorescence of chlorophyll in cells. At a glyphosate concentration of 200 μg L-1, P. micans showed signs of a late stage of apoptosis: violation of the integrity of intracellular organelles and chromatin organization, fragmentation of nuclei, condensation of cytoplasm, disorganization of chloroplasts in the cells, and the release of cell contents beyond the cell membrane. The effectiveness of using flow cytometry and laser scanning confocal microscopy methods for identifying signs and stages of cell apoptosis when exposed to glyphosate is discussed.

Physiological responses of the microalgae Thalassiosira weissflogii to the presence of the herbicide glyphosate in the medium

We evaluated changes in growth, chlorophyll fluorescence and basic physiological and biochemical parameters of the microalgae Thalassiosira weissflogii cells under the influence of the herbicide glyphosate in concentrations 0, 25, 95 and 150μgL-1 . The toxic effect of glyphosate on algae is weakly dependent on the level of cell mineral nutrition. High concentrations of the herbicide do not lead to the death of microalgae but block the process of algae cell division. An increase in the glyphosate concentration in the medium leads to a slowdown or stop of algal growth, a decrease in their final biomass, an increase in the production of reactive oxygen species (ROS), depolarisation of mitochondrial membranes and metabolic activity of algae. Glyphosate inhibits the photosynthetic activity of cells and inhibits the relative rate of electron transport in the photosynthetic apparatus. Glyphosate at the studied concentrations does not affect the size characteristics of cells and the intracellular content of chlorophyll in T. weissflogii . The studied herbicide or products of its decay retain their toxic properties in the environment for at least 9days. This result shows the need for further in-depth studies to assess the physiological response and possible acclimation changes in the functional state of oxygenic phototrophs in response to the herbicide action. The species specificity of microalgae to the effects of glyphosate in natural conditions is potentially dangerous due to a possible change in the species structure of biocoenoses, in particular, a decrease in the contribution of diatoms.

Glyphosate hormesis induced by treatment via seed stimulates the growth and biomass accumulation in soybean seedlings

Glyphosate hormesis, identified as a potential means to enhance crop yields, encounters practical constraints because it is typically assessed through foliar applications. The expression and extend of hormesis in this approach are influenced by unpredictable environmental conditions, highlighting the need to explore alternative glyphosate application methods, such as seed treatment. This study aimed to assess glyphosate hormesis on growth rates and biomass accumulation in seedlings soybean cultivars. Two dose-response experiments [doses from 0 to 2880 g acid equivalent (ae) ha-1], one via foliar and one via seed, were conducted on three soybean cultivars [one non-glyphosate-resistant (NGR) and two glyphosate-resistant (GR, one RR and one RR2)]. In a subsequent experiment, three safe glyphosate doses (0, 90 and 180 g ae ha-1) applied via seed were evaluated on four soybean cultivars (two RR and two RR2). For foliar applications, the range of glyphosate doses increasing growth rates and dry biomass by 12-28 % were 5.6-45 g ae ha-1 for the NGR cultivar, of 45-720 g ae ha-1 for RR and of 11.25-180 g ae ha-1 for RR2. In the seed treatment, biomass increases of 16-60 % occurred at 45-180 g ae ha-1 for the NGR and RR cultivars, and 90-360 g ae ha-1 for RR2. Glyphosate doses of 90 and 180 g ae ha-1, applied via seeds, provided greater growth and biomass accumulation for the RR and RR2 soybean cultivars. Both foliar and seed applications of glyphosate increased growth and biomass accumulation in soybean cultivars, with seed treatments showing greater and more consistent enhancements. These findings propose practical and viable alternative for harnessing glyphosate hormesis to facilitate the early development of soybeans and potentially enhance crop yield.

Glyphosate hormesis effects on the vegetative and reproductive development of glyphosate-susceptible and -resistant Conyza sumatrensis biotypes

Low glyphosate doses that produce hormesis may alter the susceptibility to herbicides of weeds or enhance their propagation and dispersal. The objective of this work was to evaluate the hormetic effects of glyphosate on the vegetative, phenological and reproductive development in resistant (R) and susceptible (S) Conyza sumatrensis biotypes. The glyphosate resistance level of biotype R was 11.2-fold compared to the S biotype. Glyphosate doses <11.25 g ae ha-1 induced temporary and permanent hormetic effects for the number of leaves, plant height and dry mass accumulation up to 28 d after application in both R and S biotypes. The S biotype required 15-19% fewer thermal units at 1.4 and 2.8 g ae ha-1 glyphosate than untreated plants to reach the bolting stage. Also, this biotype had less thermal units associated with the appearance (1225 vs 1408 units) and opening (1520 vs 1765 units) of the first capitulum than the R biotype. In addition, glyphosate affected reproductive traits of both biotypes compared to their controls, increasing the number of capitulum's and seeds per plant up to 37 and 41% (at 2.8 and 0.7 g ae h-1, respectively) in the S biotype, and by 48 and 114% (both at 5.6 g ae ha-1) in the R biotype. Depending on environmental parameters, glyphosate may or may not cause hormetic effects on the vegetative and phenological development of C. sumatrenis biotypes; however, this herbicide increases the speed and fecundity of reproduction, regardless of the glyphosate susceptibility level, which can alter the population dynamics and glyphosate susceptibility of future generations.

Hormetic Effect Caused by Sublethal Doses of Glyphosate on Toona ciliata M. Roem

This study aimed to evaluate the response of Toona ciliata seedlings to sublethal doses of glyphosate. The increasing use of glyphosate in agriculture concerns the scientific community, as the drift of this pollutant into aquatic systems or atmospheric currents can affect non-target species. Therefore, we need to understand how non-target species respond to small doses of this herbicide. T. ciliata seedlings (clone BV-1110) were exposed to sublethal doses of glyphosate (0, 9.6, 19.2, 38.4, 76.8 g ae ha-1). Anatomical, physiological, and photochemical analyses were performed 60 days after herbicide application, and growth assessments were carried out after 160 days of cultivation. We found that sublethal doses of glyphosate above 19.2 g ae ha-1 induced toxicity symptoms in Toona ciliata leaves. These symptoms were mild in some cases, such as chlorosis, but severe in other cases, such as tissue necrosis. We observed a positive relationship between increased plant height and photochemical yield with plant exposure to sub-doses 9.6 and 19.2 g ae ha-1. A sublethal dose of 38.4 g ae ha-1 improved the photosynthetic rate and carboxylation efficiency. Thus, we confirmed the hypothesis of a hormetic effect when T. ciliata was exposed to sub-doses of glyphosate equal to or lower than 38.4 g ae ha-1. However, the sublethal dose of 76.8 g ae ha-1 must be considered toxic, impacting photosynthetic activity and, consequently, the height of T. ciliata. The stem diameter of T. ciliata responded positively to increasing glyphosate doses. This occurs to compensate for the negative effect of glyphosate on water absorption. Further research will provide valuable information for harnessing the potential benefits of hormesis to improve the productivity of T. ciliata.

GLYPHOSATE IMPACT on human health and the environment: Sustainable alternatives to replace it in Mexico

Glyphosate is a broad-spectrum, non-selective herbicide used to control weeds and protect agricultural crops, and it is classified as potentially carcinogenic by the International Agency for Research on Cancer. In Mexico, the use of pesticides is a common practice, including glyphosate. However, on December 31st, 2020, the Mexican government decreed the prohibition of this herbicide as of January 2024. In this review, we investigate the association between glyphosate and cancer risk and found that most of the studies focused using animals showing negative effects such as genotoxicity, cytotoxicity and neurotoxicity, some studies used cancer cell lines showing proliferative effects due to glyphosate exposure. To our knowledge, in Mexico, there are no scientific reports on the association of glyphosate with any type of cancer. In addition, we reviewed the toxicological effects of the herbicide glyphosate, and the specific case of the current situation of the use and environmental damage of this herbicide in Mexico. We found that few studies have been published on glyphosate, and that the largest number of publications are from the International Agency for Research on Cancer classification to date. Additionally, we provide data on glyphosate stimulation at low doses as a biostimulant in crops and analytical monitoring techniques for the detection of glyphosates in different matrices. Finally, we have tried to summarize the actions of the Mexican government to seek sustainable alternatives and replace the use of glyphosate, to obtain food free of this herbicide and take care of the health of the population and the environment.

Glyphosate and environmental toxicity with "One Health" approach, a review

The herbicide Glyphosate (GLY), or N-(phosphonomethyl) glycine was synthesized in 1950 and applied to control weeds in agricultural production. For a long time, it was believed that it was an inert compound, but many studies have instead demonstrated over the years the dangers of GLY to the ecosystem and human health. Among the best-known effects, it is known that GLY interferes with the metabolic pathways of plants and the main groups of microorganisms, negatively influencing their growth. GLY interferes with the metabolic pathways of plants and major groups of microorganisms negatively affecting their growth. The extensive GLY application on fields results in a "slow death" of plants through the minor resistance to root pathogens and in increasing pollution of freshwaters and soils. Unfortunately, however, unlike the old beliefs, GLY can reach non-target destinations, in this regard, ecological studies and environmental epidemiology are of significant interest. In this review, we focus on the effects of acute and chronic exposure to GLY on the health of plants, animals, and humans from a One Health perspective. GLY has been linked to neurological and endocrine issues in both humans and animals, and behavioral modification on specific bioindicators, but the knowledge about the ratio cause-and-effect still needs to be better understood and elucidated. Environmental GLY residues analysis and policy acts will both require new criteria to protect environmental and human health.

Changes in the herbicide sensitivity and competitive ability of Abutilon theophrasti over 28 years: Implications for hormesis and weed evolution

BACKGROUND

The potential of weed species to respond to selection forces affecting the evolution of weedy traits such as competitive ability is poorly understood. This research characterized evolutionary growth changes in a single Abutilon theophrasti Medik. population comparing multiple generations collected from 1988 to 2016. A competition study was performed to understand changes in competitive ability, and a herbicide dose-response study was carried out to assess changes in sensitivity to acetolactate synthase-inhibiting herbicides and glyphosate over time.

RESULTS

When grown in monoculture, A. theophrasti biomass production per plant increased steadily across year-lines while leaf number decreased. In replacement experiments, A. theophrasti plants from newer year-lines were more competitive and produced more biomass and leaf area than the oldest year-line. No clear differences in sensitivity to imazamox were observed among year-lines. However, starting in 1995, this A. theophrasti population exhibited a progressive increase in growth in response to a sublethal dose of glyphosate (52 g a.e. ha-1 ), with the 2009 and 2016 year-lines having more than 50% higher biomass than the nontreated control.

CONCLUSION

This study demonstrates that weeds can rapidly evolve increased competitive ability. Furthermore, the results indicate the possibility of changes in glyphosate hormesis over time. These results highlight the importance of the role that rapid (i.e., subdecadal) evolution of growth traits might have on the sustainability of weed management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Hormetic Effect of Glyphosate on the Morphology, Physiology and Metabolism of Coffee Plants

Glyphosate is a nonselective herbicide of systemic action that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, thus compromising amino acid production and consequently the growth and development of susceptible plants. The objective of this study was to evaluate the hormetic effect of glyphosate on the morphology, physiology, and biochemistry of coffee plants. Coffee seedlings (Coffea arabica cv Catuaí Vermelho IAC-144) were transplanted into pots filled with a mixture of soil and substrate and subjected to ten doses of glyphosate: 0, 11.25, 22.5, 45, 90, 180, 360, 720, 1440, and 2880 g acid equivalent (ae) ha^-1. Evaluations were performed using the morphological, physiological, and biochemical variables. Data analysis for the confirmation of hormesis occurred with the application of mathematical models. The hormetic effect of glyphosate on coffee plant morphology was determined by the variables plant height, number of leaves, leaf area, and leaf, stem, and total dry mass. Doses from 14.5 to 30 g ae ha^-1 caused the highest stimulation. In the physiological analyses, the highest stimulation was observed upon CO₂ assimilation, transpiration, stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, electron transport rate, and photochemical efficiency of photosystem II at doses ranging from 4.4 to 55 g ae ha^-1. The biochemical analyses revealed significant increases in the concentrations of quinic acid, salicylic acid, caffeic acid, and coumaric acid, with maximum stimulation at doses between 3 and 140 g ae ha^-1. Thus, the application of low doses of glyphosate has positive effects on the morphology, physiology, and biochemistry of coffee plants.

Herbicide residues in soil decrease microbe-mediated plant protection

The residues of glyphosate are found to remain in soils longer than previously reported, affecting rhizosphere microbes. This may adversely affect crop and other non-target plants because the plant's resilience and resistance largely rely on plant-associated microbes. Ubiquitous glyphosate residues in soil and how they impact mutualistic microbes inhabiting the aboveground plant parts are largely unexplored. We studied the effects of herbicide residues in soil on Epichloë sp., which are common endophytic symbionts inhabiting aerial parts of cool-season grasses. In this symbiosis, the obligate symbiont subsists entirely on its host plant, and in exchange, it provides alkaloids conferring resistance to herbivores for the host grass that invests little in its own chemical defence. We first show decreased growth of Epichloë endophytes in vitro when directly exposed to two concentrations of glyphosate or glyphosate-based herbicides. Second, we provide evidence for a reduction of Epichloë-derived, insect-toxic loline alkaloids in endophyte-symbiotic meadow fescue (F. pratensis) plants growing in soil with a glyphosate history. Plants were grown for 2 years in an open field site, and natural herbivore infestation was correlated with the glyphosate-mediated reduction of loline alkaloid concentrations. Our findings indicate that herbicides residing in soil not only affect rhizosphere microbiota but also aerial plant endophyte functionality, which emphasizes the destructive effects of glyphosate on plant symbiotic microbes, here with cascading effects on plant-pest insect interactions.

Hormesis effects in tomato plant growth and photosynthesis due to acephate exposure based on physiology and transcriptomic analysis

BACKGROUND

Hormesis is a common phenomenon in toxicology described as low-dose stimulation due to a toxin which causes inhibition at a high dose. Pesticide hormesis in plants has attracted considerable research interest in recent years; however, the specific mechanism has not yet been clarified. Acephate is an organophosphorus insecticide that is used worldwide. Here, hormesis in tomato (Solanum lycopersicum L.) plant growth and photosynthesis after acephate exposure is confirmed, as stimulation occurred at low stress levels, whereas inhibition occurred after exposure to high concentrations.

RESULTS

We found that low acephate concentration (5-fold lower than recommended application dosage) could enhance chlorophyll biosynthesis and stimulate photosynthesis effects, and thus improve S. lycopersicum growth. A high level of acephate (5-fold higher than recommended application dosage) stress inhibited chlorophyll accumulation, decreased photosystem II efficiency and blocked antioxidant reactions in leaves, increasing reactive oxygen species levels and damaging plant growth. Transcriptomic analysis and quantitative real-time PCR results revealed that the photosynthesis - antenna proteins pathway played a crucial role in the hormesis effect, and that LHCB7 as well as LHCP from the pathway were the most sensitive to acephate hormesis.

CONCLUSION

Our results showed that acephate could induce hormesis in tomato plant growth and photosynthesis, and that photosystem II and the photosynthesis - antenna proteins pathway played important roles in hormesis. These results provide novel insights into the scientific and safe application of chemical pesticides, and new guidance for investigation into utilizing pesticide hormesis in agriculture. © 2023 Society of Chemical Industry.

Development of an inexpensive and rapidly preparable enzymatic pencil graphite biosensor for monitoring of glyphosate in waters

Glyphosate (GLY) is the most widely used non-selective broad-spectrum herbicide worldwide under well-reported side effects on the environment and human health. That's why it's necessary to control its presence in the environment. This work describes the development of an affordable, simple, and accurate electrochemical biosensor using a pencil graphite electrode as support, a horseradish peroxidase enzyme immobilized on a polysulfone membrane doped with multi-walled carbon nanotubes. The developed electrochemical sensor was used in the determination of GLY in river and drinking water samples. Cyclic voltammetry and amperometry were used as electrochemical detection techniques for the characterization and analytical application of the developed biosensor. The working mechanism of the biosensor is based on the inhibition of the peroxidase enzyme by GLY. Under optimal experimental conditions, the biosensor showed a linear response in the concentration range of 0.1 to 10 mg L^-1. The limits of detection and quantification are 0.025 ± 0.002 and 0.084 ± 0.007 mg L^-1, respectively, which covers the maximum residual limit established by the EPA for drinking water (0.7 mg L^-1). The proposed biosensor demonstrated high reproducibility, excellent analytical performance, repeatability, and accuracy. The sensor proved to be selective against other pesticides, organic acids, and inorganic salts. Application on real samples showed recovery rates ranging between 98.18 ± 0.11 % and 97.32 ± 0.23 %. The analytical features of the proposed biosensor make it an effective and useful tool for the detection of GLY for environmental analysis.

Nanobiotechnological Approaches to Enhance Drought Tolerance in Catharanthus roseus Plants Using Salicylic Acid in Bulk and Nanoform

Drought has a detrimental effect on crop production, affecting economically important plants’ growth rates and development. Catharanthus roseus is an important medicinal plant that produces many pharmacologically active compounds, some of which have significant antitumor activity. The effect of bulk salicylic acid (SA) and salicylic acid nanoparticles (SA-NPs) were evaluated on water-stressed Catharanthus roseus plants. The results showed that SA and SA-NPs alleviated the negative effects of drought in the treated plants by increasing their shoot and root weights, relative water content, leaf area index, chlorophyll content, and total alkaloids percentage. From the results, a low concentration (0.05 mM) of SA-NPs exerted positive effects on the treated plants, while the best results of the bulk SA were recorded after using the highest concentration (0.1 mM). Both treatments increased the expression level of WRKY1, WRKY2, WRKY40, LEA, and MYC2 genes, while the mRNA level of MPKK1 and MPK6 did not show a significant change. This study discussed the importance of SA-NPs in the induction of drought stress tolerance even when used in low concentrations, in contrast to bulk SA, which exerts significant results only at higher concentrations.

Can 2,4-D promote the hormesis effect in upland rice?

This study aimed to evaluate the influence of low doses of 2,4-D on the agronomic traits of upland rice applied at different stages of crop growth. The work was carried out in a randomized completly blocks, and consisted of the application of 5 low doses of the 2,4-D herbicide (0, 0.68, 1.36, 2.04, 3.40 and 5.44 g acid equivalent (e.a.) ha-1) in two stages of rice development (tillering and floral differentiation). Nitrogen contentes in leaves, SPAD index and yield are higher when low doses of 2,4-D is applied in the tillering stage. Application of 2,4-D at a dose of 2.04 g a.e ha-1 results in a 19% increase in the number of spikelet per panicle. On the other hand, there is no effect of the application of low doses of 2,4-D on height, number of stems, active tillering and weight of 100 seeds. Our results contribute to increase knowledge of the hormesis effect in plants in order to increase crop yield.

Hormesis and insects: Effects and interactions in agroecosystems

Insects in agroecosystems contend with many stressors - e.g., chemicals, heat, nutrient deprivation - that are often encountered at low levels. Exposure to mild stress is now well known to induce hormetic (stimulatory) effects in insects, with implications for insect management, and ecological structure and function in agroecosystems. In this review, we examine the major ecological niches insects occupy or guilds to which they belong in agroecosystems and how hormesis can manifest within and across these groups. The mechanistic underpinnings of hormesis in insects are starting to become established, explaining the many phenotypic hormetic responses observed in insect reproduction, development, and behavior. Whereas potential effects on insect populations are well supported in laboratory experiments, field-based hypothesis-driven research on hormesis is greatly lacking. Furthermore, because most ecological paradigms are founded within the context of communities, entomological agroecologists interested in hormesis need to 'level up' and test hypotheses that explore effects on species interactions, and community structure and functioning. Embedded in this charge is to continue experimentation on herbivorous pest species while shifting more focus towards insect natural enemies, pollinators, and detritivores - guilds that play crucial roles in highly functioning agroecosystems that have been understudied in hormesis research. Important areas for future insect agroecology research on hormesis are discussed.

Hormesis induced by silver iodide, hydrocarbons, microplastics, pesticides, and pharmaceuticals: Implications for agroforestry ecosystems health

Increasing amounts of silver iodide (AgI) in the environment are expected because of the recent massive expansion of weather modification programs. Concurrently, pharmaceuticals, microplastics, hydrocarbons, and pesticides in terrestrial ecosystems continue contaminating forests and agroforests. Our review supports that AgI induces hormesis, a biphasic dose response characterized by often beneficial low-dose responses and toxic high-dose effects, which adds to the evidence for pharmaceuticals, microplastics, hydrocarbons, and pesticides induced hormesis in numerous species. Doses smaller than the no-observed-adverse-effect-level (NOAEL) positively affect defense physiology, growth, biomass, yields, survival, lifespan, and reproduction. They also lead to negative or undesirable outcomes, including stimulation of pathogenic microbes, pest insects, and weeds with enhanced resistance to drugs and potential negative multi- or trans-generational effects. Such sub-NOAEL effects perplex terrestrial ecosystems managements and may compromise combating outbreaks of disease vectors that can threaten not only forest and agroforestry health but also sensitive human subpopulations living in remote forested areas.

Effect of low glyphosate doses on flowering and seed germination of glyphosate-resistant and -susceptible Digitaria insularis

BACKGROUND

Herbicide hormesis is characterized by stimulation of various growth and developmental parameters, such as biomass and height, at low herbicide doses. Other possible hormetic effects are earlier flowering, higher seed weight, more seeds, and a shorter plant life cycle, which could favor the propagation of the species. This study tested the early flowering in glyphosate-resistant and -susceptible Digitaria insularis biotypes under treatment with low glyphosate doses.

RESULTS

Hormesis caused by low glyphosate doses occurred in all experiments. The hormetic effects were a decrease in time necessary for the formation of inflorescences and increased seed weight and germination speed. Higher glyphosate doses were required for the hormetic effect in the glyphosate-resistant than the -susceptible D. insularis biotype.

CONCLUSIONS

Hormesis caused by low glyphosate doses in D. insularis may provide an advantage for the dissemination of this species, helping to alter the weed flora. As the doses that cause stimulation in glyphosate-resistant biotypes are higher than in glyphosate-susceptible biotypes, the selection of resistant biotypes may be favored in glyphosate-sprayed fields, increasing the rate of infestation of glyphosate-resistant biotypes.

Glyphosate applied at a hormetic dose improves ripening without impairing sugarcane productivity and ratoon sprouting

The management of sugarcane ripening is essential to ensuring the supply of high-quality raw material for the sugar-alcohol industry; chemical ripeners are frequently used to accelerate sucrose accumulation in the stalks during harvesting. The potential ripening effect of a low dose of glyphosate was evaluated in sugarcane, along with its impact on productivity and sprouting in the next crop cycle. A field experiment was conducted in 2015 and 2016 using a randomized block design with eight replicates in a split-plot scheme, with the following treatments: (1) control with only water application, (2) glyphosate at a low dose of 1.8 g a.e. ha-1 (corresponding to 0.005 L ha-1 of the commercial product (cp)), and (3) glyphosate at the commercially recommended dose for a ripener at 180 g a.e. ha-1 (corresponding to 0.50 L ha-1 of the cp) applied at 60, 45, 30, and 15 days before harvest (DBH). The harvest was performed on May 25, 2016 (0 DBH), and a total of five periods were evaluated. This study showed that the application of a hormetic dose of glyphosate to stimulate sugarcane ripening is promising, despite the limited duration of the effect. The application of the hormetic dose (1.8 g a.e. ha-1) at 30 DBH improved the technological quality of sugarcane in terms of Brix% juice, pol% cane, purity% juice, moisture% cane, reducing sugars, total reducing sugars, and total recoverable sugar. Additionally, it increased pol productivity, and did not affect ratoon sprouting in the subsequent cycle. Thus, this study provides a strategy for ripening management with a low environmental impact for sugarcane producers through a low (hormetic) dose of glyphosate.

Aminomethylphosphonic acid (AMPA) alters oxidative status during embryonic development in an amphibian species

Glyphosate's primary metabolite (aminomethylphosphonic acid, AMPA) is known to alter embryonic development at environmentally relevant concentrations in amphibians. However, we have limited understanding of the physiological mechanisms through which AMPA affects organisms. In this study, we tested whether alteration of the oxidative status is one mechanism through which AMPA affects organism performance. To this end, we analysed several oxidative status markers in hatchling tadpoles that were exposed to sublethal concentrations of AMPA during embryonic development (~16 days). We compared the influence of environmentally relevant concentrations of AMPA (from 0.07 to 3.57 μg l^-1) on the relation between developmental traits (i.e, embryonic development duration, embryonic mortality and hatchling size) and oxidative status markers known to alter homeostasis when unbalanced (superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), thiols and ratios thereof). We included measures of telomere length as an indicator of physiological state. We found that AMPA concentrations induce non-monotonic effects on some oxidative status markers with hatchlings displaying elevated antioxidant responses (elevated thiols and unbalanced SOD/(GPx + CAT) ratio). The lack of effect of AMPA on the relation between developmental traits, oxidative status and telomere length suggests that selective mortality of embryos susceptible to oxidative stress may have occurred prior to hatching in individuals less resistant to AMPA which display lower hatching success. Future studies are required to disentangle whether oxidative unbalance is a cause or a consequence of AMPA exposition. This study highlights the need to investigate effects of the metabolites of contaminants at environmental concentrations to comprehensively assess impacts of anthropogenic contamination on wildlife.

Tolerance of Hymenaea courbaril L. to glyphosate

The objective was to evaluate the effect of the glyphosate on Hymenaea courbaril L. A randomized block design with five replications was implemented. Each experimental unit was composed of one plant in a 5 L container. The treatments were 0 "control"; 96; 240; 480; and 960 g ha-1 "corresponding to 10, 25, 50, and 100% of the commercial dose of glyphosate recommended for Caryocar brasiliense crop, respectively". The evaluations were performed at 24 h and 60 days after application. Visual and anatomical evaluations did not change regardless of the dose, while the histochemical evaluation showed an accumulation of starch grains in leaf tissues. There was an increase in the photosynthetic rate, in the electron transport rate, and in the effective quantum yield of photosystem II at 24 h after application. At 60 days after the application of the treatments, the photosynthetic rate showed a slight decrease and the transpiratory rate showed quadratic behavior. An increase in plant height was observed up to the dose of 480 g ha-1, a linear increase in stem diameter and a decrease in the number of leaves with increasing glyphosate doses. These results show that the cuticle protected the plant, and that the little absorbed glyphosate increased photosynthesis and transpiration to favor the plants. We can conclude that the H. courbaril species is able to survive after contact with glyphosate during the evaluated time, with no visual and/or anatomical damage, showing increases in growth and physiological characteristics for the tested doses.

Challenges in the design of electrochemical sensor for glyphosate-based on new materials and biological recognition

Glyphosate (GLY) is the main ingredient in the weed killer Roundup and the most widely used pesticide in the world. Studies of the harmful effects of GLY on human health began to become more wide-ranging after 2015. GLY is listed by the International Agency for Research on Cancer (IARC) as a carcinogenic hazard to humans. Moreover, GLY has the property to complex with transition metals and are stable for long periods, being considered a high-risk element for different matrices, such as environmental (soil and water) and food (usually genetically modified crops). Since that, it was noticed an increment in the development of new analytical methods for its determination in different matrices like food, environmental and biological fluids. Noteworthy, the application of electrochemical techniques for downstream detection sparked interest due to the ability to minimize or eliminate the use of polluting chemicals, using simple and affordable equipment. This work aims to review the contribution of the electroanalytical methods for the determination of GLY in different food and environmental matrices. Parameters such as the electrochemical transduction techniques based on the electrical measurement signals, receptor materials for electrodes preparation, and the detection mechanisms are described in this review. The literature review shows that the electrochemical sensors are powerful detection system that can be improved by their design and by their portability to fulfil the needs of the GLY determination in laboratory benches, or even in situ analysis.

Effect of Soil Moisture Regimes on the Glyphosate Sensitivity and Morpho-Physiological Traits of Windmill Grass (Chloris truncata R.Br.), Common Sowthistle (Sonchus oleraceus L.), and Flaxleaf Fleabane [Conyza bonariensis (L.) Cronq.]

The glasshouse study was conducted with the objectives of (i) investigating the effect of soil moisture variations on the control efficiency of glyphosate on windmill grass (Chloris truncata R.Br.), common sowthistle (Sonchus oleraceus L.), and flaxleaf fleabane [Conyza bonariensis (L.) Cronq.], (ii) evaluating the tolerance of tested weed species under soil moisture variations, and (iii) determining the morphological and physiological characteristics of these species to partially explain herbicide tolerance under periods of reduced soil moisture availability (RSM). The species’ tolerance to glyphosate increased significantly under reduced soil moisture availability (p < 0.001). The lethal dose to cause herbicide injury or biomass reduction by 50% (LD50) and 80% (LD80) in relation to untreated control for water-stressed plants [i.e., moderate soil moisture availability (MSM) and RSM] was significantly higher than that of plants grown under high soil moisture availability (HSM). The tolerance factor (TF) for C. truncata, S. oleraceus, and C. bonariensis, in terms of biomass reduction under RSM, was 2.6, 2.4, and 2.6, respectively, as compared to HSM. The results showed that the glyphosate sensitivity, especially at the sub-lethal rates, of the three weed species under study decreased as soil moisture availability reduced (p< 0.01). Overall glyphosate efficacy, in relation to the recommended rate, was unaffected, except for C. truncata; the weed survived the highest tested glyphosate rate [750 g active ingredient (a.i.) ha−1] under RSM. There was significant interaction between weed species and soil moisture regimes for weed morpho-physiological traits (p < 0.001), with reduced soil moisture having a more influential impact on the growth of C. bonariensis and S. oleraceus compared to C. truncata. Changes in the leaf characteristics, such as increased leaf thickness, higher leaf chlorophyll content, reduced leaf area, and limited stomatal activity for all the tested weed species under MSM and RSM in relation to HSM, partially explain the tolerance of species to glyphosate at sublethal rates.

Hormesis of 2,4-D choline salt in productive aspects of cotton

The stimulating effect of a low dose of a substance considered to be toxic is known as hormesis. The aim of this work was to use dose-response curves to evaluate the hormesis effect provided by sub-doses of the herbicide 2,4-D choline salt on the productivity of cotton at different phenological stages. The experimental design was based on randomized blocks, with four repetitions and the treatments were distributed in a 9x3 factorial design, with nine fractions of the mean label dose of the herbicide 2,4-D choline salt formulation (0 (control); 0.4275; 0.855; 1.71; 3.42; 8.55; 17.1; 34.2 and 68.4 g a.e. ha^-1) associated with three different phenological stage of cotton, namely: V4, B4 and C4. The plants were evaluated as to the main productive parameters of the cotton plant. When applied at the V4 stage, sub-doses of the herbicide 2,4-D choline salt negatively affect the cotton crop. Sub-doses between 0.82 and 2.23 g a.e. ha^-1 of the herbicide 2,4-D choline salt applied at the B4 stage of cotton can increase all the productive variables of the crop. The productive aspects of cotton plants in the C4 stage were not influenced by the application of sub-doses of 2,4-D choline salt.

Does the glufosinate-ammonium herbicide have the potential to induce the hormesis effect in upland rice?

This study aimed to evaluate the effects of low doses of the herbicide glufosinate-ammonium in different application modes in the vegetative development of upland rice. The treatment consisted of a combination of five low doses (0; 15; 30; 60; and 100 g a.i. ha^-1) of the herbicide glufosinate-ammonium and four application modes of the low doses: single between active tillering (AT) and floral differentiation (FD); single after FD; split in two (the first at the beginning of the AT and the second between AT and FD; split in three (the first at the beginning of the AT, the second between the AT and the FD and the third after the FD, with. There was no hormesis effect on rice crop due to low doses of glufosinate-ammonium. The vegetative development of rice plants was reduced by the application of low doses in all application modes with lower plant height, dry weight, number of panicles, and effective tiller.

Can the application of low doses of paraquat induce the hormesis effect in upland rice?

This study aimed to verify the effects of the application of paraquat low doses on the agronomic traits of upland rice in two different application modes. The treatments consisted of a combination of 6 low doses of the paraquat (0; 20; 40; 60; 80 and 120 g a.i. ha^-1) and 2 application modes of low doses a) single application performed between active tillering and floral differentiation b) application split into four applications, the first being carried out at the beginning of active tillering, the second being carried out between active tillering and floral differentiation, the third application carried out after floral differentiation and the fourth application carried out after flowering with 25% of the dose in each application. The application of low doses of paraquat does not promote the hormesis effect of upland rice. The increase in the frequency of the plant to the herbicide caused by the splitting of applications negatively affected the plant height, number of spikelets per panicle, yield, leaf nitrogen and sulfur as the low doses levels were increased. On the other hand, there is no influence of paraquat low doses levels when single applied to the agronomic traits of upland rice.

Low glyphosate doses change reproduction and produce tolerant offspring in dense populations of Hordeum vulgare

BACKGROUND

Low toxin doses that do not affect mean responses in plant populations can still change the growth of subpopulations. Studies covering vegetative stages ascribed fast-growing plants higher thresholds for growth stimulation and inhibition, compared with the rest of the population. We hypothesized that such selective effects also play a role after reproduction; that is, the offspring of glyphosate-treated tolerant, fast-growing phenotypes is more tolerant than the offspring of untreated plants. An experimental, high-density barley population was exposed to a range of glyphosate concentrations in the greenhouse, and reproduction and final growth were analyzed for selective effects. Therefore, F0, F1 treated and F1 non-treated offspring were re-exposed to glyphosate.

RESULTS

Low doses of glyphosate inhibited the growth and reproduction of slow-growing plants at concentrations that did not change the population mean. Concentrations that inhibited average-sized plants hormetically increased the biomass and seed yield of fast-growing plants. Compared with F0 and F1 non-treated offspring, F1-treated offspring from hormetically stimulated fast-growing plants were more glyphosate tolerant. Hence, a pesticide can shape the reproductive pattern of a plant population and alter offspring tolerance at concentrations that have no effect on average yield.

CONCLUSIONS

Toxin levels that do not change the population mean still alter the reproductive output of individuals. Sensitive phenotypes suffer, whereas the reproduction of tolerant phenotypes is boosted compared with toxin-free conditions. Because glyphosate is one of the leading herbicides in the world, tolerant phenotypes may benefit from current agricultural practices. If these results apply to other toxicants, low toxin doses may increase the fitness of tolerant phenotypes in a way not previously anticipated. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Can the application of low doses of glyphosate induce the hormesis effect in upland rice?

The aim of this research was to verify the effect of glyphosate low doses on leaf macronutrient levels and vegetative traits of upland rice in two growth stages. The treatments were arranged in 2 × 6 factorial scheme. The first factor consisted of applications in two growth stages of rice crop (tillering and floral differentiation) and the second factor was the low doses of glyphosate (0, 10, 20, 40, 70 and 100 g e.a. ha-1). In full bloom, the chlorophyll content was determined in a sample of 30 flag leaves. In these leaves, the contents of macronutrients were determined. At the maturity of the rice plant, the stem count was performed per m2, effective tiller and the plant height was measured. The low doses did not influence the leaf content of macronutrients. The plant height was reduced with an increase in the low doses of glyphosate, having a greater effect on the floral differentiation stage. When applied low doses of glyphosate at the floral differentiation stage, chlorophyll content increases and when applied to tillering there is a linear decrease in chlorophyll content. The number of stems increases with the application of low doses at floral differentiation.

Investigations on the influence of energy source on time-dependent hormesis: A case study of sulfadoxine to Aliivibrio fischeri in different cultivation systems

Hormesis is a biphasic dose-response relationship featured by low-dose stimulation and high-dose inhibition. Although the hormetic phenomenon has been extensively studied over the past decades, there is little information regarding the influence of energy source on the occurrence of hormesis, especially the time-dependent one. In this study, to explore the role of cultivation system's energy source in time-dependent hormesis, the toxic dose-responses of Aliivibrio fischeri (A. fischeri) bioluminescence to Sulfadoxine (SDX) during 24 h were determined in four cultivation systems with different energy source conditions. The results indicated that the time-dependent hormetic effects were induced by SDX in all cultivation systems: SDX triggered hormetic phenomenon on the bioluminescence at each growth stage over 24 h in the cultivation systems with sufficient and insufficient energy source; due to the diauxic growth of A. fischeri under multiple energy source conditions, the hormetic effects of SDX gradually disappeared after the preferred energy source was used up. It was speculated that the inhibitory action of SDX was derived from its interaction with DHPS to impede the synthesis of proteins, and SDX bound with AC to upregulate the quorum sensing (QS) system to exhibit the stimulatory action. Comparing the time-dependent hormesis in each cultivation system, it was obtained that the energy source could impact the hourly maximum stimulatory rate, the EC₅₀ of SDX, and the time point that hormesis occurred, which might result from the influence of energy source on the stimulatory and inhibitory actions of SDX through regulating the metabolic system (individual level) and QS system (group level) of bacteria. This study clarifies the importance of energy source for hormesis occurrence, which may further promote the development of hormesis.

Physiological and metagenomic strategies uncover the rhizosphere bacterial microbiome succession underlying three common environmental stresses in cassava

The most common environmental pollutants such as cadmium (Cd), glyphosate and tetracycline have led to profoundly adverse impacts on plant productivity. However, how tropical crops such as cassava sense these pollutants via roots and how rhizosphere microbiome interacts with the host and pollutants remain largely unknown. In this study, we found these stresses significantly inhibited plant growth and triggered cell damage in a dosage-dependent manner, and the toxic effect on redox homeostasis was correlated with antioxidant metabolism. Using metagenomics technique, we found the rhizosphere microbiomes dynamically altered as the dose of these stresses increased. We also identified stressor-associated metagenome-assembled genomes and microbial metabolic pathways as well as mobile genetic elements in the rhizosphere microbiomes. Next, a co-occurrence network of both physiological and microbiome features was constructed to explore how these pollutants derived oxidative damage through the microbiome succession. Notably, phyllosphere transplantation of Agrobacterium tumefaciens or Pseudomonas stutzeri can significantly alleviate the negative effects of stresses on cassava growth and redox homeostasis. Collectively, this study demonstrated the dynamics of rhizosphere bacterial microbiome of cassava under three common environmental stresses, and A. tumefaciens and P. stutzeri could be developed as potential beneficial bacteria to alleviate Cd, glyphosate and tetracycline-triggered damage to cassava.

Glyphosate effects on tree species natives from Cerrado and Caatinga Brazilian biome: Assessing sensitivity to two ways of contamination

Glyphosate is applied for dissection in no-till and post-emergence management in transgenic crops in agricultural fields near the Cerrado and Caatinga biomes. These biomes together represent 33.8% of the Brazilian territory, contributing to the maintenance of great world diversity in flora and fauna. Despite actions to protect them, the proximity with agricultural areas and intense use of glyphosate puts at risk the preservation of native vegetation due to the contamination via herbicide transport processes. Our objectives were: i) to determine the sensitivity of native species from the Cerrado and Caatinga to glyphosate contamination via drift and groundwater; ii) evaluate the level of sensitivity to glyphosate among the different organs of plants. The highest intoxications (upper 80%) were observed for Bauhinia cheilantha, Mimosa caesalpiniaefolia, Mimosa tenuiflora and Amburana cearensis due to drift simullation. The species with 90% of total dry matter reduction were Bauhinia cheilantha, Enterolobium contortisiliquum, Mimosa caesalpiniaefolia, Mimosa tenuiflora, Tabebuia aurea. B. cheilantha and M. tenuiflora are most affected by exposure to glyphosate drift, with 50% of total dry matter reduction when exposed to doses below 444,0 g ha-1. Leaf growth is more sensitive to glyphosate for drift exposure for most species. Hymenaea courbaril is an exception, with greater sensitivity to root growth (50% dry matter reduction at doses below 666,0 g ha-1). B. cheilantha is the species most sensitive to drift exposure; however, it showed complete tolerance to contamination in subsurface waters. Other species such as Anadenanthera macrocarpa and M. caesalpiniifolia are also sensitive to drift, but without reach 90% of total dry matter reduction. A. macrocarpa, M. caesalpiniifolia and T. aurea were tolerant to contamination by subsurface water. The differential tolerance of trees confirms glyphosate's potential as a species selection agent in the Cerrado and Caatinga biomes.

Glyphosate Toxicity to Native Nontarget Macrophytes Following Three Different Routes of Incidental Exposure

A major goal of invasive plant management is the restoration of native biodiversity, but effective methods for invasive plant control can be harmful to native plants. Informed application of control methods is required to reach restoration goals. The herbicide glyphosate, commonly applied in invasive plant management, can be toxic to native macrophytes. Our study assessed the response of 2 macrophytes that are endangered in our study area (Ammannia robusta and Sida hermaphrodita) to glyphosate concentrations that mimic incidental exposure from nearby invasive plant control: spray drift of 4 × 10-7 % to 5% glyphosate; pulse and continuous immersion in water containing 2 to 41 µg/L glyphosate; and rhizosphere contact with 5%-glyphosate-wicked invasive plants. We assessed macrophyte sensitivity at 14-d postexposure, and quantified abundance of arbuscular mycorrhizal fungi. Glyphosate spray concentrations as low as 0.1% reduced macrophyte growth. Ammannia was more sensitive overall to glyphosate spray than Sida, although sensitivity varied among measured endpoints. Conversely, macrophytes were not affected by immersion in low concentrations of glyphosate or rhizosphere contact with a glyphosate-wicked plant. Likewise, arbuscular mycorrhizal fungi abundance in roots was similar among glyphosate-sprayed and control plants. Based on our results, we recommend that invasive plant managers reduce risks to native nontarget plants through implementing measures that limit off-target spray drift, and consider the feasibility of more targeted applications, such as with wick equipment. Integr Environ Assess Manag 2021;17:597-613. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effects of glyphosate plus foliar manganese application on the production and quality of marandu grass

In this study, the stimulatory effects of application of glyphosate herbicide coupled with manganese sulfate (8%) foliar fertilizer on the production and bromatological characteristics of Brachiaria brizantha ‘Marandu’ were evaluated. The experiments were performed using randomized complete block design with a 5×4 factorial scheme in plots subdivided over time (across four evaluations) with four repetitions, totaling 100 observations. The effects of sublethal doses of acid equivalent (a.e.) of glyphosate (5.40, 21.60, 64.80, and 108.00 g·a.e.·ha-1) and control plus manganese sulfate foliar fertilizer (1,000 g ha-1) were assessed in four successive evaluations at a defoliation frequency of 21 days. Foliage at 20 cm height (to evaluate forage production); leaf/stem ratio (LSR); and contents of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin (LIG) were measured in experimental plots with a usable area of 7.5 m2. Application of sublethal doses of glyphosate plus manganese sulfate did not increase forage production, increased LSR, reduced LIG content, and did not affect CP content in all four evaluations. NFD and ADF indicated satisfactory qualitative indices for animal feed following the application of sublethal doses of glyphosate plus manganese sulfate in all four evaluations.

Smoke-water commonly induces hormetic dose responses in plants

A detailed evaluation was made of the literature concerning the dose response features of smoke-water extracts and other types of biological pyrolysis products on seed germination and plant growth. The evaluation was undertaken to extend our research on the occurrence and importance of hormesis in plant biology, as no similar assessment on smoke water biology had been published and that a preliminary survey suggested widespread occurrence of hormesis. It was determined that hormetic-like biphasic dose responses were commonly reported within the smoke-water plant literature for seed germination and plant growth. These findings were independent of the type of plant evaluated, the type of plant material used for the smoke-water extract, and the process of pyrolysis and extraction. The magnitude of the maximal stimulation of the biphasic dose responses was consistent with the hormetic concept, with maximal responses typically being approximately 30-60% greater than control values and with a stimulatory dose/concentration width less than 10 fold. These findings, which represent dose response features of a spectrum of novel and chemically diverse complex mixtures, support the generality of the hormetic dose response and its potential utility in enhancing the quality of study designs, including selection of dose/concentration number and spacing as well as biological model and endpoint.

Glyphosate hormesis mitigates the effect of water deficit in safflower (Carthamus tinctorius L.)

BACKGROUND

The current climate change scenario may affect water availability in the soil, impacting the agricultural sector. Planting of safflower (Carthamus tinctorius L.) has increased because of its potential for cultivation under drought conditions during the off-season in Brazil and its high potential for use in biofuel production. There are several reports about the potential of low doses of glyphosate to promote plant growth and development (hormesis). Despite the concept of glyphosate hormesis being well established, little is known about any mitigating effect on plants under water deficit conditions. The hypothesis raised is that low doses of glyphosate promote water stress tolerance during the growth and reproductive phases of C. tinctorius exposed to different water regimes.

RESULTS

In regimes with and without water deficiency, growth of plants treated with low doses of glyphosate increased, reaching a maximum stimulus amplitude of ~ 131% of control. However, plants under water deficit required lower doses to achieve maximum growth and development. They maintained photosynthetic rates at the level of well-watered plants because they had reduced stomatal conductance and transpiration. Gains in plant height and leaf area were the same as for controls.

CONCLUSIONS

Low doses of glyphosate can act as mitigators of water deficit in C. tinctorius, allowing plants to maintain their metabolism, reaching levels close to those of plants without water stress, as observed for plant height and leaf area. Our findings indicate that there are even greater implications for understanding glyphosate hormesis in plants under drought conditions, given the current climate change scenario. © 2020 Society of Chemical Industry.

Proteomic mechanisms for the combined stimulatory effects of glyphosate and antibiotic contaminants on Microcystis aeruginosa

A single exposure to glyphosate or antibiotic may facilitate cyanobacterial growth at currently reported concentrations due to hormesis. However, the influence of these contaminants on cyanobacteria under combined exposure conditions has not been reported. In this study, proteomic mechanisms for the combined effects of glyphosate and a quaternary antibiotic mixture of amoxicillin, sulfamethoxazole, tetracycline, and ciprofloxacin in a dominant bloom-forming cyanobacterium (Microcystis aeruginosa) were investigated and compared with those for single exposure to glyphosate. The growth rate of M. aeruginosa, photosynthetic activity indicated by Fv/Fm, and microcystin production ability showed a typical U-shaped hormetic dose-response to glyphosate exposure. Upregulated proteins related to photosynthesis and biosynthesis, as well as increased photosynthetic activity, were responsible for the stimulated growth induced by 0.1-5 μg/L glyphosate, while the upregulation of mcyB protein contributed to increased microcystin synthesis in glyphosate-treated cells. The presence of 0.04-0.2 μg/L mixed antibiotics significantly (p < 0.05) enhanced the stimulation effects of glyphosate. Combined exposure to glyphosate and mixed antibiotics promoted microcystin synthesis through the upregulation of six microcystin synthesis regulatory proteins (mcyC, mcyF, mcyG, mcyI, MAE_56520, and ntcA) and stimulated cyanobacterial growth through the upregulation of proteins involved in photosynthesis, cell division, carbon fixation, pentose phosphate, translation, and chlorophyll synthesis. Combined exposure to glyphosate and antibiotic contaminants promoted cyanobacterial growth at no-effect concentrations of single exposure (0.04 μg/L for mixed antibiotics; 0.05, 10 and 100 μg/L for glyphosate), suggesting an increased threat from combined contamination to aquatic ecosystems through promoting the formation of cyanobacterial bloom.

Hormesis in plants: Physiological and biochemical responses

Hormesis is a favorable response to low level exposures to substance or to adverse conditions. This phenomenon has become a target to achieve greater crop productivity. This review aimed to address the physiological mechanisms for the induction of hormesis in plants. Some herbicides present a hormetic dose response. Among them, those with active ingredients glyphosate, 2,4-D and paraquat. The application of glyphosate as a hormesis promoter is therefore showing promess . Glyphosate has prominent role in shikimic acid pathway, decreasing lignin synthesis resulting in improved growth and productivity of several crops. Further studies are still needed to estimate optimal doses for other herbicides of crops or agricultural interest. Biostimulants are also important, since they promote effects on secondary metabolic pathways and production of reactive oxygen species (ROS). When ROS are produced, hydrogen peroxide act as a signaling molecule that promote cell walls malleability allowing inward water transport causing cell expansion. . Plants'ability to overcome several abiotic stress conditions is desirable to avoid losses in crop productivity and economic losses. This review compiles information on how hormesis in plants can be used to achieve new production levels.

Glyphosate: Uses Other Than in Glyphosate-Resistant Crops, Mode of Action, Degradation in Plants, and Effects on Non-target Plants and Agricultural Microbes

Glyphosate is the most used herbicide globally. It is a unique non-selective herbicide with a mode of action that is ideal for vegetation management in both agricultural and non-agricultural settings. Its use was more than doubled by the introduction of transgenic, glyphosate-resistant (GR) crops. All of its phytotoxic effects are the result of inhibition of only 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), but inhibition of this single enzyme of the shikimate pathway results in multiple phytotoxicity effects, both upstream and downstream from EPSPS, including loss of plant defenses against pathogens. Degradation of glyphosate in plants and microbes is predominantly by a glyphosate oxidoreductase to produce aminomethylphosphonic acid and glyoxylate and to a lesser extent by a C-P lyase to produce sarcosine and phosphate. Its effects on non-target plant species are generally less than that of many other herbicides, as it is not volatile and is generally sprayed in larger droplet sizes with a relatively low propensity to drift and is inactivated by tight binding to most soils. Some microbes, including fungal plant pathogens, have glyphosate-sensitive EPSPS. Thus, glyphosate can benefit GR crops by its activity on some plant pathogens. On the other hand, glyphosate can adversely affect some microbes that are beneficial to agriculture, such as Bradyrhizobium species, although GR crop yield data indicate that such an effect has been minor. Effects of glyphosate on microbes of agricultural soils are generally minor and transient, with other agricultural practices having much stronger effects.

Glyphosate and nickel differently affect photosynthesis and ethylene in glyphosate-resistant soybean plants infected by Phakopsora pachyrhizi

Nickel (Ni) and glyphosate (Gl) are able to reduce the symptoms of Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, in soybean. However, their combined effects on the energy balance and ethylene metabolism of soybean plants infected with this fungus has not been elucidated. Therefore, the effects of Ni, Gl, and the combination of Ni + Gl on ASR development, photosynthetic capacity, sugar concentrations, and ethylene concentrations in plants of a Gl-resistant cultivar, uninfected or infected with P. pachyrhizi, were investigated. Inoculated plants supplied with Ni had the highest foliar Ni concentration in all the treatments. Gl had a negative effect on the foliar Ni concentration in Ni-sprayed plants. The ASR severity was reduced in plants sprayed with Ni and Gl. Carotenoid and chlorophyll concentrations were higher in inoculated Ni, Gl, and Ni + Gl plants than in control plants. Based on the chlorophyll a fluorescence parameters, the photosynthetic apparatus of the control inoculated plants was damaged, and the least amount of energy was directed to the photochemistry process in these plants. The reduced capacity of the photosynthetic mechanism to capture light and use the energy absorbed by photosystem II in inoculated plants was reflected in their reduced capacity to process CO2 , as indicated by the high internal CO2 concentrations and low rates of net carbon assimilation. The low sugar concentrations in inoculated plants from the control treatment were linked to their reduced photosynthetic capacity due to the high ASR severity. In uninfected plants, the ethylene concentration was not affected by Ni or Gl, while the ethylene concentration decreased in inoculated plants; this decrease was more pronounced in plants from the control treatment than in treated inoculated plants. In conclusion, this study sheds light on the role played by both Ni and Gl in ASR control from a physiological perspective. Soybean plants exposed to Ni and Gl were able to maintain high ethylene concentrations and photosynthetic capacity during the P. pachyrhizi infection process; as a result, these plants consumed less of their reserves than inoculated plants not treated with Ni or Gl.

Environmental toxicology and ecotoxicology: How clean is clean? Rethinking dose-response analysis

Global agendas for sustaining clean environments target remediation of multimedia contaminants, but how clean is clean? Environmental Toxicology and Ecotoxicology focus on issues concerning "clean". However, the models used to assess the effects of environmental multimedia on individual living organisms and communities or populations in Environmental Toxicology and Ecotoxicology may fail to provide reliable estimates for risk assessment and optimize health. Recent developments in low-dose effects research provide a novel means in Environmental Toxicology and Ecotoxicology to improve the quality of hazard and risk assessment.

Low herbicide doses can change the responses of weeds to subsequent treatments in the next generation: metamitron exposed PSII-target-site resistant Chenopodium album as a case study

BACKGROUND

It is well known that exposure to mild stress can precondition organisms to better tolerate subsequent stress exposure in the same or future generations. Since herbicide hormesis also represents a moderate stress to exposed plants, a transgenerational priming is likely but not proven. Especially in herbicide-resistant weeds showing enhanced reproductive fitness after regular herbicide treatments, the ability to induce resilient offspring phenotypes via hormesis may hasten the evolution of herbicide resistance in weeds. This hypothesis was studied for the triazinone metamitron in an F1 offspring generation of PSII target-site resistant (TSR) plants of Chenopodium album propagated after parental conditioning with various metamitron doses.

RESULTS

In two independent dose-response greenhouse trials, there was a positive correlation between the strength of the stimulatory response during parental preconditioning and the magnitude of transgenerational changes in herbicide sensitivity and hormesis expression. Parental conditioning at subhormetic and toxic concentrations lead to less resilient offspring, while conditioning doses that induced a pronounced hormetic effect in F0 plants had a sensitivity-reducing and hormesis-promoting effect on the offspring. The observed reduction in sensitivity in F1 plants compared to unconditioned F1 plants was up to 2.2-fold.

CONCLUSIONS

This study demonstrates that hormetic herbicide treatments have the ability to prime weeds for enhanced tolerance to subsequent treatments in the next generation. Effects proved dose sensitive and may act in concert with other stimulatory adaptations in plant populations. This is relevant for weed control and herbicide resistance evolution, but also for herbicide side-effects that go beyond the exposed area. © 2020 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Root Microbiome Modulates Plant Growth Promotion Induced by Low Doses of Glyphosate

Glyphosate is a commonly used herbicide with a broad action spectrum. However, at sublethal doses, glyphosate can induce plant growth, a phenomenon known as hormesis. Most glyphosate hormesis studies have been performed under microbe-free or reduced-microbial-diversity conditions; only a few were performed in open systems or agricultural fields, which include a higher diversity of soil microorganisms. Here, we investigated how microbes affect the hormesis induced by low doses of glyphosate. To this end, we used Arabidopsis thaliana and a well-characterized synthetic bacterial community of 185 strains (SynCom) that mimics the root-associated microbiome of Arabidopsis We found that a dose of 3.6 × 10^-6 g acid equivalent/liter (low dose of glyphosate, or LDG) produced an ∼14% increase in the shoot dry weight (i.e., hormesis) of uninoculated plants. Unexpectedly, in plants inoculated with the SynCom, LDG reduced shoot dry weight by ∼17%. We found that LDG enriched two Firmicutes and two Burkholderia strains in the roots. These specific strains are known to act as root growth inhibitors (RGI) in monoassociation assays. We tested the link between RGI and shoot dry weight reduction in LDG by assembling a new synthetic community lacking RGI strains. Dropping RGI strains out of the community restored growth induction by LDG. Finally, we showed that individual RGI strains from a few specific phyla were sufficient to switch the response to LDG from growth promotion to growth inhibition. Our results indicate that glyphosate hormesis was completely dependent on the root microbiome composition, specifically on the presence of root growth inhibitor strains.IMPORTANCE Since the introduction of glyphosate-resistant crops, glyphosate has become the most common and widely used herbicide around the world. Due to its intensive use and ability to bind to soil particles, it can be found at low concentrations in the environment. The effect of these remnants of glyphosate in plants has not been broadly studied; however, glyphosate 1,000 to 100,000 times less concentrated than the recommended field dose promoted growth in several species in laboratory and greenhouse experiments. However, this effect is rarely observed in agricultural fields, where complex communities of microbes have a central role in the way plants respond to external cues. Our study reveals how root-associated bacteria modulate the responses of Arabidopsis to low doses of glyphosate, shifting between growth promotion and growth inhibition.

Root Microbiome Modulates Plant Growth Promotion Induced by Low Doses of Glyphosate

Glyphosate is a commonly used herbicide with a broad action spectrum. However, at sublethal doses, glyphosate can induce plant growth, a phenomenon known as hormesis. Most glyphosate hormesis studies have been performed under microbe-free or reduced-microbial-diversity conditions; only a few were performed in open systems or agricultural fields, which include a higher diversity of soil microorganisms. Here, we investigated how microbes affect the hormesis induced by low doses of glyphosate. To this end, we used Arabidopsis thaliana and a well-characterized synthetic bacterial community of 185 strains (SynCom) that mimics the root-associated microbiome of Arabidopsis We found that a dose of 3.6 × 10-6 g acid equivalent/liter (low dose of glyphosate, or LDG) produced an ∼14% increase in the shoot dry weight (i.e., hormesis) of uninoculated plants. Unexpectedly, in plants inoculated with the SynCom, LDG reduced shoot dry weight by ∼17%. We found that LDG enriched two Firmicutes and two Burkholderia strains in the roots. These specific strains are known to act as root growth inhibitors (RGI) in monoassociation assays. We tested the link between RGI and shoot dry weight reduction in LDG by assembling a new synthetic community lacking RGI strains. Dropping RGI strains out of the community restored growth induction by LDG. Finally, we showed that individual RGI strains from a few specific phyla were sufficient to switch the response to LDG from growth promotion to growth inhibition. Our results indicate that glyphosate hormesis was completely dependent on the root microbiome composition, specifically on the presence of root growth inhibitor strains.IMPORTANCE Since the introduction of glyphosate-resistant crops, glyphosate has become the most common and widely used herbicide around the world. Due to its intensive use and ability to bind to soil particles, it can be found at low concentrations in the environment. The effect of these remnants of glyphosate in plants has not been broadly studied; however, glyphosate 1,000 to 100,000 times less concentrated than the recommended field dose promoted growth in several species in laboratory and greenhouse experiments. However, this effect is rarely observed in agricultural fields, where complex communities of microbes have a central role in the way plants respond to external cues. Our study reveals how root-associated bacteria modulate the responses of Arabidopsis to low doses of glyphosate, shifting between growth promotion and growth inhibition.

Chlorophyll hormesis: Are chlorophylls major components of stress biology in higher plants?

High oxidative stress inhibits the synthesis and accumulation of chlorophylls, the pigments that absorb and use light. We collated evidence from a diverse array of studies demonstrating that chlorophyll concentration increases in response to low-level stress and decreases in response to high-level stress. These observations were from 33 species, >20 stress-inducing agents, 43 experimental setups and 177 dose responses, suggesting generality. Data meta-analysis indicated that the maximum stimulatory response did not differ significantly among species and agents. The stimulatory response maximized within a defined time window (median = 150-160% of the control response), after which it decreased but remained elevated (median = 120-130% of control response). The common stimulation of chlorophylls by low-level stress indicates that chlorophylls are major components of stress biology, with their increased concentration at low-level stress suggestive of their requirement for normal functioning and health. Increased chlorophyll concentration in response to low-level stress may equip systems with an enhanced capacity for defense against high-level (health-threatening) challenges within defined time windows, such as pollution or herbivores. These developments have wide-ranging implications in ecophysiology, biotic interactions and evolution.

Hormetic effect of glyphosate persists during the entire growth period and increases sugarcane yield

BACKGROUND

Stimulation of plant growth by low doses of a toxic compound is defined as a hormetic effect. Exposure of plants to low doses of glyphosate can cause stimulatory effects on growth or other variables. Sugarcane is the major biofuel and sugar-production crop cultivated in Brazil, but its expansion to new areas is limited; therefore, there is a demand for new technologies to improve sugarcane production per unit area. The use of pesticides to stimulate growth through the hormetic effect might be a suitable strategy to increase sugarcane yields. The purpose of this research was to investigate the effect of a low dose of glyphosate on metabolic compound accumulation, leaf phosphorus (P) concentration, and morphological variables across a one-year sugarcane cycle, as well as to determine whether the glyphosate effect was sustained and effective in improving the yield and technological quality of the sugarcane at harvest.

RESULTS

The application of a low dose of glyphosate led to higher concentrations of shikimic acid and quinic acid, higher leaf P concentrations, and improved plant growth, yield, and technological quality of the sugarcane, by increasing the Brix% juice, pol% cane, total recoverable sugar, tons of culms per hectare, and tons of pol per hectare, relative to the results for an untreated control.

CONCLUSIONS

The increased growth stimuli, observed through several variables, promoted an improvement in sugarcane yield. Therefore, the application of a low dose of glyphosate to sugarcane is a promising practice for crop management. © 2020 Society of Chemical Industry.

Is There a Possibility to Involve the Hormesis Effect on the Soybean with Glyphosate Sub-Lethal Amounts Used to Control Weed Species Amaranthus retroflexus L.?

Sub-lethal doses of herbicides can promote plant growth and have a positive effect on an organism this is called hormesis. The purpose of this study was to test the effects of sub-lethal doses of glyphosate on soybean (Glycine max (L.) Merr.) (1.8, 3.6, 7.2, 36, 180, and 720 g ha−1) and Amaranthus retroflexus L. (7.2, 36, 180, 720, 1440, and 2880 g ha−1). Different biological parameters, such as phytotoxicity, fresh weight, root length, content of photosynthetic pigments, and shikimate concentration, were measured. Glyphosate in doses of 1440 and 2880 g ha−1 destroyed A. retroflexus plants. A fresh weight of A. retroflexus at a dose of 36 g ha−1 was reduced by 76.31%, while for the soybean it was reduced by 19.26%. At the highest dose, the shikimate concentration was 145% in the soybean, while in A. retroflexus, the concentration increased by 58.80% compared to the control plants. All doses of glyphosate were statistically significantly different in terms of chlorophyll a content, while higher doses in A. retroflexus caused chlorophyll b to decrease. The change in the production of carotenoids was not statistically significant. The results showed that sub-lethal amounts of glyphosate did not lead to stimulation of measured parameters of soybean.

Response of glyphosate-resistant and susceptible biotypes of Echinochloa colona to low doses of glyphosate in different soil moisture conditions

To evaluate the hormetic effect of glyphosate on Echinochloa colona, two pot studies were done in the screenhouse at the Gatton Campus, the University of Queensland, Australia. Glyphosate was sprayed at the 3-4 leaf stage using different doses [(0, 5, 10, 20, 40, 80 and 800 g a.e. ha-1) and (0, 2.5, 5, 10, 20 and 800 g a.e. ha-1)] in the first and second study, respectively. In the second study, two soil moistures (adequately-watered and water-stressed), and two E. colona biotypes, glyphosate-resistant and glyphosate-susceptible, were included. In both studies, plants that were treated with glyphosate at 2.5-40 g ha-1 grew taller and produced more leaves, tillers, inflorescences and seeds than the control treatment. In the first study, 5 g ha-1 glyphosate resulted in the maximum aboveground biomass (increase of 34% to 118%) compared with the control treatment. In the second study, the adequately-watered and glyphosate low dose treatments caused an increase in all the measured growth parameters for both biotypes. For example, total dry biomass was increased by 64% and 54% at 5 g ha-1 in the adequately-watered treatments for the resistant and susceptible biotypes, respectively, compared with the control treatment. All measured traits tended to decrease with increasing water stress and the stimulative growth of low doses of glyphosate could not compensate for the water stress effect. The results of both studies showed a hormetic effect of low doses of glyphosate on E. colona biotypes and such growth stimulation was significant in the range of 5 to 10 g ha-1 glyphosate. Water availability was found to be effective in modulating the stimulatory outcomes of glyphosate-induced hormesis. No significant difference was observed between the resistant and susceptible biotypes for hormesis phenomenon. The study showed the importance of precise herbicide application for suppressing weed growth and herbicide resistance evolution.