Proteolytic pathways induced by herbicides that inhibit amino acid biosynthesis

Protein quality control systems in the endoplasmic reticulum and the cytosol coordinately prevent alachlor-induced proteotoxic stress in Saccharomyces cerevisiae

Alachlor, a widely used chloroacetanilide herbicide for controlling annual grasses in crops, has been reported to rapidly trigger protein denaturation and aggregation in the eukaryotic model organism Saccharomyces cerevisiae. Therefore, this study aimed to uncover cellular mechanisms involved in preventing alachlor-induced proteotoxicity. The findings reveal that the ubiquitin-proteasome system (UPS) plays a crucial role in eliminating alachlor-denatured proteins by tagging them with polyubiquitin for subsequent proteasomal degradation. Exposure to alachlor rapidly induced an inhibition of proteasome activity by 90 % within 30 min. The molecular docking analysis suggests that this inhibition likely results from the binding of alachlor to β subunits within the catalytic core of the proteasome. Notably, our data suggest that nascent proteins in the endoplasmic reticulum (ER) are the primary targets of alachlor. Consequently, the unfolded protein response (UPR), responsible for coping with aberrant proteins in the ER, becomes activated within 1 h of alachlor treatment, leading to the splicing of HAC1 mRNA into the active transcription activator Hac1p and the upregulation of UPR gene expression. These findings underscore the critical roles of the protein quality control systems UPS and UPR in mitigating alachlor-induced proteotoxicity by degrading alachlor-denatured proteins and enhancing the protein folding capacity of the ER.

Role of glutathione S-transferases in the mode of action of herbicides that inhibit amino acid synthesis in Amaranthus palmeri

Acetolactate synthase inhibitors (ALS inhibitors) and glyphosate are two classes of herbicides that act by inhibiting an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. Besides amino acid synthesis inhibition, both herbicides trigger similar physiological effects in plants. The main aim of this study was to evaluate the role of glutathione metabolism, with special emphasis on glutathione S-transferases (GSTs), in the mode of action of glyphosate and ALS inhibitors in Amaranthus palmeri. For that purpose, plants belonging to a glyphosate-sensitive (GLS) and a glyphosate-resistant (GLR) population were treated with different doses of glyphosate, and plants belonging to an ALS-inhibitor sensitive (AIS) and an ALS-inhibitor resistant (AIR) population were treated with different doses of the ALS inhibitor nicosulfuron. Glutathione-related contents, GST activity, and related gene expressions (glutamate-cysteine ligase, glutathione reductase, Phi GST and Tau GST) were analysed in leaves. According to the results of the analytical determinations, there were virtually no basal differences between GLS and GLR plants or between AIS and AIR plants. Glutathione synthesis and turnover did not follow a clear pattern in response to herbicides, but GST activity and gene expression (especially Phi GSTs) increased with both herbicides in treated sensitive plants, possibly related to the rocketing H2O2 accumulation. As GSTs offered the clearest results, these were further investigated with a multiple resistant (MR) population, compressing target-site resistance to both glyphosate and the ALS inhibitor pyrithiobac. As in single-resistant plants, measured parameters in the MR population were unaffected by herbicides, meaning that the increase in GST activity and expression occurs due to herbicide interactions with the target enzymes.

Cysteine proteases are activated in sensitive Amaranthus palmeri populations upon treatment with herbicides inhibiting amino acid biosynthesis

The herbicides glyphosate and pyrithiobac inhibit the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the aromatic amino acid biosynthetic pathway and acetolactate synthase (ALS) in the branched-chain amino acid biosynthetic pathway, respectively. Here we characterise the protease activity profiles of a sensitive (S), a glyphosate-resistant (GR) and a multiple-resistant (MR) population of Amaranthus palmeri in response to glyphosate and pyrithiobac. Amino acid accumulation and cysteine protease activities were induced with both herbicides in the S population and with pyrithiobac in the GR population, suggesting that the increase in cysteine proteases is responsible for the increased degradation of the available proteins and the observed increase in free amino acids. Herbicides did not induce any changes in the proteolytic activities in the populations with target-site resistance, indicating that this effect was only induced in sensitive plants.

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.

Unravelling the Phytotoxic Effects of Glyphosate on Sensitive and Resistant Amaranthus palmeri Populations by GC-MS and LC-MS Metabolic Profiling

Glyphosate, the most successful herbicide in history, specifically inhibits the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), one of the key enzymes in the shikimate pathway. Amaranthus palmeri is a driver weed in agriculture today that has evolved glyphosate-resistance through increased EPSPS gene copy number and other mechanisms. Non-targeted GC-MS and LC-MS metabolomic profiling was conducted to examine the innate physiology and the glyphosate-induced perturbations in one sensitive and one resistant (by EPSPS amplification) population of A. palmeri. In the absence of glyphosate treatment, the metabolic profile of both populations was very similar. The comparison between the effects of sublethal and lethal doses on sensitive and resistant populations suggests that lethality of the herbicide is associated with an amino acid pool imbalance and accumulation of the metabolites of the shikimate pathway upstream from EPSPS. Ferulic acid and its derivatives were accumulated in treated plants of both populations, while quercetin and its derivative contents were only lower in the resistant plants treated with glyphosate.

Metabolism of guarana (Paullinia cupana Kunth var. sorbilis) plants and fruit production subjected to glyphosate doses

Guarana (Paullinia cupana Kunth var. sorbilis) is a typically Amazonian plant of high economic value due to the compounds found in its seed. For guarana to reach the maximum productive potential, management practices such as weed control are necessary. The use of herbicides is a viable alternative, however, its drift may lead to adverse effects on the primary and secondary plant metabolisms and cause losses in crop production. This study evaluated the differential drift effects of glyphosate doses on the physiology of guarana plants and the production of compounds of economic interest in their seeds. Glyphosate doses (57.6, 115.2, 230.4, 460.8 g ae ha^-1) were applied to adult guarana plants after the flowering period. The photosynthetic functions and metabolism effects were evaluated. Herbicide treatments led to oxidative stress due to increased lipid peroxidation and increased carbohydrate and amino acid in their leaflets. Despite this, glyphosate showed no effect on fruit production or the content of secondary metabolites of commercial interest in seeds.

Profiling protein targets of cellular toxicant exposure

Environmental agents of exposure can damage proteins, affecting protein function and cellular protein homeostasis. Specific residues are inherently chemically susceptible to damage from individual types of exposure. Amino acid content is not completely predictive of protein susceptibility, as secondary, tertiary, and quaternary structures of proteins strongly influence the reactivity of the proteome to individual exposures. Because we cannot readily predict which proteins will be affected by which chemical exposures, mass spectrometry-based proteomic strategies are necessary to determine the protein targets of environmental toxins and toxicants. This review describes the mechanisms by which environmental exposure to toxins and toxicants can damage proteins and affect their function, and emerging omic methodologies that can be used to identify the protein targets of a given agent. These methods include target identification strategies that have recently revolutionized the drug discovery field, such as activity-based protein profiling, protein footprinting, and protein stability profiling technologies. In particular, we highlight the necessity of multiple, complementary approaches to fully interrogate how protein integrity is challenged by individual exposures.

Role of oxidative stress in the physiology of sensitive and resistant Amaranthus palmeri populations treated with herbicides inhibiting acetolactate synthase

The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H₂O₂, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H₂O₂ content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress.

Primary metabolism in an Amaranthus palmeri population with multiple resistance to glyphosate and pyrithiobac herbicides

The objective of this work was to characterize the resistance mechanisms and the primary metabolism of a multiple resistant (MR) population of Amaranthus palmeri to glyphosate and to the acetolactate synthase (ALS) inhibitor pyrithiobac. All MR plants analysed were glyphosate-resistant due to 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene amplification. Resistance to pyrithiobac was more variable among individuals and was related to point mutations at five positions in the ALS gene sequence: A122, A205, W574, S653 and G654. All MR plants were heterozygous for W574, the most abundant mutation. In nontreated plants, the presence of mutations did not affect ALS functionality, and plants with the W574L mutation showed the highest ALS resistance level to pyrithiobac. The accumulation of the transcripts corresponding to several genes of the aromatic amino acid (AAA) and branched-chain amino acid (BCAA) pathways detected in nontreated MR plants indicated additional effects of EPSPS gene amplification and ALS mutations. The physiological performance of the MR population after treatment with glyphosate and/or pyrithiobac was compared with that of a sensitive (S) population. The increase induced in total soluble sugars, AAA or BCAA content by both herbicides was higher in the S population than in the MR population. Physiological effects were not exacerbated after the mixture of both herbicides in S or in MR populations. This study provides new insights into the physiology of a multiple resistant A. palmeri, which could be very useful for achieving effective management of this weed.

Hierarchical cluster analysis of herbicide modes of action reveals distinct classes of multiple resistance in weeds

BACKGROUND

The number of weed species resistant to multiple herbicide modes of action (MoAs) has increased over the last 30 years and may in the future render existing herbicide MoAs obsolete for many cropping systems. Yet few predictive tools exist to manage this risk. Using a worldwide dataset of weed species resistant to multiple herbicide MoAs, hierarchical clustering was used to classify MoAs into similar groups in relation to the suite of resistant weed species they have in common. Network analyses then were used to explore the relative importance of species prevalence and similarity in cluster patterns.

RESULTS

Hierarchical clustering identified three similarly sized clusters of herbicide MoAs that were linked by the co-occurrence of resistant weeds: Herbicide Resistance Action Committee (HRAC) groups 2, 4, 5 and 9; HRAC groups 12, 14 and 15; and HRAC groups 1, 3 and 22. Cluster membership was consistent with similarities in the physiological or biochemical target of the herbicide MoAs. Network analyses revealed that the number of weed species resistant to two different MoAs was related to the number of weeds known to be resistant to each individual herbicide MoA.

CONCLUSIONS

Hierarchical cluster analysis provided new insights into the risk of weeds becoming resistant to more than one herbicide MoA. By clustering herbicide MoAs into three distinct groups, the potential exists for farmers to manage resistance by rotating herbicides between rather than within clusters, as far as crop, weed and environmental conditions allow.

Repeated origins, widespread gene flow, and allelic interactions of target-site herbicide resistance mutations

Causal mutations and their frequency in agricultural fields are well-characterized for herbicide resistance. However, we still lack understanding of their evolutionary history: the extent of parallelism in the origins of target-site resistance (TSR), how long these mutations persist, how quickly they spread, and allelic interactions that mediate their selective advantage. We addressed these questions with genomic data from 19 agricultural populations of common waterhemp (Amaranthus tuberculatus), which we show to have undergone a massive expansion over the past century, with a contemporary effective population size estimate of 8 x 10⁷. We found variation at seven characterized TSR loci, two of which had multiple amino acid substitutions, and three of which were common. These three common resistance variants show extreme parallelism in their mutational origins, with gene flow having shaped their distribution across the landscape. Allele age estimates supported a strong role of adaptation from de novo mutations, with a median age of 30 suggesting that most resistance alleles arose soon after the onset of herbicide use. However, resistant lineages varied in both their age and evidence for selection over two different timescales, implying considerable heterogeneity in the forces that govern their persistence. Two such forces are intra- and inter-locus allelic interactions; we report a signal of extended haplotype competition between two common TSR alleles, and extreme linkage with genome-wide alleles with known functions in resistance adaptation. Together, this work reveals a remarkable example of spatial parallel evolution in a metapopulation, with important implications for the management of herbicide resistance.

Fluctuation in amino acids content in Triticum aestivum L. cultivars as an indicator on the impact of post-emergence herbicides in controlling weeds

This study was carried out in a demonstrated field in El-Sharkia Governorate, Egypt, during the winter of season 2020 to evaluate the leverage of four post-emergence herbicides i.e., tribenuron-methyl, clodinafop- propargyl, pyroxsulam and pinoxaden compared to control on total protein and amino acid contents in three wheat cultivars (Shandwel 1, Giza 171, and Sakha 95). Generally, the use of foliar herbicides led to a significant decrease in essential, non-essential amino acids and protein contents. However, tribenuran-methyl herbicide signifcantly increased the levels of proline, glycine, arginine, and histidine, but cystine and threonine not affected as compared to control. On the other hand, foliar herbicide application was significantly increased physiological , biochemical parameters and yield of Shandweel cultivar as compared to the other varieties. The physiological and biochemical models of dual-herbicide-tolerant wheat cultivars add to our understanding of the crop. In recent agricultural systems, herbicide tolerant plants are important for long-term weed management. Therefore, the study recommended the safely usage of Tribenuran-methyl as foliar herbicide in weed managment.

Transcriptomics and enzymology combined five gene expressions to reveal the responses of earthworms (Eisenia fetida) to the long-term exposure of cyantraniliprole in soil

Cyantraniliprole is a novel diamide insecticide that acts upon the ryanodine receptor (RyR) and has broad application prospects. Accordingly, it is very important to evaluate the toxicity of cyantraniliprole to earthworms (Eisenia fetida) because of their vital role in maintaining a healthy soil ecosystem. In this study, an experiment was set up, using four concentrations (0.1, 1, 5, and 10 mg/kg) and solvent control group (0 mg/kg), to investigate the ecotoxicity of cyantraniliprole to earthworms. Our results showed that, after 28 days of exposure to cyantraniliprole, both cocoon production and the number of juvenile earthworms had decreased significantly at concentrations of either 5 or 10 mg/kg. On day 14, we measured the activities of digestive enzymes and ion pumps in the intestinal tissues of earthworms. These results revealed that cyantraniliprole exposure caused intestinal damage in earthworm, specifically changes to its intestinal enzyme activity and calcium ion content. Cyantraniliprole could lead to proteins' carbonylation under the high-dose treatments (i.e., 5 mg/kg, 10 mg/kg). At the same time, we also found that cyantraniliprole can cause the abnormal expression of key functional genes (including HSP70, CAT, RYR, ANN, and CAM genes). Moreover, the transcriptomics data showed that exposure to cyantraniliprole would affect the synthesis of carbohydrates, proteins and lipids, as well as their absorption and transformation, while cyantraniliprole would also affect signal transduction. In general, high-dose exposure to cyantraniliprole causes reproductive toxicity, genotoxicity, and intestinal damage to earthworms.

Effects of the novel HPPD-inhibitor herbicide QYM201 on enzyme activity and microorganisms, and its degradation in soil

QYM201 is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide recently registered in China for controlling grass and broadleaf weeds in wheat. It is a novel herbicide, and its potential harm to soil ecosystems has not yet been reported. This study investigates the influence of QYM201 on soil enzyme activity and microorganism quantities in two different soils at concentrations of 0.1, 1, and 5 mg kg^-1 soil. Results indicate that QYM201 initially inhibited soil protease, urease, and sucrase activity and this effect increased with concentration. During the later stages of incubation, inhibitory effects gradually weakened and by the end of the experiment (45 days), enzyme activity was restored to control levels. Catalase activity was stimulated by QYM201, with significant differences observed between the QYM201-treated groups and the control at the onset of exposure. This stimulation effect decreased during the later stages of the experiment. However, catalase activity was still significantly higher at the end of the experiment compared to the control. The effects of QYM201 on soil microorganisms differed. Initially, bacteria and actinomycetes quantities were decreased by QYM201 (10 days). As the incubation progressed, microorganism quantities in the lower concentration groups (0.1 and 1 mg kg^-1 soil) were restored to control levels, while those of the high concentration group (5 mg kg^-1 soil) did not fully recover. QYM201 did not significantly impact the quantity of fungi. The half-life and degradation rate constant (k) of QYM201 for the two studied soil types were 23.1 days and 16.1 days, and 0.030 and 0.043 day^-1, respectively.

Physiological Approach to the Use of the Natural Compound Quinate in the Control of Sensitive and Resistant Papaver rhoeas

Quinate (1,3,4,5-tetrahydroxycyclohexanecarboxylate) is a compound synthesized in plants through a side-branch of the shikimate biosynthesis pathway, which is accumulated after glyphosate and acetolactate synthase inhibiting herbicides (ALS-inhibitors) and has phytotoxic potential. The objective of this study was to evaluate the phytotoxicity of quinate on several weed species. Among the species evaluated, Cynodon dactylon, Bromus diandrus, Lolium rigidum, Sinapis alba, and Papaver rhoeas, P. rhoeas was the most sensitive, and its growth was controlled with quinate concentrations above 100 mM at the phenological stage of 6–8 true leaves. A physiological study, including the shikimate pathway and the physiological markers of ALS-inhibitors (carbohydrates and amino acids), was performed in the sensitive and resistant plants treated with sulfonylureas or quinate. The typical physiological effects of ALS-inhibitors were detected in the sensitive population (free amino acid and carbohydrate accumulation) and not detected in the resistant population. The mode of action of quinate appeared to be related to general perturbations in their carbon/nitrogen metabolism rather than to specific changes in the shikimate pathway. These results suggest the possibility of using quinate in the weed control management of P. rhoeas.

Global trends in pesticides: A looming threat and viable alternatives

Pesticides are widely used chemical compounds in agriculture to destroy insects, pests and weeds. In modern era, they form an indispensable part of agricultural and health practices. Globally, nearly 3 billion kg of pesticides are used every year with a budget of ~40 billion USD. This extensive usage has increased the crop yield as well as led to significant reduction in harvest losses and thereby, enhanced food availability. On the other hand, indiscriminate usage of these chemicals has led to several environmental implications and caused adverse effects on human health. Epidemiological evidences have revealed the harmful effects of pesticides exposure on various organs including liver, brain, lungs and colon. Recent investigations have shown that pesticides can also lead to fatal consequences such as cancer among individuals. These chemicals enter ecosystem, thus hampering the sensitive environmental equilibrium through bio-accumulation. Due to their non-biodegradable nature, they can persist in nature for years and are regarded as potent biohazard. Worldwide, very few surveillance methods have been considered, which can bring awareness among the individuals, therefore the present review is an attempt to delineate consequences induced by various types of pesticide exposure on the environment. Further, the prospective of biopesticides use could facilitate the increase of crop production without compromising human health.

Hypoxic Treatment Decreases the Physiological Action of the Herbicide Imazamox on Pisum sativum Roots

The inhibition of acetolactate synthase (ALS; EC 2.2.1.6), an enzyme located in the biosynthetic pathway of branched-chain amino acids, is the target site of the herbicide imazamox. One of the physiological effects triggered after ALS inhibition is the induction of aerobic ethanol fermentation. The objective of this study was to unravel if fermentation induction is related to the toxicity of the herbicide or if it is a plant defense mechanism. Pea plants were exposed to two different times of hypoxia before herbicide application in order to induce the ethanol fermentation pathway, and the physiological response after herbicide application was evaluated at the level of carbohydrates and amino acid profile. The effects of the herbicide on total soluble sugars and starch accumulation, and changes in specific amino acids (branched-chain, amide, and acidic) were attenuated if plants were subjected to hypoxia before herbicide application. These results suggest that fermentation is a plant defense mechanism that decreases the herbicidal effect.

Transcriptome Analysis Identifies Candidate Target Genes Involved in Glyphosate-Resistance Mechanism in Lolium multiflorum

Italian ryegrass (Lolium multiflorum; LOLMU) is one of the most troublesome weeds in temperate regions in the world. This weed species interfere with wheat, corn, rye, and oat, causing significant crop yield losses. This species has evolved glyphosate resistance, making it difficult to control. The mechanisms of glyphosate resistance are still unknown, and an understanding thereof will favor the development of new strategies of management. The present study is the first transcriptome study in LOLMU using glyphosate-resistant and -sensitive biotypes, aiming to identify and to provide a list of the candidate target genes related to glyphosate resistance mechanism. The transcriptome was assembled de novo, producing 87,433 contigs with an N50 of 740 bp and an average length of 575 bp. There were 92 and 54 up- and down-regulated genes, respectively, in the resistant biotype, while a total of 1683 were differentially expressed in the sensitive biotype in response to glyphosate treatment. We selected 14 highly induced genes and seven with repressed expression in the resistant biotype in response to glyphosate. Of these genes, a significant proportion were related to the plasma membrane, indicating that there is a barrier making it difficult for glyphosate to enter the cell.

Dipteryx alata, a tree native to the Brazilian Cerrado, is sensitive to the herbicide nicosulfuron

The expansion of land use for agricultural interests and the excessive use of herbicides are among the causes of biodiversity losses in the Brazilian Cerrado biome. Therefore, we aimed to test the hypothesis that Dipteryx alata Vogel, a common species in this biome, is sensitive to nicosulfuron because of its high phytotoxicity. We evaluated physiological, biochemical and morphological responses in D. alata plants exposed to increasing doses of the herbicide. Young plants were transplanted to 10 L pots containing substrate composed of soil and sand (2:1) after fertilization. After an acclimation period, the following doses of nicosulfuron were applied: 0 (control), 6, 12, 24, 48, and 60 g a.e. ha^-1. The experiment was conducted in a randomized block design factorial scheme with six doses of nicosulfuron, three evaluation times, and five replicates per treatment. The effects of the herbicide were assessed by measuring gas exchange, chlorophyll a fluorescence, photosynthetic pigments, membrane permeability, antioxidant enzymes and acetolactate synthase. Nicosulfuron altered the photosynthetic machinery and enzymatic metabolism of D. alata. Reductions in physiological traits, increased catalase and ascorbate peroxidase activities, enhanced malondialdehyde concentrations rate of electrolyte leakage and decreased acetolactate synthase activity in response to nicosulfuron all suggest that D. alata is sensitive to this herbicide.

Physiological performance of glyphosate and imazamox mixtures on Amaranthus palmeri sensitive and resistant to glyphosate

The herbicides glyphosate and imazamox inhibit the biosynthetic pathway of aromatic amino acids (AAA) and branched-chain amino acids (BCAA), respectively. Both herbicides share several physiological effects in the processes triggered in plants after herbicide application that kills the plant, and mixtures of both herbicides are being used. The aim of this study was to evaluate the physiological effects in the mixture of glyphosate and imazamox in glyphosate-sensitive (GS) and -resistant (GR) populations of the troublesome weed Amaranthus palmeri. The changes detected in the physiological parameters after herbicide mixtures application were similar and even less to the changes detected after individual treatments. This pattern was detected in shikimate, amino acid and carbohydrate content, and it was independent of the EPSPS copy number, as it was detected in both populations. In the case of the transcriptional pattern of the AAA pathway after glyphosate, interesting and contrary interactions with imazamox treatment were detected for both populations; enhancement of the effect in the GS population and alleviation in the GR population. At the transcriptional level, no cross regulation between AAA and BCAA inhibitors was confirmed. This study suggests that mixtures are equally or less toxic than herbicides alone, and would implicate careful considerations when applying the herbicide mixtures.

Species- and organ-specific responses of agri-environmental plants to residual agricultural pollutants

Soil pollution by anthropogenic chemicals is a major concern for sustainability of crop production and of ecosystem functions mediated by natural plant biodiversity. The complex effects on plants are however difficult to apprehend. Plant communities of field margins, vegetative filter strips or rotational fallows are confronted with agricultural pollutants through residual soil contamination and/or through drift, run-off and leaching events that result from chemical applications. Exposure to xenobiotics and heavy metals causes biochemical, physiological and developmental effects. However, the range of doses, modalities of exposure, metabolization of contaminants into derived xenobiotics, and combinations of contaminants result in variable and multi-level effects. Understanding these complex plant-pollutant interactions cannot directly rely on toxicological or agronomical approaches that focus on the effects of field-rate pesticide applications. It must take into account exposure at root level, sublethal concentrations of bioactive compounds and functional biodiversity of the plant species that are affected. The present study deals with agri-environmental plant species of field margins, vegetative filter strips or rotational fallows in European agricultural landscapes. Root and shoot physiological and growth responses were compared under controlled conditions that were optimally adjusted for each plant species. Contrasted responses of growth inhibition, no adverse effect or growth enhancement depended on species, organ and nature of contaminant. However, all of the agricultural contaminants under study (pesticides, pesticide metabolites, heavy metals, polycyclic aromatic hydrocarbons) had significant effects under conditions of sublethal exposure on at least some of the plant species. The fungicide tebuconazole and polycyclic aromatic hydrocarbon fluoranthene, which gave highest levels of responses, induced both activation or inhibition effects, in different plant species or in different organs of the same plant species. These complex effects are discussed in terms of dynamics of agri-environmental plants and of ecological consequences of differential root-shoot growth under conditions of soil contamination.

ERF-VII transcription factors induce ethanol fermentation in response to amino acid biosynthesis-inhibiting herbicides

Herbicides inhibiting either aromatic or branched-chain amino acid biosynthesis trigger similar physiological responses in plants, despite their different mechanism of action. Both types of herbicides are known to activate ethanol fermentation by inducing the expression of fermentative genes; however, the mechanism of such transcriptional regulation has not been investigated so far. In plants exposed to low-oxygen conditions, ethanol fermentation is transcriptionally controlled by the ethylene response factors-VII (ERF-VIIs), whose stability is controlled in an oxygen-dependent manner by the Cys-Arg branch of the N-degron pathway. In this study, we investigated the role of ERF-VIIs in the regulation of the ethanol fermentation pathway in herbicide-treated Arabidopsis plants grown under aerobic conditions. Our results demonstrate that these transcriptional regulators are stabilized in response to herbicide treatment and are required for ethanol fermentation in these conditions. We also observed that mutants with reduced fermentative potential exhibit higher sensitivity to herbicide treatments, thus revealing the existence of a mechanism that mimics oxygen deprivation to activate metabolic pathways that enhance herbicide tolerance. We speculate that this signaling pathway may represent a potential target in agriculture to affect tolerance to herbicides that inhibit amino acid biosynthesis.

Effects of EPSPS Copy Number Variation (CNV) and Glyphosate Application on the Aromatic and Branched Chain Amino Acid Synthesis Pathways in Amaranthus palmeri

A key enzyme of the shikimate pathway, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19), is the known target of the widely used herbicide glyphosate. Glyphosate resistance in Amaranthus palmeri, one of the most troublesome weeds in agriculture, has evolved through increased EPSPS gene copy number. The aim of this work was to study the pleiotropic effects of (i) EPSPS increased transcript abundance due to gene copy number variation (CNV) and of (ii) glyphosate application on the aromatic amino acid (AAA) and branched chain amino acid (BCAA) synthesis pathways. Hydroponically grown glyphosate sensitive (GS) and glyphosate resistant (GR) plants were treated with glyphosate 3 days after treatment. In absence of glyphosate treatment, high EPSPS gene copy number had only a subtle effect on transcriptional regulation of AAA and BCAA pathway genes. In contrast, glyphosate treatment provoked a general accumulation of the transcripts corresponding to genes of the AAA pathway leading to synthesis of chorismate in both GS and GR. After chorismate, anthranilate synthase transcript abundance was higher while chorismate mutase transcription showed a small decrease in GR and remained stable in GS, suggesting a regulatory branch point in the pathway that favors synthesis toward tryptophan over phenylalanine and tyrosine after glyphosate treatment. This was confirmed by studying enzyme activities in vitro and amino acid analysis. Importantly, this upregulation was glyphosate dose dependent and was observed similarly in both GS and GR populations. Glyphosate treatment also had a slight effect on the expression of BCAA genes but no general effect on the pathway could be observed. Taken together, our observations suggest that the high CNV of EPSPS in A. palmeri GR populations has no major pleiotropic effect on the expression of AAA biosynthetic genes, even in response to glyphosate treatment. This finding supports the idea that the fitness cost associated with EPSPS CNV in A. palmeri may be limited.

Induction of the PDH bypass and upregulation of the ALDH7B4 in plants treated with herbicides inhibiting amino acid biosynthesis

Imazamox and glyphosate represent two classes of herbicides that inhibit the activity of acetohydroxyacid synthase in the branched-chain amino acid biosynthesis pathway and the activity of 5-enolpyruvylshikimate-3-phosphate synthase in the aromatic amino acid biosynthesis pathway, respectively. However, it is still unclear how imazamox and glyphosate lead to plant death. Both herbicides inhibit amino-acid biosynthesis and were found to induce ethanol fermentation in plants, but an Arabidopsis mutant deficient in alcohol dehydrogenase 1 was neither more susceptible nor more resistant than the wild-type to the herbicides. In this study, we investigated the effects of the amino acid biosynthesis inhibitors, imazamox and glyphosate, on the pyruvate dehydrogenase bypass reaction and fatty acid metabolism in A. thaliana. We found that the pyruvate dehydrogenase bypass was upregulated following the treatment by the two herbicides. Our results suggest that the Arabidopsis aldehyde dehydrogenase 7B4 gene might be participating in the pyruvate dehydrogenase bypass reaction. We evaluated the potential role of the aldehyde dehydrogenase 7B4 upon herbicide treatment in the plant defence mechanism. Plants that overexpressed the ALDH7B4 gene accumulated less soluble sugars, starch, and fatty acids and grew better than the wild-type after herbicide treatment. We discuss how the upregulation of the ALDH7B4 alleviates the effects of the herbicides, potentially through the detoxification of the metabolites produced in the pyruvate dehydrogenase bypass.

The pattern of shikimate pathway and phenylpropanoids after inhibition by glyphosate or quinate feeding in pea roots

The shikimate pathway is a metabolic route for the biosynthesis of aromatic amino acids (AAAs) (i.e. phenylalanine, tyrosine, and tryptophan). A key enzyme of shikimate pathway (5-enolpyruvylshikimate-3-phosphate synthase, EPSPS) is the target of the widely used herbicide glyphosate. Quinate is a compound synthesized in plants through a side branch of the shikimate pathway. Glyphosate provokes quinate accumulation and exogenous quinate application to plants shows a potential role of quinate in the toxicity of the herbicide glyphosate. Based on this, we hypothesized that the role of quinate accumulation in the toxicity of the glyphosate would be mediated by a deregulation of the shikimate pathway. In this study the effect of the glyphosate and of the exogenous quinate was evaluated in roots of pea plants by analyzing the time course of a full metabolic map of several metabolites of shikimate and phenylpropanoid pathways. Glyphosate application induced an increase of the 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS, first enzyme of the shikimate pathway) protein and accumulation of metabolites upstream of the enzyme EPSPS. No common effects on the metabolites and regulation of shikimate pathway were detected between quinate and glyphosate treatments, supporting that the importance of quinate in the mode of action of glyphosate is not mediated by a common alteration of the regulation of the shikimate pathway. Contrary to glyphosate, the exogenous quinate supplied was probably incorporated into the main trunk from the branch pathway and accumulated in the final products, such as lignin, concomitant with a decrease in the amount of DAHPS protein.

Herbicide-related signaling in plants reveals novel insights for herbicide use strategies, environmental risk assessment and global change assessment challenges

Herbicide impact is usually assessed as the result of a unilinear mode of action on a specific biochemical target with a typical dose-response dynamics. Recent developments in plant molecular signaling and crosstalk between nutritional, hormonal and environmental stress cues are however revealing a more complex picture of inclusive toxicity. Herbicides induce large-scale metabolic and gene-expression effects that go far beyond the expected consequences of unilinear herbicide-target-damage mechanisms. Moreover, groundbreaking studies have revealed that herbicide action and responses strongly interact with hormone signaling pathways, with numerous regulatory protein-kinases and -phosphatases, with metabolic and circadian clock regulators and with oxidative stress signaling pathways. These interactions are likely to result in mechanisms of adjustment that can determine the level of sensitivity or tolerance to a given herbicide or to a mixture of herbicides depending on the environmental and developmental status of the plant. Such regulations can be described as rheostatic and their importance is discussed in relation with herbicide use strategies, environmental risk assessment and global change assessment challenges.

Stable Isotope Resolved Metabolomics Reveals the Role of Anabolic and Catabolic Processes in Glyphosate-Induced Amino Acid Accumulation in Amaranthus palmeri Biotypes

Biotic and abiotic stressors often result in the buildup of amino acid pools in plants, which serve as potential stress mitigators. However, the role of anabolic (de novo amino acid synthesis) versus catabolic (proteolytic) processes in contributing to free amino acid pools is less understood. Using stable isotope-resolved metabolomics (SIRM), we measured the de novo amino acid synthesis in glyphosate susceptible (S-) and resistant (R-) Amaranthus palmeri biotypes. In the S-biotype, glyphosate treatment at 0.4 kg ae/ha resulted in an increase in total amino acids, a proportional increase in both (14)N and (15)N amino acids, and a decrease in soluble proteins. This indicates a potential increase in de novo amino acid synthesis, coupled with a lower protein synthesis and a higher protein catabolism following glyphosate treatment in the S-biotype. Furthermore, the ratio of glutamine/glutamic acid (Gln/Glu) in the glyphosate-treated S- and R-biotypes indicated that the initial assimilation of inorganic nitrogen to organic forms is less affected by glyphosate. However, amino acid biosynthesis downstream of glutamine is disproportionately disrupted in the glyphosate treated S-biotype. It is thus concluded that the herbicide-induced amino acid abundance in the S-biotype is contributed by both protein catabolism and de novo synthesis of amino acids such as glutamine and asparagine.

Influence of exposure to pesticides on telomere length in tobacco farmers: A biology system approach

Various pesticides in the form of mixtures must be used to keep tobacco crops pest-free. Recent studies have shown a link between occupational exposure to pesticides in tobacco crops and increased damage to the DNA, mononuclei, nuclear buds and binucleated cells in buccal cells as well as micronuclei in lymphocytes. Furthermore, pesticides used specifically for tobacco crops shorten telomere length (TL) significantly. However, the molecular mechanism of pesticide action on telomere length is not fully understood. Our study evaluated the interaction between a complex mixture of chemical compounds (tobacco cultivation pesticides plus nicotine) and proteins associated with maintaining TL, as well as the biological processes involved in this exposure by System Biology tools to provide insight regarding the influence of pesticide exposure on TL maintenance in tobacco farmers. Our analysis showed that one cluster was associated with TL proteins that act in bioprocesses such as (i) telomere maintenance via telomere lengthening; (ii) senescence; (iii) age-dependent telomere shortening; (iv) DNA repair (v) cellular response to stress and (vi) regulation of proteasome ubiquitin-dependent protein catabolic process. We also describe how pesticides and nicotine regulate telomere length. In addition, pesticides inhibit the ubiquitin proteasome system (UPS) and consequently increase proteins of the shelterin complex, avoiding the access of telomerase in telomere and, nicotine activates UPS mechanisms and promotes the degradation of human telomerase reverse transcriptase (hTERT), decreasing telomerase activity.

Both foliar and residual applications of herbicides that inhibit amino acid biosynthesis induce alternative respiration and aerobic fermentation in pea roots

The objective of this work was to ascertain whether there is a general pattern of carbon allocation and utilisation in plants following herbicide supply, independent of the site of application: sprayed on leaves or supplied to nutrient solution. The herbicides studied were the amino acid biosynthesis-inhibiting herbicides (ABIH): glyphosate, an inhibitor of aromatic amino acid biosynthesis, and imazamox, an inhibitor of branched-chain amino acid biosynthesis. All treated plants showed impaired carbon metabolism; carbohydrate accumulation was detected in both leaves and roots of the treated plants. The accumulation in roots was due to lack of use of available sugars as growth was arrested, which elicited soluble carbohydrate accumulation in the leaves due to a decrease in sink strength. Under aerobic conditions, ethanol fermentative metabolism was enhanced in roots of the treated plants. This fermentative response was not related to a change in total respiration rates or cytochrome respiratory capacity, but an increase in alternative oxidase capacity was detected. Pyruvate accumulation was detected after most of the herbicide treatments. These results demonstrate that both ABIH induce the less-efficient, ATP-producing pathways, namely fermentation and alternative respiration, by increasing the key metabolite, pyruvate. The plant response was similar not only for the two ABIH but also after foliar or residual application.

Effects of the novel cis-nitromethylene neonicotinoid insecticide Paichongding on enzyme activities and microorganisms in yellow loam and Huangshi soils

Soil enzyme activity and microbial population play important roles in maintaining soil fertility and ensure crop yield. Paichongding (IPP) is a novel cis-nitromethylene neonicotinoid insecticide, which was recently developed in China. In this study, in order to better understand IPP ecological toxicity, the impact of IPP on soil enzyme activity and microbial population in soils was investigated. The results showed that, urease activity was inhibited by IPP before 75 days incubation, after that this inhibiting effect gradually weakened. IPP had different stimulating effects on the activities of dehydrogenase, protease, and catalase. They were consistently stimulated from the initial time in soils. The results of microbial population indicated that the number of bacteria increased after IPP application compared with the control, fungal number increased before 45 days incubation and then decreased. While actinomycete number decreased during degradation period. DT50 (half-life value), k (degradation rate constant) of IPP in S1 (yellow loam soil), and S2 (Huangshi soil) were found 90 days and 173 days, 0.0077 day(-1), and 0.0040 day(-1), respectively.

The Increasing Impact of Activity-Based Protein Profiling in Plant Science

The active proteome dictates plant physiology. Yet, active proteins are difficult to predict based on transcript or protein levels, because protein activities are regulated post-translationally in their microenvironments. Over the past 10 years, activity-based protein profiling (ABPP) is increasingly used in plant science. ABPP monitors the activities of hundreds of plant proteins using tagged chemical probes that react with the active site of proteins in a mechanism-dependent manner. Since labeling is covalent and irreversible, labeled proteins can be detected and identified on protein gels and by mass spectrometry using tagged fluorophores and/or biotin. Here, we discuss general concepts, approaches and practical considerations of ABPP, before we summarize the discoveries made using 40 validated probes representing 14 chemotypes that can monitor the active state of >4,500 plant proteins. These discoveries and new opportunities indicate that this emerging functional proteomic technology is a powerful discovery tool that will have an increasing impact on plant science.

Characterization of the Amaranthus palmeri Physiological Response to Glyphosate in Susceptible and Resistant Populations

The herbicide glyphosate inhibits the plant enzyme 5-enolpyruvylshikimate3-phosphate synthase (EPSPS) in the aromatic amino acid (AAA) biosynthetic pathway. The physiologies of an Amaranthus palmeri population exhibiting resistance to glyphosate by EPSPS gene amplification (NC-R) and a susceptible population (NC-S) were compared. The EPSPS copy number of NC-R plants was 47.5-fold the copy number of NC-S plants. Although the amounts of EPSPS protein and activity were higher in NC-R plants than in NC-S plants, the AAA concentrations were similar. The increases in total free amino acid and in AAA contents induced by glyphosate were more evident in NC-S plants. In both populations, the EPSPS protein increased after glyphosate exposure, suggesting regulation of gene expression. EPSPS activity seems tightly controlled in vivo. Carbohydrate accumulation and a slight induction of ethanol fermentation were detected in both populations.

ALOMYbase, a resource to investigate non-target-site-based resistance to herbicides inhibiting acetolactate-synthase (ALS) in the major grass weed Alopecurus myosuroides (black-grass)

Background

Herbicide resistance in agrestal weeds is a global problem threatening food security. Non-target-site resistance (NTSR) endowed by mechanisms neutralising the herbicide or compensating for its action is considered the most agronomically noxious type of resistance. Contrary to target-site resistance, NTSR mechanisms are far from being fully elucidated. A part of weed response to herbicide stress, NTSR is considered to be largely driven by gene regulation. Our purpose was to establish a transcriptome resource allowing investigation of the transcriptomic bases of NTSR in the major grass weed Alopecurus myosuroides L. (Poaceae) for which almost no genomic or transcriptomic data was available.

Results

RNA-Seq was performed from plants in one F2 population that were sensitive or expressing NTSR to herbicides inhibiting acetolactate-synthase. Cloned plants were sampled over seven time-points ranging from before until 73 h after herbicide application. Assembly of over 159M high-quality Illumina reads generated a transcriptomic resource (ALOMYbase) containing 65,558 potentially active contigs (N50 = 1240 nucleotides) predicted to encode 32,138 peptides with 74 % GO annotation, of which 2017 were assigned to protein families presumably involved in NTSR. Comparison with the fully sequenced grass genomes indicated good coverage and correct representation of A. myosuroides transcriptome in ALOMYbase. The part of the herbicide transcriptomic response common to the resistant and the sensitive plants was consistent with the expected effects of acetolactate-synthase inhibition, with striking similarities observed with published Arabidopsis thaliana data. A. myosuroides plants with NTSR were first affected by herbicide action like sensitive plants, but ultimately overcame it. Analysis of differences in transcriptomic herbicide response between resistant and sensitive plants did not allow identification of processes directly explaining NTSR. Five contigs associated to NTSR in the F2 population studied were tentatively identified. They were predicted to encode three cytochromes P450 (CYP71A, CYP71B and CYP81D), one peroxidase and one disease resistance protein.

Conclusions

Our data confirmed that gene regulation is at the root of herbicide response and of NTSR. ALOMYbase proved to be a relevant resource to support NTSR transcriptomic studies, and constitutes a valuable tool for future research aiming at elucidating gene regulations involved in NTSR in A. myosuroides.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1804-x) contains supplementary material, which is available to authorized users.

Subfamily-Specific Fluorescent Probes for Cysteine Proteases Display Dynamic Protease Activities during Seed Germination

Cysteine proteases are an important class of enzymes implicated in both developmental and defense-related programmed cell death and other biological processes in plants. Because there are dozens of cysteine proteases that are posttranslationally regulated by processing, environmental conditions, and inhibitors, new methodologies are required to study these pivotal enzymes individually. Here, we introduce fluorescence activity-based probes that specifically target three distinct cysteine protease subfamilies: aleurain-like proteases, cathepsin B-like proteases, and vacuolar processing enzymes. We applied protease activity profiling with these new probes on Arabidopsis (Arabidopsis thaliana) protease knockout lines and agroinfiltrated leaves to identify the probe targets and on other plant species to demonstrate their broad applicability. These probes revealed that most commercially available protease inhibitors target unexpected proteases in plants. When applied on germinating seeds, these probes reveal dynamic activities of aleurain-like proteases, cathepsin B-like proteases, and vacuolar processing enzymes, coinciding with the remobilization of seed storage proteins.

RNA-Seq analysis of rye-grass transcriptomic response to an herbicide inhibiting acetolactate-synthase identifies transcripts linked to non-target-site-based resistance

Non-target-site resistance (NTSR) to herbicides that disrupts agricultural weed control is a worldwide concern for food security. NTSR is considered a polygenic adaptive trait driven by differential gene regulation in resistant plants. Little is known about its genetic determinism, which precludes NTSR diagnosis and evolutionary studies. We used Illumina RNA-sequencing to investigate transcriptomic differences between plants from the global major weed rye-grass sensitive or resistant to the acetolactate-synthase (ALS) inhibiting herbicide pyroxsulam. Plants were collected before and along a time-course after herbicide application. De novo transcriptome assembly yielded a resource (LOLbase) including 92,381 contigs representing potentially active transcripts that were assigned putative annotations. Early effects of ALS inhibition consistent with the literature were observed in resistant and sensitive plants, proving LOLbase data were relevant to study herbicide response. Comparison of resistant and sensitive plants identified 30 candidate NTSR contigs. Further validation using 212 plants resistant or sensitive to pyroxsulam and/or to the ALS inhibitors iodosulfuron + mesosulfuron confirmed four contigs (two cytochromes P450, one glycosyl-transferase and one glutathione-S-transferase) were NTSR markers which combined expression levels could reliably identify resistant plants. This work confirmed that NTSR is driven by differential gene expression and involves different mechanisms. It provided tools and foundation for subsequent NTSR investigations.

Effects of the novel pyrimidynyloxybenzoic herbicide ZJ0273 on enzyme activities, microorganisms and its degradation in Chinese soils

Enzyme activity and microbial population in soils have important roles in keeping soil fertility. ZJ0273 is a novel pyrimidynyloxybenzoic-based herbicide, which was recently developed in China. The effect of ZJ0273 on soil enzyme activity and microbial population in two different soils was investigated in this study for the first time. The protease activity was significantly inhibited by ZJ0273 and this inhibiting effect gradually weakened after 60-day incubation. The results also showed that ZJ0273 had different stimulating effects on the activities of dehydrogenase, urease, and catalase. Dehydrogenase was consistently stimulated by all the applied concentrations of ZJ0273. The stimulating effect on urease weakened after 60-day incubation. Catalase activity was subject to variations during the period of the experiments. The results of microbial population showed that the number of bacteria and actinomycetes increased in ZJ0273-treated soil compared with the control after 20 days of incubation, while fungal number decreased after only 10 days of incubation in soils. DT50 (half-life value) and k (degradation rate constant) of ZJ0273 in S1 (marine-fluvigenic yellow loamy soil) and S2 (Huangshi soil) were found 69.31 and 49.50 days and 0.010 and 0.014 day(-1), respectively.

RNA-Seq analysis of rye-grass transcriptomic response to an herbicide inhibiting acetolactate-synthase identifies transcripts linked to non-target-site-based resistance

Non-target-site resistance (NTSR) to herbicides that disrupts agricultural weed control is a worldwide concern for food security. NTSR is considered a polygenic adaptive trait driven by differential gene regulation in resistant plants. Little is known about its genetic determinism, which precludes NTSR diagnosis and evolutionary studies. We used Illumina RNA-sequencing to investigate transcriptomic differences between plants from the global major weed rye-grass sensitive or resistant to the acetolactate-synthase (ALS) inhibiting herbicide pyroxsulam. Plants were collected before and along a time-course after herbicide application. De novo transcriptome assembly yielded a resource (LOLbase) including 92,381 contigs representing potentially active transcripts that were assigned putative annotations. Early effects of ALS inhibition consistent with the literature were observed in resistant and sensitive plants, proving LOLbase data were relevant to study herbicide response. Comparison of resistant and sensitive plants identified 30 candidate NTSR contigs. Further validation using 212 plants resistant or sensitive to pyroxsulam and/or to the ALS inhibitors iodosulfuron + mesosulfuron confirmed four contigs (two cytochromes P450, one glycosyl-transferase and one glutathione-S-transferase) were NTSR markers which combined expression levels could reliably identify resistant plants. This work confirmed that NTSR is driven by differential gene expression and involves different mechanisms. It provided tools and foundation for subsequent NTSR investigations.

Fermentation and alternative oxidase contribute to the action of amino acid biosynthesis-inhibiting herbicides

Acetolactate synthase inhibitors (ALS-inhibitors) and glyphosate (GLP) are two classes of herbicide that act by the specific inhibition of an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. The physiological effects that are detected after application of these two classes of herbicides are not fully understood in relation to the primary biochemical target inhibition, although they have been well documented. Interestingly, the two herbicides' toxicity includes some common physiological effects suggesting that they kill the treated plants by a similar pattern despite targeting different enzymes. The induction of aerobic ethanol fermentation and alternative oxidase (AOX) are two examples of these common effects. The objective of this work was to gain further insight into the role of fermentation and AOX induction in the toxic consequences of ALS-inhibitors and GLP. For this, Arabidopsis T-DNA knockout mutants of alcohol dehydrogenase (ADH) 1 and AOX1a were used. The results found in wild-type indicate that both GLP and ALS-inhibitors reduce ATP production by inducing fermentation and alternative respiration. The main physiological effects in the process of herbicide activity upon treated plants were accumulation of carbohydrates and total free amino acids. The effects of the herbicides on these parameters were less pronounced in mutants compared to wild-type plants. The role of fermentation and AOX regarding pyruvate availability is also discussed.

Protein kinase GCN2 mediates responses to glyphosate in Arabidopsis

BACKGROUND

The increased selection pressure of the herbicide glyphosate has played a role in the evolution of glyphosate-resistance in weedy species, an issue that is becoming a threat to global agriculture. The molecular components involved in the cellular toxicity response to this herbicide at the expression level are still unidentified.

RESULTS

In this study, we identify the protein kinase GCN2 as a cellular component that fosters the action of glyphosate in the model plant Arabidopsis thaliana. Comparative studies using wild-type and gcn2 knock-out mutant seedlings show that the molecular programme that the plant deploys after the treatment with the herbicide, is compromised in gcn2. Moreover, gcn2 adult plants show a lower inhibition of photosynthesis, and both seedlings and adult gcn2 plants accumulate less shikimic acid than wild-type after treatment with glyphosate.

CONCLUSIONS

These results points to an unknown GCN2-dependent factor involved in the cascade of events triggered by glyphosate in plants. Data suggest either that the herbicide does not equally reach the target-enzyme in a gcn2 background, or that a decreased flux in the shikimate pathway in a gcn2 plants minimize the impact of enzyme inhibition.