Ágnes Gallé

Plasma-activated water (PAW) seed treatment is an emerging green technology that enhances plant germination and growth; however, its role in drought stress tolerance remains unclear. In this study, pea (Pisum sativum L.) seeds were treated with PAW (10 mg L⁻¹ nitrite, 30 mg L⁻¹ nitrate, pH 3.9), Zn-enriched PAW (PAW+Zn; 6 mg L⁻¹ H₂O₂, 19 mg L⁻¹ nitrite, 20 mg L⁻¹ nitrate, 14 mg L⁻¹ Zn, pH 4.7), distilled water, or Zn-enriched distilled water. Subsequently, three-week-old plants were subjected to osmotic stress using PEG8000 (20% w/v). PAW induced partial hilum opening and mild seed coat damage, while PA(W+Zn) increased nitric oxide accumulation. Both treatments enhanced nutrient bioavailability and shootward translocation, particularly of Zn and Fe. Under stress, PAW promoted the formation of larger but thinner leaves, indicating adaptive morphological responses. However, stomatal conductance, relative water content, photosynthesis, and starch accumulation remained unaffected. Unchanged proline levels and reduced soluble sugars suggest that classical osmotic acclimation was not induced by PAW treatments. Instead, both PAW and PA(W+Zn) increased abscisic acid (ABA) levels and PsDHN2 expression, indicating activation of ABA-dependent stress signalling, likely mediated by nitrate-, nitrite-, and H₂O₂-derived signals. Tissue-specific cytokinin responses and enhanced antioxidant enzyme activities (superoxide dismutase, catalase) further suggest the establishment of a primed state. Overall, PAW-based seed treatments induce complex physiological and molecular responses, with morphological, ionic, hormonal, and antioxidant processes contributing to stress adaptation in pea.

Plant glutathione peroxidase-like (GPXL) enzymes are thiol-based peroxidases that reduce H₂O₂ or hydroperoxides to water or alcohols using electrons principally from thioredoxin. Arabidopsis thaliana possesses eight isoenzymes (AtGPXL1−8) located in different plant organelles and have various roles in redox-dependent processes. The determination of the redox potential of 6-day-old T-DNA insertional mutants (Atgpxl1–Atgpxl8) using a cytosolic redox-sensitive fluorescent probe (roGFP2) uncovered more oxidized redox status in the shoot and/or root of the untreated mutants, except for Atgpxl5. To investigate the involvement of AtGPXLs in the growth and abiotic stress responses of seedlings, the 4-day-old Atgpxls were exposed to salt and osmotic stresses for two weeks. The evaluation of the reactive oxygen species (ROS) levels of untreated 18-day-old plants using fluorescent microscopy revealed the elevated accumulation of total ROS in the shoots and, in some cases, the roots of the mutants. Regarding the growth of roots, both the length of primary roots and/or the number of lateral roots were affected by the mutation of AtGPXLs. A strong negative correlation was observed between the ROS level of wild type shoots and the development of lateral roots, but it was altered in mutants, while in the case of Atgpxl1, Atgpxl5, and Atgpxl7 seedlings, it disappeared; in other mutants (Atgpxl4, Atgpxl6, and Atgpxl8), the correlation became stronger. Our analysis underpins the discrete role of AtGPXL enzymes in controlling the growth and development of plants by fine tuning the ROS contents and redox status in an organ-specific way. Differences in root phenotype and metabolic activity between Atgpxl mutants and wild type plants highlight the essential role of AtGPXLs in ROS processing to support growth, which is particularly evident when one GPXL isoenzyme is absent or its activity is reduced, both under normal and abiotic stress conditions.

Plant glutathione peroxidase-like (GPXL) enzymes are thiol-based peroxidases that reduce H₂O₂ or hydroperoxides to water or alcohols using electrons principally from thioredoxin. Arabidopsis thaliana possesses eight isoenzymes located in different plant’s organelles and have various roles in redox-dependent processes. Determination of the redox potential of 6-day-old Atgpxl1-8 T-DNA insertional mutants using cytosolic redox sensitive fluorescent probe (roGFP2) uncovered more oxidized redox status in shoot and/or root of the untreated mutants except Atgpxl5. To investigate the involvement of AtGPXLs in growth and abiotic stress responses of seedlings, the 4-day-old Atgpxls were exposed to salt- and osmotic stresses for two weeks. Evaluation of the reactive oxygen species (ROS) levels of untreated 18-day-old plants using fluorescent microscopy revealed the elevated accumulation of total ROS in the shoots and, in some cases, the roots of the mutants. Regarding the growth of roots, both the length of primary roots and/or number of lateral roots were affected by mutation of AtGPXLs. Strong negative correlation was observed between the ROS level of wild type shoots and development of lateral roots, but it was altered in mutants: while in case of Atgpxl1, -5 and -7 seedlings it disappeared, in other mutants (Atgpxl4, -6 and -8) the correlation became stronger. Our analysis underpins the discrete role of AtGPXL enzymes in controlling the growth and development of plants by fine-tuning the ROS contents and redox status in an organ-specific way. Differences in root phenotype and metabolic activity between Atgpxl mutants and wild-type plants highlight the essential role of AtGPXLs in ROS processing to support growth, which is particularly evident when one GPXL isoenzyme is absent or its activity is reduced, both under normal and abiotic stress conditions.

Glutathione transferases (GSTs) are one of the most versatile multigenic enzyme superfamilies. In our experiments, the involvement of the genotype-specific induction of GST genes and glutathione- or redox-related genes in pathways regulating salt-stress tolerance was examined in tomato cultivars (Solanum lycopersicum Moneymaker, Mobil, and Elán F1). The growth of the Mobil plants was adversely affected during salt stress (100 mM of NaCl), which might be the result of lowered glutathione and ascorbate levels, a more positive glutathione redox potential (E_GSH), and reduced glutathione reductase (GR) and GST activities. In contrast, the Moneymaker and Elán F1 cultivars were able to restore their growth and exhibited higher GR and inducible GST activities, as well as elevated, non-enzymatic antioxidant levels, indicating their enhanced salt tolerance. Furthermore, the expression patterns of GR, selected GST, and transcription factor genes differed significantly among the three cultivars, highlighting the distinct regulatory mechanisms of the tomato genotypes during salt stress. The correlations between E_GSH and gene expression data revealed several robust, cultivar-specific associations, underscoring the complexity of the stress response mechanism in tomatoes. Our results support the cultivar-specific roles of distinct GST genes during the salt-stress response, which, along with WRKY3, WRKY72, DREB1, and DREB2, are important players in shaping the redox status and the development of a more efficient stress tolerance in tomatoes.

Glutathione transferases (GSTs) are enzymes that catalyse modifications and conjugations of a range of organic and often cytotoxic compounds. GST enzymes with many functions—such as their conjugation activity against herbicides and their metabolites—can be induced and show light and circadian determination. The enzyme family, which is widespread in its function, also shows great diversity in its structure, which has been linked to its enzyme kinetic characteristics and physiological role at many points. In this study, we aimed to find out the role of different glutathione transferases in the herbicide responses to flumioxazin, as well as to determine how the antioxidant and detoxification response to herbicide treatment changes in the presence and absence of light. One of the herbicide treatments was carried out during the light period in the morning (9:00 a.m.), and the other before the end of the dark period (4:00 a.m.). The decrease in the maximal quantum efficiency of PS II and the reduction in the chlorophyll concentration supported the effect of the herbicide on Papaver rhoeas. In the guaiacol peroxidase POD and GST activity, there were large differences between the cultivated plants and the weed; both enzyme activities were much higher in the case of wheat. According to the activity of the antioxidant defence enzymes and GST gene expression data, the application of the photosynthesis inhibitor herbicide, flumioxazin, in the dark could allow the wheat antioxidant defence to switch on before the herbicide effect could appear in the light period. Phi and tau group GSTs were transcriptionally upregulated by the treatments in wheat plants (especially TaGSTU1B), while fewer changes were detectable in poppy weed (PrGSTU4). Based on our results, in the background of the greater and more successful response to flumioxazin may be—among other things—the higher degree of variability of the GSTU genes of wheat compared to poppies.

Fusarium graminearum and F. culmorum cause the most widespread wheat disease Fusarium head blight (FHB). The present study describes that the Fusarium inoculation of the wheat spikes caused systemic changes in the key elements of the antioxidant/detoxification defence system in the flag leaf during the grain filling period in wheat lines differing in biotic stress susceptibility to explore changes in some components of the response. According to our data, the inoculation with both F. graminearum and F. culmorum at the anthesis changed significantly the activities of superoxide dismutase (SOD) and guaiacol peroxidase (POD) enzymes, as well as the glutathione transferase (GST) activity in the flag leaves of the selected wheat lines approx. two weeks later after the infection. In silico approach supported the expressional up-regulation of various GST genes upon Fusarium infection. Based on our results, GST sequences TaGSTF26 and TaGSTU120 were among the series of important stress response genes, which were transcriptionally up-regulated, thus possibly playing a role in the systemic response to Fusarium infection, where TaGSTF26 might have an important role in the successful defence. These GSTs can serve as effective markers of the detoxification process for breeders and plant protection in the future.

The presence or absence of light is one of the most significant environmental factors affecting plant growth and defence. Therefore, the selection of the most appropriate time of application may maximize the benefits of photosynthetic inhibitors. In this work, the concentration and daytime or night-time-dependent effects of bentazon were tested in soybean and common ragweed. The recommended dose (1440 g ha⁻¹) and also half the recommended dose significantly reduced the maximum quantum yield (F_v/F_m) and increased H₂O₂ levels in common ragweed. Interestingly, bentazon did not change F_v/F_m in soybean. The activity of superoxide dismutase changed in a dose-dependent manner only in common ragweed. The activity of ascorbate peroxidase, catalase and glutathione S-transferase (GST), as well as the contents of ascorbate (AsA) and glutathione (GSH) did not change significantly in this plant species. In soybean, alterations in H₂O₂ levels were lower but GST and APX activity, as well as AsA and GSH levels were higher compared to common ragweed. At the same time, the rate of lipid peroxidation and ion leakage increased upon bentazon, and were higher in the light phase-treated leaves in the case of both plant species. These results can contribute to optimizing the effects and uses of herbicides in agriculture.

Glutathione transferases (GSTs) play a crucial role in detoxification processes due to the fact of their glutathione (GSH) conjugating activity, and through glutathione peroxidase or dehydroascorbate reductase (DHAR) activities, they influence the redox state of GSH and ascorbate (AsA). The plant-specific tau (GSTU) group is the largest class of Arabidopsis GSTs, and their members are involved in responses to different abiotic stresses. We investigated the effect of salt stress on two-week-old Arabidopsis thaliana wild-type (Col-0), Atgstu19 and Atgstu24 mutant plants after applying 150 mM NaCl for two days. The Atgstu19 seedlings had lower GST activity and vitality both under control conditions and after salt stress than the wild-type, but the level of total ROS was similar to the Col-0 plants. The GST activity of the knockout Atgstu24 mutant was even higher under control conditions compared to the Col-0 plants, while the ROS level and its vitality did not differ significantly from the wild-type. Analysis of the AtGSTU expression pattern revealed that the mutation in a single AtGSTU gene was accompanied by the up- and downregulation of several other AtGSTUs. Moreover, elevated AsA and GSH levels, an altered GSH redox potential and increased DHAR and glutathione reductase activities could help to compensate for the mutation of AtGSTU genes. The observed changes in the mutants suggest that the investigated isoenzymes influence the redox homeostasis under control conditions and after NaCl treatment in Arabidopsis seedlings. These data indicate for the first time the more general role of a temporary shift of redox status as part of GST mechanisms and regulation.