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.

Osmotic stress induces the overproduction of reactive oxygen species (ROS), leading to oxidative damage to cellular components, with lipid peroxidation being one of the most harmful consequences. Glutathione transferases (GSTs; E.C. 2.5.1.18) play a key role in detoxifying harmful compounds through their glutathione transferase and glutathione peroxidase (GPOX) activities. To investigate the specific roles of GSTs in tomato responses to osmotic stress, two cultivars of Solanum lycopersicum (cv. Mobil and Moneymaker) were treated with increasing concentrations of polyethylene glycol (PEG 6000) over several days. Both cultivars exhibited similar symptoms of severe stress, but their enzymatic activity and the expression of GST genes differed. These gene expression patterns indicate that a specific group of tomato GSTs, including certain Tau and Theta class GSTs (GSTUs and GSTTs), may play an important role in defending against osmotic stress across various tomato varieties. Additionally, the gene expression profiles of the two cultivars likely correspond to the differences observed in their enzymatic activity: elevated GST and GPOX activity in Mobil, but in Moneymaker, solely the GPOX activity was increased. Particular focus was given to the tomato Theta class GSTs (SlGSTTs), known for their GPOX activity and substrate preference for lipid peroxides. Marked upregulation was observed of SlGSTT genes under osmotic stress. Protein modeling and molecular docking suggest that SlGSTT2 and SlGSTT3 isoenzymes may contribute to membrane protection by scavenging different lipid peroxidation products in the peroxisomes.

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.