Homoglutathione synthetase and glutathione synthetase in drought-stressed cowpea leaves: expression patterns and accumulation of low-molecular-weight thiols

Promotion of Growth and Physiological Characteristics in Water-Stressed Triticum aestivum in Relation to Foliar-Application of Salicylic Acid

The present work reports the assessment of the effectiveness of a foliar-spray of salicylic acid (SA) on growth attributes, biochemical characteristics, antioxidant activities and osmolytes accumulation in wheat grown under control (100% field capacity) and water stressed (60% field capacity) conditions. The total available water (TAW), calculated for a rooting depth of 1.65 m was 8.45 inches and readily available water (RAW), considering a depletion factor of 0.55, was 4.65 inches. The water contents corresponding to 100 and 60% field capacity were 5.70 and 1.66 inches, respectively. For this purpose, seeds of two wheat cultivars (Fsd-2008 and S-24) were grown in pots subjected to water stress. Water stress at 60% field capacity markedly reduced the growth attributes, photosynthetic pigments, total soluble proteins (TSP) and total phenolic contents (TPC) compared with control. However, cv. Fsd-2008 was recorded as strongly drought-tolerant and performed better compared to cv. S-24, which was moderately drought tolerant. However, water stress enhanced the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and membrane electrolyte leakage (EL) and modulated the activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as accumulation of ascorbic acid (AsA), proline (Pro) and glycine betaine (GB) contents. Foliar-spray with salicylic acid (SA; 0, 3 mM and 6 mM) effectively mitigated the adverse effects of water stress on both cultivars. SA application at 6 mM enhanced the shoot and root length, as well as their fresh and dry weights, and improved photosynthetic pigments. SA foliage application further enhanced the activities of antioxidant enzymes (SOD, POD, and CAT) and nonenzymatic antioxidants such as ascorbic acid and phenolics contents. However, foliar-spray of SA reduced MDA, H2O2 and membrane permeability in both cultivars under stress conditions. The results of the present study suggest that foliar-spray of salicylic acid was effective in increasing the tolerance of wheat plants under drought stress in terms of growth attributes, antioxidant defense mechanisms, accumulation of osmolytes, and by reducing membrane lipid peroxidation.

A GSHS-like gene from Lycium chinense maybe regulated by cadmium-induced endogenous salicylic acid and overexpression of this gene enhances tolerance to cadmium stress in Arabidopsis

A GSHS gene, LcGSHS , was cloned from L. chinense for the first time. Evidence is presented here that endogenous SA accumulation maybe important for the regulation of LcGSHS expression level. Glutathione (GSH) plays a pivotal role in heavy metal detoxification. GSH synthetase (GSHS) catalyzes the rate-limiting step of GSH synthesis in plants. Salicylic acid (SA) is one of the important plant hormones, which plays a critical role in triggering plant responses to different stresses such as cadmium (Cd) stress. Until now, little has been done to explore the relationship among the accumulation of endogenous SA, GSHS transcript levels and the GSH content in plants under Cd treatment and we will investigate this link in this study. The chlorophyll content, transcripts level of LcGSHS gene, endogenous SA accumulation, GSH accumulation and Cd concentration in the leaves of Lycium chinense were studied under different treatment conditions. Endogenous SA, LcGSHS transcript expression and GSH content can be induced by Cd treatment in L. chinense, however, reduced by co-treatment with 2-aminoindan-2-phosphonic acid (AIP), an inhibitor of SA biosynthesis. Strong staining was observed in the leaves of Arabidopsis expressing ProLcGSHS::GUS under Cd stress and the staining was reduced by co-treatment with AIP. The transgenic Arabidopsis expressing ProLcGSHS::LcGSHS also showed greater tolerance to Cd stress than wild types. Evidence was presented here that under Cd stress, GSH accumulation occurred via enhanced LcGSHS gene expression and the SA signaling cascade was involved in this accumulation. Furthermore, the overexpression of LcGSHS in transgenic Arabidopsis resulted in greater tolerance to Cd stress than wild-type lines.

Cadmium-induced hydrogen sulfide synthesis is involved in cadmium tolerance in Medicago sativa by reestablishment of reduced (homo)glutathione and reactive oxygen species homeostases

Until now, physiological mechanisms and downstream targets responsible for the cadmium (Cd) tolerance mediated by endogenous hydrogen sulfide (H₂S) have been elusive. To address this gap, a combination of pharmacological, histochemical, biochemical and molecular approaches was applied. The perturbation of reduced (homo)glutathione homeostasis and increased H₂S production as well as the activation of two H₂S-synthetic enzymes activities, including _L-cysteine desulfhydrase (LCD) and _D-cysteine desulfhydrase (DCD), in alfalfa seedling roots were early responses to the exposure of Cd. The application of H₂S donor sodium hydrosulfide (NaHS), not only mimicked intracellular H₂S production triggered by Cd, but also alleviated Cd toxicity in a H₂S-dependent fashion. By contrast, the inhibition of H₂S production caused by the application of its synthetic inhibitor blocked NaHS-induced Cd tolerance, and destroyed reduced (homo)glutathione and reactive oxygen species (ROS) homeostases. Above mentioned inhibitory responses were further rescued by exogenously applied glutathione (GSH). Meanwhile, NaHS responses were sensitive to a (homo)glutathione synthetic inhibitor, but reversed by the cotreatment with GSH. The possible involvement of cyclic AMP (cAMP) signaling in NaHS responses was also suggested. In summary, LCD/DCD-mediated H₂S might be an important signaling molecule in the enhancement of Cd toxicity in alfalfa seedlings mainly by governing reduced (homo)glutathione and ROS homeostases.

Endogenous hydrogen sulfide enhances salt tolerance by coupling the reestablishment of redox homeostasis and preventing salt-induced K⁺ loss in seedlings of Medicago sativa

Despite the external application of hydrogen sulfide (H2S) conferring plant tolerance against various environmental cues, the physiological significance of l-cysteine desulfhydrase (L-DES)-associated endogenous H2S production involved in salt-stress signaling was poorly understood. To address this gap, the participation of in planta changes of H2S homeostasis involved in alfalfa salt tolerance was investigated. The increasing concentration of NaCl (from 50 to 300 mM) progressively caused the induction of total l-DES activity and the increase of endogenous H2S production. NaCl-triggered toxicity symptoms (175 mM), including seedling growth inhibition and lipid peroxidation, were alleviated by sodium hydrosulfide (NaHS; 100 μM), a H2S donor, whereas aggravated by an inhibitor of l-DES or a H2S scavenger. A weaker or negative response was observed in lower or higher dose of NaHS. Further results showed that endogenous l-DES-related H2S modulated several genes/activities of antioxidant defence enzymes, and also regulated the contents of antioxidant compounds, thus counterbalancing the NaCl-induced lipid peroxidation. Moreover, H2S maintained K(+)/Na(+) homeostasis by preventing the NaCl-triggered K(+) efflux, which might be result form the impairment of SKOR expression. Together, our findings indicated that endogenous H2S homeostasis enhance salt tolerance by coupling the reestablishment of redox balance and restraining K(+) efflux in alfalfa seedlings.

A central role for thiols in plant tolerance to abiotic stress

Abiotic stress poses major problems to agriculture and increasing efforts are being made to understand plant stress response and tolerance mechanisms and to develop new tools that underpin successful agriculture. However, the molecular mechanisms of plant stress tolerance are not fully understood, and the data available is incomplete and sometimes contradictory. Here, we review the significance of protein and non-protein thiol compounds in relation to plant tolerance of abiotic stress. First, the roles of the amino acids cysteine and methionine, are discussed, followed by an extensive discussion of the low-molecular-weight tripeptide, thiol glutathione, which plays a central part in plant stress response and oxidative signalling and of glutathione-related enzymes, including those involved in the biosynthesis of non-protein thiol compounds. Special attention is given to the glutathione redox state, to phytochelatins and to the role of glutathione in the regulation of the cell cycle. The protein thiol section focuses on glutaredoxins and thioredoxins, proteins with oxidoreductase activity, which are involved in protein glutathionylation. The review concludes with a brief overview of and future perspectives for the involvement of plant thiols in abiotic stress tolerance.

Haem oxygenase-1 is involved in salicylic acid-induced alleviation of oxidative stress due to cadmium stress in Medicago sativa

This work examines the involvement of haem oxygenase-1 (HO-1) in salicylic acid (SA)-induced alleviation of oxidative stress as a result of cadmium (Cd) stress in alfalfa (Medicago sativa L.) seedling roots. CdCl(2) exposure caused severe growth inhibition and Cd accumulation, which were potentiated by pre-treatment with zinc protoporphyrin (ZnPPIX), a potent HO-1 inhibitor. Pre-treatment of plants with the HO-1 inducer haemin or SA, both of which could induce MsHO1 gene expression, significantly reduced the inhibition of growth and Cd accumulation. The alleviation effects were also evidenced by a decreased content of thiobarbituric acid-reactive substances (TBARS). The antioxidant behaviour was confirmed by histochemical staining for the detection of lipid peroxidation and the loss of plasma membrane integrity. Furthermore, haemin and SA pre-treatment modulated the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), and guaiacol peroxidase (POD), or their corresponding transcripts. Significant enhancement of the ratios of reduced/oxidized homoglutathione (hGSH), ascorbic acid (ASA)/dehydroascorbate (DHA), and NAD(P)H/NAD(P)(+), and expression of their metabolism genes was observed, consistent with a decreased reactive oxygen species (ROS) distribution in the root tips. These effects are specific for HO-1, since ZnPPIX blocked the above actions, and the aggravated effects triggered by SA plus ZnPPIX were differentially reversed when carbon monoxide (CO) or bilirubin (BR), two catalytic by-products of HO-1, was added. Together, the results suggest that HO-1 is involved in the SA-induced alleviation of Cd-triggered oxidative stress by re-establishing redox homeostasis.

Disruption of redox homeostasis and induction of apoptosis by suppression of glutathione synthetase expression in a mammalian cell line

The stable HepG2 transfectants anti-sensing expression of the glutathione synthetase (GS) gene exhibited delayed cell growth and increased reactive oxygen species (ROS) level. After the treatment with hydrogen peroxide, the intracellular ROS level was much higher in the stable transfectants than in the vector control cells. However, the GSH levels decreased more significantly in the stable transfectants than in the vector control cells, in the presence of hydrogen peroxide. Hydrogen peroxide-induced apoptosis of the stable transfectants was notably higher than that of the vector control cells. The GS anti-sense RNAs rendered the HepG2 cells more sensitive to growth arrest caused by glucose deprivation. They also sensitized the HepG2 cells to cadmium chloride (Cd) and nitric oxide (NO)-generating sodium nitroprusside (SNP). In brief, the results confirm that GS plays an important role in the defense of the human hepatoma cells against oxidative stress by reducing apoptosis and maintaining redox homeostasis.