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Glutathione (GSH) plays a critical role in plant growth, development and responses to stress. However, the mechanism by which GSH regulates tolerance to cadmium (Cd) stress still remains unclear. Here we show that inhibition of GSH biosynthesis by buthionine sulfoximine (BSO) aggravated Cd toxicity by increasing accumulation of reactive oxygen species (ROS) and reducing contents of nitric oxide (NO) and S-nitrosothiol (SNO) in tomato roots. In contrast, exogenous GSH alleviated Cd toxicity by substantially minimizing ROS accumulation and increasing contents of NO and SNO, and activities of antioxidant enzymes that eventually reduced oxidative stress. GSH-induced enhancement in Cd tolerance was closely associated with the upregulation of transcripts of several transcription factors such as ETHYLENE RESPONSIVE TRANSCRIPTION FACTOR 1 (ERF1), ERF2, MYB1 TRANSCRIPTION FACTOR- AIM1 and R2R3-MYB TRANSCRIPTION FACTOR- AN2, and some stress response genes. In addition, GSH modulated the cellular redox balance through maintaining increased GSH: GSSG and AsA: DHA ratios, and also increased phytochelatins contents. Nonetheless, GSH-induced alleviation of Cd phytotoxicity was also associated with increased sequestration of Cd into cell walls and vacuoles but not with Cd accumulation. Under Cd stress, while treatment with BSO slightly decreased vacuolar fraction of Cd, combined treatment with BSO and GSH noticeably increased that fraction. Our results suggest that GSH increases tomato tolerance to Cd stress not only by promoting the chelation and sequestration of Cd but also by stimulating NO, SNO and the antioxidant system through a redox-dependent mechanism., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Polychlorinated biphenyls (PCBs) are persistent organic pollutants often found in the atmosphere. Phytoremediation of airborne PCBs is an emerging new concept to minimize potential human exposure. However, effects of atmospheric PCBs on plant growth, photosynthesis and antioxidant defence system are poorly understood area. Brassinosteroids have been reported to alleviate different abiotic stresses including organic pollutants-induced stress. Hence, we studied the effects of PCBs and 24-epibrassinolide (EBR) on biomass accumulation, photosynthetic machinery and antioxidant system in tomato plants. PCBs (0.4, 2.0 and 10 μg/l) mist spray significantly decreased dry weight, photosynthesis, chlorophyll contents in a dose dependent manner. Both stomatal and non-stomatal factors were involved in PCBs-induced photosynthetic inhibition. Likewise, the maximal photochemical efficiency of PSII (Fv/Fm), the quantum efficiency of PSII photochemistry (Φ(PSII)) and photochemical quenching coefficient were increasingly decreased by various levels of PCBs, suggesting an induction of photoinhibition. Increased accumulation of H(2)O(2) and O(2)(-) accompanied with high lipid peroxidation confirmed occurrence of oxidative stress upon PCBs exposure. Meanwhile, antioxidant enzymes activity was decreased following exposure to PCBs. Foliar application of EBR (100 nM) increased biomass, photosynthetic capacity, chlorophyll contents and alleviated photoinhibition by enhancing Fv/Fm, Φ(PSII) and qP. EBR significantly decreased harmful ROS accumulation and lipid peroxidation through the induction of antioxidant enzymes activity. Our results suggest a protective role of EBR against PCBs stress which may strengthen phytoremediation approaches by enhancing plant tolerance., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Glutathione is one of the major endogenous antioxidants produced by cells. In plants, glutathione is crucial for both abiotic and biotic stress resistance, and also involved in the detoxification of xenobiotics in many organisms. However, as in vivo evidences of glutathione function are still lacking so far, its roles in plants are still poorly understood. In this study, we investigated the changes of thiols, glutathione homeostasis and transcripts of genes potentially involved in chlorothalonil (CHT) metabolism in tomato (Solanum lycopersicum L.). Two genes (GSH1, GSH2) encoding γ-glutamylcysteine synthetase and glutathione synthetase, respectively, and a gene for glutathione reductase (GR1) involved in glutathione regeneration were silenced by virus induced gene silencing (VIGS) approach. Silencing of GSH1, GSH2 and GR1 decreased glutathione contents and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), but increased CHT residues in plant tissues. The GSH1 and GR1 silenced plants showed the lowest GSH level and ratio of GSH/GSSG, respectively. Transcripts of P450, GST and ABC transporter genes as well as glutathione S-transferase (GST) activity were induced after CHT treatment. However, the increases of these transcripts were compromised in GSH1, GSH2 and GR1 silenced plants. This study indicates that glutathione not only serves as a substrate for CHT conjugation, but is also involved in regulation of transcripts of gene in pesticide metabolism via controlling redox homeostasis., (Published by Elsevier Ltd.)

The present study was carried out to investigate the effects of exogenously applied 24-epibrassinolide (BR) on growth, gas exchange, chlorophyll fluorescence characteristics, lipid peroxidation and antioxidant systems of tomato seedlings grown under different levels (0, 10, 30, 100 and 300μM) of phenanthrene (PHE) and pyrene (PYR) in hydroponics. A concentration-dependent decrease in growth, photosynthetic pigment contents, net photosynthetic rate (Pn), stomatal conductance (Gs), maximal quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (Φ(PSII)), photochemical quenching coefficient (qP) has been observed following PHE and PYR exposure. By contrast, non-photochemical quenching coefficient (NPQ) was increased. PHE was found to induce higher stress than PYR. However, foliar or root application of BR (50nM and 5nM, respectively) alleviated all those depressions with a sharp improvement in the activity of photosynthetic machinery. The activities of guaicol peroxidase (GPOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as content of malondialdehyde (MDA) were increased in a dose-dependent manner under PHE or PYR treatments. Compared with control the highest increments of GPOD, CAT, APX, GR and MDA by PHE/PYR alone treatments were observed following 300μM concentration, which were 67%, 87%, 53%, 95% and 74% by PHE and 42%, 53%, 30%, 86% and 62% by PYR, respectively. In addition, both reduced glutathione (GSH) and oxidized glutathione (GSSG) were induced by PHE or PYR. Interestingly, BR application in either form further increased enzymatic and non enzymatic antioxidants in tomato roots treated with PHE or PYR. Our results suggest that BR has an anti-stress effect on tomato seedlings contaminated with PHE or PYR and this effect is mainly attributed by increased detoxification activity., (Copyright © 2011 Elsevier Ltd. All rights reserved.)