Compatibility of ascorbate-glutathione cycle enzymes in cyanobacteria against low and high UV-B exposures, simultaneously exposed to low and high doses of chlorpyrifos

Managing arsenic (V) toxicity by phosphate supplementation in rice seedlings: modulations in AsA-GSH cycle and other antioxidant enzymes

The toxic and non-essential metalloid arsenic (As) is ubiquitous in the environment with its absorption from the soil into the plants' roots posing detrimental effects on the crop plants and hence the food availability and food security are also threatened. The present study was intended to reduce the As-induced toxicity in rice seedlings (Oryza sativa L.) by phosphate (PO43-). For this, three concentrations of potassium phosphate (KH2PO4), 50, 100 and 150 μM were supplemented along with 50 μM As exposure to hydroponically grown 7-day-old rice seedlings. Supplementation of PO43- significantly recovered arsenic-induced diminutions in growth parameters and photosynthetic pigment contents which were due to the significant increase in superoxide radical (SOR, O2•¯) and hydrogen peroxide (H2O2). Supplementation of 50 μM PO43- could significantly increase the activity of APX (ascorbate peroxidase) and GR (glutathione reductase) while 100 μM PO43- could increase the activity of DHAR (dehydroascorbate reductase) and monodehydroascorbate reductase (MDHAR). As the amount of PO43- was increased, the ratio of AsA/DHA (reduced to oxidized ascorbate) and GSH/GSSG (reduced to oxidized glutathione) was increased significantly due to increase in the reduced form of the non-enzymes i.e. AsA and GSH. The activity of SOD (superoxide dismutase) and GPX (guaiacol peroxidase) decreased significantly after a substantive increase in their activities due to As stress while the CAT (catalase) activity further enhanced after the supplementation of 50 and 100 μM PO43-. Thus, the As-induced oxidative stress in the rice seedlings was managed by concerted modulations in the activities of SOD, GPX, CAT and AsA-GSH cycle enzymes and metabolites.

Regulation of antioxidant defense and glyoxalase systems in cyanobacteria

Oxidative stress is common consequence of abiotic stress in plants as well as cyanobacteria caused by generation of reactive oxygen species (ROS), an inevitable product of respiration and photosynthetic electron transport. ROS act as signalling molecule at low concentration however, when its production exceeds the endurance capacity of antioxidative defence system, the organisms suffer oxidative stress. A highly toxic metabolite, methylglyoxal (MG) is also produced in cyanobacteria in response to various abiotic stresses which consequently augment the ensuing oxidative damage. Taking recourse to the common lineage of eukaryotic plants and cyanobacteria, it would be worthwhile to explore the regulatory role of glyoxalase system and antioxidative defense mechanism in combating abiotic stress in cyanobacteria. This review provides comprehensive information on the complete glyoxalase system (GlyI, GlyII and GlyIII) in cyanobacteria. Furthermore, it elucidates the recent understanding regarding the production of ROS and MG, noteworthy link between intracellular MG and ROS and its detoxification via synchronization of antioxidants (enzymatic and non-enzymatic) and glyoxalase systems using glutathione (GSH) as common co-factor.

Mitigation of zinc toxicity through differential strategies in two species of the cyanobacterium Anabaena isolated from zinc polluted paddy field

The present study describes the physiological and biochemical mechanisms of zinc tolerance in two heterocytous cyanobacteria i.e. Anabaena doliolum and Anabaena oryzae, treated with their respective LC₅₀ concentrations of zinc (3 and 4.5 mg L^-1) for eight days. The feedbacks were examined in terms of growth, metabolism, zinc exclusion, zinc accumulation, oxidative stress, antioxidants and metallothionein contents. Although the growth and metabolic activities were reduced in both the cyanobacterium, maximum adversity was noticed in A. doliolum. The higher order of abnormalities in A. doliolum was attributed to excessive accumulation of zinc and enhanced reactive oxygen species (ROS) production. However, the comparatively higher growth and metabolic activities of A. oryzae were ascribed to the lower accumulation of zinc as a result of released polysaccharides mediated zinc exclusion, synthesis of zinc chelating metallothioneins and subsequent less production of ROS. The oxidative stress and macromolecular damages were prominent in both the cyanobacterium but the condition was much harsher in A. doliolum which may be explained by its comparatively low antioxidative enzyme activities (SOD, APX and GR) and smaller amount of ascorbate-glutathione-tocopherol contents than that of A. oryzae. However, sustenance of 50% growth by A. doliolum under zinc stress despite severe cellular damages was attributed to the enhanced synthesis of phenolics, flavonoids, and proline. Thus, differential zinc tolerance in A. doliolum and A. oryzae is possibly the outcome of their distinct mitigation strategies. Although the two test organisms followed pseudo second order kinetics model during zinc biosorption yet they exhibited differential zinc biosorption capacity. The cyanobacterium A. oryzae was found to be more efficient in removing zinc as compared to A. doliolum and this efficiency makes A. oryzae a promising candidate for the phycoremediation of zinc polluted environments.

Nostoc muscorum and Phormidium foveolarum differentially respond to butachlor and UV-B stress

Present study deals with responses of two cyanobacteria viz. Nostoc muscorum and Phormidium foveolarum against butachlor [2-chloro-2,6-diethyl-N-(butoxymethyl) acetanilide] (low dose; 5 µg mL^-1 and high dose; 10 µg mL^-1) and UV-B (7.2 kJ m^-2) alone, and in combination. Butachlor and UV-B exposure, alone and in combination, suppressed growth of both the cyanobacteria. This was accompanied by inhibitory effect on whole cell oxygen evolution and photosynthetic electron transport activities. Both the stressors induced the oxidative stress as there was significant increase in superoxide radical (O₂ ^·-) and hydrogen peroxide (H₂O₂) contents resulting into increased lipid peroxidation and electrolyte leakage. In N. muscorum, low dose of butachlor and UV-B alone increased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), while activity of all these enzymatic antioxidants declined significantly at treatments with high dose of butachlor alone, and with low and high doses of butachlor and UV-B in combination. In P. foveolarum, enhanced activity of SOD, CAT and POD (except POD at high dose of butachlor and UV-B combination) was noticed. Ascorbate level in N. muscorum declined progressively with increasing intensity of stress while in P. foveolarum varied response was noticed. Proline contents increased progressively under tested stress in both the organisms. Overall results suggest that N. muscorum was more sensitive than P. foveolarum against butachlor and UV-B stresses. Hence, P. foveolarum may be preferred in paddy field for sustainable agriculture.

Hydrogen gas alleviates toxic effects of cadmium in Brassica campestris seedlings through up-regulation of the antioxidant capacities: Possible involvement of nitric oxide

Hydrogen gas (H₂) has been shown as an important factor in plant tolerance to abiotic stresses, but the underlying mechanisms remain unclear. In the present study, the effects of H₂ and its interaction with nitric oxide (NO) on alleviating cadmium (Cd) stress in Brassica campestris seedlings were investigated. NO donor (SNP) or hydrogen-rich water (HRW) treatment showed a significant improvement in growth of Cd-stressed seedlings. Cd treatment upregulated both endogenous NO and H₂ (36% and 66%, respectively), and the increase of H₂ was prior to NO increase. When treated with NO scavenger (PTIO) or NO biosynthesis enzyme inhibitors (L-NAME and Gln), HRW-induced alleviation under Cd stress was prevented. Under Cd stress, HRW pretreatment significantly enhanced the NO accumulation, and together up-regulated the activity of NR (nitrate reductase) and expression of NR. HRW induced lower reactive oxygen species (ROS), higher AsA content, enhanced activity of POD (peroxidase) and SOD (superoxide dismutase) in seedling roots were inhibited by PTIO, L-NAME and Gln. Through proteomic analysis, the level of 29 proteins were changed in response to H₂ and NO-induced amelioration of Cd stress. Nearly half of them were involved in oxidation-reduction processes (about 20%) or antioxidant enzymes (approximately 20%). These results strongly indicate that in Cd-stressed seedlings, pretreatment with HRW induces the accumulation of H₂ (biosynthesized or permeated), which further stimulates the biosynthesis of NO through the NR pathway. Finally, H₂ and NO together enhance the antioxidant capabilities of seedlings in response to Cd toxicity.

Kojic acid-mediated damage responses induce mycelial regeneration in the basidiomycete Hypsizygus marmoreus

Mechanical damage can induce fruiting body production in fungi. In this study, the antioxidant kojic acid (KA) was found to enhance injured mycelial regeneration and increase fruiting body production in Hypsizygus marmoreus. KA reduced the level of reactive oxygen species (ROS), which are harmful to mycelia when excessively generated by mechanical damage. Moreover, KA increased catalase and superoxide dismutase activities and glutathione and ascorbic acid contents by up-regulating antioxidant gene expression. These results suggest that KA promotes mycelial regeneration in response to damage by activating a “stress signal” and enhances the ability of H. marmoreus to resist oxidative damage by invoking the antioxidant system. In addition, KA increased the content of extracellular ATP, which serves as a “stress signal” in response to injury, and modulated ROS signaling, decreasing NADPH oxidase gene expression and ROS levels in the mycelial-regeneration stage. KA treatment also up-regulated the MAPK, Ca²⁺ and oxylipin pathways, suggesting their involvement in the damage response. Furthermore, laccase and cellulase activities were stimulated by KA at different developmental stages. These results demonstrate that KA regulates gene expression and activates pathways for mycelial wound healing, regeneration of damaged mycelia and reproductive structure formation in the basidiomycete H. marmoreus.

Cadmium-Induced Hydrogen Accumulation Is Involved in Cadmium Tolerance in Brassica campestris by Reestablishment of Reduced Glutathione Homeostasis

Hydrogen gas (H2) was recently proposed as a therapeutic antioxidant and signaling molecule in clinical trials. However, the underlying physiological roles of H2 in plants remain unclear. In the present study, hydrogen-rich water (HRW) was used to characterize the physiological roles of H2 in enhancing the tolerance of Brassica campestris against cadmium (Cd). The results showed that both 50 μM CdCl2 and 50%-saturated HRW induced an increase of endogenous H2 in Brassica campestris seedlings, and HRW alleviated Cd toxicity related to growth inhibition and oxidative damage. Seedlings supplied with HRW exhibited increased root length and reduced lipid peroxidation, similar to plants receiving GSH post-treatment. Additionally, seedlings post-treated with HRW accumulated higher levels of reduced glutathione (GSH) and ascorbic acid (AsA) and showed increased GST and GPX activities in roots. Molecular evidence illustrated that the expression of genes such as GS, GR1 and GR2, which were down-regulated following the addition of Cd, GSH or BSO, could be reversed to varying degrees by the addition of HRW. Based on these results, it could be proposed that H2 might be an important regulator for enhancing the tolerance of Brassica campestris seedlings against Cd, mainly by governing reduced glutathione homeostasis.

Ecotoxicity of two organophosphate pesticides chlorpyrifos and dichlorvos on non-targeting cyanobacteria Microcystis wesenbergii

Organophosphate pesticides (OPs), as a replacement for the organochlorine pesticides, are generally considered non-toxic to plants and algae. Chlorpyrifos and dichlorvos are two OPs used for pest control all over the world. In this study, the dose-response of cyanobacteria Microcystis wesenbergii on OPs exposure and the stimulating effect of OPs with and without phosphorus source were investigated. The results showed that high concentrations of chlorpyrifos and dichlorvos caused significant decrease of chlorophyll a content. The median inhibitory concentrations (EC50) of chlorpyrifos and dichlorvos at 96 h were 15.40 and 261.16 μmol L(-1), respectively. Growth of M. wesenbergii under low concentration of OPs (ranged from 1/10,000 to 1/20 EC50), was increased by 35.85 % (chlorpyrifos) and 41.83 % (dichlorvos) at 120 h, respectively. Correspondingly, the highest enhancement on the maximum quantum yield (F v/F m) was 4.20 % (24 h) and 9.70 % (48 h), respectively. Chlorophyll fluorescence kinetics, known as O-J-I-P transients, showed significant enhancements in the O-J, J-I, and I-P transients under low concentrations of dichlorvos at 144 h, while enhancements of chlorophyll fluorescence kinetics induced by low concentrations of chlorpyrifos were only observed in the J-I transient at 144 h. Significant decreases of chlorophyll content, F v/F m and O-J-I-P transients with OPs as sole phosphorus source were found when they were compared with inorganic phosphate treatments. The results demonstrated an evidently hormetic dose-response of M. wesenbergii to both chlorpyrifos and dichlorvos, where high dose (far beyond environmental concentrations) exposure caused growth inhibition and low dose exposure induced enhancement on physiological processes. The stimulating effect of two OPs on growth of M. wesenbergii was negligible under phosphate limitation.

Low and high doses of UV-B differentially modulate chlorpyrifos-induced alterations in nitrogen metabolism of cyanobacteria

The present study assessed the comparative responses on the specific growth rate, nitrogen metabolism and enzymes associated with nitrogen metabolism in two nitrogen fixing cyanobacteria-Nostoc muscorum and Phormidium foveolarum exposed to two UV-B doses (low; UV-BL: 0.5472kJm(-2) and high; UV-BH: 5.472kJm(-2)) and two doses of the insecticide chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate; low i.e. CPL, 1µgml(-1) and high i.e. CPH, 2µgml(-1)) singly and in combination. The specific growth rate, NO3(-) and NO2(-) uptake, nitrate assimilating enzymes - nitrate reductase and nitrite reductase and ammonium assimilating enzymes - glutamine synthetase and glutamate synthase were severely affected when treated either with CPH or/and UV-BH while glutamate dehydrogenase exhibited a stimulatory response. CPL also reduced all the measured parameters (except GDH activity) after 24h, however, a stimulatory effect was observed after 72h due to an increase in nitrogen metabolism (and other antioxidant) enzymes during this period. UV-BL did not cause significant alteration in the studied parameters while in combination with CP doses, it either alleviated the inhibitory effects or further enhanced the CPL induced activities of these enzymes (except GDH). Overall results indicate the resistant nature of P. foveolarum against the inhibitory doses of UV-B and chlorpyrifos in comparison to N. muscorum.

Evaluation of the oxidative deoxyribonucleic acid damage biomarker 8-hydroxy-2'-deoxyguanosine in the urine of leukemic children by micellar electrokinetic capillary chromatography

Determining the level of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidative DNA damage biomarker, is vital to the study of clinical pathogenesis and drug toxicity. The principal limitation of capillary electrophoresis (CE) with UV detection is its low sensitivity. To overcome this shortcoming, we developed a micellar electrokinetic capillary chromatography (MEKC) with solid-phase extraction (SPE) for urinary 8-OHdG analysis. The sensitivity of MEKC-UV was improved using a reasonable UV system, injection mode, and SPE. The parameters affecting MEKC and SPE were also optimized. The calibration curve was linear within the range from 1 to 500 μg L(-1). The limits of detection and quantification were 0.27 μg L(-1) and 0.82 μg L(-1), respectively. Interday and intraday precision were both <5.6%. The recovery of 8-OHdG in urine ranged from 94.5% to 103.2%. This method was used to measure urinary 8-OHdG from eight normal children, eight newly diagnosed leukemic children, and eight leukemic children undergoing chemotherapy. The results show that the proposed method can be used to assess oxidative stress in patients and the side effects of chemotherapeutic drugs by measuring urinary 8-OHdG.