Reactive oxygen species

Evidence ispresented thatligandin, an intracellular protein involved inthebinding ofsuchanions asbilirubin, indocyanine green, andpenicillin, isidentical toglutathione S-transferase B (EC2.5.1.18), an enzyme catalyzing theconjugation ofglutathione withsuchelec- trophiles as1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4- nitrobenzene, iodomethane, ethacrynic acid,andbromo- sulfophthalein. Theproteins, isolated bydistinct methods, havethesamespecificity forsubstrates andforligands, reactinidentical fashion toantibody pioducedagainst ligandin, bearentirely sinlilar physical characteristics and aminoacidcomposition, andarebothinduced inresponse tophenobarbital. Indocyanine green, oneoftheligands thatisnoteffective asasubstrate, wasshowhtocompeti- tively inhibit theconjugation reaction. Itissuggested that specificity isdirected towardcompoundswithelectrophilic sites. ligandin isacytoplasmic protein found inabundance inthe liver ofrat, man,andother species. Thisprotein iscapable ofbinding noncovalently alarge number ofcompounds, which includes bilirubin, heme,benzyl penicillin, certain steroids, andsuchdyesasbromosulfophthalein

TheIdentity ofGlutathione S-Transferase B withLigandin, aMajorBinding Protein ofLiver

The natural environment of plants is composed of a complex set of abiotic stresses and their ability to respond to these stresses is highly flexible and finely balanced through the interaction between signaling molecules. In this review, we highlight the integrated action between reactive oxygen species (ROS) and reactive nitrogen species (RNS), particularly nitric oxide (NO), involved in the acclimation to different abiotic stresses. Under stressful conditions, the biosynthesis transport and the metabolism of ROS and NO influence plant response mechanisms. The enzymes involved in ROS and NO synthesis and scavenging can be found in different cells compartments and their temporal and spatial locations are determinant for signaling mechanisms. Both ROS and NO are involved in long distances signaling (ROS wave and GSNO transport), promoting an acquired systemic acclimation to abiotic stresses. The mechanisms of abiotic stresses response triggered by ROS and NO involve some general steps, as the enhancement of antioxidant systems, but also stress-specific mechanisms, according to the stress type (drought, hypoxia, heavy metals, etc.), and demand the interaction with other signaling molecules, such as MAPK, plant hormones, and calcium. The transduction of ROS and NO bioactivity involves post-translational modifications of proteins, particularly S-glutathionylation for ROS, and S-nitrosylation for NO. These changes may alter the activity, stability, and interaction with other molecules or subcellular location of proteins, changing the entire cell dynamics and contributing to the maintenance of homeostasis. However, despite the recent advances about the roles of ROS and NO in signaling cascades, many challenges remain, and future studies focusing on the signaling of these molecules in planta are still necessary.

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When bad guys become good ones: the key role of reactive oxygen species and nitric oxide in the plant responses to abiotic stress

Plants growing under field conditions are constantly exposed, either simultaneously or sequentially, to more than one abiotic stress factor. Plants have evolved sophisticated sensory systems to perceive a number of stress signals that allow them to activate the most adequate response to grow and survive in a given environment. Recently, cross-stress tolerance (i.e. tolerance to a second, strong stress after a different type of mild primary stress) has gained attention as a potential means of producing stress-resistant crops to aid with global food security. Heat or cold priming-induced cross-tolerance is very common in plants and often results from the synergistic co-activation of multiple stress signalling pathways, which involve reactive nitrogen species (RNS), reactive oxygen species (ROS), reactive carbonyl species (RCS), plant hormones and transcription factors. Recent studies have shown that the signalling functions of ROS, RNS and RCS, most particularly hydrogen peroxide, nitric oxide (NO) and methylglyoxal (MG), provide resistance to abiotic stresses and underpin cross-stress tolerance in plants by modulating the expression of genes as well as the post-translational modification of proteins. The current review highlights the key regulators and mechanisms underlying heat or cold priming-induced cross-stress tolerance in plants, with a focus on ROS, MG and NO signalling, as well as on the role of antioxidant and glyoxalase systems, osmolytes, heat-shock proteins (HSPs) and hormones. Our aim is also to provide a comprehensive idea on the topic for researchers using heat or cold priming-induced cross-tolerance as a mechanism to improve crop yields under multiple abiotic stresses.

Heat or cold priming-induced cross-tolerance to abiotic stresses in plants: key regulators and possible mechanisms

Recent studies on applications of aquatic weed plants in phytoremediation of wastewater: A review article

High arsenic (As) concentrations are toxic to all the living organisms and the cellular response to this metalloid requires the involvement of cell signaling agents, such as nitric oxide (NO). The As toxicity and NO signaling were analyzed in Pistia stratiotes leaves. Plants were exposed to four treatments, for 24 h: control; SNP [sodium nitroprusside (NO donor); 0.1 mg L-1]; As (1.5 mg L-1) and As + SNP (1.5 and 0.1 mg L-1, respectively). The absorption of As increased the concentration of reactive oxygen species and triggered changes in the primary metabolism of the plants. While photosynthesis and photorespiration showed sharp decrease, the respiration process increased, probably due to chemical similarity between arsenate and phosphate, which compromised the energy status of the cell. These harmful effects were reflected in the cellular structure of P. stratiotes, leading to the disruption of the cells and a possible programmed cell death. The damages were attenuated by NO, which was able to integrate central plant physiological processes, with increases in non-photochemical quenching and respiration rates, while the photorespiration level decreased. The increase in respiratory rates was essential to achieve cellular homeostasis by the generation of carbon skeletons and metabolic energy to support processes involved in responses to stress, as well to maintaining the structure of organelles and prevent cell death. Overall, our results provide an integrated view of plant metabolism in response to As, focusing on the central role of NO as a signaling agent able to change the whole plant physiology.

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The Involvement of Nitric Oxide in Integration of Plant Physiological and Ultrastructural Adjustments in Response to Arsenic.

Nitric oxide increased lettuce’s tolerance to salinity by restoring its hormonal balance, consequently reducing Na + accumulation and activating defense mechanisms that allowed the attenuation of ionic, oxidative, and osmotic stresses. Agricultural crops are continually threatened by soil salinity. The plant’s ability to tolerate soil salinity can be increased by treatment with the signaling molecule nitric oxide (NO). Involvement of NO in plant metabolism and its interactions with phytohormones have not been fully described, so knowledge about the role of this radical in signaling pathways remains fragmented. In this work, Lactuca sativa (lettuce) plants were subjected to four treatments: (1) control (nutrient solution); (2) SNP [nutrient solution containing 70 μM sodium nitroprusside (SNP), an NO donor]; (3) NaCl (nutrient solution containing 80 mM NaCl); or (4) SNP + NaCl (nutrient solution containing SNP and NaCl). The plants were exposed to these conditions for 24 h, and then, the roots and leaves were collected and used to evaluate biochemical parameters (reactive oxygen species (ROS) production, cell membrane damage, cell death, antioxidant enzymes activities, and proline concentration), physiological parameters (pigments’ concentration and gas-exchange measurements), and phytohormone content. To evaluate growth, tolerance index, and nutrient concentration, the plants were exposed to the treatments for 3 days. L sativa exposure to NaCl triggered ionic, osmotic, and oxidative stress, which resulted in hormone imbalance, cell death, and decreased growth. These deleterious changes were correlated with Na+ content in the vegetative tissues. Adding NO decreased Na+ accumulation and stabilized the mineral nutrient concentration, which maintained the photosynthetic rate and re-established growth. NO-signaling action also re-established the phytohormones balance and resulted in antioxidant system activation and osmotic regulation, with consequent increase in plants tolerance to the salt.

Nitric oxide and phytohormone interactions in the response of Lactuca sativa to salinity stress.

Phytoremediation of arsenite-contaminated environments: is Pistia stratiotes L. a useful tool?

Nitric oxide (NO) is an important molecule involved in the perception of stress induced by toxic compounds such as arsenic (As). The present study investigated the role of NO applied as sodium nitroprusside (SNP) in cell signalling and the ability of NO to attenuate the toxic effects of As (in the form of sodium arsenate) in water hyacinth (Eichhornia crassipes). Water hyacinth plants were collected and assigned to one of the following treatments: control; 100 μM SNP; 20 μM As; or 20 μM As + 100 μM SNP. The plants remained under these conditions for 0, 4, 12, and 24 h. After each time interval, the plants were collected and As absorption, production of reactive oxygen species (ROS), integrity of membranes, and antioxidant enzyme activities were evaluated. The plants were able to absorb and accumulate large amounts of As, even after only four hours of exposure to the pollutant. The absorption and bioaccumulation factor of As was even greater when plants were exposed to both As and SNP. The accumulation of As triggered increases in ROS production and cell membrane damage. In the presence of SNP, the tolerance index to As increased and damage was mitigated. Therefore, from the present work, it was possible to conclude that exogenous NO influenced the ability of plants to tolerate As; this finding has implications for phytoremediation in areas contaminated by As.

Arsenic toxicity: cell signalling and the attenuating effect of nitric oxide in Eichhornia crassipes

Antioxidant enzymes are important components in the defense against arsenic (As) stress in plants. Here, we tested the hypothesis that Salvinia molesta, an aquatic fern, counteracts the harmful arsenite (AsIII) effects by activating scavenging reactive oxygen species (ROS) enzymes. Thus, our objective was to investigate the role of the superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX) in S. molesta tolerance to AsIII and indicate the use of this plant in remediation of contaminated water. Plants were grown in nutrient solution at pH 6.5 and exposed to 0, 5, 10, or 20 µM AsIII for 96 h (analyses of As absorption, mineral nutrient content, and relative growth rate) and for 24 h (analyses of oxidative stress indicators and enzymatic antioxidant defenses). In the floating leaves, there was a greater basal activity of the antioxidant enzymes and less accumulation of As than in submerged leaves. The submerged leaves, which function as roots in S. molesta, accumulated more As than floating leaves, and SOD and CAT activities were inhibited. Thus, there was a greater production of ROS and oxidative stress. Our results show that S. molesta presents enzymatic antioxidant defenses to alleviate AsIII toxicity and are more effectives in the floating leaves. These results are important to elucidate the AsIII tolerance mechanisms in S. molesta and the possibility of their use in contamined water phytoremediation. Additional studies exposing plants to more prolonged stress and using AsIII concentrations closer to those found in contaminated environments will confirm this claim.

Fernanda Vidal de Campos

Papers

The Involvement of Nitric Oxide in Integration of Plant Physiological and Ultrastructural Adjustments in Response to Arsenic.

Nitric oxide and phytohormone interactions in the response of Lactuca sativa to salinity stress.

Phytoremediation of arsenite-contaminated environments: is Pistia stratiotes L. a useful tool?

Arsenic toxicity: cell signalling and the attenuating effect of nitric oxide in Eichhornia crassipes

Phytoremediation potential of Salvinia molesta for arsenite contaminated water: role of antioxidant enzymes