Reactive oxygen species (ROS) have multifaceted roles in the orchestration of plant gene expression and gene-product regulation. Cellular redox homeostasis is considered to be an “integrator” of information from metabolism and the environment controlling plant growth and acclimation responses, as well as cell suicide events. The different ROS forms influence gene expression in specific and sometimes antagonistic ways. Low molecular antioxidants (e.g., ascorbate, glutathione) serve not only to limit the lifetime of the ROS signals but also to participate in an extensive range of other redox signaling and regulatory functions. In contrast to the low molecular weight antioxidants, the “redox” states of components involved in photosynthesis such as plastoquinone show rapid and often transient shifts in response to changes in light and other environmental signals. Whereas both types of “redox regulation” are intimately linked through the thioredoxin, peroxiredoxin, and pyridine nucleotide pools, they ...

Redox Regulation in Photosynthetic Organisms: Signaling, Acclimation, and Practical Implications

Plants cannot survive without glutathione (γ-glutamylcysteinylglycine) or γ-glutamylcysteine-containing homologues. The reasons why this small molecule is indispensable are not fully understood, but it can be inferred that glutathione has functions in plant development that cannot be performed by other thiols or antioxidants. The known functions of glutathione include roles in biosynthetic pathways, detoxification, antioxidant biochemistry and redox homeostasis. Glutathione can interact in multiple ways with proteins through thiol-disulphide exchange and related processes. Its strategic position between oxidants such as reactive oxygen species and cellular reductants makes the glutathione system perfectly configured for signalling functions. Recent years have witnessed considerable progress in understanding glutathione synthesis, degradation and transport, particularly in relation to cellular redox homeostasis and related signalling under optimal and stress conditions. Here we outline the key recent advances and discuss how alterations in glutathione status, such as those observed during stress, may participate in signal transduction cascades. The discussion highlights some of the issues surrounding the regulation of glutathione contents, the control of glutathione redox potential, and how the functions of glutathione and other thiols are integrated to fine-tune photorespiratory and respiratory metabolism and to modulate phytohormone signalling pathways through appropriate modification of sensitive protein cysteine residues.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2011.02400.x

Glutathione in plants: an integrated overview.

https://www.cell.com/trends/plant-science/pdf/S1360-1385(08)00299-9.pdf

The relationship between metal toxicity and cellular redox imbalance

Tolerance of plants to abiotic stressors such as drought and salinity is triggered by complex multicomponent signaling pathways to restore cellular homeostasis and promote survival. Major plant transcription factor families such as bZIP, NAC, AP2/ERF, and MYB orchestrate regulatory networks underlying abiotic stress tolerance. Sucrose non-fermenting 1-related protein kinase 2 and mitogen-activated protein kinase pathways contribute to initiation of stress adaptive downstream responses and promote plant growth and development. As a convergent point of multiple abiotic cues, cellular effects of environmental stresses are not only imbalances of ionic and osmotic homeostasis but also impaired photosynthesis, cellular energy depletion, and redox imbalances. Recent evidence of regulatory systems that link sensing and signaling of environmental conditions and the intracellular redox status have shed light on interfaces of stress and energy signaling. ROS (reactive oxygen species) cause severe cellular damage by peroxidation and de-esterification of membrane-lipids, however, current models also define a pivotal signaling function of ROS in triggering tolerance against stress. Recent research advances suggest and support a regulatory role of ROS in the cross talks of stress triggered hormonal signaling such as the abscisic acid pathway and endogenously induced redox and metabolite signals. Here, we discuss and review the versatile molecular convergence in the abiotic stress responsive signaling networks in the context of ROS and lipid-derived signals and the specific role of stomatal signaling.

/pdf/tolerance-to-drought-and-salt-stress-in-plants-unraveling-4cledpu8xz.pdf

Tolerance to drought and salt stress in plants: Unraveling the signaling networks.

The environmental stress is a major area of scientific concern because it constraints plant as well as crop productivity. This situation has been further worsened by anthropogenic activities. Therefore, there is a much scientific saddle on researchers to enhance crop productivity under environmental stress in order to cope with the increasing food demands. The abiotic stresses such as salinity, drought, cold, and heat negatively influence the survival, biomass production and yield of staple food crops. According to an estimate of FAO, over 6 % of the world’s land is affected by salinity. Thus, salinity stress appears to be a major constraint to plant and crop productivity. Here, we review our understanding of salinity impact on various aspects of plant metabolism and its tolerance strategies in plants.

Effect of salinity stress on plants and its tolerance strategies: a review.

Aims and methods
The molecular mechanisms and signal transduction pathways of hydrogen sulfide (H2S) in plant biology are still unclear. Here, by using pharmacological and biochemical approaches, we report that H2S promotes germination and alleviates salinity damage involving nitric oxide (NO) pathway.

Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway

Summary
In Arabidopsis thaliana, a family of four genes (HY1, HO2, HO3 and HO4) encode haem oxygenase (HO), and play a major role in phytochrome chromophore biosynthesis. To characterize the contribution of the various haem oxygenase isoforms involved in salt acclimation, the effects of NaCl on seed germination and primary root growth in Arabidopsis wild-type and four HO mutants (hy1-100, ho2, ho3 and ho4) were compared. Among the four HO mutants, hy1-100 displayed maximal sensitivity to salinity and showed no acclimation response, whereas plants over-expressing HY1 (35S:HY1) exhibited tolerance characteristics. Mild salt stress stimulated biphasic increases in RbohD transcripts and production of reactive oxygen species (ROS) (peaks I and II) in wild-type. ROS peak I-mediated HY1 induction and subsequent salt acclimation were observed, but only ROS peak I was seen in the hy1-100 mutant. A subsequent test confirmed the causal relationship of salt acclimation with haemin-induced HY1 expression and RbohD-derived ROS peak II formation. In atrbohD mutants, haemin pre-treatment resulted in induction of HY1 expression, but no similar response was seen in hy1-100, and no ROS peak II or subsequent salt acclimatory responses were observed. Together, the above findings suggest that HY1 plays an important role in salt acclimation signalling, and requires participation of RbohD-derived ROS peak II.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2011.04488.x

Evidence of Arabidopsis salt acclimation induced by up‐regulation of HY1 and the regulatory role of RbohD‐derived reactive oxygen species synthesis

Using pharmacological and biochemical approaches, the role of cadmium (Cd)-induced carbon monoxide (CO) release and the relationship between CO and oxidative stress conferred by Cd exposure in the root tissues of alfalfa (Medicago sativa) plants were investigated. Cd treatments showed a dose-dependent enhancement in lipid peroxidation. Both 100 and 200 microm CdCl(2 )treatments caused the increase of CO release, which is consistent with the changes in the activity of the CO synthetic enzyme heme oxygenase (HO) and its HO-1 transcript. A 100 microm CdCl(2) exposure enhanced the formation of nonprotein thiols (NPT), and reduced glutathione (GSH) to oxidized glutathione (GSSG), which was potentiated by the pretreatment of CO scavenger hemoglobin (Hb). Plants pretreated for 6 h with 50% CO-saturated aqueous solution, which induced the rapid endogenous CO release followed by a gradual decrease when subsequently exposed to 100 microm CdCl(2) for 72 h, effectively decreased oxidative damage. Meanwhile, CO pretreatment modulated several enzymes responsible for GSH metabolism, thus resulting in the partial restoration of GSH : GSSG ratio, which was significantly blocked by Hb. These results are suggestive of a role for CO release as a signal element for the alleviation of Cd-induced oxidative damage by modulating glutathione metabolism.

https://www.jstor.org/stable/pdfplus/4627248.pdf

Carbon monoxide alleviates cadmium-induced oxidative damage by modulating glutathione metabolism in the roots of Medicago sativa

Indole acetic acid (IAA) is an important regulator of adventitious rooting via the activation of complex signaling cascades. In animals, carbon monoxide (CO), mainly generated by heme oxygenases (HOs), is a significant modulator of inflammatory reactions, affecting cell proliferation and the production of growth factors. In this report, we show that treatment with the auxin transport inhibitor naphthylphthalamic acid prevented auxin-mediated induction of adventitious rooting and also decreased the activity of HO and its by-product CO content. The application of IAA, HO-1 activator/CO donor hematin, or CO aqueous solution was able to alleviate the IAA depletion-induced inhibition of adventitious root formation. Meanwhile, IAA or hematin treatment rapidly activated HO activity or HO-1 protein expression, and CO content was also enhanced. The application of the HO-1-specific inhibitor zinc protoporphyrin IX (ZnPPIX) could inhibit the above IAA and hematin responses. CO aqueous solution treatment was able to ameliorate the ZnPPIX-induced inhibition of adventitious rooting. Molecular evidence further showed that ZnPPIX mimicked the effects of naphthylphthalamic acid on the inhibition of adventitious rooting, the down-regulation of one DnaJ-like gene (CSDNAJ-1), and two calcium-dependent protein kinase genes (CSCDPK1 and CSCDPK5). Application of CO aqueous solution not only dose-dependently blocked IAA depletion-induced inhibition of adventitious rooting but also enhanced endogenous CO content and up-regulated CSDNAJ-1 and CSCDPK1/5 transcripts. Together, we provided pharmacological, physiological, and molecular evidence that auxin rapidly activates HO activity and that the product of HO action, CO, then triggers the signal transduction events that lead to the auxin responses of adventitious root formation in cucumber (Cucumis sativus).

Sheng Xu

Papers

Hydrogen sulfide enhances alfalfa (Medicago sativa) tolerance against salinity during seed germination by nitric oxide pathway

Evidence of Arabidopsis salt acclimation induced by up‐regulation of HY1 and the regulatory role of RbohD‐derived reactive oxygen species synthesis

Carbon monoxide alleviates cadmium-induced oxidative damage by modulating glutathione metabolism in the roots of Medicago sativa

The Heme Oxygenase/Carbon Monoxide System Is Involved in the Auxin-Induced Cucumber Adventitious Rooting Process

The Heme Oxygenase/Carbon Monoxide System Is Involved in the Auxin-Induced Cucumber Adventitious