Reviews Environmental Contamination and Toxicology

Climate change is an invisible, silent killer with calamitous effects on living organisms As the sessile organism, plants experience a diverse array of abiotic stresses during ontogenesis The relentless climatic changes amplify the intensity and duration of stresses, making plants dwindle to survive Plants convert 1-2% of consumed oxygen into reactive oxygen species (ROS), in particular, singlet oxygen (1O2), superoxide radical (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), etc as a byproduct of aerobic metabolism in different cell organelles such as chloroplast, mitochondria, etc The regulatory network comprising enzymatic and non-enzymatic antioxidant systems tends to keep the magnitude of ROS within plant cells to a non-damaging level However, under stress conditions, the production rate of ROS increases exponentially, exceeding the potential of antioxidant scavengers instigating oxidative burst, which affects biomolecules and disturbs cellular redox homeostasis ROS are similar to a double-edged sword; and, when present below the threshold level, mediate redox signaling pathways that actuate plant growth, development, and acclimatization against stresses The production of ROS in plant cells displays both detrimental and beneficial effects However, exact pathways of ROS mediated stress alleviation are yet to be fully elucidated Therefore, the review deposits information about the status of known sites of production, signaling mechanisms/pathways, effects, and management of ROS within plant cells under stress In addition, the role played by advancement in modern techniques such as molecular priming, systems biology, phenomics, and crop modeling in preventing oxidative stress, as well as diverting ROS into signaling pathways has been canvassed

Abiotic Stress and Reactive Oxygen Species: Generation, Signaling, and Defense Mechanisms

In plants, there is a complex and multilevel network of the antioxidative system (AOS) operating to counteract harmful reactive species (RS), the foremost important of which are reactive oxygen species (ROS), and maintain homeostasis within the cell. Specific AOSs for plant cells are, first and foremost, enzymes of the glutathione-ascorbate cycle (Asc-GSH), followed by phenolic compounds and lipophilic antioxidants like carotenoids and tocopherols. Evidence that plant cells have excellent antioxidative defense systems is their ability to survive at H2O2 concentrations incompatible with animal cell life. For the survival of stressed plants, it is of particular importance that AOS cooperate and participate in redox reactions, therefore, providing better protection and regeneration of the active reduced forms. Considering that plants abound in antioxidant compounds, and humans are not predisposed to synthesize the majority of them, new fields of research have emerged. Antioxidant potential of plant compounds has been exploited for anti-aging formulations preparation, food fortification and preservation but also in designing new therapies for diseases with oxidative stress implicated in etiology.

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The Significance of Reactive Oxygen Species and Antioxidant Defense System in Plants: A Concise Overview.

Various environmental stresses singly or in combination generate excess amounts of reactive oxygen species (ROS), leading to oxidative stress and impaired redox homeostasis. Generation of ROS is the obvious outcome of abiotic stresses and is gaining importance not only for their ubiquitous generation and subsequent damaging effects in plants but also for their diversified roles in signaling cascade, affecting other biomolecules, hormones concerning growth, development, or regulation of stress tolerance. Therefore, a good balance between ROS generation and the antioxidant defense system protects photosynthetic machinery, maintains membrane integrity, and prevents damage to nucleic acids and proteins. Notably, the antioxidant defense system not only scavenges ROS but also regulates the ROS titer for signaling. A glut of studies have been executed over the last few decades to discover the pattern of ROS generation and ROS scavenging. Reports suggested a sharp threshold level of ROS for being beneficial or toxic, depending on the plant species, their growth stages, types of abiotic stresses, stress intensity, and duration. Approaches towards enhancing the antioxidant defense in plants is one of the vital areas of research for plant biologists. Therefore, in this review, we accumulated and discussed the physicochemical basis of ROS production, cellular compartment-specific ROS generation pathways, and their possible distressing effects. Moreover, the function of the antioxidant defense system for detoxification and homeostasis of ROS for maximizing defense is also discussed in light of the latest research endeavors and experimental evidence.

https://www.mdpi.com/1422-0067/21/22/8695/pdf

Regulation of ROS Metabolism in Plants under Environmental Stress: A Review of Recent Experimental Evidence.

Investigating the enzymatic and non-enzymatic antioxidant defense by applying iron oxide nanoparticles in Dracocephalum moldavica L. plant under salinity stress

Exposure to a variety of environmental factors such as salinity, drought, metal toxicity, extreme temperature, air pollutants, ultraviolet-B (UV-B) radiation, pesticides, and pathogen infection leads to subject oxidative stress in plants, which in turn affects multiple biological processes via reactive oxygen species (ROS) generation. ROS include hydroxyl radicals, singlet oxygen, and hydrogen peroxide in the plant cells and activates signaling pathways leading to some changes of physiological, biochemical, and molecular mechanisms in cellular metabolism. Excessive ROS, however, cause oxidative stress, a state of imbalance between the production of ROS and the neutralization of free radicals by antioxidants, resulting in damage of cellular components including lipids, nucleic acids, metabolites, and proteins, which finally leads to the death of cells in plants. Thus, maintaining a physiological level of ROS is crucial for aerobic organisms, which relies on the combined operation of enzymatic and nonenzymatic antioxidants. In order to improve plants’ tolerance towards the harsh environment, it is vital to reinforce the comprehension of oxidative stress and antioxidant systems. In this review, recent findings on the metabolism of ROS as well as the antioxidative defense machinery are briefly updated. The latest findings on differential regulation of antioxidants at multiple levels under adverse environment are also discussed here.

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The Roles of Environmental Factors in Regulation of Oxidative Stress in Plant.

The homeostasis of resistance (R) proteins in plants must be tightly regulated to ensure precise activation of plant immune response upon pathogen infection, while avoiding autoimmunity and growth defects when plants are uninfected. The ubiquitin-proteasome system (UPS) is a universal mechanism of protein homeostasis control in eukaryotes, and it was shown to be one of the mechanisms that regulate R protein levels. In particular, E3 ubiquitin ligase directly interacts with substrate proteins and largely determines the substrate specificity targeted for ubiquitination and proteasomal degradation. It was known that CPR1, an F-box protein in the SCF E3 complex, functions as a negative regulator of plant immunity through targeting R proteins SNC1 and RPS2 for degradation. However, whether or not those R proteins are targeted by other E3 ligases is unclear. In this paper, MUSE16, which encodes a RING-type E3 ligase, was isolated from a forward genetic screen and suggested to be a negative regulator of plant immunity. Unlike CPR1, knocking out MUSE16 in Arabidopsis thaliana alone is not enough to result in defense related dwarfism, since only RPS2 out of the tested R proteins accumulated in muse16. Thus, our study identified another E3 ligase involved in NLR R protein degradation, supporting that Ub-mediated degradation is a fine-tuned mechanism for regulating the turnover of R proteins in plants, and the same R protein can be targeted by different E3 ligases for its homeostasis regulation.

The homeostasis of R protein RPS2 is negatively regulated by the RING-type E3 ligase MUSE16.

Malaria remains a serious threat to global public health. With poor efficacies of vaccines and the emergence of drug resistance, novel strategies to control malaria are urgently needed.We developed erythrocyte membrane-camouflaged nanoparticles loaded with artemether based on the growth characteristics of Plasmodium. The nanoparticles could capture the merozoites to inhibit them from repeatedly infecting normal erythrocytes, owing to the interactions between merozoites and heparin-like molecules on the erythrocyte membrane. Modification with a phosphatidylserine-targeting peptide (CLIPPKF) improved the drug accumulation in infected red blood cells (iRBCs) from the externalized phosphatidylserine induced by Plasmodium infection. In Plasmodium berghei ANKA strain (pbANKA)-infected C57BL/6 mice, the nanoparticles significantly attenuated Plasmodium-induced inflammation, apoptosis, and anemia. We observed reduced weight variation and prolonged survival time in pbANKA-challenged mice, and the nanoparticles showed good biocompatibility and negligible cytotoxicity.Erythrocyte membrane-camouflaged nanoparticles loaded with artemether were shown to provide safe and effective protection against Plasmodium infection. 

https://jnanobiotechnology.biomedcentral.com/counter/pdf/10.1186/s12951-022-01709-x

Zhouqing He

Papers

The Roles of Environmental Factors in Regulation of Oxidative Stress in Plant.

The homeostasis of R protein RPS2 is negatively regulated by the RING-type E3 ligase MUSE16.

Erythrocyte membrane with CLIPPKF as biomimetic nanodecoy traps merozoites and attaches to infected red blood cells to prevent Plasmodium infection