In the present work, bioaugmented zinc oxide nanoparticles (ZnO-NPs) were prepared from aqueous fruit extracts of Myristica fragrans The ZnO-NPs were characterized by different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and thermogravimetric analysis (TGA) The crystallites exhibited a mean size of 4123 nm measured via XRD and were highly pure, while SEM and TEM analyses of synthesized NPs confirmed their spherical or elliptical shape The functional groups responsible for stabilizing and capping of ZnO-NPs were confirmed using FTIR analysis The ζ-size and ζ-potential of synthesized ZnO-NPs were reported as 66 nm and -221 mV, respectively, via the DLS technique can be considered as moderate stable colloidal solution Synthesized NPs were used to evaluate for their possible antibacterial, antidiabetic, antioxidant, antiparasitic, and larvicidal properties The NPs were found to be highly active against bacterial strains both coated with antibiotics and alone Klebsiella pneumoniae was found to be the most sensitive strain against NPs (27 ± 173) and against NPs coated with imipinem (26 ± 15) ZnO-NPs displayed outstanding inhibitory potential against enzymes protein kinase (1223 ± 042), α-amylase (7323 ± 042), and α-glucosidase (6521 ± 049) Overall, the synthesized NPs have shown significant larvicidal activity (773 ± 18) against Aedes aegypti, the mosquitoes involved in the transmission of dengue fever Similarly, tremendous leishmanicidal activity was also observed against both the promastigote (7150 ± 070) and amastigote (6141 ± 071) forms of the parasite The biosynthesized NPs were found to be excellent antioxidant and biocompatible nanomaterials Biosynthesized ZnO-NPs were also used as photocatalytic agents, resulting in 88% degradation of methylene blue dye in 140 min Owing to their eco-friendly synthesis, nontoxicity, and biocompatible nature, ZnO-NPs synthesized from M fragrans can be exploited as potential candidates for biomedical and environmental applications

Green Synthesis of Zinc Oxide (ZnO) Nanoparticles Using Aqueous Fruit Extracts of Myristica fragrans: Their Characterizations and Biological and Environmental Applications.

Roles of the major polyamines (mPA), putrescine, spermidine, and spermine (Spm), in various developmental and physiological processes in plants have been well documented. Recently, there has been increasing focus on the link between mPA metabolism and defense response during plant-stress interactions. Empirical evidence is available for a unique role of Spm, distinct from the other mPA, in eliciting an effective defense response to (a)biotic stresses. Our understanding of the precise molecular mechanism(s) by which Spm modulates these defense mechanisms is limited. Further analysis of recent studies indicates that plant Spm functions differently during biotic and abiotic interactions in the regulation of oxidative homeostasis and phytohormone signaling. Here, we summarize and integrate current knowledge about Spm-mediated modulation of plant defense responses to (a)biotic stresses, highlighting the importance of Spm as a potent plant defense activator with broad-spectrum protective effects. A model is proposed to explain how Spm refines defense mechanisms to tailor an optimal resistance response.

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Spermine Differentially Refines Plant Defense Responses Against Biotic and Abiotic Stresses.

Thermal stress during reproductive development and grain-filling phases is a serious threat to the quality and productivity of grain legumes. The optimum temperature range for grain legume crops is 10−36°C, above which severe losses in grain yield can occur. Various climatic models have simulated that the temperature near the earth’s surface will increase (by up to 4°C) by the end of this century, which will intensify the chances of heat stress in crop plants. The magnitude of damage or injury posed by a high-temperature stress mainly depends on the defence response of the crop and the specific growth stage of the crop at the time of exposure to the high temperature. Heat stress affects grain development in grain legumes because it disintegrates the tapetum layer, which reduces nutrient supply to microspores leading to premature anther dehiscence; hampers the synthesis and distribution of carbohydrates to grain, curtailing the grain-filling duration leading to low grain weight; induces poor pod development and fractured embryos; all of which ultimately reduce grain yield. The most prominent effects of heat stress include a substantial reduction in net photosynthetic rate, disintegration of photosynthetic apparatus and increased leaf senescence. To curb the catastrophic effect of heat stress, it is important to improve heat tolerance in grain legumes through improved breeding and genetic engineering tools and crop management strategies. In this review, we discuss the impact of heat stress on leaf senescence, photosynthetic machinery, assimilate translocation, water relations, grain quality and development processes. Furthermore, innovative breeding, genetic, molecular and management strategies are discussed to improve the tolerance against heat stress in grain legumes.

https://bioone.org/journals/crop-and-pasture-science/volume-68/issue-10%e2%80%9311/CP17012/Heat-stress-in-grain-legumes-during-reproductive-and-grain-filling/10.1071/CP17012.pdf

Heat stress in grain legumes during reproductive and grain-filling phases

Atmospheric pollution is an important concern in urban environments. The impact of urban pollution on the physiological, biochemical and anatomical properties of leaves of oriental plane (Platanus orientalis L.) was studied. The leaves were collected from an urban site (Tehran, Iran) and a non-urban forest park (Chitgar Forest Park). Anatomical (stomata, parenchyma, and cuticle) and physiological (chlorophyll content, enzyme activities) properties were analyzed. The concentrations of Cd (cadmium), Pb (lead), Ni (nickel), and Cr (chromium) in leaves were significantly higher and Zn (zinc) lower at the urban site relative to the forest park. Chlorophyll a, total chlorophyll, and carotenoid content in leaves of the urban site were significantly less than those of the forest park, but there was no significant difference in chlorophyll b. In addition, the activities of superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase in urban leaves were significantly higher than in the leaves of the forest park. In the urban area, leaves experienced a significant decrease in leaf surface area, stomata density, stomata pore area, epidermis, and spongy mesophyll thickness, but a significant increase in cuticle and palisade thicknesses relative to forest park leaves. The increase in enzyme activities may indicate that the trees are attempting to cope with increased reactive oxygen species (ROS) because of pollution-induced stress. Our study suggests that oriental plane trees alter their physiological and anatomical properties when living in a polluted urban environment.

Response of Platanus orientalis leaves to urban pollution by heavy metals

Simple Summary Environmental conditions are subject to unprecedented changes due to recent progressive anthropogenic activities on our planet. Plants, as the frontline of food security, are susceptible to these changes, resulting in the generation of unavoidable byproducts of metabolism (ROS), which eventually affect their productivity. The response of plants to these unfavorable conditions is highly intricate and depends on several factors, among them are the species/genotype tolerance level, intensity, and duration of stress factors. Defensive mechanisms in plant systems, by nature, are concerned primarily with generating enzymatic and non-enzymatic antioxidants. In addition to this, plant-microbe interactions have been found to improve immune systems in plants suffering from drought and salinity stress. Abstract Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

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Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Exogenous auxin type compounds amend PEG-induced physiological responses of pea plants

Drought is a major environmental constrain with a deleterious effect on plant development leading to a considerable reduction of crop productivity worldwide. Wheat is a relatively drought tolerant crop during the vegetative stage. The herbicide Serrate® (Syngenta) is a preparation containing two active chemical substances with different modes of action, which inhibit the biosynthesis of fatty and amino acids. It is commonly used as a systemic and selective chemical agent to control annual grass and broadleaf weeds in cereal crops and particularly in wheat, which is tolerant to Serrate®. Seventeen-day-old wheat seedlings (Triticum aestivum L., cv. Sadovo-1) grown as soil culture under controlled conditions were sprayed with an aqueous solution of Serrate®. Seventy-two hours later the plantlets were subjected to drought stress for seven days to reach a severe water deficit followed by four days of recovery with a normal irrigation regime. Oxidative stress markers, non-enzymatic, and enzymatic antioxidants were analyzed in the leaves of plants from the different treatment groups (herbicide-treated, droughts-stressed, and individuals which were consecutively subjected to both treatments) at 0, 96, and 168 h of drought stress, and after 96 h of recovery. Herbicide treatment did not alter substantially the phenotype and growth parameters of the above-ground plant parts. It provoked a moderate increase in phenolics, thiol-containing compounds, catalase, superoxide dismutase, glutathione reductase, and H2O2. However, significant variations of malondialdehyde, proline, and peroxidase activity caused by the sole application of the herbicide were not detected during the experimental period. Drought and herbicide + drought treatments caused significant growth inhibition, increased oxidative stress markers, and activation of enzymatic and non-enzymatic antioxidant defense reaching the highest levels at 168 h of stress. Plant growth was restored after 96 h of recovery and the levels of the monitored biochemical parameters showed a substantial decline. The herbicide provoked an extra load of oxidative stress-related biochemical components which did not aggravate the phenotypic and growth traits of plants subjected to drought, since they exhibited a good physiological status upon recovery.

https://www.mdpi.com/2223-7747/10/4/733/pdf

Assessment of the Biochemical Responses of Wheat Seedlings to Soil Drought after Application of Selective Herbicide.

Atrazine frequently contaminates soil, groundwater, rivers, and ponds. It is well know that acute doses (1–5 mM) of atrazine induce massive generation of singlet oxygen by blocking photosystem II. The sublethal concentrations of this herbicide, similar to those found in the environment, also reduce growth and disrupt photosynthesis in a long-term aspect, but exact mechanisms remain much uncertain. In this study the effects of environmentally relevant atrazine levels, ranging from 0.1 to 10 μM, on pea plants were characterized for up to 20 days. The plants exposed to continuous influence of atrazine exhibited perturbed redox homeostasis with increases of the lipid peroxides, the total and oxidized glutathione pools and elevated guaiacol peroxidase and glutathione-S-transferase activities. In contrast, the long-term atrazine impact did not affect superoxide dismutase activity whereas the catalase was inhibited. The perturbations of the redox status and the recruitment of the antioxidant machinery imply that the sublethal atrazine concentrations alter the poise between production and scavenging of reactive oxygen species. Taken together these results show that the long-term impact of sublethal atrazine has hallmarks of oxidative stress most probably triggered by generation of singlet oxygen.

Long-term impact of sublethal atrazine perturbs the redox homeostasis in pea ( Pisum sativum L.) plants

The effects of high temperature and the polyamine spermine on the physiological and biochemical status of garden pea plants were investigated. The plants were preliminary treated with 1 mM spermine and 24 h later were subjected for 48 h to conditions with daily temperature up to 38°C. High temperature stress caused more than 20% decrease of leaf pigments content and significant suppression of net photosynthesis rate. An enhanced level of lipid peroxidation was observed in leaves suggesting that oxidative stress occurred. A decrease in the content of free proline, total phenolics, and hydrogen peroxide accompanied by an increase of the activity of catalase, superoxide dismutase, and guaiacol peroxidase was established in plants subjected to high temperature. The harmful physiological effects of high temperature were alleviated by spraying the plants with spermine. The preliminary application of spermine retarded leaf pigment loss and maintained photosynthetic rate and antioxidant enzyme activities, as well as content of non-enzymatic antioxidants.

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Responses of pea plants to heat stress and spermine treatment.

The potential of brassinosteroids to modulate the physiological responses of winter wheat (Triticum aestivum L.) to herbicide stress was evaluated. Young winter wheat seedlings were treated with 24-epibrassinolide (EBL) and 24 h later were sprayed with glyphosate. The physiological responses of treated plants were assessed 14 days after herbicide application. Wheat growth was noticeably inhibited by glyphosate. The herbicide application significantly increased the content of the stress markers proline and malondialdehyde (MDA) evidencing oxidative damage. The content of phenolic compounds was decreased in the herbicide-treated plants. Slight activation of superoxide dismutase (SOD) and catalase (CAT) and considerable increase of glutathione reductase (GR) and guaiacol peroxidase (POX) activities were found. Increased POX and glutathione S-transferase (GST) activities were anticipated to be involved in herbicide detoxification. Conjugation with glutathione in herbicide-treated plants could explain the reduction of thiols suggesting unbalanced redox state. EBL application did not alter the plant growth but a moderate activation of antioxidant defense (POX, GR, and CAT activities and phenolic levels) and detoxifying enzyme GST was observed. The hormonal priming provoked a slight decrease in MDA and proline levels. The results demonstrate that EBL-pretreatment partly restored shoot growth and has a potential to mitigate the oxidative damages in glyphosate-treated plants through activation of the enzymatic antioxidant defense and increase of the phenolic compounds.

Elena Shopova

Papers

Exogenous auxin type compounds amend PEG-induced physiological responses of pea plants

Assessment of the Biochemical Responses of Wheat Seedlings to Soil Drought after Application of Selective Herbicide.

Long-term impact of sublethal atrazine perturbs the redox homeostasis in pea ( Pisum sativum L.) plants

Responses of pea plants to heat stress and spermine treatment.

Modulation of Physiological Stress Response of Triticum aestivum L. to Glyphosate by Brassinosteroid Application.