Chitosan nanoparticles upregulate C and N metabolism in soybean plants grown under elevated levels of atmospheric carbon dioxide.

Despite the wide utilization of chitosan nanoparticles (CSNPs) as a promising approach for sustainable agriculture, their efficiency under elevated CO2 (eCO2), has not been evaluated. The interactive effects of CSNPs and eCO2 were evaluated on the growth and C and N metabolism of soybean plants. Plants were treated with CSNPs and grown under ambient CO2 (410 ppm, aCO2) or eCO2 (645 ppm). Regardless of CO2 level, CSNPs improved the net photosynthetic rate. CSNPs aggravated the effect of eCO2 treatment on the levels of non-structural carbohydrates (i.e., glucose, fructose, sucrose, and starch), especially in shoots, which was inconsistence with the upregulation of carbohydrates metabolizing enzymes. Being the most pivotal energetic and signaling organic compounds in higher plants, the synergistic action of CSNPs and eCO2 on the accumulation of soluble sugars upregulated the N metabolism as indicated by induced activities of nitrate reductase, arginase, glutamate dehydrogenase, glutamine synthetase, and glutamine oxoglutarate aminotransferase which was manifested finally as increased shoot and root total nitrogen content as well as proline and aspartate in roots. At the hormonal level, the coexistence of eCO2 with CSNPs further supports their positive impact on the contents of IAA and, to a lesser extent, GAs. The present data prove that the biofertilization capacity of CSNPs is even more potent under futuristic eCO2 levels and could even further improve the growth and resilience of plants.

Alleviation of gadolinium stress on Medicago by elevated atmospheric CO2 is mediated by changes in carbohydrates, Anthocyanin, and proline metabolism.

Rare earth elements (REE) like Gadolinium (Gd), are increasingly used in industry and agriculture and this is concomitant with the increasingly leaking of Gd into the environment. Under a certain threshold concentration, REE can promote plant growth, however, beyond this concentration, they exert negative effects on plant growth. Moreover, the effect of Gd on plants growth and metabolism under a futuristic climate with increasingly atmospheric CO2 has not yet been studied. To this end, we investigated the effect of soil contamination with Gd (150 mg/kg soil) on the growth, carbohydrates, proline, and anthocyanin metabolism of Medicago plants grown under ambient (aCO2, 410 ppm) or elevated CO2 (eCO2, 720 ppm) concentration. Gd negatively affected the growth and photosynthesis of plants and imposed oxidative stress i.e., increased H2O2 and lipid peroxidation (MDA) level. As defense lines, the level and metabolism of osmoprotectants (soluble sugars and proline) and antioxidants (phenolics, anthocyanins, and tocopherols) were increased under Gd treatment. High CO2 positively affected the growth and metabolism of Medicago plants. Moreover, eCO2 mitigated the negative impacts of Gd on Medicago growth. It further induced the levels of osmoprotectants and antioxidants. In line with increased proline and anthocyanins, their metabolic enzymes (e.g. OAT, P5CS, PAL, and CS) were also increased. This study advances our understanding of how Gd adversely affects Medicago plant growth and metabolism. It also sheds light on the biochemical mechanisms underlying the Gd stress-reducing impact of eCO2.

Improved Mineral Acquisition, Sugars Metabolism and Redox Status after Mycorrhizal Inoculation Are the Basis for Tolerance to Vanadium Stress in C3 and C4 Grasses.

Vanadium (V) can be beneficial or toxic to plant growth and the interaction between arbuscular mycorrhizal fungi (AMF) and V stress was rarely investigated at physiological and biochemical levels of plant groups (C3 and C4) and organs (roots and shoots). We tested the potential of AMF to alleviate the negative effects of V (350 mg V/Kg soil) on shoots and roots of rye and sorghum. Relative to sorghum (C4), rye (C3) showed higher levels of V and lower levels of key elements under V stress conditions. V inhibited growth, photosynthesis, and induced photorespiration (increased HDR & GO activities) and oxidative damage in both plants. AMF colonization reduced V stress by differently mitigating the oxidative stress in rye and sorghum. This mitigation was accompanied with increases in acid and alkaline phosphatase activities in plant roots and increased organic acids and polyphenols exudation into the soil, thus reduced V accumulation (29% and 58% in rye and sorghum shoot, respectively) and improved absorption of mineral nutrients including Ca, Mg and P. AMF colonization improved photosynthesis and increased the sugar accumulation and metabolism. Sugars also acted as a supplier of C skeletons for producing of antioxidants metabolite such as ascorbate. At the antioxidant level, rye was more responsive to the mitigating impact of AMF. Higher antioxidants and detoxification defence system (MTC, GST, phenolics, tocopherols and activities of CAT, SOD and POX) was recorded for rye, while sorghum (C4) improved its GR activity. The C3/C4-specificity was supported by principal component analysis. Together, this study provided both fundamental and applied insights into practical strategies to mitigate the phytotoxicity hazards of V in C3 and C4 grasses. Moreover, our results emphasize the importance of AMF as an environment-friendly factor to alleviate stress effects on plants and to improve growth and yield of unstressed plants.

An actinomycete strain of Nocardiopsis lucentensis reduces arsenic toxicity in barley and maize.

Accumulation of arsenic in plant tissues poses a substantial threat to global crop yields. The use of plant growth-promoting bacterial strains to mitigate heavy metal toxicity has been illustrated before. However, its potential to reduce plant arsenic uptake and toxicity has not been investigated to date. Here, we describe the identification and characterization of a Nocardiopsis lucentensis strain isolated from heavy metal contaminated soil. Inoculation with this bioactive actinomycete strain decreased arsenic root and shoot bioaccumulation in both C3 and C4 crop species namely barley and maize. Upon arsenate treatment, N. lucentensis S5 stimulated root citric acid production and the plant's innate detoxification capacity in a species-specific manner. In addition, this specific strain promoted biomass gain, despite substantial tissue arsenic levels. Detoxification (metallothionein, phytochelatin, glutathione-S-transferase levels) was upregulated in arsenate-exposed shoot and roots, and this response was further enhanced upon S5 supplementation, particularly in barley and maize roots. Compared to barley, maize plants were more tolerant to arsenate-induced oxidative stress (less H2O2 and lipid peroxidation levels). However, barley plants invested more in antioxidative capacity induction (ascorbate-glutathione turnover) to mitigate arsenic oxidative stress, which was strongly enhanced by S5. We quantify and mechanistically discuss the physiological and biochemical basis of N. lucentensis-mediated plant biomass recovery on arsenate polluted soils. Our findings substantiate the potential applicability of a bactoremediation strategy to mitigate arsenic-induced yield loss in crops.

Soil enrichment with actinomycete mitigates the toxicity of arsenic oxide nanoparticles on wheat and maize growth and metabolism.

The use of plant growth-promoting bacteria (PGPB) to enhance plant growth and protection against heavy metal toxicity has been extensively studied. However, its potentiality to reduce arsenate toxicity, a threat to plant growth and metabolism, has been hardly investigated. Moreover, the toxic effect of arsenic oxide nanoparticles (As-NPs) on plants and possible mechanisms for its alleviation has not yet been explored. In this study, the impact of the bioactive actinomycete Streptomyces spp. on the growth, physiology and stress-related metabolites, such as sugars and proline, on As-NPs-stressed wheat and maize plants was investigated. Soil amendment with arsenic oxide nanoparticles (As-NPs) induced the uptake and accumulation of As in the plants of both species, resulting in reduced growth and photosynthesis, but less marked in maize than in wheat plants. Under As-NPs-free conditions, Streptomyces spp. treatment markedly improved growth and photosynthesis in wheat only. The application of Streptomyces spp. reduced As accumulation, recovered the As-NPs-induced growth, photosynthesis inhibition, and oxidative damage in plants of both species. Wheat plants specifically accumulated soluble sugars, while both species accumulated proline. Under As-NPs stress, the ornithine pathway of proline biosynthesis was more important in maize than in wheat plants, while the glutamine pathway was dominant in wheat ones. The addition of Streptomyces spp. further induced the accumulation of proline and starch in both plant species. Overall, despite a different response to Streptomyces spp. under nontoxic conditions, the amendment of as-contaminated soil with Streptomyces spp. induced similar metabolic responses in the two tested species, which trigger stress recovery.

Elevated CO2 differently suppresses the arsenic oxide nanoparticles-induced stress in C3 (Hordeum vulgare) and C4 (Zea maize) plants via altered homeostasis in metabolites specifically proline and anthocyanin metabolism.

Nano-sized arsenic oxide nanoparticles (As2O3-NP) limit crop growth and productivity. As2O3-NP represent a strong environmental hazard. The predicted rise in future atmospheric CO2 could boost plant growth both under optimal and heavy metal stress conditions. So far, the phytotoxicity of As2O3-NP and their interaction with eCO2 were not investigated at physiological and metabolic levels in crop species groups such as C3 and C4. We investigated how eCO2 level (620 ppm) alleviated soil As2O3-NP toxicity induced growth and mitigated oxidative damages through analysing photosynthetic parameters, primary (sugars and amino acids) and secondary (phenolics, flavonoids and anthocyanins) metabolism in C3 (barley) and C4 (maize) plants. Compared to maize, barley accumulated higher As2O3-NP level, which inhibited growth and induced oxidative damage particularly in barley (increased H2O2 and lipid peroxidation). Interestingly, eCO2 differently mitigated As2O3-NP toxicity on photosynthesis, which consequently improved sugar metabolism. Moreover, high carbon availability in eCO2 treated plants directed to produce osmo-protectant (soluble sugars and proline) and antioxidants (anthocyanins and tocopherols). In the line with increased proline and anthocyanins, their metabolism was also improved. Notable differences occurred between the two plant species. The ornithine pathway was preferred in maize while in barley proline accumulation was mainly through glutamate pathway. Moreover, under As2O3-NP stress, barley preferentially accumulated anthocyanins while maize accumulated total phenolics and flavonoids. This work contributes to improving our understanding of the differences in growth, physiological and biochemical responses of major crops of two functional photosynthetic groups (C3 and C4 plants) under ambient and elevated CO2 grown under As2O3-NP stress.

Soil arsenic toxicity differentially impacts C3 (barley) and C4 (maize) crops under future climate atmospheric CO2.

Soil arsenic (As) contamination limits global agricultural productivity. Anthropogenic emissions are causing atmospheric CO2 levels to rise. Elevated CO2 (eCO2) boosts plant growth both under optimal and suboptimal growth conditions. However, the crop-specific interaction between eCO2 and soil arsenic exposure has not been investigated at the whole plant, physiological and biochemical level. Here, we tested the effects of eCO2 (620 ppm) and soil As exposure (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthesis and redox homeostasis in barley (C3) and maize (C4). Compared to maize, barley was more susceptible to soil As exposure at ambient CO2 levels. Barley plants accumulated more As, particularly in roots. As accumulation inhibited plant growth and induced oxidative damage in a species-specific manner. As-exposed barley experienced severe oxidative stress as illustrated by high H2O2 and protein oxidation levels. Interestingly, eCO2 differentially mitigated As-induced stress in barley and maize. In barley, eCO2 exposure reduced photorespiration, H2O2 production, and lipid/protein oxidation. In maize eCO2 exposure led to an upregulation of the ascorbate-glutathione (ASC/GSH)-mediated antioxidative defense system. Combined, this work highlights how ambient and future eCO2 levels differentially affect the growth, physiology and biochemistry of barley and maize crops exposed to soil As pollution.

Actinomycetes Enrich Soil Rhizosphere and Improve Seed Quality as well as Productivity of Legumes by Boosting Nitrogen Availability and Metabolism.

The use of actinomycetes for improving soil fertility and plant production is an attractive strategy for developing sustainable agricultural systems due to their effectiveness, eco-friendliness, and low production cost. Out of 17 species isolated from the soil rhizosphere of legume crops, 4 bioactive isolates were selected and their impact on 5 legumes: soybean, kidney bean, chickpea, lentil, and pea were evaluated. According to the morphological and molecular identification, these isolates belong to the genus Streptomyces. Here, we showed that these isolates increased soil nutrients and organic matter content and improved soil microbial populations. At the plant level, soil enrichment with actinomycetes increased photosynthetic reactions and eventually increased legume yield. Actinomycetes also increased nitrogen availability in soil and legume tissue and seeds, which induced the activity of key nitrogen metabolizing enzymes, e.g., glutamine synthetase, glutamate synthase, and nitrate reductase. In addition to increased nitrogen-containing amino acids levels, we also report high sugar, organic acids, and fatty acids as well as antioxidant phenolics, mineral, and vitamins levels in actinomycete treated legume seeds, which in turn improved their seed quality. Overall, this study shed the light on the impact of actinomycetes on enhancing the quality and productivity of legume crops by boosting the bioactive primary and secondary metabolites. Moreover, our findings emphasize the positive role of actinomycetes in improving the soil by enriching its microbial population. Therefore, our data reinforce the usage of actinomycetes as biofertilizers to provide sustainable food production and achieve biosafety.

Photoperiod stress induces an oxidative burst-like response and is associated with increased apoplastic peroxidase and decreased catalase activities.

Periodic changes of light and dark regulate numerous processes in plants. Recently, a novel type of stress caused by an extended light period has been described in Arabidopsis thaliana and was named photoperiod stress. Although photoperiod stress causes the induction of numerous stress response genes of which many are indicators of oxidative stress, the exact timing and mechanisms involved in dealing with this stress have not yet been investigated. We describe the response of the cellular redox system in wild-type Arabidopsis, the photoperiod stress sensitive cytokinin receptor mutant ahk2 ahk3 and the clock mutant cca1 lhy. Photoperiod stress caused several changes in the ROS scavenging system including a reduction of the ascorbic acid (AsA) redox status and strong peroxide formation during the night following the extended photoperiod. The changes were associated with reduced catalase (CAT) and increased apoplastic peroxidase (PRX) activities. Consistently, the expression of the apoplastic PRX genes PRX4, PRX33, PRX34 and PRX71 was strongly induced by photoperiod stress. We show that extending the light period by only few hours causes a stress response during the following night suggesting that the photoperiod stress response might occur in a natural setting.

Hormonal seed-priming improves tomato resistance against broomrape infection.

Although it is well known that parasitic weeds such as Orobanche (broomrape) significantly reduce the yield of economically important crops, their infection-induced oxidative changes need more exploration in their host plants. Moreover, applying an eco-friendly approach to minimize the infection is not yet available. This study was conducted to understand the effect of Orobanche ramosa infection on oxidative and redox status of tomato plants and the impact of hormonal (indole acetic acid (IAA); 0.09 mM and salicylic acid (SA); 1.0 mM) seed-priming upon mitigating the infection threats. Although Orobanche invades tomato roots, its inhibitory effects on shoot biomass were also indicted. Orobanche infection usually induces oxidative damage i.e., high lipid peroxidation, lipoxygenase activity and H2O2 levels, particularly for roots. Interestingly, hormonal seed-priming significantly enhanced tomato shoots and roots growth under both healthy and infected conditions. Also, IAA and SA treatment significantly reduced Orobanche infection-induced oxidative damage. The protective effect of seed-priming was explained by increasing the antioxidant defense markers including the antioxidant metabolites (i.e., total antioxidant capacity, carotenoids, phenolics, flavonoids, ASC, GSH, tocopherols) and enzymes (CAT, POX, GPX, SOD, GR, APX, MDHAR, DHAR), particularly in infected tomato seedlings. Additionally, cluster analysis indicated the differential impact of IAA- and SA-seed-priming, whereas lower oxidative damage and higher antioxidant enzymes' activities in tomato root were particularly reported for IAA treatment. The principal component analysis (PCA) also proclaimed an organ specificity depending on their response to Orobanche infection. Collectively, here and for the first time, we shed the light on the potential of seed-priming with either IAA or SA to mitigate the adverse effect of O. ramosa stress in tomato plants, especially at oxidative stress levels.

Maize roots and shoots show distinct profiles of oxidative stress and antioxidant defense under heavy metal toxicity.

Heavy metal accumulation in agricultural land causes crop production losses worldwide. Metal homeostasis within cells is tightly regulated. However, homeostasis breakdown leads to accumulation of reactive oxygen species (ROS). Overall plant fitness under stressful environment is determined by coordination between roots and shoots. But little is known about organ specific responses to heavy metals, whether it depends on the metal category (redox or non-redox reactive) and if these responses are associated with heavy metal accumulation in each organ or there are driven by other signals. Maize seedlings were subjected to sub-lethal concentrations of four metals (Zn, Ni, Cd and Cu) individually, and were quantified for growth, ABA level, and redox alterations in roots, mature leaves (L1,2) and young leaves (L3,4) at 14 and 21 days after sowing (DAS). The treatments caused significant increase in endogenous metal levels in all organs but to different degrees, where roots showed the highest levels. Biomass was significantly reduced under heavy metal stress. Although old leaves accumulated less heavy metal content than root, the reduction in their biomass (FW) was more pronounced. Metal exposure triggered ABA accumulation and stomatal closure mainly in older leaves, which consequently reduced photosynthesis. Heavy metals induced oxidative stress in the maize organs, but to different degrees. Tocopherols, polyphenols and flavonoids increased specifically in the shoot under Zn, Ni and Cu, while under Cd treatment they played a minor role. Under Cu and Cd stress, superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR) activities were induced in the roots, however ascorbate peroxidase (APX) activity was only increased in the older leaves. Overall, it can be concluded that root and shoot organs specific responses to heavy metal toxicity are not only associated with heavy metal accumulation and they are specialized at the level of antioxidants to cope with.

Exploring the potential of actinomycetes in improving soil fertility and grain quality of economically important cereals.

The search for environment-friendly, economical and healthy alternatives to agrochemicals tempted us to evaluate the potential of naturally occurring actinomycetes to improve soil properties, plant growth and photosynthesis, grain yield and chemical composition of economically important cereals (wheat, barley, oat, maize and sorghum). To this end, actinomycetes were isolated from soils of local cereals fields, then their biological activities, namely antibacterial, antiprotozoal, antioxidant, and phenolic and flavonoid contents were evaluated. The four most active isolates (9, 16, 24 and 26) were selected and used for enriching the soils until seed set. Each isolate was separately applied. Seeds of the selected cereals were grown in the actinomycete-enriched soils. The soils were analyzed for their electrical conductivity, pH values, total phenolics, organic matter and mineral content. At the vegetative stage, chlorophyll content and gas exchange rates were measured. Mature seeds were then harvested, the yield was evaluated and the seeds were analyzed for their primary and secondary metabolites. The selected isolates improved the grain yield in all tested cereals and most noticeably in barley and maize as compared to control counterparts. These positive effects were probably a result of increased carbon gain due to higher chlorophyll and photosynthetic rate. Isolate 26 showed the highest effect on grains composition profiles followed by the isolate 16. Phenolics and sugars of all grains increased by treatment with the tested isolates. Isolate 26 was the most effective in this regard. All isolates generally improved vitamins, amino acids and organic acids contents in grains. However, fatty acids profile showed a decrease in the content of all measured fatty acids by isolate 26 and an increase in the contents by isolate 16. These results emphasize the potential of actinomycete enrichment as an alternative to agrochemicals and strongly suggest that they can be used in organic farming.

High Salinity Induces Different Oxidative Stress and Antioxidant Responses in Maize Seedlings Organs.

Salinity negatively affects plant growth and causes significant crop yield losses world-wide. Maize is an economically important cereal crop affected by high salinity. In this study, maize seedlings were subjected to 75 mM and 150 mM NaCl, to emulate high soil salinity. Roots, mature leaves (basal leaf-pair 1,2) and young leaves (distal leaf-pair 3,4) were harvested after 3 weeks of sowing. Roots showed the highest reduction in biomass, followed by mature and young leaves in the salt-stressed plants. Concomitant with the pattern of growth reduction, roots accumulated the highest levels of Na(+) followed by mature and young leaves. High salinity induced oxidative stress in the roots and mature leaves, but to a lesser extent in younger leaves. The younger leaves showed increased electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) concentrations only at 150 mM NaCl. Total antioxidant capacity (TAC) and polyphenol content increased with the increase in salinity levels in roots and mature leaves, but showed no changes in the young leaves. Under salinity stress, reduced ascorbate (ASC) and glutathione (GSH) content increased in roots, while total tocopherol levels increased specifically in the shoot tissues. Similarly, redox changes estimated by the ratio of redox couples (ASC/total ascorbate and GSH/total glutathione) showed significant decreases in the roots. Activities of enzymatic antioxidants, catalase (CAT, EC 1.11.1.6) and dehydroascorbate reductase (DHAR, EC 1.8.5.1), increased in all organs of salt-treated plants, while superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione-s-transferase (GST, EC 2.5.1.18) and glutathione reductase (GR, EC 1.6.4.2) increased specifically in the roots. Overall, these results suggest that Na(+) is retained and detoxified mainly in roots, and less stress impact is observed in mature and younger leaves. This study also indicates a possible role of ROS in the systemic signaling from roots to leaves, allowing leaves to activate their defense mechanisms for better protection against salt stress.