Grassland species differentially regulate proline concentrations under future climate conditions: an integrated biochemical and modelling approach

Insights into the growth and biochemical defense responses associated with fenitrothion toxicity and uptake by freshwater cyanobacteria

The extensive use of fenitrothion (FNT) in agricultural practices induces its persistence in soil and waterways. Therefore, it is essential to implement effective management practices such as using cyanobacteria for FNT removal and accumulation, particularly under accidental contamination. To this end, we evaluated the responses of two freshwater cyanobacteria taxa, Nostoc muscorum and Anabaena laxa to mild (7.5 mg L-1) and high (15 mg L-1) levels of FNT over a period of 7 d. Compared to N. muscorum, A. laxa was more tolerant to FNT, exhibiting higher FNT uptake and removal efficiencies at mild (16.3%) and high (17.5%) levels. FNT induced a dose-dependent decrease in cell growth, Chl a, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase activities, which were more pronounced in N. muscorum. Moreover, FNT significantly increased oxidative damage markers i.e., increased lipid peroxidation (MDA), protein oxidation, H2O2 levels and NADPH oxidase enzyme activity, to more extent in N. muscorum. Compared to N. muscorum, A. laxa had high antioxidant capacity (FRAP), glutathione and increased activities of glutathione-S-transferase, glutathione reductase, glutathione peroxidase and superoxide dismutase, suggesting a robust antioxidant defense mechanism to mitigate FNT toxicity. However, N. muscorum devoted the induction of ascorbate content and the activity of catalase, peroxidase, monodehydroascorbate reductase, ascorbate peroxidase, and dehydroascorbate reductase enzymes. Although A. laxa had greater intracellular FNT, it experienced less FNT-induced oxidative stress, likely due to over production of antioxidants. Consequently, A. laxa is considered as a promising candidate for FNT phycoremediation. Our findings provide fundamental information on species-specific toxicity of FNT among cyanobacteria and the environmental risk of FNT toxicity in aquatic environments.

Improving plant adaptation to soil antimony contamination: the synergistic contribution of arbuscular mycorrhizal fungus and olive mill waste

BACKGROUND

This study aimed to investigate the alterations in biochemical and physiological responses of oat plants exposed to antimony (Sb) contamination in soil. Specifically, we evaluated the effectiveness of an arbuscular mycorrhizal fungus (AMF) and olive mill waste (OMW) in mitigating the effects of Sb contamination. The soil was treated with a commercial strain of AMF (Rhizophagus irregularis) and OMW (4% w/w) under two different levels of Sb (0 and 1500 mg kg-1 soil).

RESULTS

The combined treatment (OMW + AMF) enhanced the photosynthetic rate (+ 40%) and chlorophyll a (+ 91%) and chlorophyll b (+ 50%) content under Sb condition, which in turn induced more biomass production (+ 67-78%) compared to the contaminated control plants. More photosynthesis in OMW + AMF-treated plants gives a route for phenylalanine amino acid synthesis (+ 69%), which is used as a precursor for the biosynthesis of secondary metabolites, including flavonoids (+ 110%), polyphenols (+ 26%), and anthocyanins (+ 63%) compared to control plants. More activation of phenylalanine ammonia-lyase (+ 38%) and chalcone synthase (+ 26%) enzymes in OMW + AMF-treated plants under Sb stress indicated the activation of phenylpropanoid pathways in antioxidant metabolites biosynthesis. There was also improved shifting of antioxidant enzyme activities in the ASC/GSH and catalytic pathways in plants in response to OMW + AMF and Sb contamination, remarkably reducing oxidative damage markers.

CONCLUSIONS

While individual applications of OMW and AMF also demonstrated some degree of plant tolerance induction, the combined presence of AMF with OMW supplementation significantly enhanced plant biomass production and adaptability to oxidative stress induced by soil Sb contamination.

Rapeseed plant: biostimulation effects of plant growth-promoting Actinobacteria on metabolites and antioxidant defense system under elevated CO2 conditions

BACKGROUND

The present study set out to evaluate the potential of plant growth-promoting Actinobacteria (PGPB) in improving some physiological and molecular parameters of rapeseed (Brassica napus L.) plants under ambient and elevated CO2 conditions by assessing some nitrogen- and sulfur-containing metabolites, antioxidant defense system and antimicrobial activity. With this aim, a pot experiment was conducted where the rapeseed plants were treated with Actinobacterium sp. strain NCO2 (OQ451136) and were grown under two levels of air CO2 concentrations: ambient CO2 (aCO2 , 410 μmol CO2  mol-1 ); and elevated CO2 (eCO2 , 710 μmol CO2  mol-1 ).

RESULTS

There was an increase in the photosynthetic pigments (+35-80%) and photosynthesis rate (+20-34%) in PGPB-treated plants under eCO2 compared to control plants, resulting in further growth and biomass production (+53-294%). These results were associated with an enhancement in the content of total antioxidant capacity (+15-128%), polyphenols (+21-126%) and α-tocopherols (+20-138%) under both eCO2 and PGPB application (in combination or individual application), while only the combined treatment (eCO2  + PGPB) led to a significantly higher accumulation of antioxidant enzymes (+88-197%), β-tocopherols (+177%) and flavonoids (+155%). Moreover, nitrogen- and sulfur-containing metabolites (glucosinolates and amino acids) were improved by PGPB treatment and/or CO2 levels, in which PGPB increased the amino acid-derived glucosinolate induction by eCO2 with low levels of effective sulforaphane.

CONCLUSIONS

Therefore, the interaction effects of beneficial Actinobacteria and eCO2 are expected to boost the level of antioxidant molecules and to have a helpful role in improving plant biomass and adaptability to complicated climate changes in the future. © 2023 Society of Chemical Industry.

Humic acids enhance salt stress tolerance associated with pyrroline 5-carboxylate synthetase gene expression and hormonal alteration in perennial ryegrass (Lolium perenne L.)

Humic acid (HA) has been used as an important component in biostimulant formulations to enhance plant tolerance to salt stress, but the mechanisms underlying are not fully understood. This study was to investigate the physiological and molecular mechanisms of HA's impact on salt stress tolerance in perennial ryegrass (Lolium perenne L.). The two types of HA were extracted from weathered coal samples collected from Wutai County (WTH) and Jingle County (JLH) of Shanxi Province, China. The grass seedlings subjected to salt stress (250 mM NaCl) were treated with HA solutions containing 0.01% WTH (W/V) or 0.05% JLH (W/V), respectively. The HA treatments improved leaf photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) and reduced leaf oxidative injury (lower malondialdehyde content) and Pro and intercellular CO2 concentrations in salt-stressed perennial ryegrass. The HA treatments also reversed the decline in antioxidative enzymes ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activity and improved growth and anti-senescence hormones indole-3-acetic acid (IAA) and brassinosteroid (BR). The HA treatments reduced the relative expression of P5CS and its downstream products proline (Pro) and the stress defense hormones abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and polyamines (PA). The results of this study indicate that the application of HAs may improve salt stress tolerance by regulating P5CS gene expression related to osmotic adjustment and increasing the activity of antioxidant enzymes and anti-senescence hormones in perennial ryegrass.

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.

Alsherif E, Magdy Korany S, Hassan AHA, AbdElgawad H. Potassium Nitrate and Ascorbic Acid Priming Improved Tissue Chemical Composition and Antioxidant and Antimicrobial Activities of Linseed (Linum usitatissimum L.) Sprouts

Potassium nitrate (KNO3) and ascorbic acid (AsA) priming can effectively boost biomass accumulation and nutritional value of plants; nevertheless, few studies investigated their effects on seed sprouting. Thus, we aimed to explore the effects of KNO3 and AsA priming on linseed (Linum usitatissimum L.) sprout growth and assess the changes in bioactive compound levels, which provide valuable insights into the potential benefits of these priming treatments on sprout quality and nutritional value. To this end, germination, biomass accumulation, photosynthetic pigments, primary and secondary metabolites, and mineral profiles in the primed sprouts were evaluated. Moreover, to assess the impact on biological value, we determined the antioxidant and antimicrobial activities of the treated sprout extract. A marked enhancement was observed in germination and pigment levels of KNO3- and AsA-primed sprouts. These increases were in line with induced primary metabolites (e.g., carbohydrate and amino acid contents), particularly under KNO3 treatment. There was also an increase in amino acid metabolism (e.g., increased GS, GDH, and GOGAT enzyme activities), nitrogen level, and nitrate reductase (NR) activity. The linseed sprouts primed with AsA exhibited strong antioxidant and antibacterial activities. Consistently, high levels of polyphenols, flavonoids, total AsA, and tocopherols, as well as improved activity of antioxidant enzymes [peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD)], were recorded. This study proposes KNO3 and AsA priming as an innovative approach to improving the nutritional and health-promoting properties of linseed sprouts. This knowledge will contribute to a better understanding of the biochemical processes involved in improving the nutritional quality and functional benefits of linseed sprouts.

Arbuscular mycorrhizal fungi as an effective approach to enhance the growth and metabolism of soybean plants under thallium (TI) toxicity

Thallium (TI) is a toxic metal that can trigger harmful impacts on growth and metabolism of plants. Utilizing arbuscular mycorrhizal fungi (AMF) proves to be an effective strategy for alleviating heavy metal toxicity in plants. To this end, AMF were applied to mitigate TI toxic effects on the growth, primary and secondary metabolism of soybean plants. Here, TI stress inhibited the growth and photosynthetic parameters of soybean plants. It also increased the oxidative damage as demonstrated by increased levels of oxidative markers, (MDA and lipoxygenase (LOX) activity). However, AMF could mitigate the reduction in growth and photosynthesis induced by TI, as well as the induction of oxidative damage. To overcome TI toxicity, AMF increased the levels and metabolism of osmolytes such as proline in soybean plants. This was in line with the increased activities of key enzymes that involved in proline biosynthesis (e.g., P5CS (pyrroline-5-carboxylate synthetase), P5CR (pyrroline-5-carboxylate reductase) and OAT (ornithine aminotransferase) under the AMF and/or TI treatments. Furthermore, soybean plants could benefit from the synergism between AMF and TI to enhance the contents of individual (e.g., spermine and spermidine) and total polyamines as well as their metabolic enzymes (e.g., arginine decarboxylase and ornithine decarboxylase). Overall, the combined application of AMF emerges as a viable approach for alleviating TI toxicity in soybean plants.

Elevated CO2 reduced antimony toxicity in wheat plants by improving photosynthesis, soil microbial content, minerals, and redox status

Introduction

Antimony (Sb), a common rare heavy metal, is naturally present in soils at low concentrations. However, it is increasingly used in industrial applications, which in turn, leads to an increased release into the environment, exerting a detrimental impact on plant growth. Thus, it is important to study Sb effects on plants under the current and future CO2 (eCO2).

Methods

To this end, high Sb concentrations (1500 mg/kg soil) effects under ambient (420 ppm) and eCO2 (710 ppm) on wheat growth, physiology (photosynthesis reactions) and biochemistry (minerals contents, redox state), were studied and soil microbial were evaluated.

Results and discussion

Our results showed that Sb uptake significantly decreased wheat growth by 42%. This reduction could be explained by the inhibition in photosynthesis rate, Rubisco activity, and photosynthetic pigments (Cha and Chb), by 35%, 44%, and 51%, respectively. Sb significantly reduced total bacterial and fungal count and increased phenolic and organic acids levels in the soil to decrease Sb uptake. Moreover, it induced oxidative markers, as indicated by the increased levels of H2O2 and MDA (1.96 and 2.8-fold compared to the control condition, respectively). To reduce this damage, antioxidant capacity (TAC), CAT, POX, and SOD enzymes activity were increased by 1.61, 2.2, 2.87, and 1.86-fold, respectively. In contrast, eCO2 mitigated growth inhibition in Sb-treated wheat. eCO2 and Sb coapplication mitigated the Sb harmful effect on growth by reducing Sb uptake and improving photosynthesis and Rubisco enzyme activity by 0.58, 1.57, and 1.4-fold compared to the corresponding Sb treatments, respectively. To reduce Sb uptake and improve mineral availability for plants, a high accumulation of phenolics level and organic acids in the soil was observed. eCO2 reduces Sb-induced oxidative damage by improving redox status. In conclusion, our study has provided valuable insights into the physiological and biochemical bases underlie the Sb-stress mitigating of eCO2 conditions. Furthermore, this is important step to define strategies to prevent its adverse effects of Sb on plants in the future.

Chromium(VI) Toxicity and Active Tolerance Mechanisms of Wheat Plant Treated with Plant Growth-Promoting Actinobacteria and Olive Solid Waste

The present study aimed to assess the potential of plant growth-promoting Actinobacteria and olive solid waste (OSW) in ameliorating some biochemical and molecular parameters of wheat (Triticum aestivum) plants under the toxicity of high chromium levels in the soil. With this aim, a pot experiment was conducted, where the wheat plants were treated with a consortium of four Actinobacterium sp. (Bf treatment) and/or OSW (4% w/w) under two levels of nonstress and chromium stress [400 mg Cr(VI) per kg of soil] to estimate the photosynthetic traits, antioxidant protection machine, and detoxification activity. Both Bf and OSW treatments improved the levels of chlorophyll a (+47-98%), carotenoid (+324-566%), stomatal conductance (+17-18%), chlorophyll fluorescence (+12-28%), and photorespiratory metabolism (including +44-72% in glycolate oxidase activity, +6-72% in hydroxypyruvate reductase activity, and +5-44% in a glycine to serine ratio) in leaves of stressed plants as compared to those in the stressed control, which resulted in higher photosynthesis capacity (+18-40%) in chromium-stressed plants. These results were associated with an enhancement in the content of antioxidant metabolites (+10-117%), of direct reactive oxygen species-detoxifying enzymes (+49-94%), and of enzymatic (+40-261%) and nonenzymatic (+17-175%) components of the ascorbate-glutathione cycle in Bf- and OSW-treated plants under stress. Moreover, increments in the content of phytochelatins (+38-74%) and metallothioneins (+29-41%), as markers of detoxification activity, were recorded in the plants treated with Bf and OSW under chromium toxicity. In conclusion, this study revealed that the application of beneficial Actinobacteria and OSW as biofertilization/supplementation could represent a worthwhile consequence in improving dry matter production and enhancing plant tolerance and adaptability to chromium toxicity.

Galaxolide-contaminated soil and tolerance strategies in soybean plants using biofertilization and selenium nanoparticle supplementation

The current study aimed to address the response of soybean (Glycine max) plants to biofertilization and selenium supplementation treatments under galaxolide contamination of soil. In this regard, a pot experiment was carried out where the soybean plants were treated with the plant growth-promoting Actinobacteria (Actinobacterium sp.) as a biofertilizer (PGPB treatment) and/or selenium nanoparticles (Se treatment; 25 mg L-1) under two non-polluted and galaxolide-polluted soils (250 mg galaxolide per kg of soil) to assess the modifications in some plant physiological and biochemical traits. Although higher accumulation of oxidative biomarkers, including hydrogen peroxide (+180%), malondialdehyde (+163%), and protein oxidation (+125%), indicating oxidative stress in galaxolide-contaminated plants, an apparent decline in their contents was observed in response to biofertilization/supplementation treatments in contaminated soil, especially. It was mainly related to the higher detoxification of ROS in PGPB- and Se-treated plants under galaxolide-induced oxidative stress, in which the direct ROS-scavenging enzymes (+44 -179%), enzymatic (+34 - 293%) and non-enzymatic (+35 - 98%) components of the ascorbate-glutathione pathway, and antioxidant molecules (+38 - 370%) were more activated than in control plants. In addition, a higher accumulation of detoxification activity markers, including phytochelatins (+32%) and metallothioneins (+79%), were found in the combined treatments (PGPB+Se) under galaxolide contamination. Moreover, combined treatment with PGPB and Se ameliorated the levels of chlorophyll a content (+58%), stomatal conductance (+57%), the maximum efficiency of photosystem II (PSII) (+36%), and photorespiratory metabolism (including +99% in glycolate oxidase and +54% in hydroxypyruvate reductase activity) in leaves under galaxolide contamination, which resulted in higher photosynthesis capacity (+36%) and biomass production (+74%) in galaxolide-stressed plants as compared to control group. In conclusion, the application of beneficial Actinobacteria and selenium nanoparticles as biofertilization/supplementation is expected to be useful for improving plant toleration and adaptation against galaxolide contamination.

Physiological and biochemical responses of wheat to synergistic effects of selenium nanoparticles and elevated CO2 conditions

Elevating CO₂ (eCO₂) levels will change behavior and the effect of soil fertilizers and nutrients. Selenium NPs (SeNPs) have arisen as an alternative to conventional Se fertilizers to enrich crops. However, it remains unclear whether eCO₂ will change the biological effects of soil SeNPs on plant growth and metabolism. The current study aimed to shed new light on the interactive impacts of eCO₂ and SeNPs on wheat plants. Accordingly, the attempts were to reveal whether the application of SeNPs can modulate the eCO₂ effects on wheat (Triticum aestivum L.) physiological and biochemical traits. With this goal, a pot experiment was carried out where the seeds were primed with SeNPs and plants were grown under two levels of CO₂ concentrations (ambient CO₂ (aCO₂, 410 μmol CO₂ mol^-1; and eCO₂ (710 μmol CO₂ mol^-1)) during six weeks after sowing. Although SeNPs+eCO₂ treatment resulted in the highest accumulation of photosynthetic pigment content in leaves (+49-118% higher than control), strong evidence of the positive impacts on Rubisco activity (~+23%), and stomatal conductance (~+37%) was observed only under eCO₂, which resulted in an improvement in photosynthesis capacity (+42%). When photosynthesis parameters were stimulated with eCO₂, a significant improvement in dry matter production was detected, in particular under SeNPs+eCO₂ which was 1.8 times higher than control under aCO₂. The highest content of antioxidant enzymes, molecules, and metabolites was also recorded in SeNPs+eCO₂, which might be associated with the nearly 50% increase in sodium content in shoots at the same treatment. Taken together, this is the first research documenting the effective synergistic impacts of eCO₂ and SeNPs on the mentioned metabolites, antioxidants, and some photosynthetic parameters, an advantageous consequence that was not recorded in the individual application of these treatments, at least not as broadly as with the combined treatment.

Synergistic effect of carbon nanoparticles with mild salinity for improving chemical composition and antioxidant activities of radish sprouts

The demand for healthy foods with high functional value has progressively increased. Carbon nanoparticles (CNPs) have a promising application in agriculture including the enhancement of plant growth. However, there are few studies on the interactive effects of CNPs and mild salinity on radish seed sprouting. To this end, the effect of radish seed priming with 80mM CNPs on biomass, anthocyanin, proline and polyamine metabolism, and antioxidant defense system under mild salinity growth condition (25 mM NaCl). The results indicated that seed nanopriming with CNPs along with mild salinity stress enhanced radish seed sprouting and its antioxidant capacity. Priming boosted the antioxidant capacity by increasing antioxidant metabolites such as (polyphenols, flavonoids, polyamines, anthocyanin, and proline). To understand the bases of these increases, precursors and key biosynthetic enzymes of anthocyanin [phenylalanine, cinnamic acid, coumaric acid, naringenin, phenylalanine ammonia lyase, chalcone synthase (CHS), cinnamate-4-hydroxylase (C4H) and 4-coumarate: CoA ligase (4CL)], proline [pyrroline-5-carboxylate synthase (P5CS), proline dehydrogenase (PRODH), Sucrose, Sucrose P synthase, invertase) and polyamines [putrescine, spermine, spermidine, total polyamines, arginine decarboxylase, orinthnine decarboxylase, S-adenosyl-L-methionine decarboxylase, spermidine synthase, spermine synthase] were analyzed. In conclusion, seed priming with CNPs has the potential to further stimulate mild salinity-induced bioactive compound accumulation in radish sprouts.

The impact of chromium toxicity on the yield and quality of rice grains produced under ambient and elevated levels of CO2

Rice is a highly valuable crop consumed all over the world. Soil pollution, more specifically chromium (Cr), decreases rice yield and quality. Future climate CO₂ (eCO₂) is known to affect the growth and yield of crops as well as the quality parameters associated with human health. However, the detailed physiological and biochemical responses induced by Cr in rice grains produced under eCO₂ have not been deeply studied. Cr (200 and 400 mg Cr⁶⁺/Kg soil) inhibited rice yield and photosynthesis in Sakha 106, but to less extend in Giza 181 rice cultivar. Elevated CO₂ reduced Cr accumulation and, consequently, recovered the negative impact of the higher Cr dose, mainly in Sakha 106. This could be explained by improved photosynthesis which was consistent with increased carbohydrate level and metabolism (starch synthases and amylase). Moreover, these increases provided a route for the biosynthesis of organic, amino and fatty acids. At grain quality level, eCO₂ differentially mitigated Cr stress-induced reductions in minerals (e.g., P, Mg and Ca), proteins (prolamin, globulin, albumin, glutelin), unsaturated fatty acids (e.g., C20:2 and C24:1) and antioxidants (phenolics and total antioxidant capacity) in both cultivars. This study provided insights into the physiological and biochemical bases of eCO₂-induced grain yield and quality of Cr-stressed rice.

Understanding the Active Mechanisms of Plant (Sesuvium portulacastrum L.) against Heavy Metal Toxicity

Through metabolic analysis, the present research seeks to reveal the defense mechanisms activated by a heavy metals-resistant plant, Sesuvium portulacastrum L. In this regard, shifting metabolisms in this plant were investigated in different heavy metals-contaminated experimental sites, which were 50, 100, 500, 1000, and 5000 m away from a man-fabricated sewage dumping lake, with a wide range of pollutant concentrations. Heavy metals contaminations in contaminated soil and their impact on mineral composition and microbial population were also investigated. The significant findings to emerge from this research were the modifications of nitrogen and carbon metabolisms in plant tissues to cope with heavy metal toxicity. Increased plant amylase enzymes activity in contaminated soils increased starch degradation to soluble sugars as a mechanism to mitigate stress impact. Furthermore, increased activity of sucrose phosphate synthase in contaminated plants led to more accumulation of sucrose. Moreover, no change in the content of sucrose hydrolyzing enzymes (vacuolar invertase and cytosolic invertase) in the contaminated sites can suggest the translocation of sucrose from shoot to root under stress. Similarly, although this study demonstrated a high level of malate in plants exposed to stress, caution must be applied in suggesting a strong link between organic acids and the activation of defense mechanisms in plants, since other key organic acids were not affected by stress. Therefore, activation of other defense mechanisms, especially antioxidant defense molecules including alpha and beta tocopherols, showed a greater role in protecting plants from heavy metals stress. Moreover, the increment in the content of some amino acids (e.g., glycine, alanine, glutamate, arginine, and ornithine) in plants under metal toxicity can be attributed to a high level of stress tolerance. Moreover, strategies in the excitation of the synthesis of the unsaturated fatty acids (oleic and palmitoleic) were involved in enhancing stress tolerance, which was unexpectedly associated with an increase in the accumulation of palmitic and stearic (saturated fatty acids). Taken together, it can be concluded that these multiple mechanisms were involved in the response to stress which may be cooperative and complementary with each other in inducing resistance to the plants.

Arbuscular Mycorrhizal Fungus "Rhizophagus irregularis" impacts on physiological and biochemical responses of ryegrass and chickpea plants under beryllium stress

Heavy metals such as beryllium (Be) have been identified as toxic for plants with a negative impact on plant growth. Therefore, there is an urgent need for environmentally friendly techniques to reduce Be toxicity on plant growth and productivity. To this end, arbuscular mycorrhizal fungi (AMF) are widely applied to induce plant growth and stress tolerance. However, how AMF-plant symbiosis can support plants under Be stress has not been studied. Accordingly, we investigated the physiological and biochemical responses of AMF inoculated ryegrass and chickpea plants to Be stress. The associated changes in Be uptake and accumulation, photosynthesis, oxidative stress, carbon and nitrogen metabolism were studied. Soil contamination with Be induced higher Be accumulation, particularly in ryegrass, which consequentially reduced plant growth and photosynthesis. However, photorespiration and oxidative damage (H₂O₂ accumulation, lipid oxidation, and LOX activity) were increased, mainly in ryegrass. In both plant species, AMF inoculation reduced Be accumulation and mitigated growth inhibition and oxidative damage, but to a more extent in ryegrass. This could be explained by improved photosynthesis as well as the upregulation of osmoprotectants i.e., sucrose and proline biosynthesis pathways. The increase in proline level was consistent with higher nitrogen (N) metabolism as reflected by N level and nitrate reductase. Species-specific responses were recorded and supported by principal component analysis. This study provided insight into the mechanism of AMF's impact on Be-stressed ryegrass and chickpea plants. Hence, the current research suggested that AMF inoculation could be used as a viable strategy to mitigate Be phytotoxicity in ryegrass and chickpea plants.

Exogenous Proline Improves Salt Tolerance of Alfalfa through Modulation of Antioxidant Capacity, Ion Homeostasis, and Proline Metabolism

Alfalfa (Medicago sativa L.) is an important forage crop, and its productivity is severely affected by salt stress. Although proline is a compatible osmolyte that plays an important role in regulating plant abiotic stress resistance, the basic mechanism of proline requires further clarification regarding the effect of proline in mitigating the harmful effects of salinity. Here, we investigate the protective effects and regulatory mechanisms of proline on salt tolerance of alfalfa. The results show that exogenous proline obviously promotes seed germination and seedling growth of salt-stressed alfalfa. Salt stress results in stunted plant growth, while proline application alleviates this phenomenon by increasing photosynthetic capacity and antioxidant enzyme activities and decreasing cell membrane damage and reactive oxygen species (ROS) accumulation. Plants with proline treatment maintain a better K⁺/Na⁺ ratio by reducing Na⁺ accumulation and increasing K⁺ content under salt stress. Additionally, proline induces the expression of genes related to antioxidant biosynthesis (Cu/Zn-SOD and APX) and ion homeostasis (SOS1, HKT1, and NHX1) under salt stress conditions. Proline metabolism is mainly regulated by ornithine-δ-aminotransferase (OAT) and proline dehydrogenase (ProDH) activities and their transcription levels, with the proline-treated plants displaying an increase in proline content under salt stress. In addition, OAT activity in the ornithine (Orn) pathway rather than Δ¹-pyrroline-5-carboxylate synthetase (P5CS) activity in the glutamate (Glu) pathway is strongly increased under salt stress, made evident by the sharp increase in the expression level of the OAT gene compared to P5CS1 and P5CS2. Our study provides new insight into how exogenous proline improves salt tolerance in plants and that it might be used as a significant practical strategy for cultivating salt-tolerant alfalfa.

Biofertilisation with a consortium of growth-promoting bacterial strains improves the nutritional status of wheat grain under control, drought, and salinity stress conditions

We investigated the effect of plant growth-promoting bacterial strains (PGPB) as biofertilisers on the grain metabolic composition of durum wheat (Triticum durum Desf.). To this aim, we conducted a greenhouse experiment where we grew durum wheat plants supplied with a biofertiliser consortium of four PGPB and/or chemical fertiliser (containing nitrogen, phosphorus, potassium, and zinc), under non-stress, drought (at 40% field capacity), or salinity (150 mM NaCl) conditions. Nutrient accumulations in the grain were increased in plants treated with the biofertiliser consortium, alone or with a half dose of chemical fertilisers, compared to those in no fertilisation treatment. A clear benefit of biofertiliser application in the improvement of protein, soluble sugar, starch, and lipid contents in the grains was observed in comparison with untreated controls, especially under stress conditions. The most striking observation was the absence of significant differences between biofertiliser and chemical fertiliser treatments for most parameters. Moreover, the overall response to the biofertiliser consortium was accompanied by greater changes in amino acids, organic acids, and fatty acid profiles. In conclusion, PGPB improved the metabolic and nutrient status of durum wheat grains to a similar extent as chemical fertilisers, particularly under stress conditions, demonstrating the value of PGPB as a sustainable fertilisation treatment.

The Interaction Effect of Laser Irradiation and 6-Benzylaminopurine Improves the Chemical Composition and Biological Activities of Linseed (Linum usitatissimum) Sprouts

Even though laser light (LL) and 6-benzylaminopurine (BAP) priming are well-known as promising strategies for increasing the growth and nutritional value of several plants, no previous studies have investigated their synergistic effect. Herein, we investigated the effects of laser light, 6-benzylaminopurine (BAP) priming, and combined LL-BAP treatment on the nutritional value, chemical composition, and the biological activity of Linum usitatissimum sprouts. The fresh weight, leaf pigments, primary and secondary metabolites, enzymes, and antimicrobial activities were determined. A substantial enhancement was observed in the growth characteristics and leaf pigments of laser-irradiated and BAP-primed sprouts. Furthermore, the combined treatments improved the accumulation of minerals, vitamins, and amino acids, and also enhanced the N-metabolism more than LL or BAP alone. Furthermore, the combined priming boosted the antioxidant capacity by increasing the contents of fatty acids, phenols, and flavonoids. Antimicrobial activity and the highest increase in bioactive compounds were recorded in linseed sprouts simultaneously treated with LL and BAP. This work suggests that priming L. usitatissimum sprouts with laser light and BAP is a promising approach that can improve the nutritional value and health-promoting impacts of L. usitatissimum sprouts.

Does previous exposure to extreme precipitation regimes result in acclimated grassland communities?

Climate change will likely increase weather persistence in the mid-latitudes, resulting in precipitation regimes (PR) with longer dry and wet periods compared to historic averages. This could affect terrestrial ecosystems substantially through the increased occurrence of repeated, prolonged drought and water logging conditions. Climate history is an important determinant of ecosystem responses to consecutive environmental extremes, through direct damage, community restructuring as well as morphological and physiological acclimation in species or individuals. However, it is unclear how community restructuring and individual metabolic acclimation effects interact to determine ecosystem responses to subsequent climate extremes. Here, we investigated, if and how, differences in exposure to extreme or historically normal PR induced long-lasting (i.e. legacy) effects at the level of community (e.g., species composition), plant (e.g., biomass), and molecular composition (e.g., sugars, lipids, stress markers). Experimental grassland communities were exposed to long (extreme) or short (historically normal) dry/wet cycles in year 1 (Y1), followed by exposure to an identical PR or the opposite PR in year 2 (Y2). Results indicate that exposure to extreme PR in Y1, reduced diversity but induced apparent acclimation effects in all climate scenarios, stimulating biomass (higher productivity and structural sugar content) in Y2. In contrast, plants pre-exposed to normal PR, showed more activated stress responses (higher proline and antioxidants) under extreme PR in Y2. Overall, Y1 acclimation effects were strongest in the dominant grasses, indicating comparatively high phenotypical plasticity. However, Y2 drought intensity also correlated with grass productivity and structural sugar findings, suggesting that responses to short-term soil water deficits contributed to the observed patterns. Interactions between different legacy effects are discussed. We conclude that more extreme PR will likely alter diversity in the short-to midterm and select for acclimated grassland communities with increased productivity and attenuated molecular stress responses under future climate regimes.

Selection of Newly Identified Growth-Promoting Archaea Haloferax Species With a Potential Action on Cobalt Resistance in Maize Plants

Soil contamination with cobalt (Co) negatively impacts plant growth and production. To combat Co toxicity, plant growth-promoting microorganisms for improving plant growth are effectively applied. To this end, unclassified haloarchaeal species strain NRS_31 (OL912833), belonging to Haloferax genus, was isolated, identified for the first time, and applied to mitigate the Co phytotoxic effects on maize plants. This study found that high Co levels in soil lead to Co accumulation in maize leaves. Co accumulation in the leaves inhibited maize growth and photosynthetic efficiency, inducing oxidative damage in the tissue. Interestingly, pre-inoculation with haloarchaeal species significantly reduced Co uptake and mitigated the Co toxicity. Induced photosynthesis improved sugar metabolism, allocating more carbon to defend against Co stress. Concomitantly, the biosynthetic key enzymes involved in sucrose (sucrose-P-synthase and invertases) and proline (pyrroline-5- carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR)) biosynthesis significantly increased to maintain plant osmotic potential. In addition to their osmoregulation potential, soluble sugars and proline can contribute to maintaining ROS hemostasis. Maize leaves managed their oxidative homeostasis by increasing the production of antioxidant metabolites (such as phenolics and tocopherols) and increasing the activity of ROS-scavenging enzymes (such as POX, CAT, SOD, and enzymes involved in the AsA/GSH cycle). Inside the plant tissue, to overcome heavy Co toxicity, maize plants increased the synthesis of heavy metal-binding ligands (metallothionein, phytochelatins) and the metal detoxifying enzymes (glutathione S transferase). Overall, the improved ROS homeostasis, osmoregulation, and Co detoxification systems were the basis underlying Co oxidative stress, mitigating haloarchaeal treatment's impact.

CO2 Enrichment Differentially Upregulated Sugar, Proline, and Polyamine Metabolism in Young and Old Leaves of Wheat and Sorghum to Mitigate Indium Oxide Nanoparticles Toxicity

Soil contamination with indium oxide nanoparticles (In₂O₃-NPs) is a challenge for plant growth and productivity. Despite In₂O₃-NPs toxicity, their effects on plant growth and metabolism are largely unknown, particularly under future climate CO₂ (eCO₂). Therefore, the In₂O₃-NPs toxicity and stress mitigating impact of eCO₂ in the young and old leaves of C3 (wheat) and C4 (sorghum) plants were investigated. Overall, In₂O₃-NPs significantly retard the biomass and photosynthetic machinery of all tested crops, particularly the young leaves of C3 plants. Consequently, In₂O₃-NPs altered C and N metabolism in C3 and C4 plants. On the other hand, eCO₂ contrarily alleviated the hazardous effects of In₂O₃-NPs on growth and photosynthesis, especially in the young leaves of C4 plants. Increased photosynthesis consequently enhanced the soluble sugars' accumulation and metabolism (e.g., sucrose P synthase, cytosolic, and vacuolar invertase) in all stressed plants, but to a greater extent in C4 young leaves. High sugar availability also induced TCA organic and fatty acids' accumulation. This also provided a route for amino acids and polyamines biosynthesis, where a clear increase in proline biosynthetic enzymes [e.g., pyrroline-5-carboxylate synthetase (P5CS), ornithine aminotransferase (OAT), Pyrroline-5-carboxylate reductase (P5CR), pyrroline-5-carboxylate dehydrogenase (P5CDH), and proline dehydrogenase (PRODH)] and polyamine metabolic enzymes (e.g., spermine and spermidine synthases, ornithine decarboxylase, and adenosyl methionine decarboxylase) were mainly recorded in C4 young leaves. The observed increases in these metabolites involved in osmo- and redox-regulation to reduce In₂O₃-NPs induced oxidative damage. Overall, our study, for the first time, shed light on how eCO₂ differentially mitigated In₂O₃-NPs stress in old and young leaves of different species groups under the threat of In₂O₃-NPs contamination.

Evaluation of the phycoremediation potential of microalgae for captan removal: Comprehensive analysis on toxicity, detoxification and antioxidants modulation

Captan is one of the most widely used organochlorine fungicides, its frequent application contaminates both terrestrial and aquatic ecosystems and negatively affects their key ecological processes. This study demonstrated the toxicity and efficient removal of captan by two different taxonomic species; the green microalga Scenedesmus obliquus and cyanobacterium Nostoc muscorum. After a week of exposure to mild (15 mg/L) and severe (30 mg/L) captan doses, the intracellular captan uptake, degradation and metabolic regulation of captan detoxification were studied. Compared to N. muscorum, S. obliquus accumulated more captan, but efficiently degraded it into two safe eco-friendly by-products; phthalic acid and 1,2,3,6-tetrahydro phthalimide. S. obliquus showed less decrease in cell growth, photosynthesis activity and related parameters including Chla content and activity of PEPC and RuBisCo enzymes. Captan at the severe dose induced oxidative damage particularly in N. muscorum, as expressed by the high levels of H₂O₂, MDA, NADPH oxidase and protein peroxidation. Both species invested glutathione-s-transferase enzyme in captan detoxification however, induction of antioxidant defence system e.g. ascorbate and glutathione cycle was more pronounced in S. obliquus which could explain its tolerance ability. This study provided a better understanding of the environmental risks of captan and introduced S. obliquus as a promising captan phycoremediator.

Transgenic Medicago truncatula Plants That Accumulate Proline Display Enhanced Tolerance to Cadmium Stress

Cadmium (Cd) accumulation in agricultural soils constitutes a serious problem for crop yields and food safety. It is known that proline (Pro) can rapidly accumulate in plant tissues in response to abiotic stress. To analyze the potential protective effect of Pro accumulation against Cd toxicity, we compared the response to Cd stress of wild-type (WT) Medicago truncatula and a transgenic line that we had previously obtained and characterized (p18), which expressed the Δ ¹-pyrroline-5-carboxylate synthetase gene from Vigna aconitifolia (VaP5CS), and accumulated high Pro levels. Cadmium significantly reduced germination of WT seeds compared to p18 seeds, and seedling relative root growth, a valid indicator of metal tolerance, was significantly higher for p18 than WT seedlings. We analyzed the relative expression of genes related to Pro metabolism, phytochelatin biosynthesis. antioxidant machinery, and NADPH recycling, which are relevant mechanisms in the response to Cd stress. They presented differential expression in the seedlings of both genotypes both under control conditions and under Cd stress, suggesting that the Cd response mechanisms might be constitutively activated in the transgenic line. Pro accumulation promoted higher survival, enhanced growth performance, and minor nutrient imbalance in transgenic p18 plants compared to WT plants. These facts, together with the recorded gluthatione levels, lipid peroxidation and antioxidant enzyme activities strongly suggested that VaP5CS expression and Pro accumulation conferred enhanced Cd tolerance to M. truncatula p18 plants, which was likely mediated by changes in Pro metabolism, increased phytochelatin biosynthesis and a more efficient antioxidant response. Moreover, p18 roots accumulated significantly higher Cd amounts than WT roots, while Cd translocation to the aerial part was similar to WT plants, thus suggesting that high Pro levels increased not only Cd tolerance, but also Cd phytostabilization by rhizosequestration.

Impact of Sprouting under Potassium Nitrate Priming on Nitrogen Assimilation and Bioactivity of Three Medicago Species

Edible sprouts are rich in flavonoids and other polyphenols, as well as proteins, minerals, and vitamins. Increasing sprout consumption necessitates improving their quality, palatability, and bioactivity. The purpose of this study was to test how KNO₃ priming affects the sprouting process species on three Medicago species (Medicago indicus, Medicago interexta, and Medicago polymorpha) and their nutritional values. Targeted species of Medicago were primed with KNO₃, and the levels of different primary and secondary metabolites were determined. KNO₃ induced biomass accumulation in the sprouts of the three species, accompanied by an increased content of total mineral nutrients, pigments, vitamins, and essential amino acids. Besides, our results showed that KNO₃ enhanced the activity of nitrate reductase (NR), glutamate dehydrogenase (GDH), and glutamine synthetase (GS) enzymes, which are involved in the nitrogen metabolism and GOGAT cycle, which, in turn, increase the nitrogen and protein production. KNO₃ treatment improved the bioactive compound activities of Medicago sprouts by increasing total phenolic and flavonoid contents and enhancing the antioxidant and antidiabetic activities. Furthermore, species-specific responses toward KNO₃ priming were noticeable, where Medicago interexta showed the highest antioxidant and antidiabetic activities, followed by Medicago polymorpha. Overall, this study sheds the light on the physiological and biochemical bases of growth, metabolism, and tissue quality improvement impact of KNO₃ on Medicago sprouts.

Harnessing Endophytic Fungi for Enhancing Growth, Tolerance and Quality of Rose-Scented Geranium (Pelargonium graveolens (L'Hér) Thunb.) Plants under Cadmium Stress: A Biochemical Study

Heavy metal contamination in soil is increasing rapidly due to increasing anthropogenic activities. Despite the importance of rose-scented geranium as a medicinal plant, little attention was paid to enhancing its productivity in heavy metal-polluted soil. In this regard, endophytes improve plant resistance to heavy metal toxicity and enhance its tissue quality. Here, the impact of the three endophytic fungi Talaromyces versatilis (E6651), Emericella nidulans (E6658), and Aspergillus niger (E6657) on geranium growth, tolerance, and tissue quality under cadmium (Cd) stress was investigated. In contrast to E. nidulans, T. versatilis and A. niger enhanced geranium growth and the stimulatory effect was more pronounced under Cd-stress. The three endophytes significantly alleviated Cd accumulation and increased mineral content in geranium leaves. In addition, endophytic fungi successfully alleviated Cd-induced membrane damage and reinforced the antioxidant defenses in geranium leaves. Inoculation with endophytes stimulated all the antioxidant enzymes under Cd-stress, and the response was more obvious in the case of T. versatilis and A. niger. To reduce the toxicity of tissue-Cd levels, T. versatilis and A. niger upregulated the detoxification mechanisms; glutathione-S-transferase, phytochelatin, and metallothionein levels. Moreover, endophytic fungi improved the medicinal value and quality of geranium by increasing total antioxidant capacity (TAC), phenolic compound biosynthesis (phenylalanine ammonia-lyase), and vitamin content as well as the quantity and quality of essential oil, particularly under Cd-stress conditions. The variation in the mechanisms modulated by the different endophytic fungi was supported by Principal Component Analysis (PCA). Overall, this study provided fundamental insights into endophytes' impact as a feasible strategy to mitigate the phytotoxicity hazards of Cd-stress in geranium and enhance its quality, based on the growth and biochemical investigations.

The differential tolerance of C3 and C4 cereals to aluminum toxicity is faded under future CO2 climate

Industrial activities have led to a gradual and global increase in soil aluminum (Al) and atmospheric CO₂ concentrations. Al bioavailability strongly depends on the soil pH, which in turn is affected by atmospheric CO₂ levels. In spite of the concurrent impact which Al and elevated CO₂ (eCO₂) could have on plants, their interaction and how it might affect the growth of economically important crop species has not been investigated. Here, we have investigated the combined impact of soil Al and eCO₂ exposure on key C3 (wheat, oat) and C4 (maize, sorghum) crops, at the physiological and biochemical level. Compared to C3 plants, C4 plants accumulated less Al by stimulating soil Al retention through exudation of root organic acids. Consequently, Al-exposed C4 plants maintained photosynthetic performance and anti-oxidative capacity. Exposure to eCO₂ reduced the stress responses of C3 and C4 crops to Al exposure. Elevated CO₂ decreased Al accumulation and oxidative damage in all cereals, and ameliorated C3 plant growth. This was reflected on the biochemical level, where eCO₂ inhibited ROS production and restored RuBisCo activity in C3 crops only. Overall, our data suggest that, compared to C3 crops, C4 cereals are more tolerant to soil Al exposure under current ambient CO₂ (aCO₂) levels whereas future eCO₂ levels might stimulate Al tolerance in C3 crops.

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.

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.

Elevated CO2 improves the nutritive value, antibacterial, anti-inflammatory, antioxidant and hypocholestecolemic activities of lemongrass sprouts

Sprouts have been regarded as a big store for bioactive compounds with a wide range of biological activities. Elevated CO2 (eCO2, 620 μmol mol-1)was employed to enhance the nutritive and health promoting values of sprouts of two species of lemongrass, i.e. Cymbopogon citratus and Cymbopogon proximus. eCO2 improved the biomass production of sprouts, and their levels of primary metabolites e.g., amino acids and oils and active secondary metabolites e.g., phenolic compounds. As a result, eCO2 increased total antioxidant capacity, cytotoxicity against several human cancer cell lines, and antibacterial activities of Cymbopogon sprouts. We also recorded a significant increase in hypocholesterolaemic potential and anti-inflammatory activities of eCO2-treated sprouts, as indicated by inhibition of cholesterol micellar solubility and pancreatic lipase activity, as well as lipoxygenase and cyclooxygenase activities, respectively. Thus, the present investigation supports the use of eCO2 as a promising approach to produce lemongrass sprouts with effective phytochemicals and enhanced biological activities.

Bioactive Potential of Several Actinobacteria Isolated from Microbiologically Barely Explored Desert Habitat, Saudi Arabia

Simple Summary

Bioactive natural products have been regarded as promising tools for treatment of various ailments. Among natural sources, actinomycetes have been widely explored for their potential bioactivity. In this regard, the present study has focused on the phytochemical content and biological activities of several actinobacteria isolates, which were investigated for their phenolic and flavonoid content, as well as their antioxidant, antibacterial and antiprotozoal activities. The most active isolates were further investigated for their antileukemic activity, where such isolates were shown to exert cytotoxic activity against the tested cell lines, following a mechanism that might be due to the ability of the active isolate extracts to reduce cyclooxygenase and lipoxygenase activities. Overall, isolation and characterization of the active molecule from the potential actinomycetes strains will pave the way for the development of drugs against human diseases such as blood cancer.

Abstract

Biomolecules from natural sources, including microbes, have been the basis of treatment of human diseases since the ancient times. Therefore, this study aimed to investigate the potential bioactivity of several actinobacteria isolates form Al-Jouf Desert, Saudi Arabia. Twenty-one actinobacterial isolates were tested for their antioxidant (flavonoids, phenolics, tocopherols and carotenoids) content, and biological activities, namely FRAP, DPPH, ABTS, SOS and XO inhibition, anti-hemolytic and anti-lipid peroxidation as well as their antibacterial and antiprotozoal activities. Accordingly, five isolates (i.e., Act 2, 12, 15, 19 and 21) were selected and their 90% ethanolic extracts were used. The phylogenetic analysis of the 16S rRNA sequences indicated that the most active isolates belong to genus Streptomyces. The genus Streptomyces has been documented as a prolific producer of biologically active secondary metabolites against different cancer types. Thus, the anti-blood cancer activity and the possible molecular mechanisms by which several Streptomyces species extracts inhibited the growth of different leukemia cells, i.e., HL-60, K562 and THP-1, were investigated. In general, the five active isolates showed cytotoxic activity against the tested cell lines in a dose dependent manner. Among the potent isolates, isolate Act 12 significantly decreased the cell viability and showed maximum cytotoxic activities against both HL-60 and K562 cells, while isolate Act 15 exhibited maximum cytotoxic activity against THP-1 cells. Moreover, Act 2 and Act 12 reduced cyclooxygenase (COX-2) and lipoxygenase (LOX) activity, which is involved in the proliferation and differentiation of cancer cells and may represent a possible molecular mechanism underlying leukemia growth inhibition. The bioactive antioxidant extracts of the selected Streptomyces species inhibited leukemia cell growth by reducing the COX-2 and LOX activity. Overall, our study not only introduced a promising natural alternative source for anticancer agents, but it also sheds light on the mechanism underlying the anticancer activity of isolated actinomycetes.

C3 and C4 plant systems respond differently to the concurrent challenges of mercuric oxide nanoparticles and future climate CO2

Future climate CO₂ (eCO₂) and contamination with nano-sized heavy metals (HM-NPs) represent concurrent challenges threatening plants. The interaction between eCO₂ and HM-NPs is rarely investigated, and no study has addressed their synchronous impact on the metabolism of the multifunctional stress-related metabolites, such as sugars and amino acids. Moreover, the characteristic responses of C3 and C4 plant systems to the concurrent impact of eCO₂ and HM-NPs are poorly understood. Herein, we have assessed the impact of eCO₂ (620 ppm) and/or HgO-NPs (100 mg/Kg soil) on growth, physiology and metabolism of sugars and amino acids, particularly proline, in C3 (wheat) and C4 (maize) plant systems. Under Hg-free conditions, eCO₂ treatment markedly improved the growth and photosynthesis and induced sugars levels and metabolism (glucose, fructose, sucrose, starch, sucrose P synthase and starch synthase) in wheat (C3) only. In contrast, HgO-NPs induced the uptake, accumulation and translocation of Hg in wheat and to less extend in maize plants. Particularly in wheat, this induced significant decreases in growth and photosynthesis and increases in photorespiration, dark respiration and levels of tricarboxylic acid cycle organic acids. Interestingly, the co-application of eCO₂ reduced the accumulation of Hg and recovered the HgO-NPs-induced effects on growth and metabolism in both plants. At stress defense level, HgO-NPs induced the accumulation of sucrose and proline, more in maize, via upregulation of sucrose P synthase, ornithine amino transferase, ∆¹-pyrroline-5-carboxylate (P5C) synthetase and P5C reductase. The co-existence of eCO₂ favored reduced sucrose biosynthesis and induced proline catabolism, which provide high energy to resume plant growth. Overall, despite the difference in their response to eCO₂ under normal conditions, eCO₂ induced similar metabolic events in C3 and C4 plants under stressful conditions, which trigger stress recovery.

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.

Laser light as a promising approach to improve the nutritional value, antioxidant capacity and anti-inflammatory activity of flavonoid-rich buckwheat sprouts

Buckwheat sprouts are rich in several nutrients such as antioxidant flavonoids that have a positive impact on human health. Although there are several studies reported the positive impact of laser light on crop plants, no studies have applied laser light to enhance the nutritive values of buckwheat sprouts. Herein, the contents of health-promoting minerals, metabolites and enzymes as well as the antioxidant and anti-inflammatory activities were determined in laser-treated (He-Ne laser, 632 nm, 5 mW) common buckwheat (CBW) and tartarybuckwheat (TBW) sprouts. Out of 49 targeted minerals, vitamins, pigments and antioxidants, more than 35 parameters were significantly increased in CBW and/or TBW sprouts by laser light treatment. Also, laser light boosted the antioxidant capacity and anti-inflammatory activities through inhibiting cyclooxygenase-2 and lipoxygenase activities, particularly in TBW sprouts. Accordingly, laser light could be recommended as a promising method to improve the nutritional and health-promoting values of buckwheat sprouts.

Al exposure increases proline levels by different pathways in an Al-sensitive and an Al-tolerant rye genotype

Aluminium (Al) toxicity limits crop productivity, particularly at low soil pH. Proline (Pro) plays a role in protecting plants against various abiotic stresses. Using the relatively Al-tolerant cereal rye (Secale cereale L.), we evaluated Pro metabolism in roots and shoots of two genotypes differing in Al tolerance, var. RioDeva (sensitive) and var. Beira (tolerant). Most enzyme activities and metabolites of Pro biosynthesis were analysed. Al induced increases in Pro levels in each genotype, but the mechanisms were different and were also different between roots and shoots. The Al-tolerant genotype accumulated highest Pro levels and this stronger increase was ascribed to simultaneous activation of the ornithine (Orn)-biosynthetic pathway and decrease in Pro oxidation. The Orn pathway was particularly enhanced in roots. Nitrate reductase (NR) activity, N levels, and N/C ratios demonstrate that N-metabolism is less inhibited in the Al-tolerant line. The correlation between Pro changes and differences in Al-sensitivity between these two genotypes, supports a role for Pro in Al tolerance. Our results suggest that differential responses in Pro biosynthesis may be linked to N-availability. Understanding the role of Pro in differences between genotypes in stress responses, could be valuable in plant selection and breeding for Al resistance.

Influence of elevated CO2 on nutritive value and health-promoting prospective of three genotypes of Alfalfa sprouts (Medicago Sativa)

Alfalfa sprouts are well known for their nutritive values. Although there are several studies reported the positive impact of elevated CO₂ (eCO₂) on plants, there are no in-depth, comprehensive studies on how eCO₂ could improve the sprouting of plant seeds. Herein, the production of health-promoting metabolites was determined in eCO₂ (620 ppm)-treated Alfalfa sprout cultivars (Giza 1, Nubaria and Ismailia 1). eCO₂ increased the photosynthetic process and pigment contents, which consequently induced carbohydrates, proteins, fats and fiber accumulation. eCO₂ also boosted the levels of vitamins, phenolics, flavonoids and mineral individuals and enhanced the antioxidant capacity of alfalfa sprouts. Interestingly, eCO₂ reduced the antinutritional factor l-canavanine content in Ismailia 1 cultivar and improved the anti-inflammatory activities through inhibiting cyclooxygenase-2 and lipoxygenase activity. Therefore, eCO₂ is a promising approach to improve the health-promoting prospective of alfalfa sprouts to be a valuable source of nutritious and bioactive compounds in our daily diet.

Heat stress as an innovative approach to enhance the antioxidant production in Pseudooceanicola and Bacillus isolates

It is well known that the quality and quantity of bioactive metabolites in plants and microorganisms are affected by environmental factors. We applied heat stress as a promising approach to stimulate the production of antioxidants in four heat-tolerant bacterial strains (HT1 to HT4) isolated from Aushazia Lake, Qassim Region, Saudi Arabia. The phylogenetic analysis of the 16S rRNA sequences indicated that HT1, HT3 and HT4 belong to genus Bacillus. While HT2 is closely related to Pseudooceanicola marinus with 96.78% similarity. Heat stress differentially induced oxidative damage i.e., high lipid peroxidation, lipoxygenase and xanthine oxidase levels in HT strains. Subsequently, heat stress induced the levels of flavonoids and polyphenols in all strains and glutathione (GSH) in HT2. Heat stress also improved the antioxidant enzyme activities, namely, CAT, SOD and POX in all strains and thioredoxin activity in HT3 and HT4. While GSH cycle (GSH level and GPX, GR, Grx and GST activities) was only detectable and enhanced by heat stress in HT2. The hierarchical cluster analysis of the antioxidants also supported the strain-specific responses. In conclusion, heat stress is a promising approach to enhance antioxidant production in bacteria with potential applications in food quality improvement and health promotion.

Salinity Stress Enhances the Antioxidant Capacity of Bacillus and Planococcus Species Isolated From Saline Lake Environment

This study aims at exploiting salinity stress as an innovative, simple, and cheap method to enhance the production of antioxidant metabolites and enzymes from bacteria for potential application as functional additives to foods and pharmaceuticals. We investigated the physiological and biochemical responses of four bacterial isolates, which exhibited high tolerance to 20% NaCl (wt/vol), out of 27 bacterial strains isolated from Aushazia Lake, Qassim region, Saudi Arabia. The phylogenetic analysis of the 16S rRNA genes of these four isolates indicated that strains ST1 and ST2 belong to genus Bacillus, whereas strains ST3 and ST4 belong to genus Planococcus. Salinity stress differentially induced oxidative damage, where strains ST3 and ST4 showed increased lipid peroxidation, lipoxygenase, and xanthine oxidase levels. Consequently, high antioxidant contents were produced to control oxidative stress, particularly in ST3 and ST4. These two Planococcus strains showed increased glutathione cycle, phenols, flavonoids, antioxidant capacity, catalase, and/or superoxide dismutase (SOD). Interestingly, the production of glutathione by Planococcus strains was some thousand folds greater than by higher plants. On the other hand, the induction of antioxidants in ST1 and ST2 was restricted to phenols, flavonoids, peroxidase, glutaredoxin, and/or SOD. The hierarchical analysis also supported strain-specific responses. This is the first report that exploited salinity stress for promoting the production of antioxidants from bacterial isolates, which can be utilized as postbiotics for promising applications in foods and pharmaceuticals.

Interactive Impact of Arbuscular Mycorrhizal Fungi and Elevated CO2 on Growth and Functional Food Value of Thymus vulgare

Arbuscular mycorrhizal fungi (AMF) and elevated CO₂ (eCO₂) have been effectively integrated to the agricultural procedures as an ecofriendly approach to support the production and quality of plants. However, less attention has been given to the synchronous application of AMF and eCO₂ and how that could affect the global plant metabolism. This study was conducted to investigate the effects of AMF and eCO₂, individually or in combination, on growth, photosynthesis, metabolism and the functional food value of Thymus vulgare. Results revealed that both AMF and eCO₂ treatments improved the photosynthesis and biomass production, however much more positive impact was obtained by their synchronous application. Moreover, the levels of the majority of the detected sugars, organic acids, amino acids, unsaturated fatty acids, volatile compounds, phenolic acids and flavonoids were further improved as a result of the synergistic action of AMF and eCO₂, as compared to the individual treatments. Overall, this study clearly shows that co-application of AMF and eCO₂ induces a synergistic biofertilization impact and enhances the functional food value of T. vulgare by affecting its global metabolism.

Starch biosynthesis contributes to the maintenance of photosynthesis and leaf growth under drought stress in maize

To understand the growth response to drought, we performed a proteomics study in the leaf growth zone of maize (Zea mays L.) seedlings and functionally characterized the role of starch biosynthesis in the regulation of growth, photosynthesis and antioxidant capacity, using the shrunken-2 mutant (sh2), defective in ADP-glucose pyrophosphorylase. Drought altered the abundance of 284 proteins overrepresented for photosynthesis, amino acid, sugar and starch metabolism, and redox-regulation. Changes in protein levels correlated with enzyme activities (increased ATP synthase, cysteine synthase, starch synthase, RuBisCo, peroxiredoxin, glutaredoxin, thioredoxin and decreased triosephosphate isomerase, ferredoxin, cellulose synthase activities, respectively) and metabolite concentrations (increased ATP, cysteine, glycine, serine, starch, proline and decreased cellulose levels). The sh2 mutant showed a reduced increase of starch levels under drought conditions, leading to soluble sugar starvation at the end of the night and correlating with an inhibition of leaf growth rates. Increased RuBisCo activity and pigment concentrations observed in WT, in response to drought, were lacking in the mutant, which suffered more oxidative damage and recovered more slowly after re-watering. These results demonstrate that starch biosynthesis contributes to maintaining leaf growth under drought stress and facilitates enhanced carbon acquisition upon recovery.

Global metabolic changes induced by arbuscular mycorrhizal fungi in oregano plants grown under ambient and elevated levels of atmospheric CO2

Symbiotic plant-microorganisms interaction is a promising approach to avoid the environmental hazards of synthetic fertilizers and pesticides. Among these, arbuscular mycorrhizal fungi (AMF) are known to improve the growth and quality of many plant species; however the detailed metabolic mechanisms behind such beneficial effects are far from complete. Further, elevated levels of atmospheric CO₂ (eCO₂) could affect such AMF-plant association. Herein, we have investigated the individual and synchronous impact of AMF and eCO₂ (620 ppm) on nutrient uptake, growth, photosynthesis, respiration, and levels of primary and secondary metabolites in oregano (Oreganum vulgare), an economically important herbal plant. Enhanced AMF colonization rate and a better mycelial growth were observed in roots of oregano grown under eCO₂. Both AMF and eCO₂ treatments significantly enhanced the growth and photosynthesis of oregano plants, however much improvements were observed by their synchronous application. eCO₂ further increased the AMF-induced dark respiration and accumulation of macro and microelements. Hierarchical clustering analysis of individual primary and secondary metabolites revealed a metabolite-dependent response toward AMF and eCO₂. The synchronous application of AMF and eCO₂ resulted in promoted accumulation of the majority of the detected sugars, organic acids, amino acids, unsaturated fatty acids, phenolic acids and flavonoids, as compared with the sole treatments. Moreover, AMF and eCO₂ acted synergistically in improving the antioxidant capacity and anti-lipid peroxidation activity of oregano. Therefore, this study suggests that AMF treatment induces a global metabolic change in oregano, the effect that is strengthened under eCO₂.

Elevated CO2 improves glucosinolate metabolism and stimulates anticancer and anti-inflammatory properties of broccoli sprouts

Sprouting process enhances plant bioactive compounds. Broccoli (Brassica oleracea L) sprouts are well known for their high levels of glucosinolates (GLs), amino acids, and antioxidants, which offer outstanding biological activities with positive impacts on plant metabolism. Elevated CO₂ (eCO₂, 620 ppm) was applied for 9 days to further improve nutritive and health-promoting values of three cultivars of broccoli sprouts i.e., Southern star, Prominence and Monotop. eCO₂ improved sprouts growth and induced GLs accumulation e.g., glucoraphanin, possibly through amino acids production e.g., high methionine and tryptophan. There were increases in myrosinase activity, which stimulated GLs hydrolysis to yield health-promoting sulforaphane. Interestingly, low levels of ineffective sulforaphane nitrile were detected and positively correlated with reduced epithiospecifier protein after eCO₂ treatment. High glucoraphanin and sulforaphane levels in eCO₂ treated sprouts improved the anticarcinogenic and anti-inflammatory properties of their extracts. In conclusion, eCO₂ treatment enriches broccoli sprouts with health-promoting metabolites and bioactivities.

Differential responses of two cyanobacterial species to R-metalaxyl toxicity: Growth, photosynthesis and antioxidant analyses

Metalaxyl is a broad-spectrum chiral fungicide that used for the protection of plants, however extensive use of metalaxyl resulted in serious environmental problems. Thus, a study on the detoxification mechanism in algae/cyanobacteria and their ability for phycoremediation is highly recommended. Here, we investigated the physiological and biochemical responses of two cyanobacterial species; Anabaena laxa and Nostoc muscorum to R-metalaxyl toxicity as well as their ability as phycoremediators. Two different levels of R-metalaxyl, at mild (10 mg/L) and high dose (25 mg/L), were applied for one-week. We found that A. laxa absorbed and accumulated more intracellular R-metalaxyl compared to N. muscorum. R-metalaxyl, which triggered a dose-based reduction in cell growth, photosynthetic pigment content, and photosynthetic key enzymes' activities i.e., phosphoenolpyruvate carboxylase (PEPC) and ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo). These decreases were significantly less pronounced in A. laxa. On the other hand, R-metalaxyl significantly induced oxidative damage markers, e.g., H₂O₂ levels, lipid peroxidation (MDA), protein oxidation and NADPH oxidase activity. However, these increases were also lower in A. laxa compared to N. muscorum. To alleviate R-metalaxyl toxicity, A. laxa induced the polyphenols, flavonoids, tocopherols and glutathione (GSH) levels as well as peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-s-transferase (GST) enzyme activities. On the contrary, the significant induction of antioxidants in N. muscorum was restricted to ascorbate, catalase (CAT) and ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) enzyme activities. Although A. laxa accumulated more R-metalaxyl, it experienced less stress due to subsequent induction of antioxidants. Therefore, A. laxa may be a promising R-metalaxyl phycoremediator. Our results provided basic data for understanding the ecotoxicology of R-metalaxyl contamination in aquatic habitats and the toxicity indices among cyanobacteria.

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.

Salicylic acid confers resistance against broomrape in tomato through modulation of C and N metabolism

It is well known that parasitic weeds such as Orobanche (broomrape) significantly decrease crop growth and yield. Although hormonal priming is a well-known inducer of plant resistance against broomrapes (Orobanche spp.), the metabolic events associated with such resistance are poorly understood. Therefore, the current work was undertaken to elucidate the role of SA in inducing tomato resistance against Orobanche, considering its impact on carbon and nitrogen metabolism of the host. Total carbon and nitrogen and levels of carbon (sugars, organic acids and fatty acids) and nitrogen (amino acids and polyamines)-containing metabolites as well as the activities of some key enzymes involved in their metabolic pathways were evaluated. Broomrape infection significantly disrupted C/N ratio in the host roots. On contrary, SA treatment markedly induced accumulation of sugars, organic acids, fatty acids, amino acids as well as polyamines in healthy plants. Under broomrape challenge, SA mitigated the infection-induced growth inhibition by improving the level of nitrogen-containing osmoprotectants (proline, arginine and some polyamines). However, a decrease was observed in some C and N assimilates which are well known to be potentially transferred to the parasite, such as sucrose, asparagine, alanine, serine and glutamate. Interestingly, SA treatment induced the catapolism of polyamines and fatty acids in the host root. Accordingly, our study suggests that SA-induced resistance against broomrape relies on the rational utilization of C and N assimilates in a manner that disturbs the sink strength of the parasite and/or activates the defense pool of the host.

How Does Proline Treatment Promote Salt Stress Tolerance During Crop Plant Development?

Soil salinity is one of the major abiotic stresses restricting the use of land for agriculture because it limits the growth and development of most crop plants. Improving productivity under these physiologically stressful conditions is a major scientific challenge because salinity has different effects at different developmental stages in different crops. When supplied exogenously, proline has improved salt stress tolerance in various plant species. Under high-salt conditions, proline application enhances plant growth with increases in seed germination, biomass, photosynthesis, gas exchange, and grain yield. These positive effects are mainly driven by better nutrient acquisition, water uptake, and biological nitrogen fixation. Exogenous proline also alleviates salt stress by improving antioxidant activities and reducing Na⁺ and Cl^- uptake and translocation while enhancing K⁺ assimilation by plants. However, which of these mechanisms operate at any one time varies according to the proline concentration, how it is applied, the plant species, and the specific stress conditions as well as the developmental stage. To position salt stress tolerance studies in the context of a crop plant growing in the field, here we discuss the beneficial effects of exogenous proline on plants exposed to salt stress through well-known and more recently described examples in more than twenty crop species in order to appreciate both the diversity and commonality of the responses. Proposed mechanisms by which exogenous proline mitigates the detrimental effects of salt stress during crop plant growth are thus highlighted and critically assessed.

Appropriate Activity Assays Are Crucial for the Specific Determination of Proline Dehydrogenase and Pyrroline-5-Carboxylate Reductase Activities

Accumulation of proline is a widespread plant response to a broad range of environmental stress conditions including salt and osmotic stress. Proline accumulation is achieved mainly by upregulation of proline biosynthesis in the cytosol and by inhibition of proline degradation in mitochondria. Changes in gene expression or activity levels of the two enzymes catalyzing the first reactions in these two pathways, namely pyrroline-5-carboxylate (P5C) synthetase and proline dehydrogenase (ProDH), are often used to assess the stress response of plants. The difficulty to isolate ProDH in active form has led several researchers to erroneously report proline-dependent NAD⁺ reduction at pH 10 as ProDH activity. We demonstrate that this activity is due to P5C reductase (P5CR), the second and last enzyme in proline biosynthesis, which works in the reverse direction at unphysiologically high pH. ProDH does not use NAD⁺ as electron acceptor but can be assayed with the artificial electron acceptor 2,6-dichlorophenolindophenol (DCPIP) after detergent-mediated solubilization or enrichment of mitochondria. Seemingly counter-intuitive results from previous publications can be explained in this way and our data highlight the importance of appropriate and specific assays for the detection of ProDH and P5CR activities in crude plant extracts.

A bHLH transcription factor, MYC2, imparts salt intolerance by regulating proline biosynthesis in Arabidopsis

MYC2, a bHLH TF, acts as regulatory hub within several signaling pathways by integration of various endogenous and exogenous signals which shape plant growth and development. However, its involvement in salt stress regulation is still elusive. This study has deciphered a novel role of MYC2 in imparting salt stress intolerance by regulating delta1 -pyrroline-5-carboxylate synthase1 (P5CS1) gene and hence proline synthesis. P5CS1 is a rate-limiting enzyme in the biosynthesis of proline. Y-1-H and EMSA studies confirmed the binding of MYC2 with the 5'UTR region of P5CS1. Transcript and biochemical studies have revealed MYC2 as a negative regulator of proline biosynthesis. Proline is necessary for imparting tolerance toward abiotic stress; however, its overaccumulation is toxic for the plants. Hence, studying the regulation of proline biosynthesis is requisite to understand the mechanism of stress tolerance. We have also studied that MYC2 is regulated by mitogen-activated protein kinase (MAPK) cascade mitogen-activated protein kinase kinase 3-MPK6 and vice versa. Altogether, this study demonstrates salt stress-mediated activation of MYC2 by MAPK cascade, regulating proline biosynthesis and thus salt stress.

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.