Physiological and biochemical changes in Moroccan barley (Hordeum vulgare L.) cultivars submitted to drought stress.

Barley (Hordeum vulgare L.) is the second most consumed and cultivated cereal by the Moroccan population. However, it is predicted that frequent drought periods, caused by climate change, can cause problems in plant growth. Thus, the selection of drought-tolerant barley cultivars is essential to ensure the security of barley's needs. We aimed to screen drought stress tolerance in Moroccan barley cultivars. We tested the drought tolerance of nine Moroccan barley cultivars ('Adrar', 'Amalou', 'Amira', 'Firdaws', 'Laanaceur', 'Massine', 'Oussama', 'Taffa', and 'Tamellalt') based on physiological and biochemical parameters. Drought stress was applied by maintaining field capacity at 40% (90% for the control), and plants were randomly arranged in a greenhouse at 25 °C under natural light conditions. Drought stress decreased relative water content (RWC), shoot dry weight (SDW), and chlorophyll content (SPAD index), but significantly increased electrolyte leakage, hydrogen peroxide, malondialdehyde (MDA), water-soluble carbohydrates, and soluble protein contents, as well as catalase (CAT) and ascorbate peroxidase (APX) activities. High levels of SDW, RWC, CAT, and APX activities were recorded in 'Firdaws', 'Laanaceur', 'Massine', 'Taffa', and 'Oussama', which can be interpreted by high drought tolerance. On the other hand, 'Adrar', 'Amalou', 'Amira', and 'Tamellalt' showed higher values of MDA and H2O2 content, which can be linked with drought sensitivity. Physiological and biochemical parameter changes are discussed in terms of barley's tolerance to drought. Tolerant cultivars could be a good background for barley breeding in areas known for the alternative of long dry spells.

Improved chromium tolerance of Medicago sativa by plant growth-promoting rhizobacteria (PGPR).

BACKGROUND: Soil pollution by heavy metals increases the bioavailability of metals like hexavalent chromium (Cr (VI)), subsequently limiting plant growth and reducing the efficiency of phytoremediation. Plant growth-promoting rhizobacteria (PGPR) have substantial potential to enhance plant growth as well as plant tolerance to metal stress. The aim of this research was to investigate Cr (VI) phytoremediation enhancement by PGPR. RESULTS: The results showed that the 27 rhizobacterial isolates studied were confirmed as Cr (VI)-resistant PGPR, by using classical biochemical tests (phosphate solubilization, nitrogen fixation, indole acetic acid, exopolysaccharides, hydrogen cyanide, siderophores, ammonia, cellulase, pectinase, and chitinase production) and showed variable levels of Cr (VI) resistance (300-600 mg/L). The best four selected Cr (VI)-resistant PGPR (NT15, NT19, NT20, and NT27) retained most of the PGP traits in the presence of 100-200 mg/L concentrations of Cr (VI). The inoculation of Medicago sativa with any of these four isolates improved the shoot and root dry weight. The NT27 isolate identified using 16S rDNA gene sequence analyses as a strain of Pseudomonas sp. was most effective in terms of plant growth promotion and stress level decrease. It increased shoot and root dry weights of M. sativa by 97.6 and 95.4%, respectively, in the presence of Cr (VI) when compared to non-inoculated control plants. It also greatly increased chlorophyll content and decreased the levels of stress markers, malondialdehyde, hydrogen peroxide, and proline. The results of the effect of Pseudomonas sp. on Cr content and bioaccumulation factor (BAF) of the shoots and roots of M. sativa plants showed the increase of plant biomass concomitantly with the increase of Cr root concentration in inoculated plants. This would lead to a higher potential of Cr (VI) phytostabilization. CONCLUSIONS: This study demonstrates that the association M. sativa-Pseudomonas sp. may be an efficient biological system for the bioremediation of Cr (VI)-contaminated soils.

Phycoremediation mechanisms of heavy metals using living green microalgae: physicochemical and molecular approaches for enhancing selectivity and removal capacity.

Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.

Mycoremediation of azo dyes using Cyberlindnera fabianii yeast strain: Application of designs of experiments for decolorization optimization.

This study investigated the dye decolorization capacity of three yeast strains. Cyberlindnera fabianii was shortlisted for its high decolorization capacity and was further tested on various azo dyes. Based on the color of the biomass, and the UV-Vis analysis, Acid Red 14 was selected as a model dye, to examine the enzymatic biodegradation. The results showed significant increase in the intracellular and extracellular activities of laccase, tyrosinase, manganese peroxidase, and azoreductase. Phytotoxicity assessment indicated that the AR14 biodegradation by-products were not phytotoxic compared to the original dye molecules. Regarding the decolorization optimization, the screening of factors using the Plackett-Burman design showed that pH, dye concentration, and shaking speed had significant effects. These factors and their combined effect were evaluated using response surface methodology with the Box-Behnken model. The pH was the most significant factor, followed by dye concentration. The analysis of the contour plot and the 3D response surface diagram showed that the decolorization was inversely proportional to the increase in the initial dye concentration, but proportional to the initial pH and shaking speed. At optimal conditions (pH = 5.154, AR14 = 50 mg/L), C. fabianii could decolorize more than 97% of AR14 within 12 hr. PRACTITIONER POINTS: Cyberlindnera fabianii is a successful candidate for dye mycoremediation. Oxidase and reductase are the key enzymes involved in the biodegradation of azo dyes. By-products of Acid red 14 biodegradation are not phytoxic compared to the original dye. Design of experience tools enables to determine optimum conditions for efficient decolorization.

Wicherhamomyces anomalus biofilm supported on wood husk for chromium wastewater treatment.

A Wickeramomyces anomalus biofilm supported on wood husk was used to remediate water bodies contaminated with chromium (Cr), in batch and open systems. The favorable adhesion ability of the chromium-resistant yeast strain on the wood husk was predicted by XDLVO theory and confirmed by environmental scanning electronic microscopy. The chromium decontamination was then optimized in a batch mode using a central composite design (CCD). Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.93-0.91 for Cr(VI) and total Cr removal, respectively, ensuring a satisfactory fitting of the second-order regression model to the experimental data. In batch system, the concentration of biomass exhibited the minimal effect on the process. An acidic pH of 3.72 and 5.48, an initial chromium concentration of 10 and 16.91 mg/L and a support dose of 6.95 and 8.20 g/L were optimal for Cr(VI) and total Cr removal, respectively. The breakthrough curves were determined in open system for different initial chromium concentrations. The study of glucose concentration effect on the yeast extracellular polymeric substances (EPS) production showed that a medium exempt of glucose allowed maximal EPS production and minimal chromium removal efficiency, while 20 g/L glucose concentration of presented the optimal condition for chromium removal.

Habitat- and soil-related drivers of the root-associated fungal community of Quercus suber in the Northern Moroccan forest.

Soil fungi associated with plant roots, notably ectomycorrhizal (EcM) fungi, are central in above- and below-ground interactions in Mediterranean forests. They are a key component in soil nutrient cycling and plant productivity. Yet, major disturbances of Mediterranean forests, particularly in the Southern Mediterranean basin, are observed due to the greater human pressures and climate changes. These disturbances highly impact forest cover, soil properties and consequently the root-associated fungal communities. The implementation of efficient conservation strategies of Mediterranean forests is thus closely tied to our understanding of root-associated fungal biodiversity and environmental rules driving its diversity and structure. In our study, the root-associated fungal community of Q. suber was analyzed using high-throughput sequencing across three major Moroccan cork oak habitats. Significant differences in root-associated fungal community structures of Q. suber were observed among Moroccan cork oak habitats (Maâmora, Benslimane, Chefchaoun) subjected to different human disturbance levels (high to low disturbances, respectively). The fungal community structure changes correlated with a wide range of soil properties, notably with pH, C:N ratio (P = 0.0002), and available phosphorus levels (P = 0.0001). More than 90 below-ground fungal indicators (P < 0.01)-either of a type of habitat and/or a soil property-were revealed. The results shed light on the ecological significance of ubiquitous ectomycorrhiza (Tomentella, Russula, Cenococcum), and putative sclerotia-associated/ericoid mycorrhizal fungal taxa (Cladophialophora, Oidiodendron) in the Moroccan cork oak forest, and their intraspecific variability regarding their response to land use and soil characteristics.

[Impact of cork oak management on the ectomycorrhizal fungal diversity associated with Quercus suber in the Mâamora forest (Morocco)]. / Impact du mode de gestion de la subéraie de la Maâmora (Maroc) sur la diversité des champignons ectomycorhiziens associés à Quercus suber.

The cork oak forest is an ecosystem playing a major role in Moroccan socio-economy and biodiversity conservation. However, this ecosystem is negatively impacted by extensive human- and climate-driven pressures, causing a strong decrease in its distribution and a worsening of the desertification processes. This study aims at characterising the impact of cork oak forest management on a major actor of its functioning, the ectomycorrhizal (EcM) fungal community associated with Quercus suber, and the determination of EcM bio-indicators. The EcM fungal community has been monitored during spring and winter seasons in two sites of the Moroccan Mâamora forest, corresponding to a forest site either impacted by human activities or protected. A significant impact of cork oak forest management on the EcM fungal community has been revealed, with major differences during the summer season. The results confirmed the potential ecological significance of several EcM fungi (e.g., Cenococcum) in the sustainability of the cork oak forest functioning, but also the significant association of certain EcM fungi (Pachyphloeus, Russula, Tomentella) with a perturbation or a season, and consequently to the cork oak forest status or to climatic conditions, respectively. The development of study at the Mediterranean scale may improve the robustness of ecological models to predict the impact of global changes on this emblematic ecosystem of Mediterranean basin.

Mechanisms of hexavalent chromium resistance and removal by microorganisms.

Chromium has been and is extensively used worldwide in multiple industrial processes and is routinely discharged to the environment from such processes. Therefore, this heavy metal is a potential threat to the environment and to public health, primarily because it is non-biodegradable and environmentally persistent. Chromium exists in several oxidation states, the most stable of which are trivalent Cr(Ill) and hexavalent Cr(VI) species. Each species possesses its own individual chemical characteristics and produces its own biological effects. For example, Cr (Ill) is an essential oligoelement for humans, whereas Cr(VI) is carcinogenic and mutagenic. Several chemical methods are used to remove Cr(VI) from contaminated sites. Each of these methods has advantages and disadvantages. Currently, bioremediation is often the preferred method to deal with Cr contaminated sites, because it is eco-friendly, cost-effective and is a "natural" technology. Many yeast, bacterial and fungal species have been assessed for their suitability to reduce or remove Cr(VI) contamination. The mechanisms by which these microorganisms resist and reduce Cr(VI) are variable and are species dependent. There are several Cr-resistance mechanisms that are displayed by microorganisms. These include active efflux of Cr compounds, metabolic reduction of Cr(VI) to Cr (ill), and either intercellular or extracellular prec1p1tation. Microbial Cr (VI) removal typically involves three stages: binding of chromium to the cell surface, translocation of chromium into the cell, and reduction of Cr(VI) to Cr (ill). Cr(VI) reduction by microorganisms may proceed on the cell surface, outside the cell, or intracellularly, either directly via chromate reductase enzymes, or indirectly via metabolite reduction of Cr(VI). The uptake of chromium ions is a biphasic process. The primary step is known as biosorption, a metabolic energyindependent process. Thereafter, bioaccumulation occurs, but is much slower, and is dependent on cell metabolic activity. Choosing an appropriate bioremediation strategy for Cr is extremely important and must involve investigating and understanding the key mechanisms that are involved in microbial resistance to and removal of Cr(VI).

Hexavalent chromium removal by a novel Serratia proteamaculans isolated from the bank of Sebou River (Morocco).

The novel Serratia proteamaculans isolated from a chromium-contaminated site was tolerant to a concentration of 500 mg Cr(VI)/l. The optimum pH and temperature for reduction of Cr(VI) by S. proteamaculans were found to be 7.0 and 30 °C, respectively. The Cr(VI) reduction rate decreased with the increase in Cr(VI) concentration from 100 to 400 mg/l, suggesting the enzymatic chromium reduction. Resting and permeabilised cell assays provided the better evidence that chromate reduction in S. proteamaculans is enzymatic. Reduction by cell-free filtrate shows no extracellular chromate-reducing activity, revealing that this activity may be associated to membrane fraction and/or cytosolic fraction. Assays conducted with cytosolic and particulate fraction of S. proteamaculans confirmed the role of membrane-bound proteins in Cr(VI) reduction. Furthermore, chromium reduced by heat-treated cells suggests that membrane-associated chromate reductase activity of S. proteamaculans is preceded by its adsorption on the cell surface.