Exogenous application of agmatine improves water stress and salinity stress tolerance in turnip (Brassica rapa L.)

This study was carried out to determine the consequence of foliar application of agmatine (0 and 0.5 mM), on growth, physiological and biochemical traits, and yield of turnip (Brassica rapa L.) plants grown under water stress or salt stress conditions. The effect of three irrigation regimes (100%, 80% and 40% of field capacity) and three salt concentrations (0, 100 and 200 mM NaCl) on turnip plants grown in pots under greenhouse conditions were studied.  Water deficit developed at 40% Field capacity (FC) and salinity stress, especially at 200 mM, resulted in significant decreases in all growth parameters when compared to control plants (100% FC) including root length and diameter as well as shoot weights per plant. Water stress and high salt stress negatively affected most physiological and biochemical characteristics such as total chlorophyll, photosynthetic rate, stomatal conductance, and transpiration rate. Water use efficiency (WUE) increased under 80% FC or 100 mM NaCl. Antioxidant enzymes activity, catalase and peroxidase and glutathione reductase, increased with water stress and salt stress. Foliar application of agmatine seemed to alleviate the adverse effects of water stress and salt stress on turnip. Alleviating harmful effects of salt stress and enhancing water stress tolerance by agmatine was associated with improving leaf gas exchange, antioxidant enzymes and protein profile

Microbiome structure and response to watering in rhizosphere of Nitrosalsola vermiculata and surrounding bulk soil

The plant rhizosphere microbiomes were thought to help the plant stands adverse condition. The study aims at deciphering signatures of rhizosphere soil microbiomes of the medicinal plant Nitrosalsola vermiculata and those of the surrounding bulk soil as well as to detect influence of watering in restructuring soil microbes that can improve the plant’s ability to tolerate drought stress. Amplicon sequencing of partial 16S rRNA gene indicated that alpha diversity indices are higher in rhizosphere than in bulk soils, while no distinctive differences were observed due to the watering. Relative abundance of phylum Cyanobacteria and its descendent unidentified genus is the highest among phyla and genera of bulk soil. Relative abundance of phyla Euryarchaeota, Chloroflexi, Actinobacteria, Proteobacteria, Bacteroidetes, Firmicutes, Acidobacteria and Gemmatimonadetes as well as genera Bacillus, Ammoniphilus, Sphingomonas, Microvirga, Pontibacter, Adhaeribacter and Arthrobacter was significantly higher in rhizosphere soil. The latter taxa were reported to act as plant growth-promoting bacteria (PGPB) through symbiotic associations. We speculate that relative abundance and mutual dominance of these taxa in rhizosphere of N. vermiculata were due to the intensity and type of plant root exudates. Other factors include soil pH where microbes favoring high soil pH can show better growth in rhizosphere soil. Also, co-existence of phyla that promote sustainability of cohabiting phyla in the rhizosphere and have high synergism prevalence in biofilm formation can be one extra factor. Quorum sensing (QS) also mediates bacterial population density in a given environment and elicit specific plant responses. The low abundance of Cyanobacteria in rhizosphere soil can be due to the inhibitory effect of highly abundant members of Firmicutes, especially those of genus Bacillus. The latter conclusion was confirmed by the occurrence of high expression rate of comQ gene triggering QS in genus Bacillus. Highly abundant microbes whose abundance was not changed due to watering are phyla Firmicutes, Proteobacteria, Chloroflexi and Cyanobacteria and their descendent genera Bacillus, Ammoniphilus, Sphingomonas, Microvirga and unidentified genus of Cyanobacteria. We speculate that non-responsive taxa to watering were drought tolerant and can help plants stand adverse conditions of water scarce. In conclusion, insights on the factors involved in shaping microbiome signatures and those eliciting differential plant responses to drought stress are raised and warrant further investigations

Assessing the probiotic potential, antioxidant, and antibacterial activities of oat and soy milk fermented with Lactiplantibacillus plantarum strains isolated from Tibetan Kefir

Sufficient intake of probiotics has been shown to help in the digestion, protect the body against pathogenic microorganisms and boost the immune system. Recently, due to high prevalence of milk allergies and lactose intolerance in population, the non-dairy based probiotic alternative are becoming increasing popular. In this context, the oat milk and soya milk-based fermented products can be an ideal alternative for the development of Lactic acid bacteria bacteria based probiotics. These bacteria can not only improve the product’s flavor and bioavailability but also increases its antibacterial and antioxidant capabilities due to fermentation process. The purpose of the resent work was to assess the antioxidant and probiotic properties of oat and soy milk that had been fermented with three different strains of Lactiplantibacillus plantarum (L. plantarum) including L. plantarum 12–3, L. plantarum K25, and L. plantarum YW11 isolated from Tibetan Kefir. Different validated assays were used to evaluate the probiotic properties, adhesion and survival in the digestive system (stomach, acid and bile salts resistance), antioxidant and antimicrobial activities and safety (ABTS and DPPH scavenging assays) of these strains. Results of the study showed that soya milk and oat milk fermented with L. plantarum strains possess promising probiotic, antibacterial and antioxidant properties. These results can be helpful to produce dairy-free probiotic replacements, which are beneficial for those who are unable to consume dairy products due to dietary or allergic restrictions

Glycine-betaine induced salinity tolerance in maize by regulating the physiological attributes, antioxidant defense system and ionic homeostasis

The plants are exposed to different abiotic stresses, including the salinity stress (SS) that negatively affect the growth, metabolism, physiological and biochemical processes. Thus, this study investigated the effect of diverse levels of foliar-applied GB (0 control, 50 mM and 100 mM) on maize growth, membrane stability, physiological and biochemical attributes, antioxidant enzymes and nutrients accumulation under different levels of SS (i.e., control, 6 dS m-1, 12 dS m-1). Salt stress diminished the root and shoot length, root and shoot biomass, chlorophyll contents, photosynthetic rate (Pn), stomatal conductance (gs), relative water contents (RWC), soluble proteins (SP) and free amino acids; (FAA); and increased activities of antioxidant enzymes, electrical conductivity (EC) and accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2), Na+ and Cl− ions. GB application significantly increased root and shoot growth, leaves per plant, shoots length, chlorophyll contents, gs, Pn and membrane stability by reducing MDA and H2O2 accumulation. Moreover, GB also increased the SP, FAA accumulation, activities of antioxidant enzymes and Na+ and Cl- exclusion by favouring Ca2+ and K+ accumulation. In conclusion, the foliar-applied GB increased Pn, gs, ant-oxidants activities, and accumulation of SP and FAA; and reduced the accretion of Na+ and Cl− by favouring the Ca2+ and K+ accretion which in turns improved growth under SS

Enhancing antioxidant defense system of mung bean with a salicylic acid exogenous application to mitigate cadmium toxicity

Cadmium (Cd) accumulation is an emerging environmental hazard and has detrimental effects on plant growth and development. Salicylic acid (SA) is a well-known plant growth regulator that can initiate various molecular pathways to ameliorate Cd toxicity. The experiment was executed to scrutinize the mediatory role of SA to accelerate the defensive mechanism of mung bean in response to Cd stress. Mung bean plants were exposed to 0, 5, 10 and 15 mg Cd kg-1 of soil. Exogenous application of SA 0, 10-6 and 10-3 M was added prior flowering. Results exhibited that Cd stress considerably reduced the growth-related attributes i.e. shoot length, root length, fresh and dry biomass, total soluble protein, total amino acids, relative water contents and photosynthetic pigments. Cadmium stress showed a significant increase in antioxidants levels such as peroxidase (POD), ascorbate peroxidase (APX), ascorbic acid (AsA), and catalase (CAT) and promoted the accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents. However, exogenously applied SA significantly improved plant biomass and photosynthetic pigments under Cd stress. Moreover, SA improved the defensive system by enhancing antioxidants’ activities under the increasing concentration of Cd stress. Furthermore, SA reduced the Cd uptake, membrane damage and, H2O2 and MDA accumulation. The study's findings concluded that exogenous-applied SA enhanced plant growth, promoted the antioxidant activities, and reduced the oxidative damage in mung bean seedlings under Cd stress

Investigating the metagenomics of the bacterial communities in the rhizosphere of the desert plant Senna italica and their role as plant growth promoting factors

Natural microbial communities associated with desert plants are found in soils that face nutrient deficiencies and extreme environments, including salinity and drought. In this study, 16S rRNA metagenomic sequencing was used to screen and identify bacterial assemblies associated with the desert plant Senna italica, obtained from diverse soil samples located in the Asfan region, northeast of Jeddah, Saudi Arabia. Several studies found Senna italica as a valuable medicinal plant for treating different diseases; however, a few studies were done on its association with bacterial communities under drought conditions. This study aimed to identify bacterial communities present in the drought soil environment of the Senna italica plants. To approach our goals, we applied metagenomic techniques, discovering a new bacterial strain beneficial for biotechnological applications. Our results showed that the analysis of the 16S rRNA sequences at the taxonomic phylum level detected 15 phyla of bacterial populations in the soil samples. The most prevalent was kept for further research. Our findings demonstrated that rhizospheric bacteria may be used as indicators of plant growth rate and survival ability in hostile environments. Studying the soil microbiome's taxonomic, phylogenetic, and functional diversity will facilitate identifying new candidates for biological agents that can be used to improve agricultural and industrial processes

Field Crop Responses and Management Strategies to Mitigate Soil Salinity in Modern Agriculture: A Review

The productivity of cereal crops under salt stress limits sustainable food production and food security. Barley followed by sorghum better adapts to salinity stress, while wheat and maize are moderately adapted. However, rice is a salt-sensitive crop, and its growth and grain yield are significantly impacted by salinity stress. High soil salinity can reduce water uptake, create osmotic stress in plants and, consequently, oxidative stress. Crops have evolved different tolerance mechanisms, particularly cereals, to mitigate the stressful conditions, i.e., effluxing excessive sodium (Na+) or compartmentalizing Na+ to vacuoles. Likewise, plants activate an antioxidant defense system to detoxify apoplastic cell wall acidification and reactive oxygen species (ROS). Understanding the response of field crops to salinity stress, including their resistance mechanisms, can help breed adapted varieties with high productivity under unfavourable environmental factors. In contrast, the primary stages of seed germination are more critical to osmotic stress than the vegetative stages. However, salinity stress at the reproductive stage can also decrease crop productivity. Biotechnology approaches are being used to accelerate the development of salt-adapted crops. In addition, hormones and osmolytes application can mitigate the toxicity impact of salts in cereal crops. Therefore, we review the salinity on cereal crops physiology and production, the management strategies to cope with the harmful negative effect on cereal crops physiology and production of salt stress

Biochar and Its Broad Impacts in Soil Quality and Fertility, Nutrient Leaching and Crop Productivity: A Review

Biochar is gaining significant attention due to its potential for carbon (C) sequestration, improvement of soil health, fertility enhancement, and crop productivity and quality. In this review, we discuss the most common available techniques for biochar production, the main physiochemical properties of biochar, and its effects on soil health, including physical, chemical, and biological parameters of soil quality and fertility, nutrient leaching, salt stress, and crop productivity and quality. In addition, the impacts of biochar addition on salt-affected and heavy metal contaminated soils were also reviewed. An ample body of literature supports the idea that soil amended with biochar has a high potential to increase crop productivity due to the concomitant improvement in soil structure, high nutrient use efficiency (NUE), aeration, porosity, and water-holding capacity (WHC), among other soil amendments. However, the increases in crop productivity in biochar-amended soils are most frequently reported in the coarse-textured and sandy soils compared with the fine-textured and fertile soils. Biochar has a significant effect on soil microbial community composition and abundance. The negative impacts that salt-affected and heavy metal polluted soils have on plant growth and yield and on components of soil quality such as soil aggregation and stability can be ameliorated by the application of biochar. Moreover, most of the positive impacts of biochar application have been observed when biochar was applied with other organic and inorganic amendments and fertilizers. Biochar addition to the soil can decrease the nitrogen (N) leaching and volatilization as well as increase NUE. However, some potential negative effects of biochar on microbial biomass and activity have been reported. There is also evidence that biochar addition can sorb and retain pesticides for long periods of time, which may result in a high weed infestation and control cost

Use of Metagenomic Whole Genome Shotgun Sequencing Data in Taxonomic Assignment of Dipterygium glaucum Rhizosphere and Surrounding Bulk Soil Microbiomes, and Their Response to Watering

The metagenomic whole genome shotgun sequencing (mWGS) approach was used to detect signatures of the rhizosphere microbiomes of Dipterygium glaucum and surrounding bulk soil microbiomes, and to detect differential microbial responses due to watering. Preliminary results reflect the reliability of the experiment and the rationality of grouping microbiomes. Based on the abundance of non-redundant genes, bacterial genomes showed the highest level, followed by Archaeal and Eukaryotic genomes, then, the least abundant viruses. Overall results indicate that most members of bacteria have a higher abundance/relative abundance (AB/RA) pattern in the rhizosphere towards plant growth promotion, while members of eukaryota have a higher pattern in bulk soil, most likely acting as pathogens. The results also indicate the contribution of mycorrhiza (genus Rhizophagus) in mediating complex mutualistic associations between soil microbes (either beneficial or harmful) and plant roots. Some of these symbiotic relationships involve microbes of different domains responding differentially to plant root exudates. Among these are included the bacterial genus Burkholderia and eukaryotic genus Trichoderma, which have antagonistic activities against the eukaryotic genus Fusarium. Another example involves Ochrobactrum phage POA1180, its bacterial host and plant roots. One of the major challenges in plant nutrition involves other microbes that manipulate nitrogen levels in the soil. Among these are the microbes that perform contraversal actions of nitrogen fixation (the methanogen Euryarchaeota) and ammonia oxidation (Crenarchaeota). The net nitrogen level in the soil is originally based on the AB/RA of these microbes and partially on the environmental condition. Watering seems to influence the AB/RA of a large number of soil microbes, where drought-sensitive microbes (members of phyla Acidobacteria and Gemmatimonadetes) showed an increased AB/RA pattern after watering, while others (Burkholderia and Trichoderma) seem to be among microbes assisting plants to withstand abiotic stresses. This study sheds light on the efficient use of mWGS in the taxonomic assignment of soil microbes and in their response to watering. It also provides new avenues for improving biotic and abiotic resistance in domestic plant germplasm via the manipulation of soil microbes

Functional Interpretation of Cross-Talking Pathways with Emphasis on Amino Acid Metabolism in Rhizosphere Microbiome of the Wild Plant Moringa oleifera

The functional processes and mutual benefits of the wild plant Moringa oleifera and its rhizosphere microbiome were studied via metagenomic whole-genome shotgun sequencing (mWGS) in comparison with a bulk soil microbiome. The results indicated high gene abundance of the four KEGG categories, “Cellular Processes”, “Environmental Information Processing”, “Genetic Information Processing”, and “Metabolism”, in the rhizosphere microbiome. Most of the enriched enzymes in rhizobacteria are assigned to the pathway “Amino acids metabolism”, where soil-dwelling microbes use amino acids as a defense mechanism against phytopathogens, while promoting growth, colonizing the cohabiting commensal microbes and conferring tolerance against abiotic stresses. In the present study, it was proven that these beneficial microbes include Bacillus subtilis, Pseudomonas fluorescens, and Escherichia coli. Mineral solubilization in these rhizobacteria can make nutrients available for plant utilization. These rhizobacteria extensively synthesize and metabolize amino acids at a high rate, which makes nitrogen available in different forms for plants and microbes. Amino acids in the rhizosphere might stand mainly as an intermediate switcher for the direction of the soil nitrogen cycle. Indole acetic acid (IAA) was proven to be synthesized by these beneficial rhizobacteria via route indole-3-pyruvate (IPyA) of the pathway “Tryptophan metabolism”. This hormone might stand as a shuttle signaling molecule between M. oleifera and its rhizobacteria. Tryptophan is also metabolized to promote other processes with important industrial applications. Rhizobacteria were also proven to breakdown starch and sucrose into glucose, which is the primary metabolic fuel of living organisms. In conclusion, we assume that the metabolic processes in the rhizosphere microbiome of this wild plant can be eventually utilized in boosting the sustainability of agriculture applications and the plant’s ability to benefit from soil nutrients when they are not in the form available for plant root absorption