Response of Maize Seedlings to Silicon Dioxide Nanoparticles (SiO2NPs) under Drought Stress.

Recently, the use of nanofertilizers has received a great deal of attention in managing plants under biotic and abiotic stresses. However, studies that elucidate the role of silicon dioxide nanoparticles (SiO2NPs) in regulating maize tolerance to drought stress are still at early stages of development. In this study, plants that were treated with SiO2NPs (0.25 g/L as foliar spray) displayed considerable improvement in the growth indices, despite being subjected to drought stress. In addition, the action of SiO2NPs led to a considerable rise in the levels of chlorophylls, proline, cell membrane integrity, leaf water content, and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (G-POX)). In contrast, an inverse trend was seen in the oxidative injury, the total amount of soluble sugars, and the activity of ascorbate peroxidase (APX). At the same time, carotenoids were unaffected in SiO2NPs-treated and non-treated plants under drought stress. The results of the molecular investigation that was conducted using qRT-PCR showed that the relative expression of the D2 protein of photosystem II (PsbD) was elevated in SiO2NPs-treated plants in response to drought stress, while the expression of the osmotic-like protein (OSM-34) and aquaporin (AQPs) was downregulated in SiO2NPs-treated plants in response to drought stress. This research could pave the way for further investigations into how SiO2NPs boost plant resistance to drought stress.

Evaluating the genotoxicity of salinity stress and secondary products gene manipulation in lime, Citrus aurantifolia, plants.

Salinity is a significant abiotic stress that has a profound effect on growth, the content of secondary products, and the genotoxicity of cells. Lime, Citrus aurantifolia, is a popular plant belonging to the family Rutaceae. The interest in cultivating this plant is due to the importance of its volatile oil, which is included in many pharmaceutical industries, but C. aurantifolia plants are affected by the NaCl salinity levels. In the present study, a comet assay test has been applied to evaluate the genotoxic impact of salinity at 0, 50, 100, and 200 mM of NaCl on C. aurantifolia tissue-cultured plants. Furthermore, terpene gene expression was investigated using a semi-quantitative real-time polymerase chain reaction. Results from the two analyses revealed that 200 mM of NaCl stress resulted in high levels of severe damage to the C. aurantifolia plants' DNA tail 21.8%, tail length 6.56 µm, and tail moment 3.19 Unit. The relative highest expression of RtHK and TAT genes was 2.08, and 1.693, respectively, when plants were exposed to 200 mM of NaCl, whereas pv4CL2RT expressed 1.50 in plants subjected to 100 mM of NaCl. The accumulation of transcripts for the RTMYB was 0.951 when plants were treated with NaCl at 50 mM, and RtGPPS gene was significantly decreased to 0.446 during saline exposure at 100 mM. We conclude that the comet assay test offers an appropriate tool to detect DNA damage as well as RtHK, TAT, and pv4CL2RT genes having post-transcriptional regulation in C. aurantifolia plant cells under salinity stress. Future studies are needed to assess the application of gene expression and comet assay technologies using another set of genes that show vulnerability to different stresses on lime and other plants.

Characterization of Some Cichorium Taxa Grown under Mediterranean Climate Using Morphological Traits and Molecular Markers.

The verification of taxonomic identities is of the highest significance in the field of biological study and categorization. Morpho-molecular characterization can clarify uncertainties in distinguishing between taxonomic groups. In this study, we characterized five local taxa of the genus Cichorium using morphological and molecular markers for taxonomic authentication and probably future genetic improvement. The five Cichorium taxa grown under the Mediterranean climate using morphological traits and molecular markers showed variations. The examined taxa showed a widespread range of variations in leaf characteristics, i.e., shape, type, texture, margin, and apex and cypsela characteristics i.e., shape, color, and surface pattern. The phylogenetic tree categorized the Cichorium intybus var. intybus and C. intybus var. foliosum in a single group, whereas C. endivia var. endivia was grouped separately. However, C. endivia var. crispum and C. endivia subsp. pumilum were classified as a cluster. The recorded variance between classes using the molecular markers SCoT, ISSR, and RAPD was documented at 34.43%, 36.62%, and 40.34%, respectively. Authentication using molecular tools proved the usefulness of a dichotomous indented key, as revealed by morphological identification. The integrated methodology using morphological and molecular assessment could support improved verification and authentication of the various taxa of chicory. It seems likely that the Egyptian chicory belongs to C. endivia subsp. pumilum.

Effects of Plant-Growth-Promoting Rhizobacteria (PGPR) and Cyanobacteria on Botanical Characteristics of Tomato (Solanum lycopersicon L.) Plants.

Tomatoes are an important agricultural product because they contain high concentrations of bioactive substances, such as folate, ascorbate, polyphenols, and carotenoids, as well as many other essential elements. As a result, tomatoes are thought to be extremely beneficial to human health. Chemical fertilizers and insecticides are routinely utilized to maximize tomato production. In this context, microbial inoculations, particularly those containing PGPR, may be utilized in place of chemical fertilizers and pesticides. In this study, we investigated the effects of PGPR (Bacillus subtilis, and Bacillus amyloliquefaciens) and cyanobacteria when utilized alone, and in conjunction with each other, on the growth, quality, and yield of fresh fruits of tomato plants. The results showed that the inoculation significantly increased all measured parameters of tomato plants compared with the control. Combined use of B. subtilis and B. amyloliquefaciens had a positive impact on tomato yield, increasing fruit yield. Moreover, leaflet anatomical characteristics were altered, with increased thickness of the upper epidermis, lower epidermis, palisade tissue, spongy tissue, and vascular bundles. Tomato fruit quality was improved, as measured by an increased number of fruit per plant (76% increase), fruit weight (g; 33% increase), fruit height (cm; 50% increase), fruit diameter (cm; 50%), total soluble solids (TSS; 26% increase), and ascorbic acid (mg/100 g F.W.; 75% increase), relative to the control, in the first season. In addition, fruit chemical contents (N, P, and K) were increased with inoculation. The results suggest that inoculation with B. subtilis and B. amyloliquefaciens could be successfully used to enhance tomato plant growth and yield.

Microbial Degradation, Spectral analysis and Toxicological Assessment of Malachite Green Dye by Streptomyces exfoliatus.

Malachite green (MG) dye is a common environmental pollutant that threatens human health and the integrity of the Earth's ecosystem. The aim of this study was to investigate the potential biodegradation of MG dye by actinomycetes species isolated from planted soil near an industrial water effluent in Cairo, Egypt. The Streptomyces isolate St 45 was selected according to its high efficiency for laccase production. It was identified as S. exfoliatus based on phenotype and 16S rRNA molecular analysis and was deposited in the NCBI GenBank with the gene accession number OL720220. Its growth kinetics were studied during an incubation time of 144 h, during which the growth rate was 0.4232 (µ/h), the duplication time (td) was 1.64 d, and multiplication rate (MR) was 0.61 h, with an MG decolorization value of 96% after 120 h of incubation at 25 °C. Eleven physical and nutritional factors (mannitol, frying oil waste, MgSO4, NH4NO3, NH4Cl, dye concentration, pH, agitation, temperature, inoculum size, and incubation time) were screened for significance in the biodegradation of MG by S. exfoliatus using PBD. Out of the eleven factors screened in PBD, five (dye concentration, frying oil waste, MgSO4, inoculum size, and pH) were shown to be significant in the decolorization process. Central composite design (CCD) was applied to optimize the biodegradation of MG. Maximum decolorization was attained using the following optimal conditions: food oil waste, 7.5 mL/L; MgSO4, 0.35 g/L; dye concentration, 0.04 g/L; pH, 4.0; and inoculum size, 12.5%. The products from the degradation of MG by S. exfoliatus were characterized using high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The results revealed the presence of several compounds, including leuco-malachite green, di(tert-butyl)(2-phenylethoxy) silane, 1,3-benzenedicarboxylic acid, bis(2-ethylhexyl) ester, 1,4-benzenedicarboxylic acid, bis(2-ethylhexyl) ester, 1,2-benzenedicarboxylic acid, di-n-octyl phthalate, and 1,2-benzenedicarboxylic acid, dioctyl ester. Moreover, the phytotoxicity, microbial toxicity, and cytotoxicity tests confirmed that the byproducts of MG degradation were not toxic to plants, microbes, or human cells. The results of this work implicate S. exfoliatus as a novel strain for MG biodegradation in different environments.

Molecular Identification of Zantedeschia Culture with Determination of Its Morphometric and Metabolic Activities for Mediterranean Acclimatization.

Calla lily (Zantedeschia albomaculata (Hook.) Baill.) is an herbaceous or semi-evergreen perennial grown from rhizomes. It is commonly named "Spotted Arum". Ribosomal RNAs (rRNAs) are found in all known organisms and are known for being functionally equivalent in all of them. A completely new in vitro culture protocol was applied to Z. albomaculata with two hormones, 6-Benzylaminopurine (BAP) and kinetin, to obtain full growth and multiplication. Due to their highly conserved sequences, the analysis of small-subunit rRNAs (16S-18S rRNAs) can provide precise statistical evaluation of a wide variety of phylogenetic connections. As a result, the plant's 18S rRNA gene allowed for identification and partial sequencing. Also, the traditional floral method and the novel application technique for identification were applied to Z. albomaculata. In this paper we systemically describe the structural strategies of the plant's adaptation to the surroundings at the morphological, physiological, and anatomical scale. Most the essential oils and fatty acids found in Z. albomaculata are omega fatty acids, octadecenoic acid, linoleic acid, and palmitic acid. All these fatty acids have industrial, medicinal, and pharmaceutical applications. The significant findings are the spadix sheathing leaves, and the precipitation of raphides calcium oxalate. The mitotic index showing the division activity was recorded, and it was 17.4%. The antimicrobial activity of Z. albomaculata ethanol extract was performed via the well diffusion method. This extract has shown high activity against Escherichia coli and Pseudomonas aeruginosa, compared to its lower activity against Bacillus cereus. By defining these characteristics and in vitro culture conditions, we will be able to acclimatize the plant in greenhouses, and then transfer it to the open field. The findings of this work identified the general characteristics of Zantedeschia albomaculata as an ornamental and medicinal plant in order to acclimatize this plant for cultivation in the Mediterranean climate.

Antioxidants Application Enhances Regeneration and Conversion of Date Palm (Phoenix dactylifera L.) Somatic Embryos.

Many embryogenic systems have been designed to generate somatic embryos (SEs) with the morphology, biochemistry, and vigor uniformity of zygotic embryos (ZEs). During the current investigation, several antioxidants were added to the maturation media of the developing somatic embryos of date palm. Explant material was a friable embryogenic callus that was placed in maturation media containing ABA at 0.5 mg L-1, 5 g L-1 polyethylene glycol, and 10 g L-1 phytagel. Furthermore, α-tocopherol or reduced glutathione (GSH) were used separately at (25 and 50 mg L-1). These treatments were compared to a widely used date palm combination of reduced ascorbic acid (ASC) and citric acid at 150 and 100 mg L-1, respectively, and to the medium free from any antioxidants. The relative growth percentage of embryogenic callus (EC), globularization degree, differentiation%, and SEs number were significantly increased with GSH (50 mg L-1). Additionally, the latter treatment significantly enhanced the conversion% of SEs and the number of secondary somatic embryos (SSEs). ASC and citric acid treatment increased leaf length, while α-tochopherol (50 mg L-1) elevated the number of leaves plantlet-1. GSH at 50 mg L-1 catalyzed the activities of polyphenol oxidase (PPO) and peroxidase (POD) in EC and enhanced the accumulation of proteins in SEs.

Exogenous Paclobutrazol Reinforces the Antioxidant and Antimicrobial Properties of Lavender (Lavandula officinalis L.) Oil through Modulating Its Composition of Oxygenated Terpenes.

Plant growth regulators can affect the primary and secondary metabolites of various plant species. However, the effect of paclobutrazol (PBZ) on the composition of lavender oil, especially related to the terpenoid pathway, is still unclear in literatures. In this study, the effect of PBZ as a foliar spray (0.200, 400 and 600 ppm) on the vegetative growth, phytochemical content, and both antioxidant and antimicrobial properties of lavender oil were investigated. The results indicated that all examined PBZ treatments led to a significant (p ≤ 0.05) decrease in growth parameters compared to the untreated plants. Meanwhile, the yield of essential oil was significantly decreased by the treatment of PBZ at 200 ppm compared to the control. In contrast, applied-PBZ significantly enhanced the chlorophyll content and displayed a marked change in the composition of the essential oil. This change included an obvious and significant increase in 3-carene, eucalyptol, γ-terpinene, α-pinocarvone, caryophyllene, ß-vetivenene, ß-santalol, ledol, geranyl isovalerate, farnesol, caryophyllene oxide, and phytol percentage. Generally, the highest significant values were achieved by the treatment of 400 ppm compared to the other treatments. Furthermore, this treatment showed the highest free radical scavenging activity against DPPH (1,1-diphenyl-2-picrylhydrazyl) by 13% over the control. Additionally, to determine the antimicrobial activities of the extracted oil, each treatment was examined against two strains of Gram positive bacteria (S. aureus and B. cereus), two strains of Gram negative bacteria (S. enteritidis and E. coli), and two fungal species (C. albicans and A. niger) represent the yeast modal and filamentous fungus, respectively. The findings demonstrated that all examined species were more sensitive to the oil that was extracted from lavender plants, treated with 400 ppm PBZ, compared to the other concentrations.

Folic Acid Confers Tolerance against Salt Stress-Induced Oxidative Damages in Snap Beans through Regulation Growth, Metabolites, Antioxidant Machinery and Gene Expression.

Although the effect of folic acid (FA) and its derivatives (folates) have been extensively studied in humans and animals, their effects are still unclear in most plant species, specifically under various abiotic stress conditions. Here, the impact of FA as a foliar application at 0, 0.1, and 0.2 mM was studied on snap bean seedlings grown under non-saline and salinity stress (50 mM NaCl) conditions. The results indicated that under salinity stress, FA-treated plants revealed a significant (p ≤ 0.05) increase in growth parameters (fresh and dry weight of shoot and root). A similar trend was observed in chlorophyll (Chl b), total chlorophyll, carotenoids, leaf relative water content (RWC), proline, free amino acids (FAA), soluble sugars, cell membrane stability index (CMSI), and K, Ca, and K/Na ratio compared to the untreated plants. In contrast, a significant decrease was observed in Na and salinity-induced oxidative damage as indicated by reduced H2O2 production (using biochemical and histochemical detection methods) and rate of lipid peroxidation (malondialdehyde; MDA). This enhancement was correlated by increasing the activities of antioxidant enzymes, i.e., superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX). Gene expression analyses conducted using qRT-PCR demonstrated that genes coding for the Na+/H+ antiporter protein Salt Overly Sensitive 1 (SOS1), the tonoplast-localized Na+/H+ antiporter protein (NHX1), and the multifunctional osmotic protective protein (Osmotin) were significantly up-regulated in the FA-treated plants under both saline and non-saline treatments. Generally, treatment with 0.2 mM FA was more potent than 0.1 mM and can be recommended to improve snap bean tolerance to salinity stress.

Melatonin Mitigates Drought Induced Oxidative Stress in Potato Plants through Modulation of Osmolytes, Sugar Metabolism, ABA Homeostasis and Antioxidant Enzymes.

The effect of melatonin (MT) on potato plants under drought stress is still unclear in the available literature. Here, we studied the effect of MT as a foliar application at 0, 0.05, 0.1, and 0.2 mM on potato plants grown under well-watered and drought stressed conditions during the most critical period of early tuberization stage. The results indicated that under drought stress conditions, exogenous MT significantly (p ≤ 0.05) improved shoot fresh weight, shoot dry weight, chlorophyll (Chl; a, b and a + b), leaf relative water content (RWC), free amino acids (FAA), non-reducing sugars, total soluble sugars, cell membrane stability index, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX) compared to the untreated plants. Meanwhile, carotenoids, proline, methylglyoxal (MG), H2O2, lipid peroxidation (malondialdehyde; MDA) and abscisic acid (ABA) were significantly decreased compared to the untreated plants. These responses may reveal the protective role of MT against drought induced carbonyl/oxidative stress and enhancing the antioxidative defense systems. Furthermore, tuber yield was differentially responded to MT treatments under well-watered and drought stressed conditions. Since, applied-MT led to an obvious decrease in tuber yield under well-watered conditions. In contrast, under drought conditions, tuber yield was substantially increased by MT-treatments up to 0.1 mM. These results may imply that under water deficiency, MT can regulate the tuberization process in potato plants by hindering ABA transport from the root to shoot system, on the one hand, and by increasing the non-reducing sugars on the other hand.

Exogenous Putrescine Increases Heat Tolerance in Tomato Seedlings by Regulating Chlorophyll Metabolism and Enhancing Antioxidant Defense Efficiency.

Crops around the world are facing a diversity of environmental problems, of which high temperatures are proving to be the most serious threat to crops. Polyamine putrescine (Put) acts as a master growth regulator that contributes to optimal plant growth and development and increased stress tolerance. Here, the current study aimed to elucidate how Put functions in regulating chlorophyll (Chl) metabolism, oxidative stress, and antioxidant defense, as well as to characterize the expression of genes related to heat stress in tomato seedlings under such stress. The results revealed that Put treatment significantly attenuates heat-induced damage by promoting biomass production, increasing photosynthetic efficiency, and inhibiting excessive production of oxidative stress markers. Heat stress markedly decreased the Chl content in the tomato leaf and accelerated the leaf yellowing process. However, Put-treated tomato seedlings showed a higher Chl content, which could be associated with the functions of Put in elevating PBGD activity (Chl biosynthesis enzyme) and suppressing the activity of the Chl catabolic enzyme (Chlase and MDCase). Under high-temperature stress, the expression levels of the gene encoding factors involved in Chl biosynthesis and Chl catabolism were significantly down- and upregulated, respectively, and this trend was reversed in Put-treated heat-stressed seedlings. In addition, exogenous application of Put boosted the activity of antioxidant enzymes, along with the levels of expression of their encoding genes, only in plants that were heat stressed. Furthermore, the expression levels of heat-shock-related genes (HSP90, HSP70, and HsfA1) were elevated in Put-treated, high-temperature-stressed tomato seedlings. Taken together, our results indicate that Put treatment significantly increases the heat tolerance of tomato seedlings, by elevating Chl concentrations and suppressing Chl catabolic enzyme activity, modulating endogenous free PA content, increasing antioxidant defense efficiency, and upregulating the expression of heat-shock-related genes.

Alpha Lipoic Acid as a Protective Mediator for Regulating the Defensive Responses of Wheat Plants against Sodic Alkaline Stress: Physiological, Biochemical and Molecular Aspects.

Recently, exogenous α-Lipoic acid (ALA) has been suggested to improve the tolerance of plants to a wide array of abiotic stresses. However, there is currently no definitive data on the role of ALA in wheat plants exposed to sodic alkaline stress. Therefore, this study was designed to evaluate the effects of foliar application by ALA at 0 (distilled water as control) and 20 µM on wheat seedlings grown under sodic alkaline stress (50 mM 1:1 NaHCO3 & Na2CO3; pH 9.7. Under sodic alkaline stress, exogenous ALA significantly (p ≤ 0.05) improved growth (shoot fresh and dry weight), chlorophyll (Chl) a, b and Chl a + b, while Chl a/b ratio was not affected. Moreover, leaf relative water content (RWC), total soluble sugars, carotenoids, total soluble phenols, ascorbic acid, K and Ca were significantly increased in the ALA-treated plants compared to the ALA-untreated plants. This improvement was concomitant with reducing the rate of lipid peroxidation (malondialdehyde, MDA) and H2O2. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) demonstrated greater activity in the ALA-treated plants compared to the non-treated ones. Conversely, proline, catalase (CAT), guaiacol peroxidase (G-POX), Na and Na/K ratio were significantly decreased in the ALA-treated plants. Under sodic alkaline stress, the relative expression of photosystem II (D2 protein; PsbD) was significantly up-regulated in the ALA treatment (67% increase over the ALA-untreated plants); while Δ pyrroline-5-carboxylate synthase (P5CS), plasma membrane Na+/H+ antiporter protein of salt overly sensitive gene (SOS1) and tonoplast-localized Na+/H+ antiporter protein (NHX1) were down-regulated by 21, 37 and 53%, respectively, lower than the ALA-untreated plants. These results reveal that ALA may be involved in several possible mechanisms of alkalinity tolerance in wheat plants.

Correction: Alnusairi et al. Exogenous Nitric Oxide Reinforces Photosynthetic Efficiency, Osmolyte, Mineral Uptake, Antioxidant, Expression of Stress-Responsive Genes and Ameliorates the Effects of Salinity Stress in Wheat. Plants 2021, 10, 1693.

In the original publication [...].

Protective Effect of γ-Aminobutyric Acid Against Chilling Stress During Reproductive Stage in Tomato Plants Through Modulation of Sugar Metabolism, Chloroplast Integrity, and Antioxidative Defense Systems.

Despite the role of γ-aminobutyric acid (GABA) in plant tolerance to chilling stress having been widely discussed in the seedling stage, very little information is clear regarding its implication in chilling tolerance during the reproductive stage of the plant. Here, we investigated the influence of GABA (1 and 2mM) as a foliar application on tomato plants (Solanum lycopersicum L. cv. Super Marmande) subjected to chilling stress (5°C for 6h/day) for 5 successive days during the flowering stage. The results indicated that applied GABA differentially influenced leaf pigment composition by decreasing the chlorophyll a/b ratio and increasing the anthocyanin relative to total chlorophyll. However, carotenoids were not affected in both GABA-treated and non-treated stressed plants. Root tissues significantly exhibited an increase in thermo-tolerance in GABA-treated plants. Furthermore, applied GABA substantially alleviated the chilling-induced oxidative damage by protecting cell membrane integrity and reducing malondialdehyde (MDA) and H2O2. This positive effect of GABA was associated with enhancing the activity of phenylalanine ammonia-lyase (PAL), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX). Conversely, a downregulation of peroxidase (POX) and polyphenol oxidase (PPO) was observed under chilling stress which indicates its relevance in phenol metabolism. Interesting correlations were obtained between GABA-induced upregulation of sugar metabolism coinciding with altering secondary metabolism, activities of antioxidant enzymes, and maintaining the integrity of plastids' ultrastructure Eventually, applied GABA especially at 2mM improved the fruit yield and could be recommended to mitigate the damage of chilling stress in tomato plants.

Roles of Exogenous α-Lipoic Acid and Cysteine in Mitigation of Drought Stress and Restoration of Grain Quality in Wheat.

Cysteine (Cys) and α-lipoic acid (ALA) are naturally occurring antioxidants (sulfur-containing compounds) that can protect plants against a wide spectrum of environmental stresses. However, up to now, there are no conclusive data on their integrative roles in mitigation of drought stress in wheat plants. Here, we studied the influence of ALA at 0.02 mM (grain dipping pre-cultivation treatment) and Cys (25 and 50 ppm as a foliar application) under well watered and deficit irrigation (100% and 70% of recommended dose). The results showed that deficit irrigation markedly caused obvious cellular oxidative damage as indicated by elevating the malondialdehyde (MDA) and hydrogen peroxide content (H2O2). Moreover, water stressed plants exhibited multiple changes in physiological metabolism, which affected the quantitative and qualitative variables of grain yield. The enzymatic antioxidants, including superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POX) were improved by Cys application. SOD and APX had the same response when treated with ALA, but CAT and POX did not. Moreover, both studied molecules stimulated chlorophyll (Chl) and osmolytes' biosynthesis. In contrast, the Chl a/b ratio was decreased, while flavonoids were not affected by either of the examined molecules. Interestingly, all above-mentioned changes were associated with an improvement in the scavenging capacity of reactive oxygen species (ROS), leaf relative water content (RWC), grain number, total grain yield, weight of 1000 kernels, gluten index, falling number, and alveographic parameters (P, W, and P/L values). Furthermore, heatmap plot analysis revealed several significant correlations between different studied parameters, which may explore the importance of applied Cys and ALA as effective compounds in wheat cultivation under water deficit conditions.

Exogenous Application of Alpha-Lipoic Acid Mitigates Salt-Induced Oxidative Damage in Sorghum Plants through Regulation Growth, Leaf Pigments, Ionic Homeostasis, Antioxidant Enzymes, and Expression of Salt Stress Responsive Genes.

In plants, α-Lipoic acid (ALA) is considered a dithiol short-chain fatty acid with several strong antioxidative properties. To date, no data are conclusive regarding its effects as an exogenous application on salt stressed sorghum plants. In this study, we investigated the effect of 20 µM ALA as a foliar application on salt-stressed sorghum plants (0, 75 and 150 mM as NaCl). Under saline conditions, the applied-ALA significantly (p ≤ 0.05) stimulated plant growth, indicated by improving both fresh and dry shoot weights. A similar trend was observed in the photosynthetic pigments, including Chl a, Chl b and carotenoids. This improvement was associated with an obvious increase in the membrane stability index (MSI). At the same time, an obvious decrease in the salt induced oxidative damages was seen when the concentration of H2O2 and malondialdehyde (MDA) was reduced in the salt stressed leaf tissues. Generally, ALA-treated plants demonstrated higher antioxidant enzyme activity than in the ALA-untreated plants. A moderate level of salinity (75 mM) induced the highest activities of superoxide dismutase (SOD), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX). Meanwhile, the highest activity of catalase (CAT) was seen with 150 mM NaCl. Interestingly, applied-ALA led to a substantial decrease in the concentration of both Na and the Na/K ratio. In contrast, K and Ca exhibited a considerable increase in this respect. The role of ALA in the regulation of K+/Na+ selectivity under saline condition was confirmed through a molecular study (RT-PCR). It was found that ALA treatment downregulated the relative gene expression of plasma membrane (SOS1) and vacuolar (NHX1) Na+/H+ antiporters. In contrast, the high-affinity potassium transporter protein (HKT1) was upregulated.

GABA: A Key Player in Drought Stress Resistance in Plants.

γ-aminobutyric acid (GABA) is a non-protein amino acid involved in various physiological processes; it aids in the protection of plants against abiotic stresses, such as drought, heavy metals, and salinity. GABA tends to have a protective effect against drought stress in plants by increasing osmolytes and leaf turgor and reducing oxidative damage via antioxidant regulation. Guard cell GABA production is essential, as it may provide the benefits of reducing stomatal opening and transpiration and controlling the release of tonoplast-localized anion transporter, thus resulting in increased water-use efficiency and drought tolerance. We summarized a number of scientific reports on the role and mechanism of GABA-induced drought tolerance in plants. We also discussed existing insights regarding GABA's metabolic and signaling functions used to increase plant tolerance to drought stress.

Melatonin-mediated photosynthetic performance of tomato seedlings under high-temperature stress.

Photosynthesis is a fundamental biosynthetic process in plants that can enhance carbon absorption and increase crop productivity. Heat stress severely inhibits photosynthetic efficiency. Melatonin is a bio-stimulator capable of regulating diverse abiotic stress tolerances. However, the underlying mechanisms of melatonin-mediated photosynthesis in plants exposed to heat stress largely remain elucidated. Our results revealed that melatonin treatment (100 µM) in tomato seedlings increased the endogenous melatonin levels and photosynthetic pigment content along with upregulated of their biosynthesis gene expression under high-temperature stress (42 °C for 24 h), whereas heat stress significantly decreased the values of gas exchange parameters. Under heat stress, melatonin boosted CO2 assimilation, i.e., Vc,max (maximum rate of ribulose-1,5-bisphosphate carboxylase, Rubisco), and Jmax (electron transport of Rubisco generation) and also enhanced the Rubisco and FBPase activities, which resulted in upregulated photosynthetic related gene expression. In addition, heat stress greatly reduced the photochemical chemistry of photosystem II (PSII) and photosystem I (PSI), particularly the maximum quantum efficiency of PSII (Fv/Fm) and PSI (Pm). Conversely, melatonin supplementation increased the chlorophyll a fluorescence parameters led to amplifying the electron transport efficiency. Moreover, heat stress decreased the actual PSII efficiency (ΦPSII), electron transport rate (ETR) and photochemical quenching coefficient (qP), while increasing nonphotochemical quenching (NPQ); however, melatonin reversed these values, which helps to fostering the dissipation of excess excitation energy. Taken together, our results provide a concrete insight into the efficacy of melatonin-mediated photosynthesis performance in a high-temperature regime.

Beneficial Features of Biochar and Arbuscular Mycorrhiza for Improving Spinach Plant Growth, Root Morphological Traits, Physiological Properties, and Soil Enzymatic Activities.

Biochar and arbuscular mycorrhizal fungi (AMF) can promote plant growth, improve soil properties, and maintain microbial activity. The effects of biochar and AMF on plant growth, root morphological traits, physiological properties, and soil enzymatic activities were studied in spinach (Spinacia oleracea L.). A pot experiment was conducted to evaluate the effect of biochar and AMF on the growth of spinach. Four treatments, a T1 control (soil without biochar), T2 biochar alone, T3 AMF alone, and T4 biochar and AMF together, were arranged in a randomized complete block design with five replications. The biochar alone had a positive effect on the growth of spinach, root morphological traits, physiological properties, and soil enzymatic activities. It significantly increased the plant growth parameters, such as the shoot length, leaf number, leaf length, leaf width, shoot fresh weight, and shoot dry weight. The root morphological traits, plant physiological attributes, and soil enzymatic activities were significantly enhanced with the biochar alone compared with the control. However, the combination of biochar and AMF had a greater impact on the increase in plant growth, root morphological traits, physiological properties, and soil enzymatic activities compared with the other treatments. The results suggested that the combined biochar and AMF led to the highest levels of spinach plant growth, microbial biomass, and soil enzymatic activity.