Differential responses of Hollyhock (Alcea rosea L.) varieties to salt stress in relation to physiological and biochemical parameters.

The response of 14 Hollyhock (Alcea rosea L.) varieties to salinity were evaluated in a field experiment over two growing seasons. Carotenoid, Chl a, Chl b, total Chl, proline and MDA content, CAT, APX and GPX activity and petal and seeds yields were determined in order to investigate the mechanism of salt tolerance exhibited by Hollyhock, and too identify salt tolerant varieties. Overall, the photosynthetic pigment content,petal and seed yields were reduced by salt stress. Whereas the proline and MDA content, and the CAT, APX and GPX activities increased as salt levels increased. However, the values of the measured traits were dependent upon the on the level of salt stress, the Varietie and the interaction between the two variables. Based upon the smallest reduction in petal yield, the Masouleh variety was shown to be the most salt tolerant, when grown under severe salt stress. However, based upon the smallest reduction in seed yield, Khorrmabad was the most tolerant variety to severe salt stress. These data suggest that the selection of more salt tolerant Hollyhock genotypes may be possible based upon the wide variation in tolerance to salinity exhibited by the varieties tested.

Physiological and oxidative stress response of carrot (Daucus carota L.) to jumping plant-louse Bactericera trigonica Hodkinson (Hemiptera: Psylloidea) infestation.

BACKGROUND: Carrot is an important vegetable crop grown worldwide. The major economic problem in carrot cultivation is yellow disease caused by Bactericera trigonica, which induces biotic stress and has the greatest impact on crop productivity. Comprehensive studies on the mechanism of carrot defense response to biotic stress caused by B. trigonica infestation have yet to be conducted. METHODS: The changes in photosynthetic pigments, proline, TPC, H2O2 and MDA content, DPPH radical scavenging ability, and antioxidant enzyme activity of SOD, CAT, and POX in carrot leaves in response to insect sex (female and male), rapid response (during the first six hours), and long-term response to B. trigonica infestation were evaluated. RESULTS: The results of our study strongly suggest that B. trigonica infestation causes significant changes in primary and secondary metabolism and oxidative status of carrot leaves. Photosynthetic pigment content, TPC, and DPPH and CAT activities were significantly reduced in carrot leaves in response to insect infestation. On the other hand, proline, H2O2 content, and the activity of the antioxidant enzymes superoxide dismutase and peroxidase were increased in carrot leaves after B. trigonica infestation. The results indicate that B. trigonica attenuates and delays the oxidative stress responses of carrot, allowing long-term feeding without visible changes in the plant. Carrot responded to long-term B. trigonica infestation with an increase in SOD and POX activity, suggesting that these enzymes may play a key role in plant defense mechanisms. CONCLUSIONS: This is the first comprehensive study strongly suggesting that B. trigonica infestation causes significant changes in primary and secondary metabolism and an attenuated ROS defense response in carrot leaves that enables long-term insect feeding. The information provides new insights into the mechanisms of carrot protection against B. trigonica infestation.

Contribution of amino acids in the active site of dipeptidyl peptidase 4 to the catalytic action of the enzyme.

Dipeptidyl peptidase 4 (DP4)/CD26 regulates the biological function of various peptide hormones by releasing dipeptides from their N-terminus. The enzyme is a prominent target for the treatment of type-2 diabetes and various DP4 inhibitors have been developed in recent years, but their efficacy and side effects are still an issue. Many available crystal structures of the enzyme give a static picture about enzyme-ligand interactions, but the influence of amino acids in the active centre on binding and single catalysis steps can only be judged by mutagenesis studies. In order to elucidate their contribution to inhibitor binding and substrate catalysis, especially in discriminating the P1 amino acid of substrates, the amino acids R125, N710, E205 and E206 were investigated by mutagenesis studies. Our studies demonstrated, that N710 is essential for the catalysis of dipeptide substrates. We found that R125 is not important for dipeptide binding but interacts in the P1`position of the peptide backbone. In contrast to dipeptide substrates both amino acids play an essential role in the binding and arrangement of long natural substrates, particularly if lacking proline in the P1 position. Thus, it can be assumed that the amino acids R125 and N710 are important in the DP4 catalysed substrate hydrolysis by interacting with the peptide backbone of substrates up- and downstream of the cleavage site. Furthermore, we confirmed the important role of the amino acids E205 and E206. However, NP Y, displaying proline in P1 position, is still processed without the participation of E205 or E206.

Mycorrhizosphere bacteria inhibit chromium uptake and phytotoxicity by regulating proline metabolism, antioxidant defense system, and aquaporin gene expression in tomato.

Chromium (Cr) contamination in soil-plant systems poses a pressing environmental challenge due to its detrimental impacts on plant growth and human health. Results exhibited that Cr stress decreased shoot biomass, root biomass, leaf relative water content, and plant height. However, single and co-application of Bacillus subtilis (BS) and arbuscular mycorrhizal fungi (AMF) considerably enhanced shoot biomass (+ 21%), root biomass (+ 2%), leaf relative water content (+ 26%), and plant height (+ 13) under Cr stress. The frequency of mycorrhizal (F) association (+ 5%), mycorrhizal colonization (+ 13%), and abundance of arbuscules (+ 5%) in the non-stressed soil was enhanced when inoculated with combined BS and AMF as compared to Cr-stressed soil. The co-inoculation with BS and AMF considerably enhanced total chlorophyll, carotenoids, and proline content in Cr-stressed plants. Cr-stressed plants resulted in attenuated response in SOD, POD, CAT, and GR activities when inoculated with BS and AMF consortia by altering oxidative stress biomarkers (H2O2 and MDA). In Cr-stressed plants, the combined application of BS and AMF considerably enhanced proline metabolism, for instance, P5CR (+ 17%), P5CS (+ 28%), OAT (- 22%), and ProDH (- 113%) as compared to control. Sole inoculation with AMF downregulated the expression of SIPIP2;1, SIPIP2;5, and SIPIP2;7 in Cr-stressed plants. However, the expression of NCED1 was downregulated with the application of sole AMF. In contrast, the relative expression of Le4 was upregulated in the presence of AMF and BS combination in Cr-stressed plants. Therefore, it is concluded that co-application of BS and AMF enhanced Cr tolerance by enhancing proline metabolism, antioxidant enzymes, and aquaporin gene expression. Future study might concentrate on elucidating the molecular processes behind the synergistic benefits of BS and AMF, as well as affirming their effectiveness in field experiments under a variety of environmental situations. Long-term research on the effect of microbial inoculation on soil health and plant production might also help to design sustainable chromium remediation solutions.

Overexpression of P5CDH from Cleistogenes songorica improves alfalfa growth performance under field drought conditions.

Water stress affects the metabolic regulation and delays the growth and development of alfalfa, causing a reduction in biomass. New alfalfa germplasm was created with improved drought tolerance in greenhouse conditions by introducing the key gene P5CDH1 from C. songorica, a xerophytic grass. However, the field adaptability and response mechanism of new drought-tolerant alfalfa germplasms under water stress are still unclear. In the present study, the yield and quality traits of transgenic CsP5CDH1 alfalfa lines under water stress and normal irrigation conditions were measured and analyzed for two years. The genetic variance components of the tested traits were calculated from the data fitted by the mixed linear model. The plant height of all lines showed significant genotypic variation (σ2g) (P < 0.05), and the stem diameter, stem number, and dry weight of all lines had a significant genotype × environment interaction (σ2ge) (P < 0.05). The heritability (H) of plant height, stem diameter, stem number, dry weight and leaf-to-stem ratio of alfalfa lines were 0.87, 0.52, 0.59, 0.52 and 0.50, respectively. There were significant genotype × environment interactions (σ2ge) (P < 0.05) for the quality traits of all lines. The heritabilities (H) of acid detergent fiber and neutral detergent fiber were 0.65 and 0.64, respectively. The results of transcriptional expression analysis with RNA-seq showed that the genes MsProDH1, MsProDH4, MsProDH5, MsP5CDH1, MsP5CS5, MsP5CS9, and MsP5CR1, which are involved in the proline metabolism pathway, played an important role in the drought tolerance of innovative alfalfa germplasm. Under water stress, with the regulation of key genes in the proline metabolism pathway, the proline content of all alfalfa lines increased to varying degrees. Among them, the proline content in the shoots and roots of transgenic line L6 was 7.29 times and 12.22 times that under normal irrigation conditions, respectively. The present study helped to clarify that the new germplasm of alfalfa transformed with the CsP5CDH gene synthesized a large amount of proline under water stress, and effectively slowed leaf water loss, thus improving the drought resistance of alfalfa.

Metabolomics combined with physiology and transcriptomics reveal how Nicotiana tabacum leaves respond to cold stress.

Low temperature-induced cold stress is a major threat to plant growth, development and distribution. Unraveling the responses of temperature-sensitive crops to cold stress and the mechanisms of cold acclimation are critical for food demand. In this study, combined physiological, transcriptomic, and metabolomic analyses were conducted on Nicotiana tabacum suffering short-term 4 °C cold stress. Our results showed that cold stress destroyed cellular membrane stability, decreased the chlorophyll (Chl) and carotenoid contents, and closed stomata, resulting in lipid peroxidation and photosynthesis restriction. Chl fluorescence measurements revealed that primary photochemistry, photoelectrochemical quenching and photosynthetic electron transport in Nicotiana tabacum leaves were seriously suppressed upon exposer to cold stress. Enzymatic and nonenzymatic antioxidants, including superoxide dismutase, catalase, peroxidase, reduced glutathione, proline, and soluble sugar, were all profoundly increased to trigger the cold acclimation defense against oxidative damage. A total of 178 metabolites and 16,204 genes were differentially expressed in cold-stressed Nicotiana tabacum leaves. MEturquoise and MEblue modules identified by WGCNA were highly correlated with physiological indices, and the corresponding hub genes were significantly enriched in pathways related to photosynthesis - antenna proteins and flavonoid biosynthesis. Untargeted metabolomic analysis identified specific metabolites, including sucrose, phenylalanine, glutamine, glutamate, and proline, that enhance plant cold acclimation. Combined transcriptomics and metabolomic analysis highlight the vital roles of carbohydrate and amino acid metabolism in enhancing the cold tolerance of Nicotiana tabacum. Our comprehensive investigation provides novel insights for efforts to alleviate low temperature-induced oxidative damage to Nicotiana tabacum plants and proposes a breeding target for cold stress-tolerant cultivars.

Exogenous application of mycotoxin fusaric acid improve the morphological, cytogenetic, biochemical and anatomical parameters in salt (NaCl) stressed Allium cepa L.

Salinity is one of the most important abiotic stress factors that negatively affect plant growth and development. In contrast, fusaric acid (FA), a mycotoxin produced by Fusarium and Giberella fungal genera, has biological and metabolic effects in various plants. In this study, it was aimed to investigate the protective effect of externally applied FA (0.1 nM) against the damage caused by salt (0.15 M NaCl) stress in onion (Allium cepa L.) plant. Salt stress resulted in an increase in the chromosomal aberrations (CAs) and micronucleus (MN) frequency, a decrease in the mitotic index (MI), fresh weight, root number, germination percentage, and root length. It promoted CAs such as irregular mitosis, bilobulated nuclei, chromosome loss, bridge, unequal seperation of chromosome, vagrant chromosome and polar slip in root meristem cells. In addition, salt stress caused a enhancement in free proline (PR), catalase (CAT), superoxide dismutase (SOD) and malondialdehyde (MDA) contents in the roots of onion plant. Moreover, it revealed damage and changes that include the accumulation of some chemical substances such as proline and sugars in epidermis and cortex layer cells, epidermal cell injury, flattening of the cell nucleus, wall thickening in cortex cells, necrotic areas and indistinct transmission tissue in the anatomical structure of onion roots. On the other hand, FA application promoted bulb germination and mitotic activity, strengthened the antioxidant defense system, and reduced chromosome and anatomical structure damages. In conclusion; it has been revealed that exogenous FA application may have a positive effect on increasing the resistance of onion plants to salt stress.

Physiological and transcriptomic analysis of tomato in response to sub-optimal temperature stress.

Tomato (Solanum lycopersicum L.) is one of the most important economic crops in China. However, its quality and yield are susceptible to the adverse effects of low temperatures. In our study, two tomato cultivars, showing different tolerance to low temperatures, namely the cold-sensitive tomato cultivar (S708) and cold-tolerant tomato cultivar (T722), were grown at optimal (25/18°C) and sub-optimal (15/10°C) temperature conditions for 5 days. Our study aimed to explore the effect of sub-optimal temperature on fresh weight, chlorophyll content and chlorophyll fluorescence, soluble sugars and proline content of two tomato cultivars. Moreover, we employed RNA-Seq to analyze the transcriptomic response of tomato roots to sub-optimal temperature. The results revealed that S708 showed a more significant reduction in fresh weight, chlorophyll content, photochemical efficiency of PSII (YII), maximum quantum yield of PSII (Fv/Fm), photochemical quenching (qP) and electron transport rate (ETR) compared to T722 under the sub-optimal temperature condition. Notably, T722 maintained higher level of soluble sugars and proline in comparison to S708 uner sub-optimal temperature. RNA-seq data showed that up-regulated DEGs in both tomato cultivars were involved in "plant-pathogen interaction", "MAPK signaling pathway", "plant hormone signal transduction", and "phosphatidylinositol signaling system". Furthermore, "Amino sugar and nucleotide sugar metabolism" pathway was enriched only in T722. Moreover, under sub-optimal temperature, transcription factor genes and osmoregulation genes showed varying degrees of response in both tomato cultivars. Conclusion: In summary, our results offer detailed insights into the response characteristics of tomato to sub-optimal temperature, providing valuable references for the practical management of tomato crops under sub-optimal temperature condition.

Potassium-Switch Signaling Pathway Dictates Acute Blood Pressure Response to Dietary Potassium.

BACKGROUND: Potassium (K+)-deficient diets, typical of modern processed foods, increase blood pressure (BP) and NaCl sensitivity. A K+-dependent signaling pathway in the kidney distal convoluted tubule, coined the K+ switch, that couples extracellular K+ sensing to activation of the thiazide-sensitive NaCl cotransporter (NCC) and NaCl retention has been implicated, but causality has not been established. METHODS: To test the hypothesis that small, physiological changes in plasma K+ (PK+) are translated to BP through the switch pathway, a genetic approach was used to activate the downstream switch kinase, SPAK (SPS1-related proline/alanine-rich kinase), within the distal convoluted tubule. The CA-SPAK (constitutively active SPS1-related proline/alanine-rich kinase mice) were compared with control mice over a 4-day PK+ titration (3.8-5.1 mmol) induced by changes in dietary K+. Arterial BP was monitored using radiotelemetry, and renal function measurements, NCC abundance, phosphorylation, and activity were made. RESULTS: As PK+ decreased in control mice, BP progressively increased and became sensitive to dietary NaCl and hydrochlorothiazide, coincident with increased NCC phosphorylation and urinary sodium retention. By contrast, BP in CA-SPAK mice was elevated, resistant to the PK+ titration, and sensitive to hydrochlorothiazide and salt at all PK+ levels, concomitant with sustained and elevated urinary sodium retention and NCC phosphorylation and activity. Thus, genetically locking the switch on drives NaCl sensitivity and prevents the response of BP to potassium. CONCLUSIONS: Low K+, common in modern ultraprocessed diets, presses the K+-switch pathway to turn on NCC activity, increasing sodium retention, BP, and salt sensitivity.

Prediction of virus-host interactions and identification of hot spot residues of DENV-2 and SH3 domain interactions.

Dengue virus, particularly serotype 2 (DENV-2), poses a significant global health threat, and understanding the molecular basis of its interactions with host cell proteins is imperative for developing targeted therapeutic strategies. This study elucidated the interactions between proline-enriched motifs and Src homology 3 (SH3) domain. The SH3 domain is pivotal in mediating protein-protein interactions, particularly by recognizing and binding to proline-rich regions in partner proteins. Through a computational pipeline, we analyzed the interactions and binding modes of proline-enriched motifs with SH3 domains, identified new potential DENV-2 interactions with the SH3 domain, and revealed potential hot spot residues, underscoring their significance in the viral life cycle. This comprehensive analysis provides crucial insights into the molecular basis of DENV-2 infection, highlighting conserved and serotype-specific interactions. The identified hot spot residues offer potential targets for therapeutic intervention, laying the foundation for developing antiviral strategies against Dengue virus infection. These findings contribute to the broader understanding of viral-host interactions and provide a roadmap for future research on Dengue virus pathogenesis and treatment.

Expression Patterns and Molecular Mechanisms Regulating Drought Tolerance of Soybean [Glycine max (L.) Merr.] Conferred by Transcription Factor Gene GmNAC19.

NAC transcription factors are commonly involved in the plant response to drought stress. A transcriptome analysis of root samples of the soybean variety 'Jiyu47' under drought stress revealed the evidently up-regulated expression of GmNAC19, consistent with the expression pattern revealed by quantitative real-time PCR analysis. The overexpression of GmNAC19 enhanced drought tolerance in Saccharomyces cerevisiae INVSc1. The seed germination percentage and root growth of transgenic Arabidopsis thaliana were improved in comparison with those of the wild type, while the transgenic soybean composite line showed improved chlorophyll content. The altered contents of physiological and biochemical indices (i.e., soluble protein, soluble sugar, proline, and malondialdehyde) related to drought stress and the activities of three antioxidant enzymes (i.e., superoxide dismutase, peroxidase, and catalase) revealed enhanced drought tolerance in both transgenic Arabidopsis and soybean. The expressions of three genes (i.e., P5CS, OAT, and P5CR) involved in proline synthesis were decreased in the transgenic soybean hairy roots, while the expression of ProDH involved in the breakdown of proline was increased. This study revealed the molecular mechanisms underlying drought tolerance enhanced by GmNAC19 via regulation of the contents of soluble protein and soluble sugar and the activities of antioxidant enzymes, providing a candidate gene for the molecular breeding of drought-tolerant crop plants.

Mitigation effect of alpha-tocopherol and thermo-priming in Brassica napus L. under induced mercuric chloride stress.

Soil pollution with heavy metals has grown to be a big hassle, leading to the loss in farming production particularly in developing countries like Pakistan, where no proper channel is present for irrigation and extraction of these toxic heavy metals. The present study aims to ameliorate the damages caused by heavy metal ions (Hg-Mercury) on rapeseed (Brassica napus L.) via a growth regulator (α-tocopherol 150 mg/L) and thermopriming technique at 4 °C and 50 °C to maintain plant agronomical and physiological characteristics. In pot experiments, we designed total of 11 treatments viz.( T0 (control), T1 (Hg4ppm), T2 (Hg8ppm), T3 (Hg4ppm + 4 °C), T4 (Hg4ppm + 4 °C + tocopherol (150 m/L)), T5 (Hg4ppm + 50 °C), T6 (Hg4ppm + 50 °C + tocopherol (150 mg/L)), T7 (Hg8ppm + 4 °C), T8 (Hg8ppm + 4 °C + tocopherol (150 mg/L)), T9 (Hg8ppm + 50 °C), T10 (Hg8ppm + 50 °C + tocopherol (150 mg/L) the results revealed that chlorophyll content at p < 0.05 with growth regulator and antioxidant enzymes such as catalase, peroxidase, and malondialdehyde enhanced up to the maximum level at T5 = Hg4ppm + 50 °C (50 °C thermopriming under 4 ppm mercuric chloride stress), suggesting that high temperature initiate the antioxidant system to reduce photosystem damage. However, protein, proline, superoxide dismutase at p < 0.05, and carotenoid, soluble sugar, and ascorbate peroxidase were increased non-significantly (p > 0.05) 50 °C thermopriming under 8 ppm high mercuric chloride stress (T9 = Hg8ppm + 50 °C) representing the tolerance of selected specie by synthesizing osmolytes to resist oxidation mechanism. Furthermore, reduction in % MC (moisture content) is easily improved with foliar application of α-tocopherol and 50 °C thermopriming and 4 ppm heavy metal stress at T6 = Hg4ppm + 50 °C + α-tocopherol (150 mg/L), with a remarkable increase in plant vigor and germination energy. It has resulted that the inhibitory effect of only lower concentration (4 ppm) of heavy metal stress was ameliorated by exogenous application of α-tocopherol and thermopriming technique by synthesizing high levels of proline and antioxidant activities in maintaining seedling growth and development on heavy metal contaminated soil.

Grafting seedling rootstock strengthens tolerance to drought stress in polyploid mulberry (Morus alba L.).

The economically adaptable mulberry (Morus alba L.) has a long history of grafting in China, yet the physiological mechanisms and advantages in drought tolerance remain unexplored. In our study, we investigated the responses of self-rooted 2X (diploid), 3X (triploid), and 4X (tetraploid) plants, as well as polyploid plants grafted onto diploid seedling rootstocks (2X/2X, 3X/2X, and 4X/2X) under drought stress. We found that self-rooted diploid plants exhibited the most severe phenotypic damage, lowest water retention, photosynthetic capacity, and the least effective osmotic stress adjustment compared to tetraploid and triploid plants. However, grafted diploid and triploid plants showed effective mitigation of drought-induced damage, with higher relative water content and improved soil water retention. Grafted plants also improved the photosystem response to drought stress through elevated photosynthetic potential, closed stomatal aperture, and faster recovery of chlorophyll biosynthesis in the leaves. Additionally, grafted plants altered osmotic protective compound levels, including starch, soluble sugar, and proline content, thereby enhancing drought resistance. Absolute quantification PCR indicated that the expression levels of proline synthesis-related genes in grafted plants were not influenced after drought stress, whereas they were significantly increased in self-rooted plants. Consequently, our findings support that self-rooted triploid and tetraploid mulberries exhibited superior drought resistance compared to diploid plants. Moreover, grafting onto seedling rootstocks enhanced tolerance against drought stress in diploid and triploid mulberry, but not in tetraploid. Our study provides valuable insights for a comprehensive analysis of physiological effects in response to drought stress between stem-roots and seedling rootstocks.

Cytokinin and indole-3-acetic acid crosstalk is indispensable for silicon mediated chromium stress tolerance in roots of wheat seedlings.

The rising heavy metal contamination of soils imposes toxic impacts on plants as well as other life forms. One such highly toxic and carcinogenic heavy metal is hexavalent chromium [Cr(VI)] that has been reported to prominently retard the plant growth. The present study investigated the potential of silicon (Si, 10 µM) to alleviate the toxicity of Cr(VI) (25 µM) on roots of wheat (Triticum aestivum L.) seedlings. Application of Si to Cr(VI)-stressed wheat seedlings improved their overall growth parameters. This study also reveals the involvement of two phytohormones, namely auxin and cytokinin and their crosstalk in Si-mediated mitigation of the toxic impacts of Cr(VI) in wheat seedlings. The application of cytokinin alone to wheat seedlings under Cr(VI) stress reduced the intensity of toxic effects of Cr(VI). In combination with Si, cytokinin application to Cr(VI)-stressed wheat seedlings significantly minimized the decrease induced by Cr(VI) in different parameters such as root-shoot length (10.8% and 13%, respectively), root-shoot fresh mass (11.3% and 10.1%, respectively), and total chlorophyll and carotenoids content (13.4% and 6.8%, respectively) with respect to the control. This treatment also maintained the regulation of proline metabolism (proline content, and P5CS and PDH activities), ascorbate-glutathione (AsA-GSH) cycle and nutrient homeostasis. The protective effect of Si and cytokinin against Cr(VI) stress was minimized upon supplementation of an inhibitor of polar auxin transport- 2,3,5-triiodobenzoic acid (TIBA) which suggested a potential involvement of auxin in Si and cytokinin-mediated mitigation of Cr(VI) toxicity. The exogenous addition of a natural auxin - indole-3-acetic acid (IAA) confirmed auxin is an active member of a signaling cascade along with cytokinin that aids in Si-mediated Cr(VI) toxicity alleviation as IAA application reversed the negative impacts of TIBA on wheat roots treated with Cr(VI), cytokinin and Si. The results of this research are also confirmed by the gene expression analysis conducted for nutrient transporters (Lsi1, CCaMK, MHX, SULT1 and ZIP1) and enzymes involved in the AsA-GSH cycle (APX, GR, DHAR and MDHAR). The overall results of this research indicate towards possible induction of a crosstalk between cytokinin and IAA upon Si supplementation which in turn stimulates physiological, biochemical and molecular changes to exhibit protective effects against Cr(VI) stress. Further, the information obtained suggests probable employment of Si, cytokinin and IAA alone or combined in agriculture to maintain plant productivity under Cr(VI) stress and data regarding expression of key genes can be used to develop new crop varieties with enhanced resistance against Cr(VI) stress together with its reduced load in seedlings.

Response of leaf photosynthesis, chlorophyll content and yield of hydroponic tomatoes to different water salinity levels.

Tomato (Solanum lycopersicum L.) is an important vegetable crop that grows easily under controlled conditions, such as in greenhouses and hydroponics. To overcome freshwater scarcity, researchers are searching for alternatives to groundwater sources such as desalinated water (saline water) for irrigation. High salinity in irrigation water alters physiological functions and crop development, thereby reducing the yield. Best management practices and the use of grafted tomato plants on salt-tolerant rootstocks can alleviate salinity stress. The present study was conducted to address the impact of salinity stress on leaf transpiration (Tr), stomatal conductance (gs), photosynthesis (Pn), leaf chlorophyll content, proline content, and yield of hydroponically cultivated tomato plants. Saline (NaCl) water was used for the preparation of nutrient solution with three salinity levels, electrical conductivity (EC, dS m-1) of 2.5 (control), 6.0, and 9.5. Three commercial tomato cultivars (Valouro-RZ, Ghandora-F1, and Feisty-Red) were used. Both self-rooted plants and plants grafted onto Maxifort rootstocks were transplanted onto a perlite substrate. The recorded data revealed that all studied cultivars were critically affected by higher salinity (≈ 9.5 dS m-1) compared to low (≈ 2.5 dS m-1) and medium (≈ 6.0 dS m-1) salinity levels. The Variations in Tr, Pn, gs, chlorophyll content of leaf, and yield between medium and high salinity trials were reported at 3%, 5%, 9%, 5%, and 7.1%, respectively, whereas no significant differences were observed between low and medium salinities. However, at medium salinity levels, grafted plants performed better in photosynthesis than non-grafted plants. This is due to the accumulation of leaf proline, which maintains osmotic regulation and photosynthetic activity by preventing cell damage at medium salinities. Hence, this study confirmed the use of saline water for growing tomatoes under hydroponic conditions up to an EC of 6.0 dS m-1 including the EC of nutrient fertilizers.

Photosynthetic gas exchange, plant water relations and osmotic adjustment of three tropical perennials during drought stress and re-watering.

Planting vegetation on slopes is an effective way of improving slope stability while enhancing the aesthetic appearance of the landscape. However, plants growing on slopes are susceptible to natural drought stress (DS) conditions which commonly lead to water deficit in plant tissues that affect plant health and growth. This study investigated the photosynthetic gas exchange, plant water status and proline accumulation of three tropical perennials namely Clerodendrum paniculatum, Ipomoea pes-caprae and Melastoma malabathricum after being subjected to DS and re-watering (RW). During DS, there was a significant decrease in light-saturated photosynthetic CO2 assimilation rate (Asat), stomatal conductance (gs sat), and transpiration rate (Tr) for all three plant species. Leaf relative water content, shoot water potential, and leaf, stem and root water content also declined during DS. Proline concentration increased for all three species during DS, reaching especially high levels for C. paniculatum, suggesting that it heavily relies on the accumulation of proline to cope with DS. Most of the parameters recovered almost completely to levels similar to well-watered plants after RW, apart from M. malabathricum. Strong linear correlations were found between Asat and gs sat and between gs sat and Tr. Ultimately, C. paniculatum and I. pes-caprae had better drought tolerance than M. malabathricum.

Glutamate-dependent arginine biosynthesis requires the inactivation of spoVG, sarA, and ahrC in Staphylococcus aureus.

Genome sequencing has demonstrated that Staphylococcus aureus encodes arginine biosynthetic genes argDCJBFGH synthesizing proteins that mediate arginine biosynthesis using glutamate as a substrate. Paradoxically, however, S. aureus does not grow in a defined, glutamate-replete medium lacking arginine and glucose (CDM-R). Studies from our laboratory have found that specific mutations are selected by S. aureus that facilitate growth in CDM-R. However, these selected mutants synthesize arginine utilizing proline as a substrate rather than glutamate. In this study, we demonstrate that the ectopic expression of the argDCJB operon supports the growth of S. aureus in CDM-R, thus documenting the functionality of this pathway. Furthermore, suppressor mutants of S. aureus JE2 putA::Tn, which is defective in synthesizing arginine from proline, were selected on CDM-R agar. Genome sequencing revealed that these mutants had compensatory mutations within both spoVG, encoding an ortholog of the Bacillus subtilis stage V sporulation protein, and sarA, encoding the staphylococcal accessory regulator. Transcriptional studies document that argD expression is significantly increased when JE2 spoVG sarA was grown in CDM-R. Lastly, we found that a mutation in ahrC was required to induce argD expression in JE2 spoVG sarA when grown in an arginine-replete medium (CDM), suggesting that AhrC also functions to repress argDCJB in an arginine-dependent manner. In conclusion, these data indicate that the argDCJB operon is functional when transcribed in vitro and that SNPs within potential putative regulatory proteins are required to alleviate the repression.IMPORTANCEAlthough Staphylococcus aureus has the capability to synthesize all 20 amino acids, it is phenotypically auxotrophic for several amino acids including arginine. This work identifies putative regulatory proteins, including SpoVG, SarA, and AhrC, that function to inhibit the arginine biosynthetic pathways using glutamate as a substrate. Understanding the ultimate mechanisms of why S. aureus is selected to repress arginine biosynthetic pathways even in the absence of arginine will add to the growing body of work assessing the interactions between metabolism and S. aureus pathogenesis.

NADK-mediated proline synthesis enhances high-salinity tolerance in the razor clam.

Euryhaline organisms can accumulate organic osmolytes to maintain osmotic balance between their internal and external environments. Proline is a pivotal organic small molecule and plays an important role in osmoregulation that enables marine shellfish to tolerate high-salinity conditions. During high-salinity challenge, NAD kinase (NADK) is involved in de novo synthesis of NADP(H) in living organisms, which serves as a reducing agent for the biosynthetic reactions. However, the role of shellfish NADK in proline biosynthesis remains elusive. In this study, we show the modulation of NADK on proline synthesis in the razor clam (Sinonovacula constricta) in response to osmotic stress. Under acute hypersaline conditions, gill tissues exhibited a significant increase in the expression of ScNADK. To elucidate the role of ScNADK in proline biosynthesis, we performed dsRNA interference in the expression of ScNADK in gill tissues to assess proline content and the expression levels of key enzyme genes involved in proline biosynthesis. The results indicate that the knock-down of ScNADK led to a significant decrease in proline content (P<0.01), as well as the expression levels of two proline synthetase genes P5CS and P5CR involved in the glutamate pathway. Razor clams preferred to use ornithine as substrate for proline synthesis when the glutamate pathway is blocked. Exogenous administration of proline greatly improved cell viability and mitigated cell apoptosis in gills. In conclusion, our results demonstrate the important role of ScNADK in augmenting proline production under high-salinity stress, by which the razor clam is able to accommodate salinity variations in the ecological niche.

Analysis of heterologous expression of phaCBA promotes the acetoin stress response mechanism in Bacillus subtilis using transcriptomics and metabolomics approaches.

Acetoin, a versatile platform chemical and popular food additive, poses a challenge to the biosafety strain Bacillus subtilis when produced in high concentrations due to its intrinsic toxicity. Incorporating the PHB synthesis pathway into Bacillus subtilis 168 has been shown to significantly enhance the strain's acetoin tolerance. This study aims to elucidate the molecular mechanisms underlying the response of B. subtilis 168-phaCBA to acetoin stress, employing transcriptomic and metabolomic analyses. Acetoin stress induces fatty acid degradation and disrupts amino acid synthesis. In response, B. subtilis 168-phaCBA down-regulates genes associated with flagellum assembly and bacterial chemotaxis, while up-regulating genes related to the ABC transport system encoding amino acid transport proteins. Notably, genes coding for cysteine and D-methionine transport proteins (tcyB, tcyC and metQ) and the biotin transporter protein bioY, are up-regulated, enhancing cellular tolerance. Our findings highlight that the expression of phaCBA significantly increases the ratio of long-chain unsaturated fatty acids and modulates intracellular concentrations of amino acids, including L-tryptophan, L-tyrosine, L-leucine, L-threonine, L-methionine, L-glutamic acid, L-proline, D-phenylalanine, L-arginine, and membrane fatty acids, thereby imparting acetoin tolerance. Furthermore, the supplementation with specific exogenous amino acids (L-alanine, L-proline, L-cysteine, L-arginine, L-glutamic acid, and L-isoleucine) alleviates acetoin's detrimental effects on the bacterium. Simultaneously, the introduction of phaCBA into the acetoin-producing strain BS03 addressed the issue of insufficient intracellular cofactors in the fermentation strain, resulting in the successful production of 70.14 g/L of acetoin through fed-batch fermentation. This study enhances our understanding of Bacillus's cellular response to acetoin-induced stress and provides valuable insights for the development of acetoin-resistant Bacillus strains.

Silicon nanoparticles (SiNPs) stimulated secondary metabolism and mitigated toxicity of salinity stress in basil (Ocimum basilicum) by modulating gene expression: a sustainable approach for crop protection.

The underlying mechanisms through which silicon oxide nanoparticles (SiNPs) can confer salinity resistance to plants are poorly understood. This study explored the efficacy of supplementing nutrient solution with SiNPs (20-30 nm; 10 mg kg-1 soil) to stimulate metabolism and alleviate the risks associated with salinity (0.73 g kg-1 soil) in basil seedlings. For this purpose, variations in photosynthetic indices, proline osmoprotectant, antioxidant markers, phenylpropanoid metabolism, and transcriptional behaviors of genes were investigated. SiNPs increased shoot fresh weight (38%) and mitigated the risk associated with the salinity stress by 14%. SiNPs alleviated the inhibitory effects of salinity on the total chlorophyll concentration by 15%. The highest increase (twofold) in proline content was recorded in the SiNP-treated seedlings grown under salinity. The nano-supplement enhanced the activity of enzymatic antioxidants, including peroxidase (2.5-fold) and catalase (4.7-fold). SiNPs induced the expression of gamma-cadinene synthase (CDS) and caffeic acid O-methyltransferase (COMT) genes by 6.5- and 18.3-fold, respectively. SiNPs upregulated the eugenol synthase (EGS1) and fenchol synthase (FES) genes by six- and nine-fold, respectively. Salinity transcriptionally downregulated the geraniol synthase (GES) gene, while this gene displayed an upward trend in response to SiNPs by eight-fold. The nano-supplement transcriptionally stimulated the R-linalool synthase (LIS) gene by 3.3-fold. The terpinolene synthase (TES) gene displayed a similar trend to that of the GES gene. The highest expression (25-fold) of the phenylalanine ammonia-lyase (PAL) gene was recorded in seedlings supplemented with SiNPs. The physiological and molecular assessments demonstrated that employing SiNPs is a sustainable strategy for improving plant primary/secondary metabolism and crop protection.