Indole-3-acetic Acid Levels Research Articles

Tryptophan Levels as a Marker of Auxins and Nitric Oxide Signaling.

The aromatic amino acid tryptophan is the main precursor for indole-3-acetic acid (IAA), which involves various parallel routes in plants, with indole-3-acetaldoxime (IAOx) being one of the most common intermediates. Auxin signaling is well known to interact with free radical nitric oxide (NO) to perform a more complex effect, including the regulation of root organogenesis and nitrogen nutrition. To fathom the link between IAA and NO, we use a metabolomic approach to analyze the contents of low-molecular-mass molecules in cultured cells of Arabidopsis thaliana after the application of S-nitrosoglutathione (GSNO), an NO donor or IAOx. We separated the crude extracts of the plant cells through ion-exchange columns, and subsequent fractions were analyzed by gas chromatography-mass spectrometry (GC-MS), thus identifying 26 compounds. A principal component analysis (PCA) was performed on N-metabolism-related compounds, as classified by the Kyoto Encyclopedia of Genes and Genomes (KEGG). The differences observed between controls and treatments are mainly explained by the differences in Trp contents, which are much higher in controls. Thus, the Trp is a shared response in both auxin- and NO-mediated signaling, evidencing some common signaling mechanism to both GSNO and IAOx. The differences in the low-molecular-mass-identified compounds between GSNO- and IAOx-treated cells are mainly explained by their concentrations in benzenepropanoic acid, which is highly associated with IAA levels, and salicylic acid, which is related to glutathione. These results show that the contents in Trp can be a marker for the study of auxin and NO signaling.

Determination of the Effects of Duodenal Infusion Soy Protein Hydrolysate on Hepatic Glucose and Lipid Metabolism in Pigs Through Multi-Omics Analysis.

High animal protein intake increases hepatic lipid deposition and the risk of diabetes. However, the effects of high plant protein (HPP) intake on glycaemic responses and hepatic lipid metabolism in healthy people, as well as the underlying mechanisms, remain unclear. The current study explored the metabolomic and transcriptomic responses in the livers of pigs to assess the effects of HPP intake on host glucose and lipid metabolism. Sixteen pigs were infused with sterile saline or soy protein hydrolysate (SPH; 70 g/day) through a duodenal fistula twice daily during a 15 days experimental period. Hepatic metabolomic and transcriptomic analyses were performed, and the serum and hepatic biochemical parameters were measured. The results revealed that SPH infusion decreased serum glucose, hepatic triglyceride (TG), total cholesterol and low-density lipoprotein cholesterol levels, while it increased serum urea and eight hepatic amino acid levels (P < 0.05). Hepatic metabolomics displayed that SPH treatment produced seven different metabolites, four of which were related to lipid metabolism and one was related to glucose metabolism. In particular, lower (P < 0.05) glycocholic acid and glucose 1-phosphate levels and higher (P < 0.05) phosphatidylethanolamine (PE), arachidonic acid, prostaglandin F2α, l-carnitine and indole-3 acetic acid levels were observed following SPH infusion. A further metabolic pathway enrichment analysis found that these differential metabolites were mainly enriched in pathways related to lipid and glucose metabolism. Hepatic transcriptomics also demonstrated that multiple genes related to glucose and lipid metabolism were affected by SPH (P < 0.05). Together, SPH infusion reduced the hepatic TG levels by accelerating fatty acid β-oxidation and inhibiting TG synthesis. In addition, SPH infusion reduced the serum glucose levels by promoting hepatic glucose uptake and glycolysis. This study's result demonstrated that HPP intake regulated glycaemic responses and hepatic lipid metabolism in pigs without increasing the risk of hepatic lipid deposition and hyperglycaemia.

Nitric Oxide Enhanced Salt Stress Tolerance in Tomato Seedlings, Involving Phytohormone Equilibrium and Photosynthesis.

Nitric oxide (NO), as a ubiquitous gas signaling molecule, modulates various physiological and biochemical processes and stress responses in plants. In our study, the NO donor nitrosoglutathione (GSNO) significantly promoted tomato seedling growth under NaCl stress, whereas NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide potassium (cPTIO) treatment reversed the positive effect of NO, indicating that NO plays an essential role in enhancing salt stress resistance. To explore the mechanism of NO-alleviated salt stress, the transcriptome of tomato leaves was analyzed. A total of 739 differentially expressed genes (DEGs) were identified and classified into different metabolic pathways, especially photosynthesis, plant hormone signal transduction, and carbon metabolism. Of these, approximately 16 and 9 DEGs involved in plant signal transduction and photosynthesis, respectively, were further studied. We found that GSNO increased the endogenous indoleacetic acid (IAA) and salicylic acid (SA) levels but decreased abscisic acid (ABA) and ethylene (ETH) levels under salt stress conditions. Additionally, GSNO induced increases in photosynthesis pigment content and chlorophyll fluorescence parameters under NaCl stress, thereby enhancing the photosynthetic capacity of tomato seedlings. Moreover, the effects of NO mentioned above were reversed by cPTIO. Together, the results of this study revealed that NO regulates the expression of genes related to phytohormone signal transduction and photosynthesis antenna proteins and, therefore, regulates endogenous hormonal equilibrium and enhances photosynthetic capacity, alleviating salt toxicity in tomato seedlings.

Characterization of Source–Sink Traits and Carbon Translocation in Maize Hybrids under High Plant Density

Both compact planting and selecting superior maize (Zea mays L.) hybrids can greatly optimize the source–sink relationship and enhance maize productivity. However, the underlying physiological mechanism for regulating carbon (C) assimilate transport and influencing grain yield between maize cultivars has remained unclear under contrasting plant densities. A two-year field experiment was conducted to investigate grain yield, vascular bundle character, grain filling, C allocation in grains and other tissues, and hormone level and enzyme activity in grains under 60,000 (ND) and 90,000 plants ha−1 (HD) densities using Xianyu 335 (XY335) and Zhengdan958 (ZD958) hybrids. Compared to the ZD958, XY335 increased grain yield, kernel number per plant (KNP), and sink capacity by 11.4%, 15.7%, and 7.4%, respectively. Moreover, XY335 performed higher net photosynthetic rate and sucrose synthase activities in grains than those in ZD958, and higher levels of sucrose phosphate synthase and soluble acid invertase activity were mainly exhibited in the middle of the grain filling stage, which contributed to increasing the proportion of grain in total dry matter, grain C content and leaf C transport efficiency by 4.3%, 12.2%, and 52.9%, respectively, under HD conditions. Additionally, a greater area and number of small vascular bundle in ear of XY335 resulted in 21.3% higher matter transport efficiency and 4.8% higher maximum grain filling rate than ZD958 under HD conditions. In addition, grains of XY335 exhibited generally higher levels of indole acetic acid (IAA) and abscisic acid (ABA), as well as ABA/GA3 ratio after maize pollination relative to those from ZD958, conducive to regulating C translocation from leaves to grains. Overall, our study illustrates that stronger source activity, sink characteristics, and matter transport channels for maize hybrids are significant for C assimilate transport to grain for achieving high grain yield under higher plant density.

Structural and biochemical basis for the substrate specificity of Pad-1, an indole-3-pyruvic acid aminotransferase in auxin homeostasis

Phytohormone indole-3-acetic acid (IAA) plays a vital role in regulating plant growth and development. Tryptophan-dependent IAA biosynthesis participates in IAA homeostasis by producing IAA via two sequential reactions, which involve a conversion of tryptophan to indole-3-pyruvic acid (IPyA) by tryptophan aminotransferase (TAA1) followed by the irreversible formation of IAA in the second reaction. Pad-1 from Solanaceae plants regulates IAA levels by catalyzing a reverse reaction of the first step of IAA biosynthesis. Pad-1 is a pyridoxal phosphate (PLP)-dependent aminotransferase, with IPyA as the amino acceptor and l-glutamine as the amino donor. Currently, the structural and functional basis for the substrate specificity of Pad-1 remains poorly understood. In this study, we carried out structural and kinetic analyses of Pad-1 from Solanum melongena. Pad-1 is a homodimeric enzyme, with coenzyme PLP present between a central large α/β domain and a protruding small domain. The active site of Pad-1 includes a vacancy near the phosphate group (P-side) and the 3′-O (O-side) of PLP. These features are distinct from those of TAA1, which is homologous in an overall structure with Pad-1 but includes only the P-side region in the active site. Kinetic analysis suggests that P-side residues constitute a binding pocket for l-glutamine, and O-side residues of Phe124 and Ile350 are involved in the binding of IPyA. These studies illuminate distinct differences in the active site between Pad-1 and TAA1, and provide structural and functional insights into the substrate specificity of Pad-1.

Uniconazole Augments Abscisic Acid in Promoting Somatic Embryogenesis in Cotton (Gossypium hirsutum L.).

During somatic embryogenesis (SE), somatic cells initiate embryogenic development under appropriate conditions. Uniconazole, a plant growth regulator, was found to inhibit the proliferation of callus but promoted the conversion of callus into an embryogenic callus (EC) in cotton. The supplementation of uniconazole in the culture medium significantly suppressed the endogenous auxin [indole acetic acid (IAA)] level in callus tissues in both the callus initiation and proliferation stage but enhanced the abscisic acid (ABA) level only in the callus proliferation stage. Exogenous ABA and uniconazole showed cooperative effects on promoting the differentiation rate of callus into EC. These findings were verified by RNA-seq analysis, which elucidated that the genes involved in the IAA biosynthesis, metabolism, and signaling, and ABA metabolism pathways were regulated by uniconazole during the callus development and SE. Overall, the results suggest that uniconazole could modulate callus proliferation and callus differentiation rate by regulating the endogenous levels of IAA and ABA.

Determination of age-dependent endogenous indole-3 acetic acid (IAA) level in different organs of tomato plants

Indole-3-acetic acid (IAA), a phytohormone, is a crucial modulator of plant growth and development. As increased levels of endogenous IAA is responsible for inhibitory effects on plants, knowing its concentration would be helpful for controlling exogenous IAA input. An optimum endogenous IAA level is required for proper growth and development of plant with good health status. Hence, in this study, we have detected and measured IAA present in tomato root, shoot, leaves and fruits at two different ages (25 days and 50 days) by Reversed-Phase High Performance Liquid Chromatography (RP-HPLC), a suitable chromatographic method for separating molecules based on hydrophobicity. We observed that the endogenous level of IAA was significantly higher in roots, shoots, leaves and fruits at 50-days old plant compared to 25-days old mature plant (p-value &lt;0.01). These results suggested that the IAA level may increase with the increase of the age of tomato plants. The tomato plants showed good vigor with IAA range 0.3-3.0 µg/g.F.W (25 days) and 3.4-7.5 µg/g.F.W (50 days) of age, respectively, implying that IAA might be used as a possible plant health indicator. Further study is needed to manipulate the IAA concentration for adequate plant growth and development.

Salt-Specific Gene Expression Reveals Elevated Auxin Levels in Arabidopsis thaliana Plants Grown Under Saline Conditions.

Soil salinization is increasing globally, driving a reduction in crop yields that threatens food security. Salinity stress reduces plant growth by exerting two stresses on plants: rapid shoot ion-independent effects which are largely osmotic and delayed ionic effects that are specific to salinity stress. In this study we set out to delineate the osmotic from the ionic effects of salinity stress. Arabidopsis thaliana plants were germinated and grown for two weeks in media supplemented with 50, 75, 100, or 125 mM NaCl (that imposes both an ionic and osmotic stress) or iso-osmolar concentrations (100, 150, 200, or 250 mM) of sorbitol, that imposes only an osmotic stress. A subsequent transcriptional analysis was performed to identify sets of genes that are differentially expressed in plants grown in (1) NaCl or (2) sorbitol compared to controls. A comparison of the gene sets identified genes that are differentially expressed under both challenge conditions (osmotic genes) and genes that are only differentially expressed in plants grown on NaCl (ionic genes, hereafter referred to as salt-specific genes). A pathway analysis of the osmotic and salt-specific gene lists revealed that distinct biological processes are modulated during growth under the two conditions. The list of salt-specific genes was enriched in the gene ontology (GO) term “response to auxin.” Quantification of the predominant auxin, indole-3-acetic acid (IAA) and IAA biosynthetic intermediates revealed that IAA levels are elevated in a salt-specific manner through increased IAA biosynthesis. Furthermore, the expression of NITRILASE 2 (NIT2), which hydrolyses indole-3-acetonitile (IAN) into IAA, increased in a salt-specific manner. Overexpression of NIT2 resulted in increased IAA levels, improved Na:K ratios and enhanced survival and growth of Arabidopsis under saline conditions. Overall, our data suggest that auxin is involved in maintaining growth during the ionic stress imposed by saline conditions.

Heat Stress Resistance Mechanisms of Two Cucumber Varieties from Different Regions.

High temperatures affect the yield and quality of vegetable crops. Unlike thermosensitive plants, thermotolerant plants have excellent systems for withstanding heat stress. This study evaluated various heat resistance indexes of the thermotolerant cucumber (TT) and thermosensitive cucumber (TS) plants at the seedling stage. The similarities and differences between the regulatory genes were assessed through transcriptome analysis to understand the mechanisms for heat stress resistance in cucumber. The TT plants exhibited enhanced leaf status, photosystem, root viability, and ROS scavenging under high temperature compared to the TS plants. Additionally, transcriptome analysis showed that the genes involved in photosynthesis, the chlorophyll metabolism, and defense responses were upregulated in TT plants but downregulated in TS plants. Zeatin riboside (ZR), brassinosteroid (BR), and jasmonic acid (JA) levels were higher in TT plants than in TS. The heat stress increased gibberellic acid (GA) and indoleacetic acid (IAA) levels in both plant lines; however, the level of GA was higher in TT. Correlation and interaction analyses revealed that heat cucumber heat resistance is regulated by a few transcription factor family genes and metabolic pathways. Our study revealed different phenotypic and physiological mechanisms of the heat response by the thermotolerant and thermosensitive cucumber plants. The plants were also shown to exhibit different expression profiles and metabolic pathways. The heat resistant pathways and genes of two cucumber varieties were also identified. These results enhance our understanding of the molecular mechanisms of cucumber response to high-temperature stress.

Can Resveratrol Supplementation Reduce Uremic Toxin Plasma Levels From the Gut Microbiota in Nondialyzed Patients With Chronic Kidney Disease?

Uremic toxins such as indoxyl sulfate (IS), p-cresyl sulfate (pCS), and indole-3-acetic acid (IAA) produced by the gut microbiota are recognized as risk factors for many comorbidities, including cardiovascular diseases. Patients with chronic kidney disease (CKD) have an accumulation of these toxins, and nutritional strategies have been proposed to mitigate gut dysbiosis and, consequently, reduce these toxins. This study aimed to evaluate the effects of resveratrol supplementation on the plasma levels of IS, pCS, and IAA in nondialyzed patients with CKD. In this placebo-controlled crossover study, twenty nondialyzed patients were randomly divided into two groups: they received either one capsule/day containing 500mg of trans-resveratrol (63±7.5years, glomerular filtration rate [GFR]: 34±14mL/min, body mass index: 26.8±5.6kg/m2) or a placebo containing 500mg wheat flour (62±8.4years, GFR: 34±13mL/min, body mass index: 28.6±4.4kg/m2) during 4weeks. After 8weeks of washout (no supplementation), another 4weeks of supplementation with crossover was initiated. IS, IAA, and pCS plasma levels were quantified by the reverse phase high-efficiency liquid chromatography method with fluorescent detection. The mRNA expression of nuclear factor erythroid 2-related factor 2 and nuclear factor kappa B in peripheral blood mononuclear cells was evaluated by polymerase chain reaction. C-reactive protein plasma levels were also evaluated. As expected, the uremic toxin levels were negatively correlated with the GFR, but no effect of trans-resveratrol supplementation was found on levels of IS, IAA, and pCS. There was a positive correlation between IS and nuclear factor erythroid 2-related factor 2 (r=0.24, P=.03) and also between IS and C-reactive protein (r=0.21, P=.05). Supplementation with trans-resveratrol did not reduce the plasma levels of IS, pCS, and IAA in nondialyzed patients with CKD. The interactions among uremic toxins and anti-inflammatory and proinflammatory pathways deserve more studies.

Abstract WP240: Beneficial Gut Microbiome-Derived Ligands Can Outcompete Detrimental Brain-Derived Ligands Of Aryl Hydrocarbon Receptor After Stroke

Microbiome-derived ligands of the aryl hydrocarbon receptor (AHR) including tryptophan-derived indole acetic acid (IAA) have anti-inflammatory effects in some tissues. However, their effect on neuroinflammation after stroke is unknown. Brain-derived ligands of AHR (e.g. kynurenine) increase post-ischemia and are detrimental. Consistently, pharmacological inhibition of AHR after stroke reduces deleterious effects of kynurenine-mediated activation of AHR and improves outcome. However, whether IAA-mediated activation of AHR is detrimental or beneficial after stroke is unknown. We hypothesized that post-stroke treatment with IAA will reduce neuroinflammation and improve outcomes via beneficial activation of microglial (MG) AHR. We used a reversible middle cerebral artery occlusion (MCAO) model in aged (18mo) WT male mice to investigate temporal changes in biome-derived (IAA) versus host-derived (kynurenine) AHR ligands. Using metabolomics analysis, we determined that plasma levels of IAA can be restored in naïve aged mice by oral probiotics administration of AHR ligand producers. We found that brain kynurenine increases but plasma IAA decreases as early as 3 hours after MCAO in aged mice (n=4/gp, p=0.0029 ) while brain IAA levels remain unchanged. Our 16S rRNA-sequencing shows that aging leads to reduction in AHR ligand-producers (e.g. Bifidobacterium [B] and Lactobacillus [L] ). Oral gavage with AHR ligand-producing BBL-probiotic cocktail restored the age-related decline in plasma IAA both acutely (24 hours post-treatment) and chronically (weekly for 6 weeks, n=8/gp, p=0.0086 and p=0.0073 , respectively). Further, the increase in plasma levels of IAA after probiotic bacteriotherapy with AHR ligand producers was associated with modulation of AHR activity in the brain (decreased AHR expression in MG, n=8/gp, p=0.0119 ) and reduced MG activation ( p=0.0069 ). Our results show that IAA modulates MG-mediated neuroinflammation after stroke. We plan to utilize post-stroke treatment with IAA in aged WT mice and in inducible knock-out mice with microglial Ahr deletion to further validate our hypothesis. Future studies are needed to focus on the regulatory function of other biome-derived AHR ligands in post-stroke neuroinflammation.

Transcriptomic analyses provide insight into adventitious root formation of Euryodendron excelsum H. T. Chang during ex vitro rooting

Euryodendron excelsum H. T. Chang, a critically endangered species endemic to China, is a source of valuable material for the furniture and construction industries. However, this species has some challenges associated with rooting during in vitro propagation that have yet to be resolved. In this study, we optimized rooting and conducted a transcriptomic analysis to appreciate its molecular mechanism, thereby promoting the practical application of in vitro propagation of E. excelsum, and providing technical support for the ecological protection of this rare and endangered species. Results showed that ex vitro rooting performed the highest rooting percentage with 98.33% at 25 days. During ex vitro rooting, there was a wide fluctuation of endogenous levels of indole-3-acetic acid (IAA) and hydrogen peroxide (H2O2) at the stage of root primordia formation. Transcriptome analysis revealed multiple differentially expressed genes (DEGs) involved in adventitious root (AR) development. DEGs involved in plant hormone signal transduction, such as genes encoding auxin-induced protein, auxin-responsive protein, and auxin transporter-like protein, and in response to H2O2, oxidative stress, abiotic and biotic stimuli were significantly up- or down-regulated by ex vitro treatment with 1 mM indole-3-butyric acid (IBA). Our results indicate that ex vitro rooting is an effective method to induce AR from E. excelsum plantlets during micropropagation. DEGs involved in the plant hormone signal transduction pathway played a crucial role in AR formation. H2O2, produced by environmental stimulation, might be related to AR induction as a result of the synergistic action with IBA, ultimately regulating the level of endogenous IAA. Under ex vitro rooting, a synergistic action between H2O2 produced by environmental stimulation and IBA played crucial role in the regulation of AR formation from E. excelsum plantlets during micropropagation.

Isolation, Classification, and Growth-Promoting Effects of Pantoea sp. YSD J2 from the Aboveground Leaves of Cyperus Esculentus L. var. sativus.

Plant growth-promoting (PGP) bacteria are an environmental-friendly alternative to chemical fertilizers for promoting plant development. We isolated and characterized a PGP endophyte, YSD J2, from the leaves of Cyperus esculentus L. var. sativus. Specific PGP characteristics of this strain, such as phosphate solubilization ability, potassium-dissolving ability, siderophore and indole-3-acetic acid (IAA) production, and salt tolerance, were determined in vitro. In addition, positive mutants were screened using the atmospheric and room-temperature plasma (ARTP) technology, with IAA level and organic phosphorus solubility as indices. Furthermore, the effect of the positive mutant on biomass production and antioxidant abilities of greengrocery seedling was evaluated and the genome was mined to explore the underlying mechanisms. The strain YSD J2 showed a good performance of PGP characteristics, such as the production of indole acetic acid and siderophores, solubilization ability of phosphate, and potassium-dissolving ability. It was recognized through 16S rRNA sequencing together with morphological and physiological tests and confirmed as Pantoea sp. The strain exposed to a mutation time of 125 s by ARTP had the highest IAA and organic phosphate (lecithin) concentrations of 10.34 mg/L and 16.52 mg/L, 42.06% and 34.15% higher than those of the initial strain. Inoculation of mutant strain YSD J2 significantly increased plant growth attributes and the activities of peroxidase and superoxide dismutase, respectively, but decreased the content of malondialdehyde significantly compared with the control. Furthermore, genome annotation and functional analysis were performed through whole-genome sequencing and PGP-related genes were identified. Our results indicated that the YSD J2 with PGP characteristics is a potential candidate for the development of biofertilizers.

Prospecting the plant growth–promoting activities of endophytic bacteria Franconibacter sp. YSD YN2 isolated from Cyperus esculentus L. var. sativus leaves

PurposePlant growth–promoting (PGP) bacteria are an environment-friendly alternative to chemical fertilizers for promoting plant growth and development. We isolated and characterized a PGP endophyte, YSD YN2, from the leaves of Cyperus esculentus L. var. sativus.MethodsSpecific PGP characteristics of this strain, such as phosphate solubilization ability, potassium-dissolving ability, siderophore and indole-3-acetic acid (IAA) production, and salt tolerance, were determined in vitro. In addition, positive mutants were screened using the atmospheric and room temperature plasma (ARTP) technology, with IAA level and organic phosphate solubility as indices. Furthermore, the effect of the positive mutant on seed germination, biomass production, and antioxidant abilities of greengrocery seedling was evaluated, and the genome was mined to explore the underlying mechanisms.ResultsThe strain YSD YN2 showed a good performance of PGP characteristics, such as the production of indole acetic acid and siderophores, solubilization ability of phosphate, and potassium-dissolving ability. It was recognized through 16S rRNA sequencing together with morphological and physiological tests and confirmed as Franconibacter sp. The strain exposed to a mutation time of 125 s by ARTP had the highest IAA and organic phosphate (lecithin) concentrations of 9.25 mg/L and 16.50 mg/L, 50.41% and 30.54% higher than those of the initial strain. Inoculation of mutant strain YSD YN2 significantly increased the seed germination, plant growth attributes, and the activities of peroxidase (POD) and superoxide dismutase (SOD), respectively, but decreased the content of malondialdehyde (MDA) significantly compared with the control. Furthermore, genome annotation and functional analysis were performed through whole-genome sequencing, and PGP-related genes were identified.ConclusionOur results indicated that the mutant strain YSD YN2 with PGP characteristics is a potential candidate for the development of biofertilizers.

Caracterização do teor de ácido indole-3-acético em frações de inoculante e seu efeito no crescimento vegetal

ABSTRACT Indole-3-acetic acid (IAA) is a phytohormone produced by many rhizobacterial species to mediate plant colonization while promoting plant growth. The colorimetric assay is widely used to analyze the bacterial IAA biosynthesis because it is a straightforward, cost-effective and fast technique. However, the characterization of parts or fractions of inoculant formulations is rarely performed. This study aimed to determine the fraction of the inoculant that is effective in promoting the plant growth, whether the bacteria or media growth can induce the phytohormones to expand the radicular zone of the plant, and whether the seed bacterization or foliar application can alter the plant growth. The inoculum samples (homemade and commercial) were obtained in a Luria-Bertani growth medium with and without tryptophan-L and the inoculants were divided into two fractions: pellet and supernatant. For the IAA quantification, the pellet fraction was subjected to physical (sonication) and chemical (lysozyme) treatments alone and combined. The IAA levels were evaluated using the colorimetric assay, and the effect on plant growth was determined by the inoculation of maize seedlings. The homemade and commercial formulations showed distinct patterns, in terms of IAA synthesis. The supernatant fraction provided higher amounts of IAA and was effective in improving the root area. Lysozyme was superior to sonication in mediating the release of IAA from bacterial cells. No significant differences were observed between seed or foliar inoculation.

Optimization of cultural conditions using response surface methodology and modeling of indole-3-acetic acid production by Saccharothrix texasensis MB15

This study aimed to develop a low-cost medium based on wheat waste (leaves and roots) to enhance Indole-3-Acetic Acid (IAA) production by the actinobacterial strain Saccharothrix texasensis MB15, using the Response Surface Methodology (RSM). Among eighteen endophytic or rhizospheric actinobacterial strains, Saccharothrix texasensis MB15 secreted high levels of IAA under standard cultural conditions. A Placket-Burman screening design was conducted to estimate the composition of low-cost medium and cultural conditions for S. texasensis MB15. Three factors, l-tryptophan, leaves extract, and inoculum quantity, respectively, showed a significant effect on IAA production by S. texasensis MB15. The RSM optimization step, for the three main factors, showed that improvement of IAA production was very significant, passing from 47 μg/ml within 120 h to more than 148 μg/ml within 96 h under RSM optimized conditions. From RSM analysis, the amounts of produced IAA were increased to an overall 2.65-fold in fermentation liquor, with a coefficient of determination R2 of 0.993, which indicates that 99.30% of the variability in the response can be accounted for by the model. This is the first paper reporting RSM-based medium optimization of IAA by S. texasensis MB15, isolated from the hypersaline soil in an arid region of Algeria, exploring organic wastes.

Modulation of the Wheat Seed-Borne Bacterial Community by Herbaspirillum seropedicae RAM10 and Its Potential Effects for Tryptophan Metabolism in the Root Endosphere.

Plants and their associated microbiota share ecological and evolutionary traits that are considered to be inseparably woven. Their coexistence foresees the use of similar metabolic pathways, leading to the generation of molecules that can cross-regulate each other’s metabolism and ultimately influence plant phenotype. However, the extent to which the microbiota contributes to the overall plant metabolic landscape remains largely unexplored. Due to their early presence in the seed, seed-borne endophytic bacteria can intimately colonize the plant’s endosphere while conferring a series of phytobeneficial services to their host. Understanding the dynamics of these endophytic communities is a crucial step toward the formulation of microbial inoculants that can modulate the functionality of the plant-associated microbiota for improved plant fitness. In this work, wheat (Triticum aestivum) roots non-inoculated and inoculated with the bacterium Herbaspirillum seropedicae strain RAM10 were analyzed to explore the impact of inoculant–endophyte–wheat interrelationships on the regulation of tryptophan (Trp) metabolism in the endosphere environment. Root inoculation with H. seropedicae led to phylum-specific changes in the cultivable seed-borne endophytic community. This modulation shifted the metabolic potential of the community in light of its capacity to modulate the levels of key Trp-related metabolites involved in both indole-3-acetic acid (IAA) biosynthesis and in the kynurenine pathway. Our results support a mode of action of H. seropedicae relying on a shift in both the composition and functionality of the seed-borne endophytic community, which may govern important processes such as root growth. We finally provide a conceptual framework illustrating that interactions among roots, inoculants, and seed-borne endophytes are critical to fine-tuning the levels of IAA in the endosphere. Understanding the outcomes of these interactions is a crucial step toward the formulation of microbial inoculants based on their joint action with seed-borne endophytic communities to promote crop growth and health in a sustainable manner.

Evaluation of drought tolerance in three commercial pomegranate cultivars using photosynthetic pigments, yield parameters and biochemical traits as biomarkers

Drought stress during the ripening phenological period has adverse effects on pomegranate (Punica granatum L.) fruit productivity, characteristics and composition, depending on the drought severity and specific cultivar. This fact underlines the importance of understanding the physiological and biochemical responses of pomegranate under drought stress to improve the quality of fruits. The responses of three commercial Iranian cultivars (‘Malase Saveh’, ‘Mikhosh’ and ‘Rabab-Neyriz’) to slight, moderate or intense drought stress were evaluated, considering yield-related (fruit yield, number of fruits per tree, fruit weight and fruit cracking), metabolite [glucose, fructose, total soluble solids (TSS), titratable acidity, total phenolics (TPC), ellagic acid, total anthocyanins (TAC), abscisic acid (ABA), indole acetic acid (IAA), proline, ascorbic (Asc) and carboxylic acids], and physiological parameters (oxidative stress indexes and activities of key antioxidant enzymes in leaves). Significant decreases in fruit yield (58–68%), number of fruits per tree (39–44%), fruit weight (30–41%), and leaf photosynthetic pigments (23–39%) were observed among cultivars in response to intense drought. On the other hand, significant increases in the levels of ABA, IAA, proline, malondialdehyde (MDA), and hydrogen peroxide (H2O2), as well as the activities of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and ascorbate peroxidase (APX) antioxidant enzymes were observed in the leaves of all cultivars under intense drought stress. With respect to fruit juice quality, intense drought caused a considerable decrease in the contents of sugars, TAC, TPC, ellagic acid, Asc, TSS, and TA relative to control conditions, while carboxylic acids increased. Slight drought caused small increases in the concentrations of sugars, TPC and ellagic acid in juice. The ‘Malase Saveh’ cultivar showed a better adaptive response to drought stress than the ‘Rabab-e-Neyriz’ and ‘Mikhosh’ ones, suggesting that this pomegranate cultivar could be used in breeding programs to develop new ones with beneficial water stress-adaptive traits and better fruit quality.

H2O2 Functions as a Downstream Signal of IAA to Mediate H2S-Induced Chilling Tolerance in Cucumber.

Hydrogen sulfide (H2S) plays a crucial role in regulating chilling tolerance. However, the role of hydrogen peroxide (H2O2) and auxin in H2S-induced signal transduction in the chilling stress response of plants was unclear. In this study, 1.0 mM exogenous H2O2 and 75 μM indole-3-acetic acid (IAA) significantly improved the chilling tolerance of cucumber seedlings, as demonstrated by the mild plant chilling injury symptoms, lower chilling injury index (CI), electrolyte leakage (EL), and malondialdehyde content (MDA) as well as higher levels of photosynthesis and cold-responsive genes under chilling stress. IAA-induced chilling tolerance was weakened by N, N′-dimethylthiourea (DMTU, a scavenger of H2O2), but the polar transport inhibitor of IAA (1-naphthylphthalamic acid, NPA) did not affect H2O2-induced mitigation of chilling stress. IAA significantly enhanced endogenous H2O2 synthesis, but H2O2 had minimal effects on endogenous IAA content in cucumber seedlings. In addition, the H2O2 scavenger DMTU, inhibitor of H2O2 synthesis (diphenyleneiodonium chloride, DPI), and IAA polar transport inhibitor NPA reduced H2S-induced chilling tolerance. Sodium hydrosulfide (NaHS) increased H2O2 and IAA levels, flavin monooxygenase (FMO) activity, and respiratory burst oxidase homolog (RBOH1) and FMO-like protein (YUCCA2) mRNA levels in cucumber seedlings. DMTU, DPI, and NPA diminished NaHS-induced H2O2 production, but DMTU and DPI did not affect IAA levels induced by NaHS during chilling stress. Taken together, the present data indicate that H2O2 as a downstream signal of IAA mediates H2S-induced chilling tolerance in cucumber seedlings.

Quantitative and qualitative study of endogenous and exogenous growth regulators in eggplant (Solanum melongena) microspore cultures

In eggplant microspore embryogenesis, embryos are produced and then transformed into undifferentiated calli, instead of developing as true embryos. This is the main current bottleneck that precludes this process from being efficient. In this work we aimed to shed light on the factors involved in the successful in vitro development of eggplant haploid embryos by evaluating the role of growth regulators (GRs) in this process. We analyzed the endogenous levels of different GRs, including auxins, cytokinins and gibberelins, as well as salicylic, jasmonic and abscisic acid, in microspores and microspore-derived embryos at different culture stages. We also analyzed the same GR profiles in leaf and anther wall tissues of different eggplant backgrounds. Finally, we assessed the application of different GR combinations to the culture medium. Our results showed that in eggplant there are no genotype-specific endogenous GR profiles that can be associated to a high embryogenic response. Instead, the embryogenic response seems related to different GR accumulation patterns during in vitro culture. The changes observed in the endogenous levels of salicylic and abscisic acid were not related to the embryo transition. There were, however, changes in the levels of indole acetic acid and dihydrozeatin. The best GR combination to promote callus production was 0.5 mg/L 1-naphthaleneacetic acid (NAA) and 0.5 mg/L 6-benzylaminopurine (BAP). A 20% reduction of NAA and BAP reduced embryo production but produced structures more anatomically similar to embryos. These results shed light on the role of GRs during the development of microspore-derived embryos in eggplant microspore cultures.