Indole-3-acetic Acid Levels Research Articles

Nitrate stimulates adventitious rooting by increasing auxin content and regulating auxin- and root development-related genes expression in apple

Adventitious root (AR) formation is critical for cutting survival and nutrient absorption re-establishment. This complex genetic trait involves the interplay of nitrogen, endogenous hormones, and several key genes. In this study, we treated GL-3 apple (Malus domestica) in vitro shoots with nitrate and ammonium to determine their impact on AR formation, hormonal content, and gene expression patterns. Nitrate treatment significantly promotes adventitious rooting by increasing cell division, differentiation, and AR primordia formation compared to ammonium treatment. Elevated indole-3-acetic acid (IAA), reduced abscisic acid, and zeatin riboside concentrations were consistently observed with nitrate, likely crucial for promoting ARs over ammonium. Furthermore, Malus domestica auxin resistance1 (MdAUX1) expression was induced, increasing IAA levels. MdIAA23 was upregulated. Further results indicate that the higher expression levels of Malusdomestica WUSCHEL-relatedHomeobox gene 11 (MdWOX11), Malus domestica lateral organ boundariesdomaingene 16 (MdLBD16), and MdLBD29, and increased cell cycle-related gene expressions, contribute to auxin-stimulated adventitious rooting under nitrate conditions. In conclusion, this study establishes that auxin content and associated genes related to root development and cell cycle contribute to superior ARs in response to nitrate.

Transcriptomic and metabolomic analysis of changes in grain weight potential induced by water stress in wheat

The sink strength of developing ovaries in wheat determines the grain weight potential. The period from booting to the grain setting stage is critical for ovary growth and development and potential sink capacity determination. However, the underlying regulatory mechanism during this period by which the wheat plant balances and coordinates the floret number and ovary/grain weight under water stress has not been clarified. Therefore, we designed two irrigation treatments of W0 (no seasonal irrigation) and W1 (additional 75 mm of irrigation at the jointing stage) and analyzed the responses of the ovary/grain weight to water stress at the phenotypic, metabolomic, and transcriptomic levels. The results showed that the W0 irrigation treatment reduced the soil water content, plant height, and green area of the flag leaf, thus reducing grain number, especially for the inferior grains. However, it improved the grain weight of the superior and inferior grains as well as average grain weight at maturity, while the average ovary/grain weight and volume during –3 to 10 days after anthesis (DAA) also increased. Transcriptomic analysis indicated that the genes involved in both sucrose metabolism and phytohormone signal transduction were prominently accelerated by the W0 treatment, accompanied by greater enzymatic activities of soluble acid invertase (SAI) and sucrose synthase (Sus) and elevated abscisic acid (ABA) and indole-3-acetic acid (IAA) levels. Thus, the sucrose content decreased, while the glucose and fructose contents increased. In addition, several TaTPP genes (especially TaTPP-6) were down-regulated and the IAA biosynthesis genes TaTAR1 and TaTAR2 were up-regulated under the W0 treatment before anthesis, which further increased the IAA level. Collectively, water stress reduced the growth of vegetative organs and eliminated most of the inferior grains, but increased the ABA and IAA levels of the surviving ovaries/grains, promoting the enzymatic activity of Sus and degrading sucrose into glucose and fructose. As a result, the strong sucrose utilization ability, the enhanced enzymatic activity of SAI and the ABA- and IAA-mediated signaling jointly increased the weight and volume of the surviving ovaries/grains, and ultimately achieved the trade-off between ovary/grain weight and number in wheat under water stress.

Ca and Mg stimulate protein synthesis in maize kernel through the action of endogenous hormones and defense enzymes

Soil calcium (Ca) and magnesium (Mg) mineral states in rain-fed arid regions of Northwest China are inefficient, and their levels of substitution and water-soluble states are far below the lowest threshold required for maize growth, resulting in frequent physiological diseases, restricting synthesis of kernel protein (CRP). Our study set up different levels of foliar spraying of Ca and Mg fertilizers before maize pollination to examine the response characteristics of physiological and biochemical indicators in kernel, and the driving process of CRP synthesis. The main findings were: (1) Ca and Mg significantly increased the levels of CRP and endogenous hormones, and the activities of defense enzymes and CRP synthesis enzymes, which decreased significantly and stabilized at the maturity stage of maize. (2) The synthesis and accumulation of CRP were synergistically regulated by endogenous hormones, defense enzymes, and CRP synthase enzymes, with the degree of regulation varying with the level of Ca and Mg supplementation. Indole-3-acetic acid (IAA), gibberellin (GA), zeatin riboside (ZR), catalase (CAT), malondialdehyde (MDA), and glutamate dehydrogenase (GDH) were the primary physiological driving indicators of CRP synthesis, with CRP having a significant synergistic relationship with CAT and a remarkable trade-off with other driving indicators. (3) The dominant driving pathway of CRP synthesis was “Ca, Mg-IAA or GA or ZR-CAT-GDH-CRP”. Ca and Mg positively affected IAA and GA levels, and IAA and GA positively regulated CAT activity. However, CAT negatively regulated GDH levels, causing GDH to negatively influence the synthesis and accumulation of CRP and its components. The findings provide theoretical support for further study of inter-root endogenous hormones and soil microbe-driven processes in the regulation of maize quality by Ca and Mg.

In vitro rooting of Quercus robur, activated charcoal vs. exogenous auxin: a morphophysiological approach

In plant cultivation, morphophysiological status of the plantlets is crucial. We aimed to assess how activated charcoal (AC) and synthetic auxins, separately and in combination, affect the biochemistry, anatomy, and physiology of Quercus robur plantlets. Two concurrent experiments were conducted using indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) as exogenous auxins, with or without AC. Plantlets grown without exogenous auxins and AC displayed weak root development, reduced functionality, lower photosynthetic pigments, and elevated starch and free IAA content. Incorporating IAA or IBA into the medium triggered positive morphophysiological changes, such as aerenchyma formation, increased hydrogen peroxide, and reduced free IAA levels in the in vitro-produced clones. Plantlets cultured with 2 g L−1 AC exhibited higher biomass and more photosynthetic pigments. AC also enhanced the photosynthetic apparatus, as indicated by higher total performance index (PI(TOTAL)) values. Importantly, AC improved rooting success and overall morphophysiological condition, regardless of exogenous auxin presence. These findings provide novel insights into in vitro rooting modulation with AC and exogenous auxins, promising advancements in the growth and performance of Q. robur plantlets.

The Contribution of Hormonal Changes to the Protective Effect of Endophytic Bacterium Bacillus subtilis on Two Wheat Genotypes with Contrasting Drought Sensitivities under Osmotic Stress.

A comparative analysis was conducted to evaluate the effects of seed priming with endophytic bacterium Bacillus subtilis 10-4 (BS) on the hormonal system and cell wall tolerance (lipid peroxidation (LPO), electrolyte leakage (EL), and root lignin deposition) of two Triticum aestivum L. (wheat) varieties with contrasting drought sensitivities (Ekada 70-drought-tolerant (DT); Salavat Yulaev-drought-sensitive (DS)) under normal conditions and 12% polyethylene glycol-6000 (PEG)-induced osmotic stress. The results showed that under normal conditions, the growth stimulation in wheat plants by BS was attributed to changes in the hormonal balance, particularly an increase in endogenous indole-3-acetic acid (IAA) accumulation. However, under stress, a significant hormonal imbalance was observed in wheat seedlings, characterized by a pronounced accumulation of abscisic acid (ABA) and a decrease in the levels of IAA and cytokinins (CK). These effects were reflected in the inhibition of plant growth. BS exhibited a protective effect on stressed plants, as evidenced by a significantly lower amplitude of stress-induced changes in the hormonal system: maintaining the content of IAA at a level close to the control, reducing stress-induced ABA accumulation, and preventing CK depletion. These effects were further reflected in the normalization of growth parameters in dehydrated seedlings, as well as a decrease in leaf chlorophyll degradation, LPO, and EL, along with an increase in lignin deposition in the basal part of the roots in both genotypes. Overall, the findings demonstrate that BS, producing phytohormones, specifically IAA and ABA, had a more pronounced protective effect on DT plants, as evidenced by a smaller amplitude of stress-induced hormonal changes, higher leaf chlorophyll content, root lignin deposition, and lower cell membrane damage (LPO) and permeability (EL) compared to DS plants.

Continuous In Vivo Monitoring of Indole-3-Acetic Acid and Salicylic Acid in Tomato Leaf Veins Based on an Electrochemical Microsensor.

Indole-3-acetic acid (IAA) and salicylic acid (SA), as critical plant hormones, are involved in multiple physiological regulatory processes of plants. Simultaneous and continuous in vivo detection of IAA and SA will help clarify the mechanisms of their regulation and crosstalk. First, this study reports the development and application of an electrochemical microsensor for simultaneous and continuous in vivo detection of IAA and SA. This electrochemical microsensor system consisted of a tip (length, 2 mm) of platinum wire (diameter, 0.1 mm) modified with carbon cement and multi-walled carbon nanotubes, an untreated tip (length, 2 mm) of platinum wire (diameter, 0.1 mm), as well as a tip (length, 2 mm) of Ag/AgCl wire (diameter, 0.1 mm). It was capable of detecting IAA in the level ranging from 0.1 to 30 µM and SA ranging from 0.1 to 50 µM based on the differential pulse voltammetry or amperometric i-t., respectively. The dynamics of IAA and SA levels in tomato leaf veins under high salinity stress were continuously detected in vivo, and very little damage occurred. Compared to conventional detection methods, the constructed microsensor is not only suitable for continuously detecting IAA and SA in microscopic plant tissue in vivo, it also reduces the damage done to plants during the detection. More importantly, the continuous and dynamic changes in IAA and SA data obtained in stiu through this system not only can help clarify the interaction mechanisms of IAA and SA in plants, it also helps to evaluate the health status of plants, which will promote the development of basic research in botany and precision agriculture.

Effect of Zinc Oxide (ZnO) Nanoparticles on the Storability of Onion (Allium cepa L.) Seeds under Ambient Condition

Zinc oxide nanoparticles (ZnO-NPs) are considered a bio safe material for organisms. Earlier studies have demonstrated the potential of ZnO-NPs for stimulation of seed germination and plant growth as disease suppression and plant protection by virtue of their antimicrobial activity. Zinc oxide is an inorganic compound it appears in white powder. (ZnO) have a potential application as a bacteriostatic agent and can be used to control the spread and infection of variety of pathogens. These results could indicate that a low zincs concentration in seeds has an important physiological role during seed germination and early seedling growth. Zinc is a constituent of an enzyme influencing the secretion of indole acetic acid (IAA), which is a phytohormone (auxin) which significantly regulates plant growth by increasing the level of IAA, zinc gives a positive response in seed germination The lab experiment was conducted on Onion seed storage using ZnO Nano-particles under ambient conditions for 3 months at Seed testing laboratory, Department of genetics and plant breeding, Sam Higginbottom University of Agriculture Technology and Sciences, Prayagraj, (U.P.). The present investigation was carried out, in different concentrations of ZnO Nano particle (10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140) ppm along with control (untreated) and stored in two types of packaging materials aluminium foil pouch(P1) and tin container (P2), and onion seed variety is Pusa round. The Lab experiment was conducted in factorial CRD with 4 Replications. The Observations recorded on the storage containers of the onion seedling on physiological and biochemical parameters. The results of lab experiment revealed that Aluminium foil pouch (P1) packaging material is better in germination percent, speed of germination, first count, root length, shoot length, seedling length, fresh weight, dry weight, vigour index, seed density, dehydrogenase activity, catalase activity and exhibited moisture percent and electrical conductivity as compared to tin container at end of 3 months storage. Seeds are treated with ZnO @50 ppm (T5) for 2 hours soaking in distilled water, exhibits the better results in seed quality parameters. As compared to control followed by ZnO @70ppm (T7) at the end of 3 months of storage. The study concluded that the seed germination and seedling length is increased in lower concentrations, however showed decreased in higher concentration.

Auxin mediated elevated CO2-induced stolon growth and soluble sugar accumulation in creeping bentgrass

Stolon is crucial for competitive ability, stresses tolerance, as well as carbohydrate and nutrition storage in plants. In our previous study, stolon growth as well as the content of both indole-3-acetic acid (IAA) and carbohydrates (glucose, sucrose, and fructose) in stolon nodes and internodes were found to be increased due to elevated CO2 in stoloniferous creeping bentgrass. The objectives of this study were to determine the roles of auxin and the underlying mechanism of auxin in regulating elevated CO2-induced improvement on stolon growth and carbohydrate accumulation in stolon nodes and internodes of creeping bentgrass. Plants were treated with foliar applications of auxin (1-naphthalene acetic acid, NAA) and auxin transport inhibitor (2,3,5-triiodobenzoic acid, TIBA) at different concentrations to observe their effects on stolon growth. Hence, 10 mg⋅L−1 NAA and 100 mg⋅L−1 TIBA were selected as optimal concentrations to foliarly spray plants grown under either ambient CO2 (400 µmol⋅mol−1) or elevated CO2 (800 µmol⋅mol−1). Under water control and NAA treatments, stolon growth (stolon internode number, total stolon length, and stolon biomass) and contents of carbohydrate (glucose, sucrose, and fructose) were significantly increased by elevated CO2, but no positive effects were found in TIBA treatments in stolon nodes and internodes of creeping bentgrass. The results confirmed that IAA mediated elevated CO2-enhancement in stolon growth and carbohydrates accumulation in stolon nodes and internodes. The increase in IAA level was mainly associated with genes involved in auxin synthesis and transport in stolon nodes and internodes of creeping bentgrass. Our results would provide new insights for the rapid growth of stoloniferous plants under the scenario of continuous rise of the atmosphere CO2 concentration.

Exposure of Maize Seeds to Liquid Nitrogen Modifies the Morphology and Hormonal Response of Young Plants

BACKGROUND: Cryopreservation currently represents the most suitable strategy for the long-term conservation of plant germplasm. While much effort has focused on the development of protocols to enable successful cryostorage, there are few, if any reports, that consider the effect of cryogenic temperatures on the phytohormone status of the seed and developing seedlings. OBJECTIVE: To investigate the effect of cryopreservation on external seed coat features as well as levels of indole-3- acetic acid (IAA), abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) in maize. MATERIALS AND METHODS: Two groups of seeds at 6% moisture content were compared: one was maintained at 4°C (control) while the other was exposed to LN within cryo-vials. RESULTS: Seeds exposed to cryogenic temperatures were characterized by the presence of large cracks in the seed coat compared with control seeds. Cryogenic exposure also resulted in a reduction in biomass and plant height. Results from the phytohormone analysis showed an initial reduction in the levels of IAA, ABA and ACC after 7 days of growth followed by sharp increase in levels relative to the control by 14 days. Whilst the roles of ABA and ethylene (and by extension, its precursor ACC) are well studied as stress response molecules, much less is known about the potentially vital role of auxins in regulating plant growth under conditions of low temperature stress. CONCLUSION: It is postulated that the interaction of all three hormones modulate crosstalk between various stress responses and recovery pathways to ameliorate the damage caused by freezing stress and enable plant survival. Given the dearth of information on phytohormones in cryobiology, more studies are needed to fully elucidate these relationships in the context of freezing stress caused by liquid nitrogen.

Alteration of Plasma Indoles in Polycystic Ovary Syndrome.

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive-aged women. The occurrence of PCOS was reported to be associated with the alteration of gut microbiota. Microbiota-derived indoles may possibly play a key role in glycemic control. The purpose of this work is to reveal the alteration of plasma indoles in PCOS patients and to investigate the correlation between indoles levels and glucose metabolism. Sixty-five patients with PCOS and twenty-eight age-matched women were enrolled in this work. The concentrations of plasma indoles, including indoxyl sulfate (IS), indole-3-acetic acid (IAA), indole-3-propionate (IPA), indole (IND), and 3-methylindole (3-MI), were measured by HPLC with the fluorescence detection. The plasma levels of IS, IAA, and IND were significantly elevated in patients with PCOS compared to those in the control group (p < 0.05). Furthermore, the plasma levels of IS, IAA, and IND were positively correlated with fasting glucose, fasting insulin, and the homeostatic model of insulin resistance index (HOMA-IR) (p < 0.05). Besides, the 3-MI level in the plasma was positively correlated with the fasting glucose level, whereas plasma levels of IS, IAA, IND, and 3-MI were negatively correlated with glucagon-like peptide 1 (p < 0.05). Moreover, IS and IND were considered to be risk factors for PCOS after age, BMI, T, LH, and HOMA-IR adjustment. The area under the receiver-operating characteristic curve of the combined index of five indoles was 0.867 for PCOS diagnosis. Additionally, plasma indoles altered in PCOS, which was closely associated with the glucose metabolism.

The Natural Alternatives: The Impact of Plant Extracts on Snowbush (Breynia disticha Forst.) Cuttings’ Morpho-Physiological and Biochemical Characteristics

The utilization of cuttings remains a prevalent method for vegetative propagation in various plant species. Synthetic rooting hormones have conventionally been employed to enhance the rooting process; however, their high cost and potential environmental risks have necessitated the exploration of natural alternative compounds. In this study, the efficacy of natural plant extracts (pure honey, aloe extract, willow extract, moringa extract, and cinnamon powder) and synthetic auxin derivatives (indole-3-butyric acid and α-naphthaleneacetic acid) at a concentration of 2000 ppm was compared for their influence on rooting and vegetative growth of snowbush (Breynia disticha) cuttings, a significant ornamental and medicinal shrub. Results demonstrated that while the synthetic hormones produced the highest survival percentages and root number, the roots were consistently short, thick, friable, and largely void of secondary roots. Conversely, the alternative natural plant extracts, particularly aloe extract, exhibited promising outcomes, showcasing good rooting percentage and root number, significantly increased root length, and fresh and dry root weight. Furthermore, aloe extract demonstrated the potential to enhance shoot length and alter the chemical constituents of the cuttings. The highest values of total phenols and nitrogen percentage were recorded with cuttings treated with indole-3-butyric acid, followed by cuttings treated with aloe extract. While using aloe extract, we recorded the highest values of total carbohydrates, phosphorus, and potassium percentages. Notably, the highest endogenous levels of indole acetic acid and gibberellic acid, along with the lowest abscisic acid concentration in cutting tissues, were associated with the highest rooting percentage observed with indole-3-butyric acid, followed by the use of aloe extract. We hypothesized that natural plant extracts, specifically aloe extract, have potential as a viable alternative for synthetic auxins in promoting successful rooting and vegetative growth in snowbush cuttings. Further research is warranted to explore the underlying mechanisms and optimize the application of these natural compounds in vegetative propagation techniques.

A New Function of MbIAA19 Identified to Modulate Malus Plants Dwarfing Growth.

The primary determinants of apple (Malus) tree architecture include plant height and internode length, which are the significant criteria for evaluating apple dwarf rootstocks. Plant height and internode length are predominantly governed by phytohormones. In this study, we aimed to assess the mechanisms underlying dwarfism in a mutant of Malus baccata. M. baccata dwarf mutant (Dwf) was previously obtained through natural mutation. It has considerably reduced plant height and internode length. A comparative transcriptome analysis of wild-type (WT) and Dwf mutant was performed to identify and annotate the differentially expressed genes responsible for the Dwf phenotype using RNA-seq and GO and KEGG pathway enrichment analyses. Multiple DEGs involved in hormone signaling pathways, particularly auxin signaling pathways, were identified. Moreover, the levels of endogenous indole-3-acetic acid (IAA) were lower in Dwf mutant than in WT. The Aux/IAA transcription factor gene MbIAA19 was downregulated in Dwf mutant due to a single nucleotide sequence change in its promoter. Genetic transformation assay demonstrated strong association between MbIAA19 and the dwarf phenotype. RNAi-IAA19 lines clearly exhibited reduced plant height, internode length, and endogenous IAA levels. Our study revealed that MbIAA19 plays a role in the regulation of dwarfism and endogenous IAA levels in M. baccata.

Impact of Susceptibility on Plant Hormonal Composition during Clubroot Disease Development in Canola (Brassica napus).

Clubroot, caused by Plasmodiophora brassicae, is a soilborne disease of crucifers associated with the formation of large root galls. This root enlargement suggests modulation of plant hormonal networks by the pathogen, stimulating cell division and elongation and influencing host defense. We studied physiological changes in two Brassica napus cultivars, including plant hormone profiles-salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), the auxin indole-3-acetic acid (IAA), and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC)-along with their selected derivatives following inoculation with virulent and avirulent P. brassicae pathotypes. In susceptible plants, water uptake declined from the initial appearance of root galls by 21 days after inoculation, but did not have a significant effect on photosynthetic rate, stomatal conductance, or leaf chlorophyll levels. Nonetheless, a strong increase in ABA levels indicated that hormonal mechanisms were triggered to cope with water stress due to the declining water uptake. The free SA level in the roots increased strongly in resistant interactions, compared with a relatively minor increase during susceptible interactions. The ratio of conjugated SA to free SA was higher in susceptible interactions, indicating that resistant interactions are linked to the plant's ability to maintain higher levels of bioactive free SA. In contrast, JA and its biologically active form JA-Ile declined up to 7-fold in susceptible interactions, while they were maintained during resistant interactions. The ACC level increased in the roots of inoculated plants by 21 days, irrespective of clubroot susceptibility, indicating a role of ethylene in response to pathogen interactions that is independent of disease severity. IAA levels at early and later infection stages were lower only in susceptible plants, suggesting a modulation of auxin homeostasis by the pathogen relative to the host defense system.

Exploring Exogenous Indole-3-acetic Acid's Effect on the Growth and Biochemical Profiles of Synechocystis sp. PAK13 and Chlorella variabilis.

Microalgae have garnered scientific interest for their potential to produce bioactive compounds. However, the large-scale industrial utilization of microalgae faces challenges related to production costs and achieving optimal growth conditions. Thus, this study aimed to investigate the potential role of exogenous indole-3-acetic acid (IAA) application in improving the growth and production of bioactive metabolites in microalgae. To this end, the study employed different concentrations of exogenously administered IAA ranging from 0.36 µM to 5.69 µM to assess its influence on the growth and biochemical composition of Synechocystis and Chlorella. IAA exposure significantly increased IAA levels in both strains. Consequentially, improved biomass accumulation in parallel with increased total pigment content by approximately eleven-fold in both strains was observed. Furthermore, the application of IAA stimulated the accumulation of primary metabolites. Sugar levels were augmented, providing a carbon source that facilitated amino acid and fatty acid biosynthesis. As a result, amino acid levels were enhanced as well, leading to a 1.55-fold increase in total amino acid content in Synechocystis and a 1.42-fold increase in Chlorella. Total fatty acids content increased by 1.92-fold in Synechocystis and by 2.16-fold in Chlorella. Overall, the study demonstrated the effectiveness of exogenously adding IAA as a strategy for enhancing the accumulation of microalgae biomass and biomolecules. These findings contribute to the advancement of microalgae-based technologies, opening new avenues to produce economically important compounds derived from microalgae.

Metabolic profiles of 2-oxindole-3-acetyl-amino acid conjugates differ in various plant species.

Auxins are a group of phytohormones that play a key role in plant growth and development, mainly presented by the major member of the family - indole-3-acetic acid (IAA). The levels of free IAA are regulated, in addition to de novo biosynthesis, by irreversible oxidative catabolism and reversible conjugation with sugars and amino acids. These conjugates, which serve as inactive storage forms of auxin and/or degradation intermediates, can also be oxidized to form 2-oxindole-3-acetyl-1-O-ß-d-glucose (oxIAA-glc) and oxIAA-amino acids (oxIAA-AAs). Until now, only oxIAA conjugates with aspartate and glutamate have been identified in plants. However, detailed information on the endogenous levels of these and other putative oxIAA-amino acid conjugates in various plant species and their spatial distribution is still not well understood but is finally getting more attention. Herein, we identified and characterized two novel naturally occurring auxin metabolites in plants, namely oxIAA-leucine (oxIAA-Leu) and oxIAA-phenylalanine (oxIAA-Phe). Subsequently, a new liquid chromatography-tandem mass spectrometry method was developed for the determination of a wide range of IAA metabolites. Using this methodology, the quantitative determination of IAA metabolites including newly characterized oxIAA conjugates in roots, shoots and cotyledons of four selected plant models - Arabidopsis thaliana, pea (Pisum sativum L.), wheat (Triticum aestivum L.) and maize (Zea mays L.) was performed to compare auxin metabolite profiles. The distribution of various groups of auxin metabolites differed notably among the studied species as well as their sections. For example, oxIAA-AA conjugates were the major metabolites found in pea, while oxIAA-glc dominated in Arabidopsis. We further compared IAA metabolite levels in plants harvested at different growth stages to monitor the dynamics of IAA metabolite profiles during early seedling development. In general, our results show a great diversity of auxin inactivation pathways among angiosperm plants. We believe that our findings will greatly contribute to a better understanding of IAA homeostasis.

Conferring High IAA Productivity on Low-IAA-Producing Organisms with PonAAS2, an Aromatic Aldehyde Synthase of a Galling Sawfly, and Identification of Its Inhibitor.

Gall-inducing insects often contain high concentrations of phytohormones, such as auxin and cytokinin, which are suggested to be involved in gall induction, but no conclusive evidence has yet been obtained. There are two possible approaches to investigating the importance of phytohormones in gall induction: demonstrating either that high phytohormone productivity can induce gall-inducing ability in non-gall-inducing insects or that the gall-inducing ability is inhibited when phytohormone productivity in galling insects is suppressed. In this study, we show that the overexpression of PonAAS2, which encodes an aromatic aldehyde synthase (AAS) responsible for the rate-limiting step in indoleacetic acid (IAA) biosynthesis in a galling sawfly (Pontania sp.) that contains high levels of endogenous IAA, conferred high IAA productivity on Caenorhabditis elegans, as the model system. This result strongly suggests that PonAAS2 can also confer high IAA productivity on low-IAA-producing insects. We also successfully identified an inhibitor of PonAAS2 in a chemical library. This highly selective inhibitor showed stronger inhibitory activity against AAS than against aromatic amino acid decarboxylase, which belongs to the same superfamily as AAS. We also confirm that this inhibitor clearly inhibited IAA productivity in the high-IAA-producing C. elegans engineered here.

Mixed Enterobacter and Klebsiella bacteria enhance soybean biological nitrogen fixation ability when combined with rhizobia inoculation

Biological nitrogen fixation is a key process for nitrogen geochemical cycling and plant‒microbe interactions. At present, little is known about the possible effects of nonnodulating microbes on rhizobia nodulation in soils. Here, we show that Enterobacter sp. Z1 and Klebsiella sp. Z2 significantly improved soybean growth and nitrogen fixation in the presence of Bradyrhizobium diazoefficiens USDA110. Soil metabolomic analysis showed that the application of mixed strains Z1 and Z2 significantly increased the levels of flavonoids, indoleacetic acid (IAA), salicylic acid (SA), and taurine in rhizosphere soil. The addition of IAA, SA, or taurine increased nitrogenase activity, nodule production, and chlorophyll content in soybean. Flavonoids were the determinant of the interaction between soybeans and rhizobia. Moreover, strains Z1 and Z2 produced an abundance of IAA and SA, thus increasing the expression of flavonoid synthesis-related genes and eventually increasing the accumulation of flavonoids. Both strains Z1 and Z2 exhibited two metabolic pathways of taurine, and they catalyzed taurine to produce acetyl-CoA, a key flavonoid synthesis substrate in soybeans. This study revealed the mechanism by which rhizosphere microorganisms mediated soybean-rhizobium interactions, thus promoting soybean nitrogen fixation.

Bacillus velezensis Strain HN-Q-8 Induced Resistance to Alternaria solani and Stimulated Growth of Potato Plant.

Bacillus velezensis HN-Q-8, isolated in our previous study, has an antagonistic effect on Alternaria solani. After being pretreated with a fermentation liquid with HN-Q-8 bacterial cell suspensions, the potato leaves inoculated with A. solani displayed smaller lesion areas and less yellowing than the controls. Interestingly, the activity levels of superoxide dismutase, peroxidase, and catalase in potato seedlings were enhanced by the addition of the fermentation liquid with bacterial cells. Additionally, the overexpression of key genes related to induced resistance in the Jasmonate/Ethylene pathway was activated by the addition of the fermentation liquid, suggesting that the HN-Q-8 strain induced resistance to potato early blight. In addition, our laboratory and field experiments showed that the HN-Q-8 strain can promote potato seedling growth and significantly increase tuber yield. The root activity and chlorophyll content of potato seedlings were significantly increased along with the levels of indole acetic acid, gibberellic acid 3, and abscisic acid upon addition of the HN-Q-8 strain. The fermentation liquid with bacterial cells was more efficient in inducing disease resistance and promoting growth than bacterial cell suspensions alone or the fermentation liquid without bacterial cells. Thus, the B. velezensis HN-Q-8 strain is an effective bacterial biocontrol agent, augmenting the options available for potato cultivation.

Pantoea conspicua promoted sunflower growth and engulfed rhizospheric arsenate by secreting exopolysaccharide

A rhizobacterium, Pantoea conspicua, was examined against sunflower seedlings' growth under arsenate stress. Sunflower upon exposure to arsenate resulted in compromised growth that might be due to the accumulation of higher concentrations of arsenate and reactive oxygen species (ROS) in seedlings' tissues. The deposited arsenate led to oxidative damage and electrolyte leakage, making the sunflower seedlings vulnerable to compromise its growth and development. However, inoculation of sunflower seedlings with P. conspicua alleviated arsenate stress in host by initiating a multilayered defence mechanism. In fact, P. conspicua filtered out 75.1% of the arsenate from growth medium that were available to the plant roots in the absence of the said strain. To accomplish such activity, P. conspicua secreted exopolysaccharides as well as altered lignification in host roots. The arsenate (24.9%) that made its way to plant tissues was countered by helping the host seedlings to produce higher levels of indole acetic acid, non enzymatic antioxidants (phenolics and flavonoids) and antioxidant enzymes (catalase, ascorbte peroxidase, peroxidase, superoxide dismutase). As a result, ROS accumulation and electrolyte leakage were brought back to normal levels as observed in control seedlings. Hence, the rhizobacterium associated host seedlings achieved higher net assimilation (127.7%) and relative growth rate (113.5%) under 100 ppm of arsenate stress. The work concluded that P. conspicua alleviated arsenate stress in the host plants by imposing physical barrier as well as improving host seedlings’ physiology and biochemistry.

Impact of Soil Conditioners and Cyanobacteria under Varied Irrigation Levels on Growth and Productivity of Wheat (Triticum aestivum L.) in Sandy Soil

During the winter seasons 2021/2022 and 2022/2023, two field experiments were conducted at the Ismailia Experiment Research Station in Ismailia Governorate, Egypt, to assess the effect of soil conditioners and cyanobacteria at different irrigation levels on the growth and productivity of wheat plants grown in sandy soil. The experimental treatments were arranged in the split-split plot design shown below: Two bio fertilizer treatments were represented by subplot A0: no application and A1: cyanobacteria (Anabaena crcinalis) inoculation. Four natural soil conditioner treatments at a rate of 2.4 mg ha-1 were arranged in sub-sub plot (control): no application, (Z) zeolite, (B) bentonite, and (F) feldspar. The results revealed that cyanobacteria inoculation combined with natural soil conditioners resulted in positive and statistically significant increases in all parameters studied. The highest mean values were obtained in the majority of cases when cyanobacteria and feldspar were combined in a 70% irrigation level, with no significant difference when cyanobacteria and feldspar were combined in full irrigation level. All growth parameters were increased per plant. The investigated factors had a significant impact on NPK uptake by grains and straw, total amino acid percentages in wheat grains, and available NPK in soil. Furthermore, the presence of cyanobacteria associated with soil conditioners led to an increase in soil dehydrogenase, indole acetic acid levels. Therefore, the objectives of this study were to use cyanobacteria and soil conditioners as natural resources to minimize water use while boosting the production and growth characteristics of wheat plants. Finally, the findings of this study suggested that inoculating wheat plants with cyanobacteria in combination with soil conditioners can reduce up to 30% of the total amount of water required by wheat plants, and that using natural resources and bio fertilizer can be recommended to improve soil fertility while minimizing the environmental impact of chemical fertilizer.