High Levels Of Indole-3-acetic Acid Research Articles

Exploring the Relationship between Gut Microbiome Composition and Blood Indole-3-acetic Acid in Hemodialysis Patients.

Indole-3-acetic acid (IAA), a protein-bound uremic toxin resulting from gut microbiota-driven tryptophan metabolism, increases in hemodialysis (HD) patients. IAA may induce endothelial dysfunction, inflammation, and oxidative stress, elevating cardiovascular and cognitive risk in HD patients. However, research on the microbiome-IAA association is limited. This study aimed to explore the gut microbiome's relationship with plasma IAA levels in 72 chronic HD patients aged over 18 (August 2016-January 2017). IAA levels were measured using tandem mass spectrometry, and gut microbiome analysis utilized 16s rRNA next-generation sequencing. Linear discriminative analysis effect size and random forest analysis distinguished microbial species linked to IAA levels. Patients with higher IAA levels had reduced microbial diversity. Six microbial species significantly associated with IAA levels were identified; Bacteroides clarus, Bacteroides coprocola, Bacteroides massiliensi, and Alisteps shahii were enriched in low-IAA individuals, while Bacteroides thetaiotaomicron and Fusobacterium varium were enriched in high-IAA individuals. This study sheds light on specific gut microbiota species influencing IAA levels, enhancing our understanding of the intricate interactions between the gut microbiota and IAA metabolism.

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.

Plant Growth-Promoting Activities of Bacteria Isolated from an Anthropogenic Soil Located in Agrigento Province.

Bacteria producers of plant growth-promoting (PGP) substances are responsible for the enhancement of plant development through several mechanisms. The purpose of the present work was to evaluate the PGP traits of 63 bacterial strains that were isolated from an anthropogenic soil, and obtained by modification of vertisols in the Sicily region (Italy) seven years after creation. The microorganisms were tested for the following PGP characteristics: indole acetic acid (IAA), NH3, HCN and siderophore production, 1-aminocyclopropane-1-carboxylate deaminase activity (ACC) and phosphate solubilization. The results of principal component analysis (PCA) showed that Bacillus tequilensis SI 319, Brevibacterium frigoritolerans SI 433, Pseudomonas lini SI 287 and Pseudomonas frederiksbergensis SI 307 expressed high levels of IAA and production of ACC deaminase enzyme, while for the rest of traits analyzed the best performances were registered with Pseudomonas genus, in particular for the strains Pseudomonas atacamensis SI 443, Pseudomonas reinekei SI 441 and Pseudomonas granadensis SI 422 and SI 450. The in vitro screening provided enough evidence for future in vivo growth promotion tests of these eight strains.

Interaction of Subculture Cycle, Hormone Ratio, and Carbon Source Regulates Embryonic Differentiation of Somatic Cells in Pinus koraiensis

During somatic embryogenesis of Pinus koraiensis, the ability of the embryogenic callus to produce embryos gradually decreases with long-term proliferative culture, which seriously affects large-scale application of this technology. In this study, embryogenic calli of Korean pine 1–100 cell line were used as materials. It was found that in the 7-day subculture cycle of embryogenic calli the somatic embryogenic potential of Korean pine remained for the longer time. In comparison with a subculture cycle of 14 days, indoleacetic acid (IAA), soluble sugar, and starch contents in embryogenic callus were higher with a subculture cycle of 7 days, while hydrogen peroxide (H2O2) content showed the opposite trend. Further, low levels of endogenous abscisic acid (ABA) and high levels of IAA could inhibit somatic embryogenesis of P. koraiensis calli. Among different carbon sources, maltose produced more storage materials and higher superoxide dismutase (SOD) and catalase (CAT) activities than sucrose, which was conducive to cell differentiation and somatic embryogenesis. The results revealed the physiological characteristics of the loss of embryogenic capacity of Korean pine embryogenic callus and provided a basis for the long-term maintenance of its somatic embryogenic capacity.

PbrARF4 contributes to calyx shedding of fruitlets in ‘Dangshan Suli’ pear by partly regulating the expression of abscission genes

Fruitlet calyx shedding in pear plants is apparently regulated via numerous pathways that involve both environmental triggers and phytohormones cues such as auxin. In this study, we found at 10 days after full bloom (DAFB) higher levels of indoleacetic acid (IAA) and tryptophan (Trp) in calyx persistence fruitlet (CPF) than calyx shedding fruitlet (CSF) of ‘Danshan Suli’ pear (Pyrus bretschneideri Rhed.). Consisting with this, the activity of indolealdehyde oxidase (IAAIdO), which promotes IAA synthesis, was remarkably increased, and that of peroxidase (POD), which degrades IAA, dropped markedly in CPF but not in CSF. Further, qRT-PCR results revealed that most of 31 PbrARFs (encoding auxin response factors) in Pyrusbretschneideri were highly expressed in CPF, whereas PbrARF4, PbrARF24 and PbrARF26 were significantly down-regulated in CPF vis-a-vis CSF. Phylogenetic analysis revealed that 6 PbrARFs clustered in the group Ⅲ, where PbrARF4 showed the closest affinity with AtARF1 that promotes organ abscission, indicating a putative role of PbrARF4 in mediating the process of calyx shedding in pear. In fact, the ectopic overexpression of PbrARF4 in Solanum lycopersicum resulted in an earlier-formed and deeper abscission layer (AL) in the transgenic plants, whose calyxes were more prone to wilt at the mature red stage (MR) compared with the control plants (wild-type). More importantly, expression levels of the abscission genes SlLS and SlCel2 in transgenic plants overexpressing PbrARF4 were significantly up-regulated in comparation with the WT, whereas those of SlBI and SlTAPG2 were considerably inhibited. Further, PbrJOINTLESS and PbrIDA, the two genes related to calyx shedding in pear, were up-regulated more in CSF than CPF. The findings contribute to a better understanding of PbrARFs involved in fruitlet calyx shedding of pear, which could prove beneficial to improving the quality of pear fruit.

Endophytic Candida membranifaciens from Euphorbia milii L. Alleviate Salt Stress Damages in Maize

Fungal endophytes are not widely known for their role in bioactive metabolite production and salinity stress alleviation in different crop plants. Presently, we investigated the salt stress (NaCl, KCl, and H2SO4) mitigation capabilities of fungal endophyte Candida membranifaciens (FH15) isolated from Euphorbia milii L. The pure culture filtrate (CF) of C. membranifaciens revealed siderophore production and solubilization of phosphate, with high levels of indoleacetic acid (IAA: 35.8µg/mL), phenolics (70 µg/mL), and flavonoids (50 µg/mL) by using a UV spectrophotometer. The LC/MS analysis of the CF showed different phenols and flavonoids that were identified as Salicylic acid, Baicalein, Aconitic acid, Feruloylquinic acid, Coniferyl aldehyde hexoside, Pentose, Chlorogenic acid, Myricetin, Propoxyphene, and Amino-flunitrazepam. Inoculation of maize seedlings with C. membranifaciens significantly (p = 0.05) enhanced the fresh and dry biomass, carotenoid, and chlorophyll contents under 100 mM salt stress conditions. Similarly, the catalase, peroxidase activity, phenols, proline flavonoids and relative water contents (RWC) of the maize plants were enhanced. More interestingly, the inoculation of C. membranifaciens on maize revealed a higher endogenous IAA level as compared to non-inoculated control plants. Endophyte C. membranifaciens inoculation on maize seedlings under salt stress revealed a 20.87% and 16.60% increase in fresh and dry biomass, as well as significantly enhanced root shoot length and allied growth attributes, in addition to an alleviation of the adverse effects of salinity stress. Conclusively, endophytic C. membranifaciens significantly enhanced the growth attributes of maize and mitigated the adverse effects of salinity stress. Such endophytic fungal strain could be used for further field trails to enhance agricultural productivity and facilitate sustainable agricultural practices.

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.

Influence of cadmium-resistant Streptomycetes on plant growth and cadmium uptake by Chlorophytum comosum (Thunb.) Jacques.

This work aims to explore the role of cadmium-resistant actinomycetes on promoting plant growth and cadmium uptake in Chlorophytum comosum (Thunb.) Jacques, a spider plant. Actinomycetes isolated from the plant roots in peat swamp forests were screened for their cadmium resistance and the production of indole-3-acetic acid (IAA) and siderophores. The results found that K5PN1 and 11-10SHTh produced high levels of IAA and siderophores, respectively. K5PN1 and 11-10SHTh were identified to be Streptomyces rapamycinicus and Streptomyces cyaneus, respectively. Both strains were able to remove cadmium from aqueous solution and survive under cadmium stress in contaminated soil. The results of pot experiments found that the selected Streptomyces inoculation increased the root and shoot biomass and cadmium accumulation in the root and shoot of C. comosum planted in a cadmium-contaminated soil. The highest cadmium accumulation and translocation ability of cadmium from the root to shoot was found in C. comosum with S. rapamycinicus inoculation. In addition, plant with S. cyaneus inoculation had the highest phytoextraction coefficient and bioaccumulation factor. Our findings concluded that S. rapamycinicus and S. cyaneus stimulated the growth and cadmium uptake in C. comosum, suggesting a combined approach using the selected Streptomyces and C. comosum for phytoremediation of cadmium-polluted soil.

A Genetic and Metabolomic Perspective on the Production of Indole-3-Acetic Acid by Pantoea agglomerans and Use of Their Metabolites as Biostimulants in Plant Nurseries.

The species Pantoea agglomerans includes strains that are agronomically relevant for their growth-promoting or biocontrol traits. Molecular analysis demonstrated that the IPDC pathway involved in the conversion of tryptophan (Trp) to indole-3-acetic acid (IAA) is highly conserved among P. agglomerans strains at both gene and protein levels. Results also indicated that the promoter region controlling the inducible expression of ipdC gene differs from the model system Enterobacter cloacae, which is in accordance with the observation that P. agglomerans accumulates higher levels of IAA when cells are collected in the exponential phase of growth. To assess the potential applications of these microorganisms for IAA production, P. agglomerans C1, an efficient auxin-producer strain, was cultivated in 5 L fermenter so as to evaluate the effect of the medium formulation, the physiological state of the cells, and the induction timing on the volumetric productivity. Results demonstrated that higher IAA levels were obtained by using a saline medium amended with yeast extract and saccharose and by providing Trp, which acts both as a precursor and an inducer, to a culture in the exponential phase of growth. Untargeted metabolomic analysis revealed a significant effect of the carbon source on the exometabolome profile relative to IAA-related compounds and other plant bioactive signaling molecules. The IAA-enriched metabolites secreted in the culture medium by P. agglomerans C1 were used as plant biostimulants to run a series of trials at a large-scale nursery farm. Tests were carried out with in vitro and ex vitro systems following the regular protocols used for large-scale plant tree agamic propagation. Results obtained with 4,540 microcuttings of Prunus rootstock GF/677 and 1,080 plantlets of Corylus avellana L. showed that metabolites from strain C1 improved percentage of rooted-explant, number of adventitious root formation, plant survival, and quality of plant as vigor, with an increase in the leaf area between 17.5 and 42.7% compared to IBA-K (indole-3-butyric acid potassium salt)–treated plants.

Increased arbuscular mycorrhizal fungal colonization reduces yield loss of rice (Oryza sativa L.) under drought

Drought reduces the availability of soil water and the mobility of nutrients, thereby limiting the growth and productivity of rice. Under drought, arbuscular mycorrhizal fungi (AMF) increase P uptake and sustain rice growth. However, we lack knowledge of how the AMF symbiosis contributes to drought tolerance of rice. In the greenhouse, we investigated mechanisms of AMF symbiosis that confer drought tolerance, such as enhanced nutrient uptake, stomatal conductance, chlorophyll fluorescence, and hormonal balance (abscisic acid (ABA) and indole acetic acid (IAA)). Two greenhouse pot experiments comprised three factors in a full factorial design with two AMF treatments (low- and high-AMF colonization), two water treatments (well-watered and drought), and three rice varieties. Soil water potential was maintained at 0 kPa in the well-watered treatment. In the drought treatment, we reduced soil water potential to − 40 kPa in experiment 1 (Expt 1) and to − 80 kPa in experiment 2 (Expt 2). Drought reduced shoot and root dry biomass and grain yield of rice in both experiments. The reduction of grain yield was less with higher AMF colonization. Plants with higher AMF colonization showed higher leaf P concentrations than plants with lower colonization in Expt 1, but not in Expt 2. Plants with higher AMF colonization exhibited higher stomatal conductance and chlorophyll fluorescence than plants with lower colonization, especially under drought. Drought increased the levels of ABA and IAA, and AMF colonization also resulted in higher levels of IAA. The results suggest both nutrient-driven and plant hormone-driven pathways through which AMF confer drought tolerance to rice.

Efficient adventitious root formation in Petunia hybrida cuttings: when signals meet resources

Each year, in Europe several hundreds of million cuttings are rooted for production of ornamental young plants. This involves a complex chain including cutting production at low latitude sites and storage and transport of cuttings to rooting stations. Using Petunia hybrida as model, we analysed indole-3-acetic acid (IAA) levels, different metabolites, enzyme activities and gene expression to investigate the contribution of auxin-related pathways, of carbohydrate and nitrogen metabolism and the interaction of both to adventitious root (AR) formation. Blocking of polar auxin transport (PAT) eliminated the 24 h-peak of IAA, reduced the activities of cell wall and vacuolar invertases in the rooting zone and severely inhibited AR formation. Under standard rooting conditions genes controlling PAT and signalling via the Aux/IAA-ARF interaction showed phase-specific regulation indicating particular functions during the induction and differentiation of ARs. Enhanced AR formation after cold dark storage of cuttings was associated with rooting zone-dominated activation of cell wall invertase and induction of one particular member of the cell wall invertase-encoding gene family. Further, amino acids accumulated in cutting tissues under darkness. Moreover, higher levels of IAA were found in the stem base under dark compared to cultivation under light, which was further associated with upregulation of genes controlling one auxin efflux transporter and components of the auxin signalling cascade. These results strongly suggest that a coordinated remobilization of nitrogen within the cutting, establishment of the new sink in the rooting zone and activation of auxin-related pathways contribute to the induction and formation of root meristemoids under the dark phase and to accelerated AR differentiation and growth when the cuttings are subsequently planted.

The study of hormonal metabolism of Trincadeira and Syrah cultivars indicates new roles of salicylic acid, jasmonates, ABA and IAA during grape ripening and upon infection with Botrytis cinerea

Hormones play an important role in fruit ripening and in response to biotic stress. Nevertheless, analyses of hormonal profiling during plant development and defense are scarce. In this work, changes in hormonal metabolism in grapevine (Vitis vinifera) were compared between a susceptible (Trincadeira) and a tolerant (Syrah) variety during grape ripening and upon infection with Botrytis cinerea. Infection of grapes with the necrotrophic pathogen Botrytis cinerea leads to significant economic losses worldwide.Peppercorn-sized fruits were infected in the field and mock-treated and infected berries were collected at green, veraison and harvest stages for hormone analysis and targeted qPCR analysis of genes involved in hormonal metabolism and signaling. Results indicate a substantial reprogramming of hormonal metabolism during grape ripening and in response to fungal attack. Syrah and Trincadeira presented differences in the metabolism of abscisic acid (ABA), indole-3-acetic acid (IAA) and jasmonates during grape ripening that may be connected to fruit quality. On the other hand, high basal levels of salicylic acid (SA), jasmonates and IAA at an early stage of ripening, together with activated SA, jasmonates and IAA signaling, likely enable a fast defense response leading to grape resistance/ tolerance towards B. cinerea.The balance among the different phytohormones seems to depend on the ripening stage and on the intra-specific genetic background and may be fundamental in providing resistance or susceptibility. In addition, this study indicated the involvement of SA and IAA in defense against necrotrophic pathogens and gains insights into possible strategies for conventional breeding and/or gene editing aiming at improving grape quality and grape resistance against Botrytis cinerea.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P.

Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Deciphering the growth pattern and phytohormonal content in Saskatoon berry (Amelanchier alnifolia) in response to in vitro cytokinin application

Clonal propagation plays a critical integral role in the growth and success of a global multi-billion dollar horticulture industry through a constant supply of healthy stock plants. The supply chain depends on continuously improving the micropropagation process, thus, understanding the physiology of in vitro plants remains a core component. We evaluated the influence of exogenously applied cytokinins (CKs, N6-benzyladenine = BA, isopentenyladenine = iP, meta-topolin = mT, 6-(3-hydroxybenzylamino)-9-(tetrahydropyran-2-yl)purine = mTTHP) in Murashige and Skoog (MS)-supplemented media on organogenic response and accumulation of endogenous CK and indole-3-acetic acid (IAA) metabolites. The highest shoot proliferation (30 shoots/explant) was obtained with 20 μM mT treatment. However, the best quality regenerants were produced in 10 μM mT treatment. Rooting of Amelanchier alnifolia in vitro plantlets was observed at the lowest CK concentrations, with the highest root proliferation (3 roots/explant) in 1 μM mTTHP regenerants. Similar to the organogenic response, high levels of endogenous bioactive CK metabolites (free bases, ribosides, and nucleotides) were detected in mT and mTTHP-derived regenerants. The level of O-glucosides was also comparatively high in these cultures. All CK-treated plants had high levels of endogenous free IAA compared to the control. This may suggest an influence of CKs on biosynthesis of IAA.

Effects of endogenous hormones on variation of shoot branching in a variety of non-heading Chinese cabbage and related gene expression

Shoot branching (tillering) primarily determines plant shoot architecture and has been studied in many plants. Shoot branching is an important trait in non-heading Chinese cabbage (Brassica rapa ssp. chinensis Makino). The B. rapa ssp. chinensis var. multiceps exhibits unique and multiple shoot branching characteristics. Here, we analyzed the variation in shoot branching between ‘Maertou,’ with multiple shoot branching, and ‘Suzhouqing,’ a common variety. The levels of endogenous indole-3-acetic acid (IAA), zeatin riboside and active gibberellins in the shoot meristem tissues of the two cultivars were quantified by enzyme-linked immunosorbent assay during the vegetative growth stage. High levels of IAA maintained axillary bud dormancy and repressed axillary bud outgrowth allowing shoot branching to form in the vegetative stage in ‘Suzhouqing.’ In contrast, low levels of IAA did not inhibit axillary buds in ‘Maertou,’ while a high level of cytokinin promoted axillary bud growth and branch shoot development. Exogenous hormone (rac-GR24 and 6-benzylaminopurine) treatment showed that ‘Maertou’ was relatively sensitive to cytokinin, because the fold changes of cytokinin-responsive genes in ‘Maertou’ were significantly more frequent than those in ‘Suzhouqing’. Cytokinin was the direct regulator for axillary bud growth of ‘Maertou’. Compared with ‘Suzhouqing’, ‘Maertou’ was sensitive to cytokinin and this weakened the strigolactone–cytokinin branching pathway.

Enhanced Plant Performance in Cicer arietinum L. Due to the Addition of a Combination of Plant Growth-Promoting Bacteria

Current agriculture is based on external fertilizers that jeopardize soil fertility. Alternative fertilization systems might come from the use of soil-borne bacteria with plant growth enhancing ability. Here, six bacterial strains that produce varying concentrations of indole acetic acid (IAA) were tested individually and in consortia for plant growth promotion and fitness-related traits of Cicer arietinum. The nitrogen fixer Mesorhizobium ciceri consistently increased biomass production and N content. In the absence of this strain, IAA Psedomonas putida and Bacillus megaterium hindered plant growth and fitness-related traits. The application of mixes of the three strains always resulted in better plant performance when M. ciceri was present. Mixes that included a P. putida strain that produced low levels of IAA appeared more likely to promote plant growth than mixes that included P. putida strains that produced high levels of IAA or mixes that included B. megaterium. The low levels of IAA produced by the selected strains, compared to the high IAA-producing strains had a significantly greater positive effect on plant biomass accumulation, flower, pod, and seed production, and total plant nitrogen and nitrogen concentrations in seeds.

Endogenous phytohormone profiles in male and female floral buds of the persimmons (Diospyros kaki Thunb.) during development

Despite great interest from both the basic science community and from economic stakeholders, research on sex differentiation in persimmons (Diospyros kaki Thunb.) remains limited. Our previous study found that the developmental processes of both male and female floral buds were divided morphologically into 11 stages, of which stage 2 (on June 17) and stage 8 (on April 17 of the following year) were the two crucial morphological stages for sex differentiation. In this study, we used high-performance liquid chromatography-electrospray ionisation tandem mass spectrometry to measure the amounts of indole-3-acetic acid (IAA), gibberellin 3 (GA3), zeatin (ZT), abscisic acid (ABA), and jasmonic acid (JA) in both male and female floral buds at stages 1, 1.5, 2, 6, 7, 8, 10, and 11 to uncover the regulatory effects of endogenous phytohormones on sex differentiation. The results showed that low levels of IAA, ABA, as well as the ratio of ABA to IAA, and high levels of GA3 in male floral buds in the middle of June were related to the formation of three-flower cymes. Moreover, high levels of GA3 in male floral buds at stage 8 may accelerate the arrest of pistil primordia and the development of stamen primordia in the middle of the following April. In addition, high levels of the ratio of ABA to ZT from stages 6–11 might promote the differentiation of male floral buds. However, high levels of IAA from stages 7–10 as well as ZT and ABA from stages 6–10 in female floral buds may stimulate the abortion of stamen primordia and promote the development of pistil primordia, leading to female unisexual flowers. These results are relevant for future research on the regulation of controlled sex differentiation and pollination with exogenous phytohormones.

Euphorbia milii-native bacteria interactions under airborne formaldehyde stress: Effect of epiphyte and endophyte inoculation in relation to IAA, ethylene and ROS levels

Better understanding of plant-bacteria interactions under stress is of the prime importance for enhancing airborne pollutant phytoremediation. No studies have investigated plant-epiphyte interactions compared to plant-endophyte interactions under airborne formaldehyde stress in terms of plant Indole-3-acetic acid (IAA), ethylene, reactive oxygen species (ROS) levels and pollutant removal efficiency. Euphorbia milii was inoculated with native plant growth-promoting (PGP) endophytic and epiphytic isolates individually to investigate plant-endophyte compared to plant-epiphyte interactions under continuous formaldehyde fumigation. Under airborne formaldehyde stress, endophyte interacts with its host plant closely and provides higher levels of IAA which protected the plant against formaldehyde phytotoxicity by lowering intracellular ROS, ethylene levels and maintaining shoot epiphytic community; hence, higher pollutant removal. However, plant-epiphyte interactions could not provide enough IAA to confer protection against formaldehyde stress; thus, increased ROS and ethylene levels, large decrease in shoot epiphytic population and lower pollutant removal although epiphyte contacts with airborne pollutant directly (has greater access to gaseous formaldehyde). Endophyte-inoculated plant synthesized more tryptophan as a signaling molecule for its associated bacteria to produce IAA compared to the epiphyte-inoculated one. Under stress, PGP endophyte interacts with its host closely; thus, better protection against stress and higher pollutant removal compared to epiphyte which has limited interactions with the host plant; hence, lower pollutant removal.

Dynamics and control of phloem loading of indole-3-acetic acid in seedling cotyledons ofRicinus communis

During seed germination, sugars and auxin are produced from stored precursors or conjugates respectively, and transported to the seedling axis. To elucidate the mode of travel of indole-3-acetic acid (IAA) into the phloem, a solution of [(3)H]IAA, together with [(14)C]sucrose, was injected into the endosperm cavity harboring the cotyledons of germinating seedlings of Ricinus communis Phloem exudate from the cut hypocotyl was collected and the radioactivity recorded. Sucrose loading into the phloem was inhibited at higher IAA levels, and the rate of filling of the transient pool(s) was reduced by IAA. IAA was detected within 10min, with the concentration increasing over 30min and reaching a steady-state by 60min. The kinetics indicated that phloem loading of IAA involving both an active, carrier-based, and a passive, diffusion-based component, with IAA traveling along a pathway containing an intermediary pool, possibly the protoplasts of mesophyll cells. Phloem loading of IAA was altered by sucrose, K(+), and a range of non-specific and IAA-specific analogs and inhibitors in a manner that showed that IAA moves into the phloem from the extra cotyledonary solution by multiple pathways, with a carrier-mediated pathway playing a principal role.

Rhizobacteria isolated from a metal-polluted area enhance plant growth in zinc and cadmium-contaminated soil

In this work, we evaluated the ability of rhizobacteria isolated from a metal-contaminated site to produce plant growth-promoting substances, such as indole-3-acetic acid (IAA), ammonia, hydrogen cyanide, siderophores and extracellular enzymes, to solubilize phosphate and for 1-aminocyclopropane-1-carboxylate (ACC)-deaminase activity, while assessing their capacity to enhance Trifolium repens growth. The rhizobacteria that better performed were used as bioinoculants for plants grown in zinc- and cadmium-spiked soils. Rhizobacteria were inoculated onto white clover seedlings growing in 250 and 500 mg kg−1 of zinc and in 10 and 30 mg kg−1 of cadmium-spiked soils and plant traits determined. The available and exchangeable rhizosphere metal concentrations were analyzed. Twenty rhizobacteria stimulated white clover growth under axenic conditions. Overall, strains Rhodococcus erythropolis EC 34, Achromobacter sp. 1AP2 and Microbacterium sp. 3ZP2 increased clover biomass in the absence and in presence of metals; however, in soils with 250 mg kg−1 of zinc, bacterial inoculation did not enhance plant biomass. Biomass enhancement may be related to the multiple bacterial promoting traits, especially the production of high levels of IAA and siderophores and the activity of ACC-deaminase. To the best of our knowledge, this is the first study reporting the potential of R. erythropolis to increase plant growth in metal-contaminated soils. In general, strains Microbacterium sp. 3ZP2 and Arthrobacter sp. EC 10 enhanced the available and exchangeable metal concentrations in rhizosphere showing their potential to improve phytoremediation efficiency. This work clearly indicates that rhizobacteria are promising for the development of bioinoculants useful for phytoremediation of polluted soils.