Indole-3-acetic Acid In Plants Research Articles

Biocompatible Fluorescent Biosensor Reveals the Level and Distribution of Indole-3-Acetic Acid Signals in Plants.

To fully understand the function of the phytohormone indole-3-acetic acid (IAA) in regulating plant growth and development, we need to monitor their levels and distribution with high spatial and temporal resolution. In this work, an anthracene-based fluorescent biosensor for IAA was prepared using bovine serum albumin (BSA) as a bio-template. The single linear oxygen (1O2) specifically produced by IAA catalyzed with horseradish peroxidase (HRP) turns on the fluorescence of the probe, enabling specific trace sensing of IAA in the presence of multiple structural analogues. The presence of the bio-template BSA extends the biocompatibility of the probe, enabling visual monitoring of the level and distribution signal of endogenous IAA of plants in the field of bioimaging. In addition, the strategy has shown potential for application in portable paper-based sensors and in vivo fluorescent flower culture. This work provides a technical and theoretical basis for exploring the growth regulatory mechanisms of IAA in plants at the molecular level.

Attenuation of vanillic acid toxicity by foliar application with indole-3-acetic acid in tomato seedlings

ABSTRACT The allelopathic compound vanillic acid (VA), a phenol present in tomato (Solanum lycopersicum L.), behaves as a potent autotoxin and hampers growth processes. Indole-3-acetic acid (IAA) regulates growth and metabolism of plants under various environmental extremes. The work was undertaken to determine alleviating effects of IAA (1 mM) on biochemical and physiological responses of tomato plants exposed to VA toxicity (0.5 or 1 mM). Plants were grown under glasshouse conditions, treated with VA by root exposure and IAA through foliar application. The VA restrained plant growth at both doses by reducing pigment content, relative water content, protein content, nitrate reductase activity and anthocyanin content. Increased antioxidant enzyme activity, electrolyte leakage, lipid peroxidation, hydrogen peroxide, proline content and phenylalanine ammonia lyase activity were measured in stressed plants. Foliar application of IAA in plants treated with VA alleviated biophysical and biochemical parameters to promote restoration. The foliar IAA application could protect plant cellular mechanisms against endogenous autotoxins in plants grown in fields under monocropping. The IAA may protect plants exposed to VA toxicity by accelerating defense mechanisms.

Ericoid mycorrhizal fungus enhances microcutting rooting of Rhododendron fortunei and subsequent growth

Adventitious root (AR) formation is a unique feature of plant reproduction and plays a vital role in crop production as many horticultural and forestry plants are propagated through cuttings. A growing number of reports have shown that microbes, particularly mycorrhizal fungi are able to promote AR formation, but the underlying mechanisms remain largely unclear. This study established an in vitro culture system and investigated AR formation in microcuttings of Rhododendron fortunei Lindl. inoculated with Oidiodendron maius Barron Om19, an ericoid mycorrhizal fungus strain. Hormones and precursors involved in the biosynthesis of indole-3-acetic acid (IAA) in Om19 mycelium were analyzed. Om19 was able to produce a large quantity of tryptophan (Trp) and also indole-3-pyruvate (IPA) and IAA, indicating that IAA biosynthesis in Om19 could be through a Trp-dependent pathway. After inoculation of Om19, ARs were quickly formed in microcuttings. Symbiosis related genes were activated in ARs, and Om19 effectively colonized the roots. YUC3, a key gene in plant biosynthesis of IAA and genes involved in nitrogen (N) uptake and metabolism, phosphorus (P) uptake were highly upregulated. Plants absorbed significantly greater quantity of mineral nutrients, and their growth was substantially enhanced compared to the control plants without Om19 inoculation. A working model for Om19 enhanced AR formation was proposed. The rapid formation of ARs in cuttings could be due in part to the induction of IAA biosynthesized by Om19 and also attributed to Trp catalyzed biosynthesis of IAA in plants. AR formation, in turn, provided Om19 preferred sites for colonization. Our study suggested that in addition to promoting AR formation, Om19 could potentially be used as a new biofertilizer for enhancing production of ericaceous plants, such as blueberry, cranberry, and rhododendron.

Disposable stainless steel-based electrochemical microsensor for in vivo determination of indole-3-acetic acid in soybean seedlings

In vivo detecting of plants signal molecules is of great importance for the precision farming, crop management and plant phenotyping. In this work, for in vivo detecting indole-3-acetic acid (IAA), one of phytohormones, fine stainless steel (SS) wire was used as electrode material. Highly ordered nanopores, popcorn-like Au nanostructures, Pt nanoparticles and reduced graphene oxide (ERGO) nanocomposite films, and polymerized ST film (PST) were fabricated on the SS microelectrode in turn for improving the detection effect. Using the as-prepared SS microelectrode as working electrode, two untreated SS wires as reference electrode and counter electrode respectively, a disposable electrochemical microsensor for IAA were developed. The microsensor exhibited excellent selectivity and high sensitivity with low detection limit (LOD) of 43 pg mL−1. The limit of quantity (LOQ) is 143 pg mL−1. The RSD was 7% for 12 different PST/Pt-ERGO/Au/a-SS microsensors in presence of 100 µg mL−1 IAA. Using this microsensor, IAA of the stem of soybean seedlings was detected in vivo under salt stress. Our result was also confirmed by ultra-performance liquid chromatography-mass spectrum (UPLC-MS). This is the first report for the in vivo detection of IAA in plants using SS-based electrochemical microsensor. Our sensor provides an excellent sensing platform for detecting IAA in plants in vivo.

The trans and cis zeatin isomers play different roles in regulating growth inhibition induced by high nitrate concentrations in maize

Abscisic acid (ABA), auxins, and cytokinins (CKs) are known to be closely linked to nitrogen signaling. In particular, CKs control the effects of nitrate availability on plant growth. Our group has shown that treatment with high nitrate concentrations limits root growth and leaf development in maize, and conditions the development of younger roots and leaves. CKs also affect source-sink relationships in plants. Based on these results, we hypothesized that CKs regulate the source-sink relationship in maize via a mechanism involving complex crosstalk with the main auxin indole-3-acetic acid (IAA) and ABA. To evaluate this hypothesis, various CK metabolites, IAA, and ABA were quantified in the roots and in source and sink leaves of maize plants treated with high and normal nitrate concentrations. The data obtained suggest that the cis and trans isomers of zeatin play completely distinct roles in maize growth regulation by a complex crosstalk with IAA and ABA. We demonstrate that while trans-zeatin (tZ) and isopentenyladenine (iP) regulate nitrate uptake and thus control final leaf sizes, cis-zeatin (cZ) regulates source and sink strength, and thus controls leaf development. The implications of these findings relating to the roles of ABA and IAA in plants’ responses to varying nitrate concentrations are also discussed.

Optimal plant growth-promoting concentration of Azospirillum brasilense inoculated to cucumber, lettuce and tomato seeds varies between bacterial strains

Azospirillum brasilenseis a well-known plant growth-promoting rhizobacteria (PGPR) that can have positive impact on plant growth when present in sufficient density. The production of phytohormones byAzospirillumhas been proposed as one of the major mechanisms responsible for the observed plant growth effects. In particular, this plant growth-promoting effect could be mediated by IAA (indole-3-acetic acid), a phytohormone produced byAzospirillumin substantial amount, because the effect of inoculation with higher inoculum density on root morphology mimicked the increasing concentration of exogenous IAA applied to the seed. This study evaluated the effect of inoculation with different bacterial concentrations of threeA. brasilensestrains (Sp7, Sp7-S and Sp245) on the early seedling growth and endogenous plant IAA of cucumber, lettuce and tomato. Seeds were inoculated with 8, 7 and 6 log cfu ml−1of each strain before germinating in Petri dishes. The early seedling growth of vegetables was affected by the inoculation with theA. brasilensestrains. In cucumber, seeds inoculated with Sp7 at log 8 and 6 cfu ml−1, Sp7-S and Sp245 at log 8 and 7 increased seedling growth, vigor index and endogenous plant IAA by up to 55%. In lettuce, the inoculation with log 6 of Sp7, log 7 and 6 of Sp7-S, and log 8 and 7 of Sp245 yielded superior seedling growth with improved seedling vigor. In addition, log 7 and 8 of Sp7 and Sp7-S, respectively, increased IAA concentration by more than 20%. In tomato, Sp7 at log 6, Sp7-S and Sp245 at log 7 exerted more positive effects on root biomass. IAA concentrations increased up to 171% by inoculation with all concentrations of Sp7 and Sp7-S and more than 300% by Sp245 at log 8. The bacteria-elicited promotion of plant IAA production might improve plant function via effects on metabolism and morphology. These results demonstrate that seed inoculation with the strains at the studied range of cell concentrations stimulated early seedling development. However, the optimal promoting concentration varied between strains. Strain Sp7 appeared to be more beneficial at log 6 cfu ml−1while Sp7-S and Sp245 were more beneficial at log 7 or higher.

Early seedling growth response of lettuce, tomato and cucumber to Azospirillum brasilense inoculated by soaking and drenching

Mangmang J.S., Deaker R., Rogers G. (2015): Early seedling growth response of lettuce, tomato and cucumber to Azospirillum brasilense inoculated by soaking and drenching . Hort. Sci. (Prague), 42: 37–46. This study evaluated the effects of three A. brasilense strains (i.e. Sp7, Sp7-S and Sp245) on the early seedling growth of lettuce, tomato and cucumber. Seeds were inoculated by soaking and drenching before and after sowing, respectively. Results show that inoculation effect varied greatly with plant species, inoculation methods and PGPR strains which could be dependent on inoculum concentration and IAA (indole-3-acetic acid) production. Generally, the magnitude of inoculation impact on the early growth of vegetables was more pronounced with Sp7-S, followed by Sp245 and Sp7. In particular, Sp7-S and Sp245 strongly enhanced root and shoot growth, germination value and vigour of tomato when inoculated by soaking. Sp245 increased the level of endogenous plant IAA of cucumber and lettuce. Despite the diverse crop responses to inoculation methods, soaking appeared to be a better technique, and majority of the strains demonstrated more consistent beneficial effects on tomato.

Maximizing Fish Effluent Utilization for Vegetable Seedling Production by Azospirillum Brasilense

Recycling of nutrients from organic sources and modifying farming practices towards sustainable agriculture have gained considerable attention in recent years. This is due to the growing awareness of the declining environmental quality and arable land, and significant depletion of oil and water reserves that drive agriculture production. This study evaluated the impacts of three Azospirillum brasilense strains (i.e. Sp7, Sp7-S and Sp245) on the growth of vegetable seedlings (i.e. tomato, lettuce and cucumber) fertilized with fish effluent. Seeds and seedlings were inoculated prior to germination and transplanting, respectively, and were grown in a greenhouse with natural light. Results show that inoculation with these strains increased root length and endogenous plant IAA (indole-3-acetic acid) of all vegetables. Inoculated tomato seedlings produced bigger leaves, higher dry plant biomass and protein content. Likewise, taller plants with bigger stems and more leaves, and higher fresh plant biomass were documented, but with Sp7 only. Strain Sp245 also triggered an increase of peroxidase enzyme activity. In lettuce, inoculation produced taller seedlings, more leaves and higher peroxidase activity. Chlorophyll and protein content were also increased, but with Sp7 only. In cucumber, inoculated seedlings increased seedling root biomass with higher total phosphorus content and peroxidase activity. Furthermore, inoculation caused little or no adverse impact on the fish effluent bacterial community indicating that these strains can be integrated into production system that utilizes fish effluent as a fertilizer, e.g. Aquaponics. A. brasilense could be a valuable agent to help maximize the usefulness of fish effluent or wastewater from freshwater aquaculture for plant production.

Trichoderma spp. Improve Growth of Arabidopsis Seedlings Under Salt Stress Through Enhanced Root Development, Osmolite Production, and Na+ Elimination Through Root Exudates

Salt stress is an important constraint to world agriculture. Here, we report on the potential of Trichoderma virens and T. atroviride to induce tolerance to salt in Arabidopsis seedlings. We first characterized the effect of several salt concentrations on shoot biomass production and root architecture of Arabidopsis seedlings. We found that salt repressed plant growth and root development in a dose-dependent manner by blocking auxin signaling. Analysis of the wild type and eir1, aux1-7, arf7arf19, and tir1abf2abf19 auxin-related mutants revealed a key role for indole-3-acetic acid (IAA) signaling in mediating salt tolerance. We also found that T. virens (Tv29.8) and T. atroviride (IMI 206040) promoted plant growth in both normal and saline conditions, which was related to the induction of lateral roots and root hairs through auxin signaling. Arabidopsis seedlings grown under saline conditions inoculated with Trichoderma spp. showed increased levels of abscissic acid, L-proline, and ascorbic acid, and enhanced elimination of Na⁺ through root exudates. Our data show the critical role of auxin signaling and root architecture to salt tolerance in Arabidopsis and suggest that these fungi may enhance the plant IAA level as well as the antioxidant and osmoprotective status of plants under salt stress.

The pathway of auxin biosynthesis in plants

The plant hormone auxin, which is predominantly represented by indole-3-acetic acid (IAA), is involved in the regulation of plant growth and development. Although IAA was the first plant hormone identified, the biosynthetic pathway at the genetic level has remained unclear. Two major pathways for IAA biosynthesis have been proposed: the tryptophan (Trp)-independent and Trp-dependent pathways. In Trp-dependent IAA biosynthesis, four pathways have been postulated in plants: (i) the indole-3-acetamide (IAM) pathway; (ii) the indole-3-pyruvic acid (IPA) pathway; (iii) the tryptamine (TAM) pathway; and (iv) the indole-3-acetaldoxime (IAOX) pathway. Although different plant species may have unique strategies and modifications to optimize their metabolic pathways, plants would be expected to share evolutionarily conserved core mechanisms for auxin biosynthesis because IAA is a fundamental substance in the plant life cycle. In this review, the genes now known to be involved in auxin biosynthesis are summarized and the major IAA biosynthetic pathway distributed widely in the plant kingdom is discussed on the basis of biochemical and molecular biological findings and bioinformatics studies. Based on evolutionarily conserved core mechanisms, it is thought that the pathway via IAM or IPA is the major route(s) to IAA in plants.

Metabolism of indole-3-acetic acid in rice: Identification and characterization of N-β- d-glucopyranosyl indole-3-acetic acid and its conjugates

A search was made for conjugates of indole-3-acetic acid (IAA) in rice ( Oryza sativa) using liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS/MS) in order to elucidate unknown metabolic pathways for IAA. N-β- d-Glucopyranosyl indole-3-acetic acid (IAA- N-Glc) was found in an alkaline hydrolysate of rice extract. A quantitative analysis of 3-week-old rice demonstrated that the total amount of IAA- N-Glc was equal to that of IAA. A LC–ESI–MS/MS-based analysis established that the major part of IAA- N-Glc was present as bound forms with aspartate and glutamate. Their levels were in good agreement with the total amount of IAA- N-Glc during the vegetative growth of rice. Further detailed analysis showed that both conjugates highly accumulated in the root. The free form of IAA- N-Glc accounted for 60% of the total in seeds but could not be detected in the vegetative tissue. An incorporation study using deuterium-labeled compounds showed that the amino acid conjugates of IAA- N-Glc were biosynthesized from IAA-amino acids. IAA- N-Glc and/or its conjugates were also found in extracts of Arabidopsis, Lotus japonicus, and maize, suggesting that N-glucosylation of indole can be the common metabolic pathway of IAA in plants.

Three oxidative metabolites of indole-3-acetic acid from Arabidopsis thaliana

Three metabolites of indole-3-acetic acid (IAA), N-(6-hydroxyindol-3-ylacetyl)-phenylalanine (6-OH-IAA-Phe), N-(6-hydroxyindol-3-ylacetyl)-valine (6-OH-IAA-Val), and 1- O-(2-oxoindol-3-ylacetyl)-β- d-glucopyranose (OxIAA-Glc), were found by a liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS)-based search for oxidative IAA metabolites during the vegetative growth of Arabidopsis. Their structures were confirmed by making a comparison of chromatographic characteristics and mass spectra between naturally occurring compounds and synthetic standards. An incorporation study using deuterium-labeled compounds showed that 6-OH-IAA-Phe and 6-OH-IAA-Val were biosynthesized from IAA-Phe and IAA-Val, respectively, which strongly suggested the formation of these amino acid conjugates of IAA in plants. Both 6-OH-IAA-Phe and 6-OH-IAA-Val were inactive as auxins, as indicated by no significant root growth inhibition in Arabidopsis. Quantitative analysis demonstrated that OxIAA-Glc was present in the largest amount among the metabolites of IAA in Arabidopsis, suggesting that the conversion into OxIAA-Glc represents the main metabolic process regarding IAA in Arabidopsis.

Induction And Characterization of an Indole-3-acetyl-L-alanine Hydrolase From Arthrobacter Ilicis

Indole-3-acetic acid (IAA)-amino acid amide conjugates have been found to be present in many plants, and they are proposed to function in the regulation of plant IAA metabolism in a variety of ways. IAA-amino acid conjugate hydrolase activities, and the genes that encode them, are therefore potentially important tools for modification of IAA metabolism, both for agronomic reasons as well as for determination of the mechanisms of IAA regulation. We have developed a simple and economical method to induce IAA-amino acid conjugate hydrolases in bacteria with N-acetyl-L-amino acids. Using this method, we identified four bacterial strains that can be induced to produce IAA-Ala hydrolases: Arthrobacter ureafaciens C-10, Arthrobacter ureafaciens C-50, Arthrobacter ilicis D-50, and Cellulomonas fimi D-100. The enzyme kinetics and the biochemical characteristics of IAA-Ala hydrolase from one specific bacterium, Arthrobacter ilicis D-50, have been determined. The enzyme has a unique substrate specificity for IAA-amino acid conjugates compared to a bacterial IAA-Asp hydrolase previously characterized.

Anatomy of Cranberry Stem Gall and Localization of Bacteria in Galls

ABSTRACT Cranberry stem gall is characterized by tumors that girdle stems, thereby killing all distal leaves, flowers, and fruit. Bacteria that produce high levels of the plant growth hormone indole-3-acetic acid (IAA) are associated with and believed to cause cranberry stem gall. The anatomy of naturally occurring galls on woody cranberry plants and galls caused by inoculation of micropropagated cranberry plants with Pantoea agglomerans strain 4/99 was consistent with elevated levels of IAA in plants. Field galls exhibited hypertrophy and hyperplasia of tissue external to the vascular cambium, resulting in extensive stem swelling and splitting of the periderm. Similarly, galls on micropropagated plants contained enlarged cortical parenchyma cells. The current year's xylem vessels in field galls were narrow and dense compared with xylem vessels of healthy stems. Curved xylem elements apparently developed de novo within field galls and galls on inoculated plants. Cavities and fissures in both types of galls contained dense aggregates of bacteria. Treatment of micropropagated plants with synthetic IAA caused hypertrophy of cortical parenchyma and formation of adventitious roots. The results support the hypothesis that IAA-producing bacteria cause cranberry stem gall.

ILR2, a novel gene regulating IAA conjugate sensitivity and metal transport in Arabidopsis thaliana

Plants can regulate levels of the auxin indole-3-acetic acid (IAA) by conjugation to amino acids or sugars, and subsequent hydrolysis of these conjugates to release active IAA. These less active auxin conjugates constitute the majority of IAA in plants. We isolated the Arabidopsis ilr2-1 mutant as a recessive IAA-leucine resistant mutant that retains wild-type sensitivity to free IAA. ilr2-1 is also defective in lateral root formation and primary root elongation. In addition, ilr2-1 is resistant to manganese- and cobalt-mediated inhibition of root elongation, and microsomal preparations from the ilr2-1 mutant exhibit enhanced ATP-dependent manganese transport. We used a map-based positional approach to clone the ILR2 gene, which encodes a novel protein with no predicted membrane-spanning domains that is polymorphic among Arabidopsis accessions. Our results demonstrate that ILR2 modulates a metal transporter, providing a novel link between auxin conjugate metabolism and metal homeostasis.

The excessive production of indole-3-acetic acid and its significance in studies of the biosynthesis of this regulator of plant growth and development.

Because of the importance of indole-3-acetic acid (IAA) in the growth and development of plants, extensive studies of the biosynthesis of IAA have been performed during the four decades since the discovery of IAA as a plant hormone. The pathway for the biosynthesis of IAA in plants remains, however, to be unelucidated, even though studies within the past decade have revealed unexpected aspects of such biosynthesis. By contrast, two pathways to IAA have been characterized in bacteria at the molecular level: the indole-3-acetamide (IAM) pathway (L-tryptophan-->IAM-->IAA); the indole-3-pyruvic acid pathway (L-tryptophan-->indole-3-pyruvic acid-->indole-3-acetaldehyde-->IAA) (Fig. 1). In both pathways, the details of the biosynthesis of IAA were clarified using IAA-overproducing bacteria. After a description of recent advances of the studies of the biosynthesis of IAA in plants, this review focuses on the excessive production of IAA in several organisms and its significance in the studies of the biosynthesis of IAA.

Partial Purification and Characterization of an Inducible Indole-3-Acetyl-L-Aspartic Acid Hydrolase from Enterobacter agglomerans.

Indole-3-acetyl-amino acid conjugate hydrolases are believed to be important in the regulation of indole-3-acetic acid (IAA) metabolism in plants and therefore have potential uses for the alteration of plant IAA metabolism. To isolate bacterial strains exhibiting significant indole-3-acetyl-aspartate (IAA-Asp) hydrolase activity, a sewage sludge inoculation was cultured under conditions in which IAA-Asp served as the sole source of carbon and nitrogen. One isolate, Enterobacter agglomerans, showed hydrolase activity inducible by IAA-L-Asp or N-acetyl-L-Asp but not by IAA, (NH4)2SO4, urea, or indoleacetamide. Among a total of 17 IAA conjugates tested as potential substrates, the enzyme had an exclusively high substrate specificity for IAA-L-Asp. Substrate concentration curves and Lineweaver-Burk plots of the kinetic data showed a Michaelis constant value for IAA-L-Asp of 13.5 mM. The optimal pH for this enzyme was between 8.0 and 8.5. In extraction buffer containing 0.8 mM Mg2+ the hydrolase activity was inhibited to 80% by 1 mM dithiothreitol and to 60% by 1 mm CuSO4; the activity was increased by 40% with 1 mM MnSO4. However, in extraction buffer with no trace elements, the hydrolase activity was inhibited to 50% by either 1 mM dithiothreitol or 1% Triton X-100 (Sigma). These results suggest that disulfide bonding might be essential for enzyme activity. Purification of the hydrolase by hydroxyapatite and TSK-phenyl (HP-Genenchem, South San Francisco, CA) preparative high-performance liquid chromatography yielded a major 45-kD polypeptide as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Stable Isotope Labeling, in Vivo, of d- and l-Tryptophan Pools in Lemna gibba and the Low Incorporation of Label into Indole-3-Acetic Acid

We present evidence that the role of tryptophan and other potential intermediates in the pathways that could lead to indole derivatives needs to be reexamined. Two lines of Lemna gibba were tested for uptake of [(15)N-indole]-labeled tryptophan isomers and incorporation of that label into free indole-3-acetic acid (IAA). Both lines required levels of l-[(15)N]tryptophan 2 to 3 orders of magnitude over endogenous levels in order to obtain measurable incorporation of label into IAA. Labeled l-tryptophan was extractable from plant tissue after feeding and showed no measurable isomerization into d-tryptophan. d-[(15)N]tryptophan supplied to Lemna at rates of approximately 400 times excess of endogenous d-tryptophan levels (to yield an isotopic enrichment equal to that which allowed detection of the incorporation of l-tryptophan into IAA), did not result in measurable incorporation of label into free IAA. These results demonstrate that l-tryptophan is a more direct precursor to IAA than the d isomer and suggest (a) that the availability of tryptophan in vivo is not a limiting factor in the biosynthesis of IAA, thus implying that other regulatory mechanisms are in operation and (b) that l-tryptophan also may not be a primary precursor to IAA in plants.