Role Of Indole-3-acetic Acid Research Articles

Lactobacillus rhamnosus ameliorates acne vulgaris in SD rats via changes in gut microbiota and associated tryptophan metabolism.

The depletion of beneficial bacteria in the gut has been found in patients with acne vulgaris, and in previous studies, the supplement of Lactobacillus rhamnosus led to the improvement of adult acne. Nevertheless, the potential mechanism of L. rhamnosus in the amelioration of acne vulgaris has not been elucidated yet. To mimic the human intestinal environment, a pseudo-germ-free rat model was used, and then gut microbiota from healthy individuals and acne patients were transplanted into rats. The effects of L. rhamnosus and tryptophan (Trp) metabolites on a rat acne model were investigated by gavage. Then, 16S rRNA analysis and targeted measurement of metabolites were performed to discover the differences in gut microbiota and metabolites between groups. Finally, HaCaT cells pretreated with Cutibacterium acnes were employed to validate the effect and mechanism of Trp metabolites on acne. L. rhamnosus significantly improved acne-like symptoms in rats by suppressing the level of inflammatory cytokines such as IL-1β, IL-6, and TNF-α. L. rhamnosus induced an increase in the production of indole-3-acetic acid (IAA) and indole via targeted Trp metabolic analyses. Furthermore, L. rhamnosus promoted bacterial diversity and also enhanced the Firmicutes/Bacteroidota (F/B) ratio, which was positively related to both IAA and indole. Finally, the roles of IAA and indole in alleviating acne vulgaris were confirmed both in vitro and in vivo, which could be reversed by AhR inhibitors. Our study demonstrated that L. rhamnosus could exert its therapeutic effects on acne vulgaris by modulating the gut microbiota and regulating associated Trp metabolites.

Expression Profiling of Salt-Responsive Genes and Transcription Factors in Leaf Transcriptome of Arabidopsis thaliana

This investigation discerns the expression profiles of genes within the leaf transcriptome of Arabidopsis thaliana subjected to salt stress (200 mM NaCl). Notably, the pivotal role of indole acetic acid emerged as a keystone orchestrating a multifaceted cascade of regulatory events aimed at enhancing the plant’s adaptability under salt-induced stress. Cluster analysis elucidated upregulation of gene families with pivotal roles in supporting the availability of carbon dioxide, ameliorating photosynthetic processes and mitigating the deleterious effects of reactive oxygen species under salt stress. Analysis also unveiled the participation of several transcription factor families in the orchestration of a multitude of genes under salt stress. The investigation singled out a solitary TF, denominated as BH100, which was validated through RNA-Seq and qPCR, utilizing a VIGS line featuring the knockdown of the BH100 gene. This transcription factor was implicated in the upregulation of the FRO gene, thereby establishing a link between the synchronized expression of these two genes and their role in promoting iron acquisition under salt stress. In summation, our study unveiled the regulatory frameworks and salt-responsive genes underpinning the response of Arabidopsis to salt stress. We present compelling arguments for the potential applicability of this information in the realm of molecular breeding programs.

Lysinibacillus spp.: an IAA-producing endospore forming-bacteria that promotes plant growth

Lysinibacillus is a bacterial genus that has generated recent interest for its biotechnological potential in agriculture. Strains belonging to this group are recognized for their mosquitocidal and bioremediation activity. However, in recent years some reports indicate its importance as plant growth promoting rhizobacteria (PGPR). This research sought to provide evidence of the PGP activity of Lysinibacillus spp. and the role of the indole-3-acetic acid (IAA) production associated with this activity. Twelve Lysinibacillus spp. strains were evaluated under greenhouse conditions, six of which increased the biomass and root architecture of corn plants. In most cases, growth stimulation was evident at 108 CFU/mL inoculum concentration. All strains produced IAA with high variation between them (20–70 µg/mL). The bioinformatic identification of predicted genes associated with IAA production allowed the detection of the indole pyruvic acid pathway to synthesize IAA in all strains; additionally, genes for a tryptamine pathway were detected in two strains. Extracellular filtrates from all strain’s cultures increased the corn coleoptile length in an IAA-similar concentration pattern, which demonstrates the filtrates had an auxin-like effect on plant tissue. Five of the six strains that previously showed PGPR activity in corn also promoted the growth of Arabidopsis thaliana (col 0). These strains induced changes in root architecture of Arabidopsis mutant plants (aux1-7/axr4-2), the partial reversion of mutant phenotype indicated the role of IAA on plant growth. This work provided solid evidence of the association of Lysinibacillus spp. IAA production with their PGP activity, which constitutes a new approach for this genus. These elements contribute to the biotechnological exploration of this bacterial genus for agricultural biotechnology.

A novel small molecule inhibitor of vascular endothelin signaling and hypertension

Augmented endothelin-1 (ET-1) signaling causes profound vasoconstriction, smooth muscle proliferation, endothelial dysfunction, oxidative stress, and vascular inflammation and sensitivity, which are often present in resistant hypertension, salt-sensitive hypertension and hypertension among African Americans. Here, we sought to examine the role of indole-3 acetic acid (IAA) as a novel inhibitor of vascular ET-1 signaling and hypertension. IAA, popularly known as auxin, is the most potent plant growth hormone, which is also produced in the human body via tryptophan metabolism by gut microbiota. Although the role of IAA as a potent plant growth hormone has been characterized, little is known about the biological activity of this compound in humans. Importantly, studies on the role of IAA as a regulator of arterial contractility, vascular inflammation and hypertension remain completely unexplored. Our data demonstrates that IAA inhibits ET-1-evoked vasoconstriction in resistance mesenteric arteries, ROS production in human aortic SMCs, expression of adhesion molecule VCAM-1 on EC surface, leukocyte adhesion, and ECE-1 activity. IAA dose-dependently inhibits the activity of a purified human endothelin converting enzyme-1 (ECE-1) that converts the precursor big ET to its active form ET-1 and is upregulated in hypertension. Consistent with these findings, we show that treatment of Dahl salt-sensitive (DSS) hypertensive rats, a model of augmented ET-1 signaling, with an oral extended-release, in situ gel-based formulation of IAA (IAA-oragel) reduces blood pressure (BP) elevation, suggesting a key role for IAA in BP regulation. Taken together, this study presents a novel inquiry into regulation of ET-1 function by IAA and could identify IAA as the first dual action inhibitor of the ET system. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Role of IAA in Regulating Root Architecture of Sweetpotato (Ipomoea batatas [L.] Lam) in Response to Potassium Deficiency Stress.

Plants can adapt to the spatial heterogeneity of soil nutrients by changing the morphology and architecture of the root system. Here, we explored the role of auxin in the response of sweetpotato roots to potassium (K+) deficiency stress. Two sweetpotato cultivars, Xushu 32 (low-K-tolerant) and Ningzishu 1 (low-K-sensitive), were cultured in low K+ (0.1 mmol L-1, LK) and normal K+ (10 mmol L-1, CK) nutrient solutions. Compared with CK, LK reduced the dry mass, K+ content, and K+ accumulation in the two cultivars, but the losses of Xushu 32 were smaller than those of Ningzishu 1. LK also affected root growth, mainly impairing the length, surface area, forks number, and crossings number. However, Xushu 32 had significantly higher lateral root length, density, and surface area than Ningzishu 1, closely related to the roots' higher indole-3-acetic acid (IAA) content. According to the qPCR results, Xushu 32 synthesized more IAA (via IbYUC8 and IbTAR2) in leaves but transported and accumulated in roots through polar transport (via IbPIN1, IbPIN3, and IbAUX1). It was also associated with the upregulation of auxin signaling pathway genes (IbIAA4 and IbIAA8) in roots. These results imply that IAA participates in the formation of lateral roots and the change in root architecture during the tolerance to low K+ stress of sweetpotato, thus improving the absorption of K+ and the formation of biomass.

Auxin Participates in the Regulation of the Antioxidant System in Malus baccata Borkh. Roots under Sub-Low Temperature by Exogenous Sucrose Application

Malus baccata Borkh., an apple rootstock, is found to be damaged by oxidation at sub-low root-zone temperature. In previous studies, we have found that exogenous sucrose could alleviate oxidative damage and increase the indole acetic acid (IAA) in roots under sub-low temperature (L). However, the role of IAA in sucrose-induced tolerance to L remains unclear. A pot experiment was conducted to evaluate the effects of exogenous sucrose and IAA synthesis/transport inhibitors (2,3,5-triiodobenzoic acid, TIBA; 4-biphenylboronic acid, BBo) on growth, IAA levels, sugars, and the antioxidant system of M. baccata under L. The results showed that the L treatment decreased IAA contents by 23.69% (48 h) and induced significant increases in root contents of malondialdehyde (MDA) and reactive oxygen (ROS), along with increasing catalase (CAT), ascorbate peroxidase (APX), and glucose-6-phosphate dehydrogenase (G6PDH) activities, while superoxide dismutase (SOD) and monodehydroascorbate reductase (MDHAR) activities first increased (24 h) and then decreased (48 h), and glutathione reductase (GR) and peroxidase (POD) activities significantly decreased. The L treatment also decreased ascorbate/oxidized ascorbate (AsA/DHA), glutathione/oxidized glutathione (GSH/GSSG), and coenzyme II/oxidized coenzyme II (NADPH/NADP+) ratios. Furthermore, the L treatment increased the contents of sucrose, fructose, glucose and sorbitol in the roots and suppressed plant growth. Sucrose pretreatment significantly increased IAA contents (12.42%, 24 h and 14.44%, 48 h) and decreased MDA and ROS contents, which improved the activities of antioxidant enzymes other than APX and increased the contents of AsA, GSH, and NADPH, and increased sucrose, fructose, and sorbitol contents and promoted plant growth. However, the sucrose + TIBA or BBo treatments decreased IAA contents and attenuated or almost abolished the positive effects of exogenous sucrose under sub-low temperature. Our findings indicate that IAA is involved in the sucrose-induced regulation of the antioxidant system in M. baccata roots under sub-low temperature and we provided theoretical references for further study on the adaptability of apple roots to low temperature.

Mitigation of arsenate toxicity by indole-3-acetic acid in brinjal roots: Plausible association with endogenous hydrogen peroxide

The role of indole-3-acetic acid (IAA) and hydrogen peroxide (H2O2) crosstalk in regulating metal stress is still less known. Herein, role of IAA in alleviating arsenate (AsV) toxicity in brinjal seedlings along with its probable relation with endogenous H2O2 was investigated. Arsenate hampered root growth due to greater accumulation of As and decrease in phosphorus uptake that resulted into inhibited photosynthesis and cell death. Further, AsV induced oxidative stress markers and damage to macromolecules (lipids and proteins) due to alterations in redox status of glutathione as a result of inhibition in activity of glutathione synthetase and glutathione reductase. However, application of IAA with AsV improved root growth by significantly declining As accumulation and oxidative stress markers, sequestrating As into vacuoles, and improving redox status of glutathione which collectively protected roots from cell death. Interestingly, addition of diphenylene iodonium (DPI, an inhibitor of NADPH oxidase) further increased AsV toxicity even in the presence of IAA. However, application of H2O2 rescued negative effect of DPI. Overall, the results suggested that in IAA-mediated mitigation of AsV toxicity in brinjal roots, endogenous H2O2 might have acted as a downstream signal.

Phytohormone up-regulates the biochemical constituent, exopolysaccharide and nitrogen metabolism in paddy-field cyanobacteria exposed to chromium stress

BackgroundCyanobacteria are well known for their inherent ability to serve as atmospheric nitrogen fixers and as bio-fertilizers; however, increased contaminants in aquatic ecosystem significantly decline the growth and function of these microbes in paddy fields. Plant growth regulators play beneficial role in combating the negative effects induced by heavy metals in photoautotroph. Current study evaluates the potential role of indole acetic acid (IAA; 290 nm) and kinetin (KN; 10 nm) on growth, nitrogen metabolism and biochemical constituents of two paddy field cyanobacteria Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 exposed to two concentrations of chromium (CrVI; 100 μM and 150 μM).ResultsBoth the tested doses of CrVI declined the growth, ratio of chlorophyll a to carotenoids (Chl a/Car), contents of phycobiliproteins; phycocyanin (PC), allophycocyanin (APC), and phycoerythrin (PE), protein and carbohydrate associated with decrease in the inorganic nitrogen (nitrate; NO3— and nitrite; NO2—) uptake rate that results in the decrease in nitrate and ammonia assimilating enzymes; nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT) except glutamate dehydrogenase (GDH). However, exogenous supplementation of IAA and KN exhibited alleviating effects on growth, nitrogen metabolism and exopolysaccharide (EPS) (first protective barrier against metal toxicity) contents in both the cyanobacteria, which probably occurred as a result of a substantial decrease in the Cr uptake that lowers the damaging effects.ConclusionOverall result of the present study signifies affirmative role of the phytohormone in minimizing the toxic effects induced by chromium by stimulating the growth of cyanobacteria thereby enhancing its ability as bio-fertilizer that improved fertility and productivity of soil even in metal contaminated condition.

Yucasin and cinnamic acid inhibit IAA and flavonoids biosynthesis minimizing interaction between maize and endophyte Aspergillus nomius

Chemical crosstalk between plant roots and associated microbes is imperative for the initiation of symbiosis. Phenolics, flavonoids and indole-3-acetic acid (IAA) are acclaimed as signaling molecules in developing plant-microbe symbiosis. The role of IAA and flavonoids in establishing a symbiotic relationship between Aspergillus nomius wlg2 and maize roots have also been observed during the present study. The isolate A. nomius wlg2 and maize roots have secreted flavonoids and IAA that helped in A. nomius-maize association. However, the suppression of either flavonoids or IAA secretion reduced the endophyte colonization of the maize roots by 77% and 67%, respectively. The main flavonoids secreted by maize were identified as luteolin, calycosin, phenolics cis-caftaric acid, and caffeoyl-d-glucose. The identified flavonoids were most likely to be involved in the root-endophyte association. To establish a plant-microbe interaction, the complex chemical dialogue is necessary for which IAA and flavonoids play a central role.

Deciphering metal toxicity responses of flax (Linum usitatissimum L.) with exopolysaccharide and ACC-deaminase producing bacteria in industrially contaminated soils

Rapid industrialization is the main reason of heavy metals contamination of soil colloids and water reservoirs. Heavy metals are persistent inorganic pollutants; deleterious to plants, animals and human beings because of accumulation in food chain. The aim of the current work was to evaluate the role of indole acetic acid (IAA), exopolysaccharide (EPS) and ACC-deaminase producing plant growth promoting rhizobacteria (PGPR) i.e .B. gibsonii PM11 and B. xiamenensis PM14 in metal phytoremediation of metals, their survival and plant growth promotion potential in metal polluted environment as well as alterations in physio-biochemical responses of inoculated L. usitatissimum plants towards heavy metal toxicity. Two bacterial strains Bacillus gibsonii (PM11) and Bacillus xiamenensis (PM14), previously isolated from sugarcane's rhizosphere, were screened for metal tolerance (50 mg/l to 1000 mg/l) and plant growth promoting traits like IAA, ACC-deaminase, EPS production and nitrogen fixing ability under metal stress. The response of flax plant (Linum usitatissimum L.) was analyzed in a pot experiment containing both industrially contaminated and non-contaminated soils. Experiment was comprised of six different treatments, each with three replicates. At the end of the experiment, role of metal tolerant plant growth promoting bacterial inoculation was elucidated by analyzing the plant growth parameters, chlorophyll contents, antioxidative enzymes, and metal uptake both under standard and metal contaminated rhizospheres. Results revealed that root and shoot length, plant's fresh and dry weight, proline content, chlorophyll content, antioxidant enzymatic activity was increased in plants inoculated with plant growth promoting bacteria as compared to non-inoculated ones both in non-contaminated and industrial contaminated soils. In current study, inoculation of IAA, EPS and ACC-deaminase producing bacteria enhances plant growth and nutrient availability by minimizing metal-induced stressed conditions. Moreover, elevated phytoextraction of multi-metals from industrial contaminated soils by PGPR inoculated L. usitatissimum plants reveal that these strains could be used as sweepers in heavy metals polluted environment.

Radial water transport in arbuscular mycorrhizal maize plants under drought stress conditions is affected by indole-acetic acid (IAA) application

Drought stress is one of the most devastating abiotic stresses, compromising crop growth, reproductive success and yield. The arbuscular mycorrhizal (AM) symbiosis has been demonstrated to be beneficial in helping the plant to bear with water deficit. In plants, development and stress responses are largely regulated by a complex hormonal crosstalk. Auxins play significant roles in plant growth and development, in responses to different abiotic stresses or in the establishment and functioning of the AM symbiosis. Despite these important functions, the role of indole-3acetic acid (IAA) as a regulator of root water transport and stress response is not well understood. In this study, the effect of exogenous application of IAA on the regulation of root radial water transport in AM plants was analyzed under well-watered and drought stress conditions. Exogenous IAA application affected root hydraulic parameters, mainly osmotic root hydraulic conductivity (Lo), which was decreased in both AM and non-AM plants under water deficit conditions. Under drought, the relative apoplastic water flow was differentially regulated by IAA application in non-AM and AM plants. The effect of IAA on the internal cell component of root water conductivity suggests that aquaporins are involved in the IAA-dependent inhibition of this water pathway.

Production and roles of IAA and ABA during development of superior and inferior rice grains.

Current understanding of the role of plant hormones during cereal grain filling is confounded by contradictory reports on hormone production that is based on poor methodology. We report here on the accurate measurement of indole-3-acetic acid (IAA) and abscisic acid (ABA) by combined liquid chromatography-tandem mass spectrometry in multiple reaction-monitoring mode with heavy isotope labelled internal standards. ABA and IAA contents of superior versus inferior rice grains (ABA maxima 159 ng g-1 FW and 109 ng g-1 FW, IAA maxima 2 µg g-1 FW and 1.7 µg g-1 FW respectively) correlated with the expression of biosynthetic genes and with grain fill. Results confirm that grain ABA is produced primarily by OsNCED2(5), but suggest that ABA import and metabolism also play important roles in ABA regulation. The IAA content of grains is primarily influenced by OsYUC9 and OsYUC11. However, the distinct expression profile of OsYUC12 suggests a specific role for IAA produced by this enzyme. Co-expression of OsYUC12 with OsIAA29 indicates their involvement in a common signalling pathway. Co-expression and cis-element analysis identified several aleurone-specific transcriptional regulators as well as glutelin as strong candidates for detailed investigation for direct regulation by the auxin-signalling pathway.

Indole-3-acetic acid metabolism and growth in young kiwifruit berry

The patterns of auxin concentration and metabolism were investigated in distinct kiwifruit portions and compared with the rate of fruit growth during early developmental stages. Indole-3-acetic acid (IAA) level was higher in inner fruit tissues, particularly in younger fruit, while the hormone was barely detectable in outer tissues. Modulation of free IAA concentration did not appear to depend tightly on conjugation of the hormone. Despite the lack of a strong correlation between the levels of IAA and enzymes involved in its catabolism, in some portions of the fruit a low hormone level corresponded to a higher IAA degradation activity. An inverse correlation was also observed between hormone levels and the appearance/increase in some bands with high mobility in peroxidase gel activity assay. Phenols, compounds with a potential auxin-protecting activity, appeared to be involved mostly in photoprotection of the fruit than in the regulation of IAA levels. Beyond catabolism and conjugation, other metabolic pathways, particularly those occurring in the developing seeds, may have decisively influenced auxin levels in fruit tissues, as well as the amount of the hormone exported from the fruit. The latter, estimated by analyzing the concentration of IAA in the sap exuded from the pedicel, showed a time course which was similar to that displayed by inner fruit tissues. Furthermore, similarities were found between the pattern of IAA concentration in inner fruit tissues and fruit growth rate. The possible role of IAA in promoting growth during early fruit development is discussed.

Indole acetic acid is responsible for protection against oxidative stress caused by drought in soybean plants: The role of heme oxygenase induction

ObjectivesThis study was focused on the role of indole acetic acid (IAA) in the defense against oxidative stress damage caused by drought in soybean plants and to elucidate whether heme oxygenase-1 (HO-1) and nitric oxide (NO) are involved in this mechanism. IAA is an auxin that participates in many plant processes including oxidative stress defense, but to the best of our knowledge no information is yet available about its possible action in drought stress.MethodsTo this end, soybean plants were treated with 8% polyethylene glycol (PEG) or 100 µM IAA. To evaluate the behavior of IAA, plants were pretreated with this compound previous to PEG addition. Lipid peroxidation levels (thiobarbituric acid reactive substances (TBARS)), glutathione (GSH) and ascorbate (AS) contents, catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (POD) activities were determined to evaluate oxidative damage.ResultsDrought treatment (8% PEG) caused a significant increase in TBARS levels as well as a marked decrease in the non-enzymatic (GSH and AS) and enzymatic (CAT, SOD, and POD) antioxidant defense systems. Pre-treatment with IAA prevented the alterations of stress parameters caused by drought, while treatment with IAA alone did not produce changes in TBARS levels, or GSH and AS contents. Moreover, the activities of the classical enzymes involved in the enzymatic defense system (SOD, CAT, and POD) remained similar to control values. Furthermore, this hormone could enhance HO-1 activity (75% with respect to controls), and this increase was positively correlated with protein content as well as gene expression. The direct participation of HO-1 as an antioxidant enzyme was established by performing experiments in the presence of Zn-protoporphyrin IX, a well-known irreversible inhibitor of this enzyme. It was also demonstrated that HO-1 is modulated by NO, as shown by experiments performed in the presence of an NO donor (sodium nitroprusside), an NO scavenger (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), or an NO synthesis inhibitor (N-nitro-l-arginine methyl ester, NAME).DiscussionIt is concluded that IAA is responsible, at least in part, for the protection against oxidative stress caused by drought in soybean plants through the modulation of NO levels which, in turn, enhances HO-1 synthesis and activity.

Indole-3-acetic acid in plant–microbe interactions

Indole-3-acetic acid (IAA) is an important phytohormone with the capacity to control plant development in both beneficial and deleterious ways. The ability to synthesize IAA is an attribute that many bacteria including both plant growth-promoters and phytopathogens possess. There are three main pathways through which IAA is synthesized; the indole-3-pyruvic acid, indole-3-acetamide and indole-3-acetonitrile pathways. This chapter reviews the factors that effect the production of this phytohormone, the role of IAA in bacterial physiology and in plant-microbe interactions including phytostimulation and phytopathogenesis.

Association of non-heterocystous cyanobacteria with crop plants

Cyanobacteria have the ability to form associations with organisms from all domains of life, notably with plants, which they provide with fixed nitrogen, among other substances. This study was aimed at developing artificial associations between non-heterocystous cyanobacteria and selected crop plants. We isolated several non-heterocystous cyanobacteria from various rice fields. The cultures were tested for their capacity to produce the plant hormone indole-3-acetic acid (IAA), and the possible role of IAA in the association of cyanobacteria with seedling roots was evaluated. Axenic cultures were co-inoculated with 10-day-old plant seedlings of Triticum aestivum, Vigna radiata and Pisum sativum and incubated for 1 week. Cyanobacterial association with the roots of these seedlings was quantified by measuring chlorophyll-a. Cyanobacterial association with the roots was observed by light microscopy as well as by confocal laser scanning microscopy (CLSM). Based on sequence analysis of the 16S rRNA gene, the isolates were identified as Synechocystis sp., Chroococcidiopsis sp., Leptolyngbya sp., and Phormidium sp. CLSM observations revealed the intimate association of cyanobacteria with the seedling roots as well as invasion of the roots and root cells. Strains producing IAA were more efficient in the colonization of the roots than those that lacked this ability. IAA-producing cyanobacteria possess a tryptophan-dependent pathway, and these cyanobacteria showed IAA synthesis activity in the presence of roots in media lacking tryptophan. Based on the results of this study, we conclude that non-heterocystous cyanobacteria also have the potential for use in agriculture to improve the growth and yield of crop plants that do not naturally form associations with cyanobacteria.

Potential of bacterial indoleacetic acid to induce adventitious shoots in plant tissue culture

The main aim of this study was to investigate the possible role of indoleacetic acid (IAA) from bacteria to induce in vitro adventitious shoots in internodal explants of Brassica oleracea L. Culture supernatant of Halomonas sp. RE1 and Halomonas sp. HT1 that contain 21 and 40 microg ml(-1) IAA, respectively, was used to supplement Murashige and Skoog (MS) medium. Two combinations that were supplemented with bacterial supernatant (BS) are MS + BS and MS + BS + 10%CW (coconut water) while basal MS medium was used as control. The amounts of BS used in this experiment were 50, 100, 150 and 200 microl in 5 ml MS medium in each combination. In vitro-grown internodal explants of B. oleracea were inoculated on these media combinations and incubated in a growth chamber at 25 +/- 1 degrees C and exposed to 16-h cool fluorescent light. After 5-6 weeks of incubation adventitious shoot induction was observed in all treatments that were supplemented with BS as compared with the controls where very low response was observed. The frequency of shoot induction was high in media that were supplemented with 10%CW in the presence of bacterial auxin. It was concluded that IAA of microbial origin has the potential to induce adventitious shoots in internodal explants. IAA from bacteria can be effectively used in plant tissue culture; especially a combination of MS + BS + 10%CW is very cost-effective as compared with synthetic phytohormones for in vitro studies.

Growth stimulation and fruit yield improvement of greenhouse tomato plants by inoculation with Pseudomonas putida or Trichoderma atroviride: Possible role of indole acetic acid (IAA)

Five bacteria ( Pseudomonas fluorescens, P. fluorescens subgroup G strain 2, P. marginalis, P. putida subgroup B strain 1 and P. syringae strain 1) and three fungi ( Penicillium brevicompactum, P. solitum strain 1 and Trichoderma atroviride) were evaluated to determine their promoting effect on the growth of mature healthy tomato plants grown under hydroponic conditions. P. putida and T. atroviride were shown to improve fruit yields in rockwool and in organic medium. The production or degradation of indole acetic acid (IAA) by the two microorganisms was investigated as possible mechanisms for plant growth stimulation. Both P. putida and T. atroviride were shown to produce IAA. The production of IAA by the two microorganisms was stimulated in vitro by the addition of l-tryptophan, tryptamine and tryptophol (200 μg ml −1) in the culture medium. P. putida and T. atroviride also increased the fresh weight of both the shoot and the roots of tomato seedlings grown in the presence of increasing concentrations of l-tryptophan (up to 0.75 mM). Both microorganisms showed partial degradation of IAA in vitro when grown in a minimal medium with or without sucrose. In addition, the capacity of these microorganisms to reduce the deleterious effect of exogenous IAA was investigated using tomato seedlings. The results showed that the roots of tomato seedlings grown in the presence of increasing concentrations of IAA (0–10 μg ml −1) were significantly longer when seeds were previously treated with P. putida or T. atroviride. The reduction in the detrimental effect of IAA on root elongation could be associated with a reduced ethylene production resulting from a decrease of its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) by microbial degradation of IAA in the rhizosphere and/or by ACC deaminase activity present in both microorganisms.

Indole‐3‐acetic acid attenuates the fungal lesions in infected potato tubers

In this report, we demonstrated that potato tubers pre‐treated with 100 µM of indole‐3‐acetic acid (IAA) and then inoculated with Fusarium solani f. sp. eumartii (F. eumartii) showed a decrease in the fungal lesion compared with non‐IAA pre‐treated and inoculated tubers. Consequently, we tested the addition of different concentrations of IAA on the fungal growth and on the proteolytic activity when the fungus was grown in liquid culture medium. Fungal growth did not change under different phytohormone concentrations, but the activity of Fusarium extracellular serine protease (FESP) clearly decreased. The inhibition of FESP activity by IAA was dose dependent. Moreover, FESP as well as others extracellular pectinolytic activities detected in IAA pre‐treated and inoculated tubers decreased compared with controls. In addition, the ability of IAA production by F. eumartii was tested, and the role of IAA on potato–F. eumartii interaction is discussed.

Physiological and biochemical changes associated with cotton fiber development: IX. Role of IAA and PAA

Fibers of three cotton cultivars Gossypium hirsutum hybrid-4 (H-4), hybrid-8 (H-8), and G. arboreum G. Cot-15 were analyzed to study the role of auxin in fiber elongation, in vitro and in vivo. The cultivars exhibited variation in final fiber length. Fibers were analyzed for growth, free and conjugated indole acetic acid (IAA) content and phenyl acetic acid (PAA) content during the entire period of their development. Antibodies against IAA and PAA were raised and endogenous contents of IAA and PAA were estimated by indirect ELISA. Cotton fiber development is divided into four phases viz. (i) initiation (0–3 days post-anthesis (DPA)), (ii) elongation (3–24 DPA), (iii) secondary thickening (18–42 DPA) and (iv) maturation (42 DPA onwards). During the phase of rapid cell elongation, water content increased and then decreased after the fiber entered the secondary thickening phase, in all three cultivars. A positive correlation between final fiber length and free and conjugated IAA and PAA content was observed. In in vitro grown fiber, media supplemented with IAA or napthyl acetic acid (NAA) significantly increased the length of fiber in middle and short staple cultivars, whereas PAA promoted fiber length in the short staple cultivar only. The results of cultured cotton fiber suggest an important role of auxin in cotton fiber development, which may help for the selection of gene(s) for better fiber development.