Presence Of Indole-3-acetic Acid Research Articles

Optimizing callus formation in the endangered medicinal tree Hydnocarpus macrocarpa using phytohormone

Hydnocarpus macrocarpa (Flacourtiaceae) is one of the endemic and endangered medicinal tree, was selected to investigate the influence of plant growth regulators on callus formation. H. macrocarpa is majorly distributed at low and medium elevations of the Southern Western Ghats. The seeds of this plant are used for the treatment of ulcers, biliousness, leprosy and epilepsy. An experiment was carried out with two different methods. In the first method Murashige and Skoog (MS) medium supplemented with cytokinin alone or combined with auxin (2–4-Dichlorophenoxy acetic acid; Naphthalene acetic acid; Indole acetic acid; Indole butyric acid and Gibberellic acid) at different concentrations (1, 2, 3, 4 and 5 µM) were used; in the seond method, MS medium supplemented with coconut endosperm (Solid and liquid) extract (1, 2, 3, 4 and 5 %) with Aloe vera jelly extract at different concentrations (1, 2, 3, 4 and 5 %) in combination and separately were used. Among the different treatments, good callus proliferation was obtained using MS medium supplemented with Benzylaminopurine and in combination with Naphthalene acetic acid and 2–4-Dichlorophenoxyacetic acid (3 µM and 4 µM). But the best callus proliferation, shoot tip proliferation; auxiliary root and shoot formation were observed in MS medium supplemented with Aloe vera jelly extract in combination with coconut endosperm extract. The natural growth regulators supplemented with the media gave a positive response for plant growth. The results showed that the natural growth regulators, such as coconut endosperm and Aloe vera jelly extracts were found to be more efficient than the synthetic growth regulators (auxin and cytokinin). The presence of Indole acetic acid and Indole butyric acid in both Aloe vera jelly extracts and coconut endosperm were confirmed by High performance liquid chromatography and Fourier transform infrared spectroscopy analysis.

Heavy toxic sludge tolerance in microalgae: Effect of energy generation metabolisms from C. humicola under IAA applications

Industrial sludge is characterized by high moisture content, complex composition, and significant organic toxicity. This research aimed to improve the performance of Chlorococcum humicola in removing hydroquinone-domesticated sludge toxicity through the addition of indole-3-acetic acid (IAA). The maximum cell density and dry weight of C. humicola were attained when the IAA concentration was 5.0 × 10−6 mol/L, at 6.79 × 107 cells/mL and 2.60 g/L, respectively. The toxicity of the sludge degradation rate reached its peak level of 59.70% on the 20th day. The toxicity reduction was consistent with the decrease of RNA degradation-related proteins such as A5FN12, which can be hydrolyzed and absorbed by C. humicola via active transport. In the presence of IAA, C. humicola increased its energy production processes, such as glycolysis and oxidative phosphorylation, to facilitate active transport. Moreover, the efficiency of signal transduction was improved, leading to enhanced cellular metabolism. The suppression of biosynthesis of glutathione and arginine at the molecular level may contribute to this observed trend. Overall, this study provides new insights into the mechanism by which IAA promotes the degradation of sludge toxicity by C. humicola, offering a novel method and theoretical basis for the safe and resource-based utilization of industrial sludge.

Characterization of the IAA-Producing and -Degrading Pseudomonas Strains Regulating Growth of the Common Duckweed (Lemna minor L.).

The rhizosphere represents a center of complex and dynamic interactions between plants and microbes, resulting in various positive effects on plant growth and development. However, less is known about the effects of indole-3-acetic acid (IAA) on aquatic plants. In this study, we report the characterization of four Pseudomonas strains isolated from the rhizosphere of the common duckweed (Lemna minor) with IAA-degradation and -utilization ability. Our results confirm previous reports on the negative effect of IAA on aquatic plants, contrary to the effect on terrestrial plants. P. putida A3-104/5 demonstrated particularly beneficial traits, as it exhibited not only IAA-degrading and -producing activity but also a positive effect on the doubling time of duckweeds in the presence of IAA, positive chemotaxis in the presence of IAA, increased tolerance to oxidative stress in the presence of IAA and increased biofilm formation related to IAA. Similarly, P. gessardii C31-106/3 significantly shortened the doubling time of duckweeds in the presence of IAA, while having a neutral effect in the absence of IAA. These traits are important in the context of plant-bacteria interactions and highlight the role of IAA as a common metabolite in these interactions, especially in aquatic environments where plants are facing unique challenges compared to their terrestrial counterparts. We conclude that IAA-degrading and -producing strains presented in this study might regulate IAA effects on aquatic plants and confer evolutionary benefits under adverse conditions (e.g., under oxidative stress, excess of IAA or nutrient scarcity).

Role of an antagonistic bacterium, Bacillus subtilis PE7, in growth promotion of netted melon (Cucumis melo L. var. reticulatus Naud.).

The aim of this study was to determine the plant growth-promoting effect of Bacillus subtilis PE7 on growth of melon plants. B. subtilis PE7 isolated from kimchi was identified based on colonial and microscopic morphology along with analyses of 16S rRNA and pycA gene sequences. Strain PE7 showed different levels of inhibition on phytopathogens and was able to grow at variable temperatures and pH values. Strain PE7 had the ability to produce siderophores, indole-3-acetic acid (IAA), ammonia, exopolysaccharides, and 1-aminocyclopropane-1-carboxylic acid deaminase, as well as solubilize insoluble phosphate and zinc. The IAA secretion of strain PE7 showed a concentration-dependent pattern based on the concentration of l-tryptophan supplemented in the fertilizer-based culture medium. The LC-MS analysis indicates the presence of IAA in the culture filtrate of strain PE7. Treatment of the B. subtilis PE7 culture containing different metabolites, mainly IAA, significantly promoted melon growth in terms of higher growth parameters and greater plant nutrient contents compared to treatments with the culture without IAA, fertilizer, and water. The cells of B. subtilis PE7 attached to and firmly colonized the roots of the bacterized melon plants. Based on our results, B. subtilis PE7 can be utilized as a potential microbial fertilizer to substitute chemical fertilizers in sustainable agriculture.

Colletotrichum truncatum, an endophytic fungus derived from Musa acuminata (AAA group): antifungal activity against Aspergillus isolated from COVID-19 patients and indole-3-acetic acid (IAA) production

Fungal endophyte is a fungal that lives in plant organism as mutualism association. The role of fungal endophyte is a growth promoter or/and microbial pathogen inhibitor. This study investigated antifungal activity of Colletotrichum truncatum E10, an endophytic fungus derived from Musa acuminata (AAA group), against 7 isolates of Aspergillus obtained from lower respiratory samples of COVID-19 patients. In addition, IAA production of this strain was also observed. All isolates of Aspergillus were identified using MALDI-TOF MS. The fungal endophyte, C. truncatum E10, was screened for IAA induction with and without 0.1, 2 and 8 mg/mL of L-tryptophan based on colorimetric method using Salkowski reagent which produced pinkish to reddish solution indicating the presence of IAA. Antagonist activity was based on dual culture assay measured in colony growth inhibition (CGI). C. truncatum E10 produced the highest IAA concentration of 112.81±0.12 µg/mL when 8 mg/mL of L-tryptophan added. The strong antagonist activities were shown by C. truncatum E10 against 5 Aspergillus isolates including 2 A. fumigatus: sp442/6 (CGI=57.83±5.11%) and sp269/11 (CGI=53.01±8.52%), 1 A. niger sp26/7 (CGI=57.83±15.33%) and 2 A. flavus: sp26/7 (CGI=56.63±13.63%) and sp36/7 (CGI=57.23±0.85%), whereas the colony growth inhibition (CGI) of other 2 isolates including A. fumigatus sp567/6 and A. flavus sp269/11 were less than 50%. In this study, C. truncatum E10 produced substances that inhibited human fungal pathogen including A. fumigatus, A. flavus and A. niger. Moreover, it can produce IAA activity. Further investigations are being conducted to expand the plant growth promotion effects and determine IAA biosynthesis pathway. For antifungal activity, the bioactive metabolites produced by this endophytic fungal isolate should be characterized to specify the effective compounds. Asian Australas. J. Biosci. Biotechnol. 2023, 8 (2), 23-29

Label-Free Quantitative Proteomic Analysis of the Global Response to Indole-3-Acetic Acid in Newly Isolated Pseudomonas sp. Strain LY1.

Indole-3-acetic acid (IAA), known as a common plant hormone, is one of the most distributed indole derivatives in the environment, but the degradation mechanism and cellular response network to IAA degradation are still not very clear. The objective of this study was to elucidate the molecular mechanisms of IAA degradation at the protein level by a newly isolated strain Pseudomonas sp. LY1. Label-free quantitative proteomic analysis of strain LY1 cultivated with IAA or citrate/NH4Cl was applied. A total of 2,604 proteins were identified, and 227 proteins have differential abundances in the presence of IAA, including 97 highly abundant proteins and 130 less abundant proteins. Based on the proteomic analysis an IAA degrading (iad) gene cluster in strain LY1 containing IAA transformation genes (organized as iadHABICDEFG), genes of the β-ketoadipate pathway for catechol and protocatechuate degradation (catBCA and pcaABCDEF) were identified. The iadA, iadB, and iadE-disrupted mutants lost the ability to grow on IAA, which confirmed the role of the iad cluster in IAA degradation. Degradation intermediates were analyzed by HPLC, LC-MS, and GC-MS analysis. Proteomic analysis and identified products suggested that multiple degradation pathways existed in strain LY1. IAA was initially transformed to dioxindole-3-acetic acid, which was further transformed to isatin. Isatin was then transformed to isatinic acid or catechol. An in-depth data analysis suggested oxidative stress in strain LY1 during IAA degradation, and the abundance of a series of proteins was upregulated to respond to the stress, including reaction oxygen species (ROS) scavenging, protein repair, fatty acid synthesis, RNA protection, signal transduction, chemotaxis, and several membrane transporters. The findings firstly explained the adaptation mechanism of bacteria to IAA degradation.

Co-application of indole-3-acetic acid/gibberellin and oxalic acid for phytoextraction of cadmium and lead with Sedum alfredii Hance from contaminated soil

Exogenous application of plant-growth promoting substances in combination with chelators is a common way to enhance the phytoextraction of heavy metals. A pot experiment was used to explore the influences of indole-3-acetic acid (IAA)/gibberellin (GA3) alone or together with oxalic acid (OA) on the growth, physiological response, and nutrient contents of hyperaccumulator Sedum alfredii Hance, and cadmium (Cd) and lead (Pb) phytoextraction efficiency. The results showed that a foliar spray of IAA/GA3 alone or together with OA increased plant growth. The largest shoot biomass with increase by 29.7% was produced by the 50 μmol L−1 IAA combined with 2.5 mmol kg−1 OA (50I+2.5OA) treatment as compared with the control treatment (CK). The presence of IAA and GA3 enhanced the chlorophyll a, carotenoid, and potassium contents in leaves and decreased the malondialdehyde content. The Cd content in leaf and the translocation factor (TFshoot) value from 50I+2.5OA treatment was increased by 4.29% and 21.4%, and the Pb content in stem and shoot, and the TFshoot of Pb after applying 50 μmol L-1 GA3 combined with 2.5 mmol kg−1 OA was enhanced by 32.5%, 13.4%, and 57.6%, compared with CK, respectively. The optimal Cd and Pb phytoextraction efficiency occurred from 50I+2.5OA treatment with increase by 82.4% and 79.3% as compared with CK, respectively. Therefore, the results showed that a combined application of 50 μmol L−1 IAA and 2.5 mmol kg−1 OA could effectively enhance S. alfredii Hance phytoremediation of Cd and Pb co-contaminated soil.

English

Indole-3-acetic acid (IAA) is an important plant growth regulator. As the very first endeavor, the study is aimed at extracting and quantifying IAA from seedlings of Bambusa tulda and evaluating its bioactivity. The extraction of IAA was performed in organic solvent followed by sample evaporation and TLC with a mobile phase composed of chloroform, methanol and formic acid (77:22:1 v/v) in isocratic mode. The extract obtained from preparatory TLC was subjected to HPLC with acetic acid and methanol (75:25 v/v) as the mobile phase in isocratic mode at a flow rate of 0.8 ml/min and operation pressure of 54 MPa at 30°C, and detection was monitored at 280 nm. Bioassay of the extracted IAA was carried out in Abelmoschus esculentus seedlings. The similar Rf value (0.412) of the extract during TLC analysis and similar peak of HPLC chromatogram with retention time 28.71 min to that of standard IAA indicated the presence of IAA in B. tulda seedling extract. The extracted IAA was quantified to be 10.28 µg/ml. In bioassay experiment, the extracted IAA significantly enhanced root length, root fresh weight, root dry weight, shoot length, shoot fresh weight, shoot dry weight and significant increase of total chlorophyll and protein in A. esculentus leaves. Therefore, B. tulda seedlings could be a potential source of IAA, and it can be utilized for production of bio-fertilizer at a commercial scale. Key words: Abelmoschus esculentus, Bamboo, High performance liquid chromatography, indole-3 acetic acid.

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.

Auxin perception in Agave is dependent on the species\u2019 Auxin Response Factors

Auxins are one of the most important and studied phytohormones in nature. Auxin signaling and perception take place in the cytosol, where the auxin is sensed. Then, in the nucleus, the auxin response factors (ARF) promote the expression of early-response genes. It is well known that not all plants respond to the same amount and type of auxins and that the response can be very different even among plants of the same species, as we present here. Here we investigate the behavior of ARF in response to various auxins in Agave angustifolia Haw., A. fourcroydes Lem. and A. tequilana Weber var. Azul. By screening the available database of A. tequilana genes, we have identified 32 ARF genes with high sequence identity in the conserved domains, grouped into three main clades. A phylogenetic tree was inferred from alignments of the 32 Agave ARF protein sequences and the evolutionary relationship with other species was analyzed. AteqARF 4, 15, 21, and 29 were selected as a representative diverse sample coming from each of the different subclades that comprise the two main clades of the inferred phylogenetic reconstruction. These ARFs showed differential species-specific expression patterns in the presence of indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D). Interestingly, A. angustifolia showed different phenotypes in the presence and absence of auxins. In the absence of auxin, A. angustifolia produces roots, while shoots are developed in the presence of IAA. However, in the presence of 2,4-D, the plant meristem converts into callus. According to our results, it is likely that AteqARF15 participates in this outcome.

Variation of isoflavone content and DPPH• scavenging capacity of phytohormone-treated seedlings after in vitro germination of cape broom (Genista monspessulana)

Plants of the genus Genista has gained interest due to its high content of alkaloids and flavonoids, especially isoflavones, because of their phytoestrogenic activity. Genista monspessulana (Fabaceae) is endemic of the Mediterranean area, known as “Cape broom”, but it is also considered as an invasive plant in some places into neotropical area. This plant is also known for its high content of secondary products with multi-pharmacological activity, e.g. antioxidant and phytoestrogenic, which has attracted attention for their potential use in preventive medicine. Thus, the present study was carried out to determine the variation on the DPPH• scavenging capacity and isoflavone content of in vitro seedlings of Cape broom after the stimulus of phytohormones such as indole-3-acetic acid (IAA) and kinetin (KIN), as a biochemical response for future biotechnological studies. Results indicated that the highest germination percentage was achieved in seeds separately exposed to IAA (at 2.5 µM under darkness and 7.5 µM under light) and KIN (at 0.25 µM under light and 0.75 µM under darkness. DPPH• free radical scavenging capacity, total phenolic and total flavonoid contents for in vitro seedlings of G. monspessulana treated with phytohormones were generally higher to that of intact plant. Additionally, in vitro seedlings showed enhanced concentrations of glycosylated isoflavones in the presence of IAA under light exposition. Results indicated that phytohormones (IAA or KIN) affected total phenolic/flavonoid contents, DPPH• scavenging capacity and isoflavone concentrations on in vitro seedlings, which constitutes a biotechnological opportunity to expand the exploitation of isoflavones from G. monspessulana.

Bacillus methylotrophicus M4-96 Stimulates the Growth of Strawberry (Fragaria × ananassa ‘Aromas’) Plants In Vitro and Slows Botrytis cinerea Infection by Two Different Methods of Interaction

Bacillus methylotrophicus M4-96 is a beneficial rhizobacterium that has been isolated from the rhizosphere of maize (Zea mays). In this study, we investigated its efficacy as a plant growth promoter for strawberry in vitro, as well as its ability to induce callose deposition in leaves to reduce the severity of Botrytis cinerea infection. Two methods of plant-bacterial interaction were used: inoculation near the root and emission of volatile compounds with no physical contact. Plant biomass increased under both treatments, but with developmental parameters of the plants differentially stimulated by each method. Root inoculation increased petiole number and root length, whereas bacterial volatiles increased petiole length and root number. A chemical analysis of the bacterial culture revealed the presence of indole acetic acid (0.21 μg L−1) and gibberellic acid (6.16 μg L−1). Acetoin was previously identified as the major volatile produced by the bacteria, and its application to strawberry explants increased their growth and development. Furthermore, when acetoin and both phytoregulators were added to the culture media, these positive effects were enhanced. The inoculation method also affected the size and quantity of callose deposits in the leaves. Treatment with volatiles increased callose deposition in the leaves by up to five-fold, which promoted a rapid defense reaction that inhibited the incidence of gray mold by reinforcing cell wall. Taken together, our results show that B. methylotrophicus M4-96 promotes growth and induces systemic resistance in strawberry plants.

Potential of indole-3-acetic acid-producing rhizobacteria to resist Pb toxicity in polluted soil

ABSTRACTHeavy metal toxicity in industrial polluted area is imparting serious consequences on crops. Two Pb-tolerant bacteria were isolated from maize growing in a dumping site of Attock Oil Refinery, Rawalpindi. The oil-polluted field had a higher geo-accumulation index (Igeo) and pollution load index (PLI) value for Pb than standard. The soil accumulated higher Cd, Zn, and Mn contents too. Maize leaves and roots accumulated higher Pb and Zn and exhibited biological concentration factor (BCF), biological accumulating factor (BAC), and translocation factor (TF) Zn. Two bacterial strains (Exiguobacterium aurantiacum and Bacillus firmus) were isolated from maize rhizosphere growing in an oil-polluted field and applied as bio-inoculants on maize in a greenhouse experiment for 80 days. Both bio-inoculants were tolerant to Pb at 500 ppm and had the potential to produce indole-3-acetic acid (IAA) in the presence or absence of Pb. Results revealed that single inoculation of bio-inoculants decreased Pb contents in the soil, leaves, and roots of maize by 30% over the control. Growth and physiological attributes of maize were also improved by 25% in a single application of bio-inoculants. Application of Pb with bio-inoculants decreased the efficiency of PGPR, and there were only 10–15% increases in growth and physiological attributes over single inoculation. Bio-inoculants exhibited the best results in the presence of IAA and Pb application by intensive root growth (60% better than control), reducing Pb toxicity (38%) and increasing growth and physiological attributes by 10–15% over single inoculation of bio-inoculants. Application of bio-inoculants with IAA may decrease the deleterious effects of Pb toxicity in oil-polluted agriculture fields.

Modulation of CycD3;1-CDK complexes by phytohormones and sucrose during maize germination.

Maize CycD3;1 associates to CDKA or CDKB1;1 proteins during germination and the complexes formed develop kinase activity. These complexes appear to vary in size as germination proceeds, suggesting association to different sets of proteins. CycD3;1 and associated CDK proteins respond to phytohormones and sucrose. Results revealed a reduction in the CycD3;1 protein amount along germination in the presence of indoleacetic acid (IAA) or abscisic acid (ABA), although in the latter protein levels recover at the end of germination. While the levels of CDKA increase with IAA, they decrease with ABA. Both phytohormones, IAA and ABA, increase levels of CDKB1;1 only during the early germination times. CycD3;1 associated kinase activity is only reduced by both phytohormones towards the end of the germination period. On the other hand, lack of sucrose in the imbibition medium strongly reduces CycD3;1 protein levels without affecting the levels of neither CDKA nor CDKB1;1. The corresponding CycD3;1 associated kinase activity is also severely decreased. The presence of sucrose in the medium appears to stabilize the CycD3;1 protein levels.

Endophytes from medicinal plants and their potential for producing indole acetic acid, improving seed germination and mitigating oxidative stress.

Medicinal plants have been used by marginal communities to treat various ailments. However, the potential of endophytes within these bio-prospective medicinal plants remains unknown. The present study elucidates the endophytic diversity of medicinal plants (Caralluma acutangula, Rhazya stricta, and Moringa peregrina) and the endophyte role in seed growth and oxidative stress. Various organs of medicinal plants yielded ten endophytes, which were identified as Phoma sp. (6 isolates), Alternaria sp. (2), Bipolaris sp. (1), and Cladosporium sp. (1) based on 18S rDNA sequencing and phylogenetic analysis. The culture filtrates (CFs; 25%, 50%, and 100% concentrations) from these endophytes were tested against the growth of normal and dwarf mutant rice lines. Endophytic CF exhibited dose-dependent growth stimulation and suppression effects. CF (100%) of Phoma sp. significantly increased rice seed germination and growth compared to controls and other endophytes. This growth-promoting effect was due to the presence of indole acetic acid in endophytic CF. The gas chromatography/mass spectrometry (GC/MS) analysis showed the highest indole acetic acid content ((54.31±0.21) µmol/L) in Bipolaris sp. In addition, the isolate of Bipolaris sp. exhibited significantly higher radical scavenging and anti-lipid peroxidation activity than the other isolates. Bipolaris sp. and Phoma sp. also exhibited significantly higher flavonoid and phenolic contents. The medicinal plants exhibited the presence of bio-prospective endophytic strains, which could be used for the improvement of crop growth and the mitigation of oxidative stresses.

Inhibition of IAA oxidase activity of wheat anionic peroxidase by chitooligosaccharides

The study demonstrated that chitooligosaccharides with a molecular weight of 5–10 kDa and a degree of acetylation of 65% exhibited an auxin-like effect in wheat plants and also played an important role in regulating the activity of polysaccharide (chitin)–specific anion isoenzymes of peroxidase oxidizing indole acetic acid. Changes in the kinetic parameters of the interaction of the wheat anionic chitin-specific peroxidase with pI ∼3.5 with chitin oligomers in the presence of indoleacetic acid were pH-depended and indicated that chitooligosaccharides significantly impair the ability of the enzyme for oxidation at pH levels of 4.2 and 6.0. It can be assumed that chitooligosaccharides not only induce protective plant systems but also increase the accumulation of auxin in plant tissues, thus adversely affecting a number of components of the plant protective system against pathogens.

Shoot organogenesis from roots of seabuckthorn (Hippophaë rhamnoides L.): structure, initiation and effects of phosphorus and auxin

Shoots from roots formed on seedlings in vitro in the groove of lateral roots as on plants growing in a natural habitat. The finding has ecological and applied relevance. Shoot organogenesis from roots (root suckers, shoots from roots, SfRs) allows vegetative propagation of the small tree seabuckthorn (Hippophae rhamnoides L.) in addition to sexual propagation and is an important trait associated with the root system. Using an in vitro system, we studied initiation, localization and development of SfRs and interacting roles of phosphorus (P) and indole-3-acetic acid (IAA). After transfer of seedlings to the W4 medium (WPM medium with added IAA, benzyl adenine and giberellic acid), SfRs protruded after 2 weeks from the primary root initially at the groove of lateral roots (LR) as seen by scanning electron microscopy and light microscopy. This is also the location of SfRs on plants growing in natural conditions, which suggests a similar developmental pathway. To localize SfR initiation, staining by the DNA-binding fluorochrome 4′,6-diamidino-2-phenylindole in root cross sections revealed a high density of small cells as in meristems in the pericycle area between endodermis and vascular tissue. During 8–10 weeks, SfRs emerged also in other positions on the primary root, concomitantly with senescence of existing LRs and suppression of new LR formation. Since SfR formed in relation to LRs, we hypothesized that P and IAA play a role in SfR formation. Highest production of SfRs occurred in W4 medium after pre-treatment with high P in the presence of IAA while LR production in WPM was stimulated by IAA in low and middle P. SfRs developed in vitro on seedlings originating from three subspecies of H. rhamnoides showing this trait to be common. This experimental system allowed studies of organogenesis of SfRs and LRs in response to plant growth regulators, P and IAA and may be further implemented in basic studies and in applied clonal propagation of seabuckthorn.

Nitric oxide metabolism and indole acetic acid biosynthesis cross-talk in Azospirillum brasilense SM

Production of nitric oxide (NO) and the presence of NO metabolism genes, nitrous oxide reductase (nosZ), nitrous oxide reductase regulator (nosR) and nitric oxide reductase (norB) were identified in the plant-associated bacterium (PAB) Azospirillum brasilense SM. NO presence was confirmed in all overexpressing strains, while improvement in the plant growth response of these strains was mediated by increased NO and indole-3-acetic acid (IAA) levels in the strains. Electron microscopy showed random distribution to biofilm, with surface colonization of pleiomorphic Azospirilla. Quantitative IAA estimation highlighted a crucial role of nosR and norBC in regulating IAA biosynthesis. The NO quencher and donor reduced/blocked IAA biosynthesis by all strains, indicating their common regulatory role in IAA biosynthesis. Tryptophan (Trp) and l-Arginine (Arg) showed higher expression of NO genes tested, while in the case of ipdC, only Trp and IAA increased expression, while Arg had no significant effect. The highest nosR expression in SMnosR in the presence of IAA and Trp, along with its 2-fold IAA level, confirmed the relationship of nosR overexpression with Trp in increasing IAA. These results indicate a strong correlation between IAA and NO in A. brasilense SM and suggest the existence of cross-talk or shared signaling mechanisms in these two growth regulators.

Induction of oxidative stress in Prototheca zopfii by indole-3-acetic acid/HRP or 2,4-pentanedione/HRP systems and their oxidation products.

We investigated the toxic effects on Prototheca zopfii of indole-3-acetic acid (IAA) and 2,4-pentanedione (PD) combined with horseradish peroxidase (HRP) alongside the oxidation products of 3-methyl-2-oxindole (MOI) and indole-3-carbinol (I3C) from the IAA/HRP system and methylglyoxal (MGO) from the PD/HRP system. The microorganism was incubated in the absence (control) or presence of IAA, PD, IAA/HRP, PD/HRP, MOI, I3C and MGO and determined: (1) cytotoxicity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium) assay; (2) growth inhibitory concentration by resazurin assay and (3) antioxidant enzymes activities of: catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD). P. zopfii was more susceptible to IAA at 40 mM than PD at the same concentration, which seems to indicate that IAA was more effective at initiating cell death. These data corroborate results from the resazurin assay. Concentrations of 40 mM of IAA, IAA/HRP and PD/HRP, 20 mM of PD/HRP, 10 mM of MOI, 2 mM of I3C and 8 mM of MGO inhibited the growth of P. zopfii. With sub-inhibitory concentrations of IAA and IAA/HRP at 30 mM, MOI at 8 mM and I3C at 1 mM, the activities of CAT and GR increased, whereas no statistical difference was observed for CAT activity with IAA/HRP. Thus, PD at 30 mM and MGO at 6 mM increased the activities of CAT and GR, whereas PD/HRP system at 15 mM decreased CAT activity and PD/HRP and MGO showed no statistical difference for SOD activity. In conclusion, IAA/HRP or PD/HRP systems and their oxidation products exert cytotoxic effects on P. zopffi; however, I3C and MGO appear to exert greater microbicidal effect on P. zopfii.

The role of phenolics in the control of auxin in galls of Piptadenia gonoacantha (Mart.) MacBr (Fabaceae: Mimosoideae)

Gall inducers manipulate the biochemistry of plant cells, benefiting their own life cycles, and influencing on the growth of their host plants. Such manipulation may involve (poly)phenols and growth regulators, such as the indole-3-acetic acid (IAA). Some other molecules, the reactive oxygen species (ROS), may co-occur at the sites of (poly)phenols accumulation, indicating the generation of oxidative stress, which may trigger this accumulation. Herein we focused on the possible co-occurrence of ROS, (poly)phenols and IAA at the same gall tissues, and their involvement in growth and development of different gall morphotypes. This co-occurrence, together with indole-3-acetaldehyde (IAld), was confirmed in galls of Piptadenia gonoacantha (Mart.) MacBr. (Fabaceae) by histochemical tests. Developed color for commercial standards of IAA and IAld in TLC was used as controls. The presence of IAA and IAld in gall extracts was confirmed through ultraviolet–visible spectroscopy. The distinct compound is supposed to be auxin-(poly)phenol adducts, evidencing the metabolic interaction among ROS, phenolics and auxin. Current results suggest the associated role of (poly)phenols, ROS and auxin in gall development, and led to the conclusion that phenolics seem to act primarily as growth regulators and secondarily as a chemical defense against natural enemies in gall systems.