Amount Of Indole-3-acetic Acid Research Articles

Screening and Optimization of IAA Production by PGPR isolated from Rhizosphere of a Pterocarpus marsupium Roxb. and their Effect on Plant Growth

Indole Acetic Acid (IAA) production is important attribute of PGPR that promote plant growth and development. The rhizosphere is hotspot in the soil that harbors PGPR. The present study was aimed with isolation and screening of IAA producing bacteria from the rhizosphere of Pterocarpus marsupium Roxb. Optimum culture conditions (pH, temperature, incubation period and L-tryptophan concentration for IAA production were studied for selected isolates and their effect on wheat growth and root development was evaluated. Among twenty four IAA producing isolates five isolates (Et1, Rp1, Rp5, Rp6, and Rp9) produced maximum IAA in range of 50-70 μg/mL and was used in optimization studies. Maximum IAA was produced in 96 hours of incubation, at pH 7 and with 0.1mg/mL of L-tryptophan by all five isolates. 30oC is the most suitable temperature for Et1, Rp1, Rp5, Rp9; whereas Rp6 produced nearly same amount of IAA at wide range of temperature 30-35oC (77-84.12 μg/mL) and at pH 7-8 ( 73-74μg/mL). Out of the five isolates, Rp6 exhibits the highest potential, having a maximum IAA of 84.12 μg/mL at 35°C and pH 7. Although tryptophan influences IAA synthesis but at higher concentration of tryptophan inhibits IAA synthesis. To validate the production of IAA, crude extracts were analyzed using thin layer chromatography (TLC). A spot of standard IAA with the same Rf value (0.91) was found to match a specific spot from the crude IAA.

Unraveling the potential of Acinetobacter calcoaceticus for arsenic resistance and plant growth promotion in contaminated lentil field

The legume crop, lentil is often found to be contaminated with arsenic (As) across the globe, and becomes a serious problem when consumed as dietary component. Bioremediation techniques are considered to be sustainable, and low cost measures to combat this problem. The current study has been aimed at identifying the As-resistant endophytic bacteria from the root nodule of lentil plants grown in As-contaminated soil, assess their capacity to tolerate As, and establish their contribution in plant growth promotion. Four As-resistant endophytic bacteria were isolated from the lentil nodules in the contaminated (17.1 and 1.54 mg kg−1 of total and available As) field (Uttar Panchponta, Nadia, West Bengal, India located at 23° 05′ N and 88° 54′ E). The results showed that among all isolates, ARGNCAR-1 exhibits the highest As resistant capacity (200.0 mM for arsenate and 21.0 mM for arsenite). Interestingly, the ARGNCAR-1(Acinetobacter calcoaceticus, KX882106) is also able to solubilize phosphate (8.59-8.6 µg mL−1 under arsenate stress and 8.0-8.1 µg mL−1 under arsenite stress) and produce significant amount of indole acetic acid (10.2-10.4 µg mL−1 under the arsenate stress and 9.4-9.5 µg mL−1 under arsenite stress). The presence of aoxB gene was detected in these four As (III) oxidizing isolates. A pot experiment was conducted with the contaminated soil and the isolated strains were inoculated. The strain ARGNCAR-1 was found to be the most efficient in reducing about 20% As from soil and 22% As from the lentil seeds and ensured significant plant yield enhancement (5.17 g plant−1) than uninoculated soil (4.54 g plant−1) mainly through their corresponding increase in pod plant−1 (110) and biomass (6.51 g plant−1). Considering the efficacy of curbing As load as well as improving plant growth, the ARGNCAR-1(Acinetobacter calcoaceticus KX882106) emerged as one of the most promising candidates in As contaminated belts.

Indole acetic acid (IAA) production by endophytic bacterial isolate Agrobacterium tumefaciens BE-1 from roots of Musa acuminata

We have screened 23 endophytic isolates to estimate the production of indole acetic acid (IAA) from the root of the banana (Musa spp) by using Salkowski’s reagent spectrophotometric method with and without L- tryptophan supplement. Amongst 23 isolates only eight isolates, showed the ability to produce IAA. It is observed that one isolates out of eight produced maximum amount of IAA supplemented with and without L-tryptophan in medium. Based on morphological, cultural, biochemical and 16s rRNA gene sequencing method, this promising endophytic bacterial isolate (BE 1) was identified as Agrobacterium tumefaciens. IAA production of BE-1 was further confirmed by Thin-layer chromatography as well as by High-Performance Liquid Chromatography with and without L-tryptophan in medium. Statistical analysis was carried out using paired t-test to test whether the production of IAA significantly increased by using L-tryptophan in medium.

Unveiling the Potential of Bacillus paramycoides, a Halotolerant Endophytic Bacterium with Heavy Metal Tolerance and Plant Growth Promotion Properties

The use of heavy metal resistant plant growth promoting endophytes is an effective method for improving crop yield and cleaning up contaminated sites. In our study, we have isolated thirteen bacterial endophytes from the shoots of Alternanthera philoxeroides, an aquatic plant from Bellandur lake, Bangalore, India. Among the isolates, Bacillus paramycoides showed significant plant growth promotion properties including an extortionate amount of indole acetic acid (IAA) production (144.69 ± 1.01 μg/mL) along with other plant growth promoting attributes like ammonia production, nitrogen fixation, phosphate, potassium solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore production. The isolate also demonstrated the ability to resist pathogen attacks by producing extracellular enzymes, which could have potential industrial uses. Furthermore, it displayed resistance to multiple heavy metals like chromium (Cr), copper (Cu), lead (Pb), zinc (Zn) and cadmium (Cd) as well as the ability to tolerate high salt concentrations (up to 7% NaCl). These characteristics make it an ideal candidate for promoting plant growth in stressful environments and as an effective bioremediation agent.

STUDY OF THE ABILITY OF RHIZOSPHERE MICROORGANISMS TO PRODUCE IAA AND THEIR INFLUENCE ON PLANT GROWTH

A primary screening was conducted to assess the ability of rhizosphere microorganisms from cultivated and wild plants of arid ecosystems in the Astrakhan region to produce indoleacetic acid (IAA) and exhibit phytotoxic properties. The amount of synthesised IAA was determined using a photometric method, and the phytotoxicity of microbial culture liquid was evaluated on seeds of red round radish Raphanus sativus L. convar. radicula. It was found that all isolates had the ability for tryptophan-induced IAA synthesis. Out of the 50 examined isolates, 19 synthesised IAA at levels comparable to industrial producers 80 µg/ml and higher. The evaluation of the influence of microbial culture liquid on the growth and development of radish seeds revealed complete inhibition of the root system and seedling effect for all isolates. Among the examined isolates, 16 completely suppressed the growth of test plant seeds. Seed germination using the suspension of other isolates ranged from 7.1% to 63.3%. The experiment established that phytotoxic effects also increased with an increase in the amount of IAA synthesised by isolates. The influence of exogenous auxin on plant development can have positive and negative effects. The optimal concentration range of IAA for a specific plant can be extremely narrow, and any deviation from this concentration can lead to inhibitory effects. Therefore, further research is needed to explore the biotechnological potential of isolated strains with increased IAA production as industrial producers of this substance or as the basis for a biological preparation for plant growth stimulation.

Colon-Targeted Delivery of Indole Acetic Acid Helps Regulate Gut Motility by Activating the AHR Signaling Pathway.

Intestinal peristalsis is vital for gastrointestinal physiology and host homeostasis and is frequently dysregulated in intestinal disorders. Gut microbiota can regulate gut motility, especially through the tryptophan metabolism pathway. However, the role of indoles as microbial tryptophan metabolites in colonic function requires further exploration. Here, we show that the delivery of indole acetic acid (IAA) targeting the colon can improve gut motility by activating the aryl hydrocarbon receptor (AHR). To achieve colon-targeted delivery, Eudragit S-100 (ES) and chitosan (CS) were used as drug carriers. After optimisation, IAA-loaded ES-coated CS nanoparticles exhibited an encapsulation efficiency of 83% and a drug-loading capacity of 16%. These nanoparticles exhibited pH-dependent characteristics and remained stable in acidic conditions and the upper intestine. In simulated intestinal fluid (pH 7.4) and colonic lumen, considerable amounts of IAA were released after approximately 4 h. Compared with free IAA, the nanoparticles exerted enhanced therapeutic effects on gut movement disorders induced by loperamide. The efficacy of IAA treatment was attributable to the activation of the AHR signalling pathway and increased levels of AHR agonists. Furthermore, the oral administration of IAA-loaded nanoparticles promoted serotonin secretion and maintained the intestinal barrier function. The experimental outcomes demonstrate the efficiency of the proposed colon-specific delivery system and highlight the role of IAA, produced by gut microbiota metabolism, in regulating gut peristalsis through AHR activation.

Antifungal Trait and Plant Growth Promotion Potential of Bacillus Spp. from Rhizosphere Soils of Black Aromatic Rice, ‘Chakhao’

Manipuri black aromatic rice, ‘Chakhao’, is a nutrient rich unique local rice cultivar of Manipur, India. Rhizosphere bacteria may have potential as antifungal agent and seedling growth promoter. Hence, the current investigation was aimed at screening, for the above traits, using bacteria, Bacillus spp., isolated from the soil of Rhizosphere of six Chakhao rice cultivars. Altogether, 323 bacterial isolates were obtained from the rhizospheric soils of 6 different cultivars of Chakhao, namely Chakhao Amubi (CA), Chakhao Poireiton (CP), Chakhao Sempak (CS), Chakhao Angoubi (CAng), Chakhao Angangbi (CR) and Chakhao Wairi (CW). All the rhizobacterial isolates were screened for antifungal activity against 5 rice fungal pathogens viz. Rhizoctonia solani (RS), Fusarium oxysporum (FO), Curvularia oryzae (CO), Pyricularia oryzae (PO) and Aspergillus niger (AN). The isolates were also subjected to PGP (plant growth promotion) assays such as ammonia, indole acetic acid (IAA), siderophore and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and phosphate solubilization. Of 323 isolates obtained, 64 were found to exhibit antifungal activity while 69 showed PGP traits. Twenty-five (25) isolates were found to be positive for both antifungal and PGP traits. Of 25 bioactive isolates, 4 (CR12, CW11, CA2 and CP2) potent isolates were shortlisted for further studies. The shortlisted potent isolates were subjected to quantitative estimation of PGP activities like phosphate solubilization, IAA and siderophore production. The strains could produce significant amount of IAA and siderophore and solubilize phosphate. Molecular characterization by 16S rDNA sequence analyses revealed the identity of the isolates: CR12: Bacillus subtilis (Accn. No.OM866257), CW11: Bacillus paralicheniformis (Accn. No.OM868047), CA2: Bacillus sp. CCMB1014 (Accn. No.OM868070) and CP2: Bacillus licheniformis (Accn. No.OM892495). Seedling vigor assays of the shortlisted potent strains were carried out on Chakhao Amubi rice. The isolates exhibited higher seedling vigor indices (CR12: 668.00, CA2: 618.66, CP2: 510.92 and CW11: 478.91) over the control (164.48). These rhizospheric strains have the potential to be developed as bioinoculants or biostimulants for enhancing Chakhao rice growth.

Characterization of plant growth-promoting bacteria isolated from rhizosphere of lentil (Lens culinaris L.) grown in two different soil orders of eastern India.

Lentil, which is an important grain legume, can be co-inoculated with plant growth-promoting rhizobia and rhizobacteria to boost nitrogen fixation, increase biomass, and a possibility for early nodulation. The goal of the ongoing study was to identify plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of lentil growing soils in eastern India. Sixteen rhizosphere bacteria were isolated from two different soil orders, and their capacity to solubilize phosphate and generate hydrogen cyanide (HCN), siderophore, and indole acetic acid (IAA) was assessed. The three best strains were selected for compatibility study with twenty Rhizobium isolated from lentil root nodules. The isolated rhizobacteria were able to produce ammonia and different mycolytic enzymes. Isolate B3 produced the highest amount of IAA and siderophore; the highest amount of phosphate solubilized by PSB1 strain; and isolates AB1, AB2, B3, PS2, and PSB2 produced considerable amount of HCN gas. Among all the isolates, B3, PSB1, and PS2 performed better based on different plant growth-promoting abilities. These three bacterial isolates showed compatible reaction with most of the Rhizobium strains. Isolates B3, PS2, and PSB1 were identified as Bacillus subtilis (MT729775), Pseudomonas palmensis (MT729782), and Paraburkholderia caribenis (MZ956803), respectively. Lentil shoot weight, root length, nodule number, N uptake, and P uptake were increased in the pot culture experiment when inoculated with these strains. PGPR strain B3 performed best among the three strains in the pot culture experiment. Strain B3 can be used as potential biofertilizer along with compatible Rhizobium species for better production of lentil.

Evaluation of brassinosteroids and plant growth-promoting bacteria on the growth and yield of Lactuca sativa L. under soilless cultivation conditions

Soilless crops have become an important alternative for large-scale vegetable production because of the quality of their products and optimization of resources. Brassinosteroids (Brs) and Plant Growth-Promoting Bacteria (PGPB), has been reported to promote growth and physiological parameters in soil crops, but there are few reports on the application of these compounds in soilless crops. The effects of Brs ((25R)-3β 5α-dihydroxy-spirostan-6-one) and three strains of PGPB (Bacillus velezensis, Pseudomona sp., and Azospirillum brasilense) on the growth and yield of lettuce under hydroponic conditions were evaluated. Two separate experiments were carried out: one using a substrate in pots under greenhouse conditions and the other using a deep-flow hydroponic system in a growth room with artificial LED lighting. Plant physiological parameters (yield, dry weight, root surface area, and leaf area) and PGPB attributes under in vitro tests (phosphate solubilization and indole-3-acetic acid (IAA) synthesis) were determined using in vitro tests. A completely randomized design was used in all experiments. The results showed that in in vitro tests Azospirillum brasilense and Pseudomonas sp. were the strains that synthesized the highest amounts of IAA (36 mg mL−1 and 34 mg mL−1, respectively). Phosphorus solubilization was significantly higher in the Pseudomonas sp. strain (110.35 µg mL−1). Regarding physiological and quality parameters, the application of Brs (0.5 ppm), Bacillus velezensis, and Azospirillum brasilense (1 × 106 CFU mL−1) caused an increase between 20% and 40% on variables such as plant yield, leaf area, root surface area, and colorimetry of lettuce for substrate or hydroponic conditions, respectively.

Efficacy of IAA for affecting nitrate reductase activity and yield attributes of mash [Vigna Mungo (L.)] hepper

In order to investigate the potential of Indole Acetic Acid (IAA) for affecting yield contributing factors and Nitrate Reductase Activity, an experiment was conducted on four Vigna mungo genotypes. The four mash bean genotypes, 80, 88, 97, and ES-1, were examined against Indole Acetic Acid concentrations of 25, 50, 75, 10, 12, and 150.0 mgL-1. Plants were grown in pots which were randomly placed in the Botanical garden of Bahauddin Zakariya University, Multan. Pakistan. Four replicates of each treatment were developed and evaluated. Aforementioned amounts of Indole Acetic Acid were sprayed thrice, with intervals of ten days each. Ist spray was conducted at twenty days after germination. Nitrate Reductase Activity, grains number fruit-1, legumes number plant-1, and plant total yield were the traits chosen for study. After ten days of completion of three sprays of Indole Acetic Acid, Nitrate Reductase Activity (NRA) in the leaves was evaluated, and yield plant-1and its contributing factors were noted when the crop reached at its physiological maturity. Typically, an exponential increase in the number of grains, legume per plant, total yield, and Nitrate Reductase Activity (NRA) was seen as Indole Acetic Acid concentration increased from 75.0 to125.0mgL-1. By using a statistical technique, it was found that the responses of different genotypes to Indole Acetic Acid concentrations varied. MASH 97 was proved to be the most influenced in term of total yield plant-1, the number of grains plants-1 and the Nitrate Reductase Activity (NRA). While, MASH ES-1 performance lagged behind all other genotypes. Keywords: Indole Acetic Acid; Legumes; Nitrate Reductase; Vigna; Yield; Pods

Performance of Plant-Growth-Promoting Rhizobacteria (PGPR) Isolated from Sandy Soil on Growth of Tomato (Solanum lycopersicum L.).

The plant-growth-promoting rhizobacteria (PGPR) in the rhizosphere affect plant growth, health, and productivity, as well as soil-nutrient contents. They are considered a green and eco-friendly technology that will reduce chemical-fertilizer usage, thereby reducing production costs and protecting the environment. Out of 58 bacterial strains isolated in Qassim, Saudi Arabia, four strains were identified by the 16S rRNA as the Streptomyces cinereoruber strain P6-4, Priestia megaterium strain P12, Rossellomorea aquimaris strain P22-2, and Pseudomonas plecoglossicida strain P24. The plant-growth-promoting (PGP) features of the identified bacteria involving inorganic phosphate (P) solubilization, the production of indole acetic acid (IAA), and siderophore secretion were assessed in vitro. Regarding the P solubilization, the previous strains' efficacy reached 37.71%, 52.84%, 94.31%, and 64.20%, respectively. The strains produced considerable amounts of IAA (69.82, 251.70, 236.57, and 101.94 µg/mL) after 4 days of incubation at 30 °C. Furthermore, the rates of siderophore production reached 35.51, 26.37, 26.37, and 23.84 psu, respectively, in the same strains. The application of the selected strains in the presence of rock phosphate (RP) with tomato plants under greenhouse conditions was evaluated. The plant growth and P-uptake traits positively and significantly increased in response to all the bacterial treatments, except for some traits, such as plant height, number of leaves, and leaf DM at 21 DAT, compared to the negative control (rock phosphate, T2). Notably, the P. megaterium strain P12 (T4), followed by R. aquimaris strain P22-2 (T5), revealed the best values related to plant height (at 45 DAT), number of leaves per plant (at 45 DAT), root length, leaf area, leaf-P uptake, stem P uptake, and total plant P uptake compared to the rock phosphate. The first two components of the PCA (principal component analysis) represented 71.99% (PCA1 = 50.81% and PCA2 = 21.18%) of the variation at 45 DAT. Finally, the PGPR improved the vegetative-growth traits of the tomato plants through P solubilization, IAA, and siderophore production, and ameliorated the availability of nutrients. Thus, applying in PGPR in sustainable agriculture will potentially reduce production costs and protect the environment from contamination by chemical fertilizers and pesticides.

Production of Indole Acetic Acid (IAA) from Endophytic Bacteria Isolated from Saussurea Obvallata

Endophytes are plant beneficial bacteria that thrive inside plant and improve plant growth under normal and challenging condition as they contain growth regulators. Endophytes are capable of synthesizing bioactive compounds which protect plants against pathogens. Endophytic bacteria can improve plant health by targeting pest and pathogens by antibiotic, hydrolytic enzymes production and creating nutrient limitations. Saussurea obvallata is a species of flowering plant considered as medicinal herb in Tibetan medicine. The leaves of Saussurea obvallata were selected for isolation of endophytic bacteria. A total number of three endophytic bacteria were isolated and they were designated as IS-1, IS-2, IS-3. All the three isolates were screened for their ability to produce IAA using Salkowski’s reagent. The two isolates showing IAA producing ability were subjected to IAA production using Nutrient broth tryptophan medium Isolate IS-2 was found to be producing 380 g/ml amount of IAA in presence of 7 g/ml tryptophan in the medium. The endophytic bacterial isolate IS-2 which has been tentatively identified as Micrococcus luteus and found promising isolate for IAA production.

Exploring the Plant Growth-Promotion of Four Streptomyces Strains from Rhizosphere Soil to Enhance Cucumber Growth and Yield

The genus Streptomyces is the most abundant and essential microbes in the soil microbial community. Streptomyces are familiar and have great potential to produce a large variety of bioactive compounds. This genus considers an efficient biofertilizer based on its plant growth-promoting activities. Based on their ability to produce a wide varieties of bioactive molecules, the present study aimed to explore the potential plant growth promotion of four Streptomyces strains and their role in enhancing cucumber growth and yield under greenhouse conditions. Streptomyces sp. strain HM2, Streptomyces thinghirensis strain HM3, Streptomyces sp. strain HM8, and Streptomyces tricolor strain HM10 were chosen for the current study. Plant growth-promoting (PGP) features, i.e., indole acetic acid (IAA) production, siderophore excretion, and solubilizing phosphate, were evaluated in vitro. All four strains produced IAA, siderophore, and immobilized inorganic phosphate. Following 4 days of incubation at 30 °C, strains HM2, HM3, HM8, and HM10 produced copious amounts of IAA (18, 22, 62, and 146 µg/mL, respectively) and siderophores (42.59, 40.01, 16.84, 64.14% SU, respectively). At the same time, P solubilization efficacy scored 64.3%, 84.4%, 57.2%, and 81.6% with the same frequency. During in planta evaluation, selected Streptomyces strains combined with rock phosphate were assessed as biofertilizers on the growth and yield of cucumber plants. Under all treatments, positive and significant differences in studied traits were manifested except dry stem matter (SDM), net assimilation rate (NAR), relative growth rate (RGR), and fruit firmness (FF). Treatment T4 (rock phosphate + strain HM3) followed by T5 (rock phosphate + strain HM8) revealed the best results for plant height (PH), number of leaves per plant (NLPP), root length (RL), number of fruits per plant (NFPP), fruit length (FL), fruit diameter (FD), fruit fresh weight per plant (FFWPP), soil P (SP) after 21 DAT, and soil P at the end of the experiment. Notably, T6 (rock phosphate + strain HM10) caused a considerable increase in leaf area (LA). Plant growth-promoting bacteria enhance plant growth and yield through phosphorus solubilizing, improve nutrient availability, produce phytohormones, and support plant growth under abiotic stress. These features are important for sustainable agriculture and reducing environmental pollution with chemical fertilizers and pesticides.

Zinc-Solubilizing Streptomyces spp. as Bioinoculants for Promoting the Growth of Soybean (Glycine max (L.) Merrill).

Zinc-solubilizing bacteria can convert the insoluble form of zinc into soluble forms available to plants. This study was conducted to isolate and screen zinc-solubilizing actinobacteria from rhizosphere soils and to assess their effect on vegetable soybean growth. In total, 200 actinobacteria strains belonging to 10 genera were isolated from rhizosphere soil samples. Among these isolates, four showed zinc solubilization with solubilizing index values ranging from 3.11 to 3.78 on Bunt and Rovira agar supplemented with 0.1% zinc oxide. For the quantitative assay, in broth culture, strains CME34 and EX51 solubilized maximum available zinc contents of 529.71 and 243.58 μg/ml. Furthermore, indole-3-acetic acid (IAA) and ammonia were produced by these two strains, the strain CME34 produced the highest amount of IAA 4.62 μg/ml and the strain EX51 produced the highest amount of ammonia 361.04 μg/ml. In addition, the phosphate-solubilizing abilities in Pikovskaya's medium of CME34 and EX51 were 64.67 and 115.67 μg/ml. Based on morphological and biochemical characterization and 16S rDNA sequencing, the strains CME34 and EX51 were closely related to the genus Streptomyces. In a greenhouse experiment, single-strain inoculation of Streptomyces sp. CME34 or EX51 significantly increased the shoot length, root length, plant dry weight, number of pods per plant and number of seeds per plant of vegetable soybean plants compared to the uninoculated control. These findings facilitated the conclusion that the two Streptomyces strains have potential as zinc solubilizers and can be suggested as bioinoculants to promote the growth and yield of soybean.

Aspergillus violaceofuscus alleviates cadmium and chromium stress in Okra through biochemical modulation.

Endophytic fungi from the Chilli were used to help okra plants exposed to cadmium (Cd) or chromium (Cr) stress. Initially, the strain Ch06 produced higher amounts of indole acetic acid (IAA) (230.5 μg/mL), sugar (130.7 μg/mL), proteins (128.2 μg/mL), phenolics (525.6 μg/mL) and flavonoids (98.4 μg/mL) in Czapek broth supplemented with Cd or Cr. The production of IAA and other metabolites in such a higher concentration suggested that Ch06 might improve plant growth under heavy metal stress. For this reason, an experiment was designed, in which biomass of Ch06 (at 2g/100g of sand) were applied to the okra plants exposed to Cd or Cr stress (at 100 or 500 μg/g). The results exhibited that Ch06 improved the total chlorophyll (36.4±0.2 SPAD), shoot length (22.6±0.2 cm), root length (9.1±0.6 cm), fresh weight (5±0.6 g), dry weight (1.25±0.01 g), sugars (151.6 μg/g), proteins (114.8 μg/g), proline (6.7 μg/g), flavonoids (37.9 μg/g), phenolics (70.7 μg/g), IAA (106.7 μg/g), catalase (0.75 enzyme units/g tissue) and ascorbic acid oxidaze (2.2 enzyme units/g tissue) of the associated okra plants. Similar observations have been recorded in Ch06 associated okra plants under Cd and Cr stress. Also, Ch06 association reduced translocation of Cd (35% and 45%) and Cr (47% and 53%) to the upper parts of the okra plants and thus reduced their toxicity. The internal transcribed spacer (ITS) region amplification of 18S rDNA (ribosomal deoxyribo nucleic acid) exhibited that the potent strain Ch06 was Aspergillus violaceofuscus. The results implied that A. violaceofuscus has the ability to promote host species growth exposed to Cd and Cr. Moreover, it helped the host plants to recover in Cd and Cr polluted soils, hence can be used as biofertilizer.

The key role of indole-3-acetic acid biosynthesis by Bacillus thuringiensis RZ2MS9 in promoting maize growth revealed by the ipdC gene knockout mediated by the CRISPR-Cas9 system

The bacterial biosynthesis of indole-3-acetic acid (IAA) is often related to the beneficial effects of plant growth-promoting rhizobacteria (PGPR) on plant development. In PGPR belonging to the Bacillus genus, the synthesis of IAA may occur through different metabolic pathways that are still poorly understood. B. thuringiensis (Bt) is well known for its insecticidal properties; however, its beneficial features are not limited to pest control. Our group has been studed the beneficial effects of Bt strain RZ2MS9 as growth promoter in a range of plant crops, including soybean, tomato, and maize. We recently demonstrated that bacterial IAA biosynthesis plays an important role in the ability of RZ2MS9 to benefit plant development. However, the molecular involved mechanisms in the IAA biosynthesis by this bacterium in the beneficial interaction with plants remain unclear. Here, we investigated the genetic basis of IAA biosynthesis by RZ2MS9. We knocked out the ipdC gene, involved in IAA biosynthesis via the tryptophan-dependent IPyA pathway, using the CRISPR-Cas9 system. Our results showed that, by disrupting the IPyA pathway, the amount of IAA synthesized by the mutant RZ2MS9 (ΔipdC) in the presence of tryptophan drops 57%. The gene knockout did not affect the bacterial growth, but it did affect its ability to colonize maize. Moreover, deactivating the ipdC gene in RZ2MS9 significantly reduces its ability to promote maize growth. ΔipdC performed worse than RZ2MS9 in almost all evaluated plant parameters, including total root length, projected root area, lateral roots, aerial part dry matter, and germination speed index. Therefore, we demonstrated that tryptophan-dependent IAA biosynthesis via the IPyA pathway by RZ2MS9 is strongly influenced by the ipdC gene. Furthermore, IAA biosynthesis by RZ2MS9 is a major mechanism used by this PGPR to promote maize growth.

Effective biofertilizer Trichoderma spp. isolates with enzymatic activity and metabolites enhancing plant growth.

Trichoderma species have been widely recognized as biofertilizer fungi for their ability to produce phytohormones and enhance plant growth. In our current study, fifteen strains of Trichoderma spp. (T1-T15) were screened for their capacity to produce phytohormones and metabolites eliciting plant growth. The stains were previously isolated from olive rhizosphere soil in northern Algeria. Plant growth promoting (PGP) potential of Trichoderma spp. was evaluated in vitro through the production of phosphatases, siderophores, hydrogen cyanide (HCN), and ammonia (NH3). Besides, plant growth phytohormones such as gibberellic acid and indole-3-acetic acid (IAA) were assessed quantitatively by a colorimetric assay. Results showed an effective potential of Trichoderma spp. in plant growth-promoting biomolecule production. Importantly, qualitative estimation of phosphate solubilization indicates that T10 gave the highest phosphate solubilization on medium Pikovskaya's with a solubilization index (SI) of 3, whereas, the high capacity nitrogen-fixing was related to T8. On the other hand, quantitative analysis of indole-3-acetic acid and gibberellic acid revealed a production varying between (1.30μgmL-1 to 21.15μgmL-1) and (0.53μgmL-1 to 7.87μgmL-1), respectively; the highest amount of both phytohormones was obtained by T11 isolate. Indeed, an analysis of ethyl acetate extracts of T11 isolate by high-performance liquid chromatography (HPLC) revealed a high amount (71.19mg L-1) of IAA. Overall, the results showed clearly that isolate T11 has promising plant growth-promoting properties. Hence, this native Trichoderma isolate (T11) identified as Trichoderma harzianum strain (OL587563) could be used later as biofertilizer for sustainable olive crop agriculture.

Production of indole-3-acetic acid by endophytic fungi of halophyte plants under salt stress

The auxin-synthesizing activity of endophytic fungi from desert halophyte plants Aeluropus litoralis, Halocnemum strobilaceum, Climacoptera crassa, Suaeda heterophylla were studied. In addition, screening of indole-3-acetic acid (IAA) was carried out at the cultivation of endophytes in the presence of 10% NaCl. All isolates produced IAA, but the highest level was observed in two Penicillium strains from C. crassa and H. strobilaceum, which produced significant amounts of extracellular IAA at a relatively low biomass level.

Ameliorative effects of endogenous and exogenous indole-3-acetic acid on atrazine stressed paddy field cyanobacterial biofertilizer Cylindrospermum stagnale

Across the world, paddy fields naturally harbour cyanobacteria that function as biofertilizers and secrete various compounds like Indole-3-acetic acid (IAA) that help organisms in regulating their growth. Also, paddy field farming utilizes large amounts of pesticides (e.g. atrazine); but their continued application in the agricultural field causes toxicity in non-target cyanobacterial species that hinder their performance as a biofertilizer. Hence, the current study is an attempt to ameliorate the atrazine stress in cyanobacterium Cylindrospermum stagnale by addition of IAA (1 mM each) under different atrazine levels (0, 60, 80, 100, 120, 140 µg/l). Atrazine toxicity affected C. stagnale in a dose-dependent manner further experiments revealed that both the exogenous and endogenous IAA mitigated the detrimental effects of atrazine. It reduced MDA content and simultaneously increased chlorophyll content, total protein content, and multiple antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)] at 140 µg/l. A molecular docking study revealed that the pesticide binds to the D1 protein of the photoelectric chain in photosynthesis. Hence, the application of IAA or cyanobacterial biofertilizer that secretes a sufficient amount of IAA may assist sustainable agriculture in counteracting the atrazine toxicity.

Facilitation of auxin biosynthesis and metabolism by salt stress in rice plants

To investigate the effects of salt stress on the auxin in rice plants, we analyzed indole-3-acetic acid (IAA) and its metabolites in hydroponically grown rice plant seedlings (Oryza sativa cv. Nipponbare) and in the culture medium using LC-ESI/MS/MS. We found that the IAA level in the culture medium was increased 39-fold due to salt stress treatment, while those in the shoots and roots were increased by less than 2-fold. The culture medium also contained high amounts of oxidized metabolites such as OxIAA, DiOxIAA, DiOxIAA-Glu, and DiOxIAA-Asp. The total amount of IAA and its metabolites in the shoots, roots, and culture medium was significantly increased with salt treatment. A salt stress-responsive increase in the IAA metabolites was observed in 9 tested cultivars of rice. The results indicate that salt stress facilitates the metabolic turnover of IAA in rice plants and may open new insight into the role of auxin.