Indole-3-acetic Acid Content Research Articles

Bromide ion enhancing the phytodegradation of emerging phenolic pollutants and its mechanisms mediating wheat resistance to phenolic pollutants stress

The phytodegradation of emerging phenolic pollutants (EPPs) has attracted widespread attention. However, the impact of bromide ions (Br−) on the phytodegradation of EPPs and its mechanism mediating wheat resistance to EPPs stress have rarely been reported. Our research discovered that Br− enhanced the removal of EPPs (7.5, 15 mg/L) in a dark hydroponic wheat system. The degradation efficiency of acetaminophen (ACE), bisphenol A (BPA) and 1-naphthol (1-NP) increased 2.2, 2.8 and 1.28 times as Br− concentration increased from 0 to 1 mM, respectively. In the presence of Br−, the mono- and dibromo-products of ACE and BPA were produced in the dark hydroponic wheat system, while 1-NP showed higher degradation efficiency but no bromine substitution formation. EPPs induced oxidative damage and root growth inhibition in wheat. The addition of Br− enhanced the chlorophyll content, indole-3-acetic acid (IAA) content and antioxidant potential to alleviate EPPs stress. Principal component analysis (PCA) revealed significant separation of different Br− stimuli, that is, the low concentrations of Br− (0.1 mM) enhanced the content of IAA by 28.6%, while higher concentrations of Br− (0.5, 1 mM) alleviated membrane lipid peroxidation by improving peroxidase (POD) activity. This is the first report that Br− could stimulate the synthesis of IAA via indole acetonitrile (IAN) pathway and hydrolysis of IAA-conjugates. This study provides more support for the feasibility of phytoremediation techniques for phenolic pollutants and references for the assessment of ecological risks and health hazards of EPPs.

Trans-cinnamaldehyde-related overproduction of benzoic acid and oxidative stress on Arabidopsis thaliana.

Trans-cinnamaldehyde is a specialised metabolite that naturally occurs in plants of the Lauraceae family. This study focused on the phytotoxic effects of this compound on the morphology and metabolism of Arabidopsis thaliana seedlings. To evaluate the phytotoxicity of trans-cinnamaldehyde, a dose-response curve was first performed for the root growth process in order to calculate the reference inhibitory concentrations IC50 and IC80 (trans-cinnamaldehyde concentrations inducing a 50% and 80% inhibition, respectively). Subsequently, the structure and ultrastructure of the roots treated with the compound were analysed by light and electron microscopy. Based on these results, the following assays were carried out to in depth study the possible mode of action of the compound: antiauxinic PCIB reversion bioassay, determination of mitochondrial membrane potential, ROS detection, lipid peroxidation content, hormone quantification, in silico studies and gene expression of ALDH enzymes. Trans-cinnamaldehyde IC50 and IC80 values were as low as 46 and 87 μM, reducing the root growth and inducing the occurrence of adventitious roots. At the ultrastructural level, the compound caused alterations to the mitochondria, which were confirmed by detection of the mitochondrial membrane potential. The morphology observed after the treatment (i.e., appearance of adventitious roots) suggested a possible hormonal mismatch at the auxin level, which was confirmed after PCIB bioassay and hormone quantification by GC-MS. The addition of the compound caused an increase in benzoic, salicylic and indoleacetic acid content, which was related to the increased gene expression of the aldehyde dehydrogenase enzymes that can drive the conversion of trans-cinnamaldehyde to cinnamic acid. Also, an increase of ROS was also observed in treated roots. The enzyme-compound interaction was shown to be stable over time by docking and molecular dynamics assays. The aldehyde dehydrogenases could drive the conversion of trans-cinnamaldehyde to cinnamic acid, increasing the levels of benzoic, salicylic and indoleacetic acids and causing the oxidative stress symptoms observed in the treated seedlings. This would result into growth and development inhibition of the trans-cinnamaldehyde-treated seedlings and ultimately in their programmed-cell-death.

Genome-wide identification of Aux/IAA and ARF gene families reveal their potential roles in flower opening of Dendrobium officinale

BackgroundThe auxin indole-3-acetic acid (IAA) is a vital phytohormone that influences plant growth and development. Our previous work showed that IAA content decreased during flower development in the medicinally important orchid Dendrobium officinale, while Aux/IAA genes were downregulated. However, little information about auxin-responsive genes and their roles in D. officinale flower development exists.ResultsThis study validated 14 DoIAA and 26 DoARF early auxin-responsive genes in the D. officinale genome. A phylogenetic analysis classified the DoIAA genes into two subgroups. An analysis of cis-regulatory elements indicated that they were related by phytohormones and abiotic stresses. Gene expression profiles were tissue-specific. Most DoIAA genes (except for DoIAA7) were sensitive to IAA (10 μmol/L) and were downregulated during flower development. Four DoIAA proteins (DoIAA1, DoIAA6, DoIAA10 and DoIAA13) were mainly localized in the nucleus. A yeast two-hybrid assay showed that these four DoIAA proteins interacted with three DoARF proteins (DoARF2, DoARF17, DoARF23).ConclusionsThe structure and molecular functions of early auxin-responsive genes in D. officinale were investigated. The DoIAA-DoARF interaction may play an important role in flower development via the auxin signaling pathway.

Effect of Natural Phytohormones on Growth, Nutritional Status, and Yield of Mung Bean (Vigna radiata L.) and N Availability in Sandy-Loam Soil of Sub-Tropics

Climate changes and poor soil nutrient profiles in sub-tropics are determinant factors to estimate crop productivity. This study aims to evaluate the impact of phytohormones, e.g., indole acetic acid (IAA) and gibberellic acid (GA3), on mung bean yield, seed nutritional profile, and soil N availability in the sub-tropical region of Pakistan. The mung bean plants were treated with three levels (0, 30, and 60 mg L−1) of IAA and GA3 individually and/or in combination using a hydraulic sprayer. The amendments were applied in the flowering stage (approximately 25 days after germination) in a randomized complete block design. The results revealed that the 60 mg L−1 concentration of IAA and GA3 led to significant changes in the growth and yield traits compared to non-treated plants. For example, GA3 positively influenced the biological yield (35.0%), total carbohydrate (7.0%), protein (16.0%), and nitrogen (14.0%) contents in mung bean seeds, compared to the control (CK). Additionally, the combined foliar treatment of IAA and GA3 (IAA2 + GA2) displayed a much stronger influence on yield attributes, such as the number of pods by 66.0%, pods’ weights by 142.0%, and seed yield by 106.5%, compared with the CK. Mung bean plants showed a significant improvement in leaf photosynthetic pigments under a higher level (60 mg L−1) of sole and combined treatments of IAA and GA3. Moreover, except abscisic acid, the endogenous concentration of IAA, GA3, and zeatin was enhanced by 193.0%, 67.0%, and 175.0% after the combined application of IAA and GA3 (IAA2 + GA2) compared to the CK treatment. In addition, soil N availability was increased by 72.8% under the IAA2 treatment and 61.5% under IAA2 + GA2, respectively, compared with the control plot. It was concluded that the combined treatment of IAA and GA3 (IAA2 + GA2) followed by the sole application of GA3 and IAA at a 60 mg L−1 concentration were most effective treatments to improve the morpho-physiology and nutrient profile of mung beans; however, the underlying molecular mechanisms need to be explored further.

Microassay validation for bacterial IAA estimation as a new fine-tuned PGPR screening assay

The detection and quantification of Indole -3 Acetic Acid (IAA) produced by Plant growth promoting rhizobacteria (PGPR) rely on a standard well-documented assay, which remains time-consuming, laborious, and costly. These drawbacks led to sway interest to economic and reliable assays. The aim of this work is to validate and standardize a fast, reliable, and cost-effective microassay to quantify IAA produced by bacteria with an easy microplate method. In order to validate the accuracy of the IAA microplate assay, bacterial samples from different genera were assayed using two methods: the conventional IAA estimation assay and the IAA micro- assay. The microassay shows a prominent reduction in used bacterial supernatant volume as well as Salkowski reagent volume of about 92.5%. It is considerably cheaper than the conventional one of around 56%. The newly performed microplate assay is 23 times faster. The result of IAA quantitative analysis for 13 bacterial strains showed that Bacillus muralis and Bacillus toyonensis produced the highest IAA concentration (23.64±0.003μg/ml and 23.35±0.006μg/ml, respectively). The obtained data from both methods were highly correlated with an R-value of 0.979. The microassay offers the ability to read the optical density of all samples simultaneously since used volumes of bacterial supernatants and Salkowski reagent were minimized to place the mixture in 96-well microplates, which reduces greatly required labor. Furthermore, the application of the IAA micro-plate assay reduces drastically the reagent waste and toxicity hazard of Salkowski reagent in the environment, thus, we can classify it as eco-friendly respecting the Green Chemistry concept according to Environmental Protection Agency (EPA). The IAA microassay is a, reliable, rapid and cost-effective and eco-friendly method to screen plant growth promoting potential of more than 23 bacterial strains by microplate. It could be an alternative for the conventional IAA assay as a routine research tool.

Changes and transcriptome regulation of endogenous hormones during somatic embryogenesis in Ormosia henryi Prain.

Ormosia henryi is a rare and endangered plant growing in southern China. Somatic embryo culture is an effective measure for the rapid propagation of O. henryi. It has not been reported how regulatory genes induce somatic embryogenesis by regulating endogenous hormone changes during the process of somatic embryogenesis in O. henryi. In this study, we analysed the endogenous hormone levels and transcriptome data of nonembryogenic callus (NEC), embryogenic callus (EC), globular embryo (GE) and cotyledon embryo (CE) in O. henryi. The results showed that the indole-3-acetic acid (IAA) content was higher and the cytokinins (CKs) content was lower in EC than in NEC, and the gibberellins (GAs) and abscisic acid (ABA) contents were significantly higher in NEC than in EC. The contents of IAA, CKs, GAs and ABA increased significantly with EC development. The expression patterns of differentially expressed genes (DEGs) involved in the biosynthesis and signal transduction of auxin (AUX) (YUCCA and SAUR), CKs (B-ARR), GAs (GA3ox, GA20ox, GID1 and DELLA) and ABA (ZEP, ABA2, AAO3, CYP97A3, PYL and ABF) were consistent with the levels of endogenous hormones during somatic embryogenesis (SE). In this study, 316 different transcription factors (TFs) regulating phytohormones were detected during SE. AUX/IAA were downregulated in the process of EC formation and GE differentiation into CE, but other TFs were upregulated and downregulated. Therefore, we believe that relatively high IAA content and low CKs, GAs and ABA contents contribute to EC formation. The differential expression of AUX, CKs, GAs and ABA biosynthesis and signal transduction genes affected the endogenous hormone levels at different stages of SE in O. henryi. The downregulated expression of AUX/IAA inhibited NEC induction, promoted EC formation and GE differentiation into CE.

Aboveground Biomass and Endogenous Hormones in Sub-Tropical Forest Fragments

Associated endogenous hormones were affected by forest fragmentation and significantly correlated with aboveground biomass storage. Forest fragmentation threatens aboveground biomass (AGB) and affects biodiversity and ecosystem functioning in multiple ways. We ask whether and how forest fragmentation influences AGB in forest fragments. We investigated differences in AGB between forest edges and interiors, and how plant community characteristics and endogenous hormones influenced AGB. In six 40 m × 40 m plots spread across three forest fragments, AGB was significantly higher in plots in the forest interior than in those at the edge of forests. The proportion of individuals with a large diameter at breast height (DBH > 40 cm) in the forest edges is higher than that in the forest interiors. Further, trees within a 15–40 cm DBH range had the highest contribution to AGB in all plots. Trees in interior plots had higher abscisic acid (ABA) and lower indole-3-acetic acid (IAA) concentrations than those in edge plots. In addition, AGB was significantly positively and negatively correlated with ABA and IAA concentrations at the community scale. In this study, we provide an account of endogenous hormones’ role as an integrator of environmental signals and, in particular, we highlight the correlation of these endogenous hormone levels with vegetation patterns. Edge effects strongly influenced AGB. In the future, more endogenous hormones and complex interactions should be better explored and understood to support consistent forest conservation and management actions.

The microRNA ppe-miR393 mediates auxin-induced peach fruit softening by promoting ethylene production.

Auxin can inhibit or promote fruit ripening, depending on the species. Melting flesh (MF) peach fruit (Prunus persica L. Batsch) cultivars produce high levels of ethylene caused by high concentrations of indole-3-acetic acid (IAA), which leads to rapid fruit softening at the late stage of development. In contrast, due to the low concentrations of IAA, the fruit of stony hard (SH) peach cultivars does not soften and produces little ethylene. Auxin seems necessary to trigger the biosynthesis of ethylene in peach fruit; however, the mechanism is not well understood. In this study, we identified miRNA gene family members ppe-miR393a and ppe-miR393b that are differentially expressed in SH and MF fruits. RNA ligase-mediated 5' rapid amplification of cDNA ends and transient transformation of Nicotiana benthamiana revealed TRANSPORT INHIBITOR RESPONSE 1 (PpTIR1), part of the auxin perception and response system, as a target of ppe-miR393a and b. Yeast 2-hybrid assay and bimolecular fluorescence complementation assay revealed that PpTIR1 physically interacts with an Aux/IAA protein PpIAA13. The results of yeast 1-hybrid assay, electrophoretic mobility shift assay, and dual-luciferase assay indicated that PpIAA13 could directly bind to and trans-activate the promoter of 1-aminocyclopropane-1-carboxylic acid synthase 1 (PpACS1), required for ethylene biosynthesis. Transient overexpression and suppression of ppe-miR393a and PpIAA13 in peach fruit induced and repressed the expression of PpACS1, confirming their regulatory role in ethylene synthesis. Gene expression analysis in developing MF and SH fruits, combined with postharvest α-naphthalene acetic acid (NAA) treatment, supports a role for a ppe-miR393-PpTIR1-PpIAA13-PpACS1 module in regulating auxin-related differences in ethylene production and softening extent in different types of peach.

Serendipita indica promotes P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and phosphate transporter gene expression.

The culturable endophytic fungus Serendipita indica has many beneficial effects on plants, but whether and how it affects physiological activities and phosphorus (P) acquisition of tea seedlings at low P levels is unclear. The objective of this study was to analyze the effects of inoculation with S. indica on growth, gas exchange, chlorophyll fluorescence, auxins, cytokinins, P levels, and expressions of two phosphate transporter (PT) genes in leaves of tea (Camellia sinensis L. cv. Fudingdabaicha) seedlings grown at 0.5 μM (P0.5) and 50 μM (P50) P levels. Sixteen weeks after the inoculation, S. indica colonized roots of tea seedlings, with root fungal colonization rates reaching 62.18% and 81.34% at P0.5 and P50 levels, respectively. Although plant growth behavior, leaf gas exchange, chlorophyll values, nitrogen balance index, and chlorophyll fluorescence parameters of tea seedlings were suppressed at P0.5 versus P50 levels, inoculation of S. indica mitigated the negative effects to some extent, along with more prominent promotion at P0.5 levels. S. indica inoculation significantly increased leaf P and indoleacetic acid concentrations at P0.5 and P50 levels and leaf isopentenyladenine, dihydrozeatin, and transzeatin concentrations at P0.5 levels, coupled with the reduction of indolebutyric acid at P50 levels. Inoculation of S. indica up-regulated the relative expression of leaf CsPT1 at P0.5 and P50 levels and CsPT4 at P0.5 levels. It is concluded that S. indica promoted P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and CsPT1 and CsPT4 expression.

Potential of Bacillus sp. from Kebun Raya Liwa as a Producer of Indole Acetic Acid (IAA) Hormone

Kebun Raya Liwa’s soil has the potential to allow for a population of microorganisms such as the Bacillus sp. Bacillus sp. Kebun Raya Liwa are known to produce phytohormones that have the potential to help plant growth and development, one of which is the hormone Indole Acetic Acid (IAA). This study aims to determine the potential of Bacillus sp. from the soil of Kebun Rawa Liwa in producing IAA hormones. The research method included taking soil samples, preparing Nutrient Agar (NA) medium, measuring soil pH samples, isolating soil bacteria, purifying and characterizing Bacillus sp., preparing IAA standard curves, and testing the potency of Bacillus sp. IAA production was carried out in two ways, namely measuring the content of IAA with the addition of tryptophan and without the addition of tryptophan. IAA concentration was measured using a spectrophotometer with a wavelength of 520 nm. The data obtained is presented in tabular form. The isolation results obtained 10 isolates that were able to produce IAA hormone with and without tryptophan. The highest IAA production without tryptophan was isolate BP 5 with a concentration of 1.18 ppm, and the isolate that was able to produce the highest IAA with tryptophan was isolate BP 13 with a concentration of 3.90 ppm. This indicates that the isolate Bacillus sp. from the soil rhizosphere Kebun Raya Liwa can produce IAA hormones.

Dynamic Changes of Endogenous Hormones in Different Seasons of Idesia polycarpa Maxim

Idesia polycarpa Maxim is a native dioecious tree from East Asia cultivated for its fruits and as an ornamental plant throughout temperate regions. Given the economic potential, comparative studies on cultivated genotypes are of current interest. This study aims to discover the dynamic changes and potential functions of endogenous hormones in I. polycarpa, as well as the differences in endogenous hormone contents in different growth stages among different I. polycarpa provenances. We used High-Performance Liquid Chromatography (HPLC) to measure and compare the levels of abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellin A3 (GA3), and trans-Zeatin-riboside (tZR) in the leaves, flowers, and fruits of I. polycarpa from various provenances between April and October. Our findings indicated that changes in the ABA and GA3 content of plants from Jiyuan and Tokyo were minimal from April to October. However, the levels of these two hormones in Chengdu plants vary greatly at different stages of development. The peak of IAA content in the three plant materials occurred primarily during the early fruit stage and the fruit expansion stage. The concentration of tZR in the three plant materials varies greatly. Furthermore, we discovered that the contents of endogenous hormones in I. polycarpa leaves, flowers, and fruits from Chengdu provenances were slightly higher than those from Tokyo and Jiyuan provenances. The content of IAA was higher in male flowers than in female flowers, and the content of ABA, GA3, and tZR was higher in female flowers than in male flowers. According to the findings, the contents of these four endogenous hormones in I. polycarpa are primarily determined by the genetic characteristics of the trees and are less affected by cultivation conditions. The gender of I. polycarpa had a great influence on these four endogenous hormones. The findings of this study will provide a theoretical foundation and practical guidance for artificially regulating the flowering and fruiting of I. polycarpa.

Exogenous IBA stimulated adventitious root formation of Zanthoxylum beecheyanum K. Koch stem cutting: Histo-physiological and phytohormonal investigation

Poor rooting performance of Chinese pepper (Zanthoxylum beecheyanum K. Koch) shrub is a restriction for its commercial production. This investigation was carried out to assess the effectiveness of the exogenous application of indole-3-butyric acid (IBA) on adventitious root (AR) formation and some morpho-physiological, biochemical, and histological alterations associated with rhizogenesis events. IBA, at 1500 or 2000 mg kg-1, gave comparable effects for improving the performance of rooting architecture compared to the control treatment. The AR primordia of Z. beecheyanum originated from two distinct developmental pathways: (i) direct genesis from cells in the cambial zone and nearby tissues, and (ii) indirect genesis from cells in callus tissues. Rooting process involved four phases: (i) induction at 0–10 days after planting (DAP), (ii) initiation at 10–15 DAP, (iii) formation of the root primordia (Rp) at 15–20 DAP, and (iv) root extension at 20–30 DAP. Cuttings' inductive phase correlated temporarily with intensive cell divisions, high levels of endogenous indole-3-acetic acid (IAA) and gibberellins (GA3). However, IBA application led to a pronounced increase in soluble sugars and phenolic content. The initiation phase was accompanied by a histological appearance of meristemoids. This phase was also stimulated by the subsequent generation of low IAA and high GA3 contents. In the development of Rp and root extension phases, prominent Rp formation in the cambium and complete differentiation with vascular tissues continued with that of the stem cuttings. In essence, the current study provides insights into the morphological, histo-physiological, and phytohormonal alterations in stem cuttings.

The Effect of Different Plant Growth Hormones and Concentrations on the Reproduction of Rosmarinus officinalis L. with Seedling Production

To evaluate the proper concentration of plant growth hormone and the suitable plant growth hormone in Rosmarinus officinalis L., a significant fragrant, medicinal and herbaceous plant, the study was carried out in a greenhouse during the vegetative period of 2022. In the experiment, peat and vermicompost mixture (3 peat / 1 vermicompost) as the rooting medium, Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA) and 1-Naphthaleneacetic acid (NAA) hormones were used as plant growth regulators and the concentrations of these hormones were 0, 1000, 2000, 3000, 4000 ppm The Randomised Plot Experiment Design were established three times in the Multiple Comparison Test “LSD”. In seedlings removed three months after planting, properties such as seedling height (cm), number of roots (pieces), root length (cm), maximum root length (cm), number of laterals (pieces) and lateral length (cm) were examined. The highest seedling length (19.88 cm) and number of shoots (12.60 pcs), 3000 ppm concentration of Indole-3-acetic acid (IAA), root length (16.30 cm), and 3000 ppm concentration of 1-Naphthaleneacetic acid (NAA) at the highest root length (22.82 cm) came to the fore. In terms of root number, the values found at 3000 ppm concentration of indole acetic acid (19.25 pieces) and naphthalene acetic acid (20.09 pcs) were combined into one statistical group and made up the maximum number of roots. The lateral length control seedlings statistically prevented other applications and produced the highest lateral length (1.99 cm). Therefore, it can be said that Indole-3-acetic acid (IAA) and 1-Naphthaleneacetic acid (NAA), both of which have a concentration of 3000 ppm, are the most suited growth hormones.

Dissecting the effect of ethylene in the transcriptional regulation of chilling treatment in grapevine leaves

Ethylene (ETH) plays important roles in various development programs and stress responses in plants. In grapevines, ETH increased dramatically under chilling stress and is known to positively regulate cold tolerance. However, the role of ETH in transcriptional regulation during chilling stress of grapevine leaves is still not clear. To address this gap, targeted hormone profiling and transcriptomic analysis were performed on leaves of Vitis amurensis under chilling stress with and without aminoethoxyvinylglycine (AVG, a inhibitor of ETH synthesis) treatment. APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) and WRKY transcription factors (TF) were only the two highly enriched TF families that were consistently up-regulated during chilling stress but inhibited by AVG. The comparison of leaf transcriptomes between chilling treatment and chilling with AVG allowed the identification of potential ETH-regulated genes. Potential genes that are positively regulated by ETH are enriched in solute transport, protein biosynthesis, phytohormone action, antioxidant and carbohydrate metabolism. Conversely, genes related to the synthesis and signaling of ETH, indole-3-acetic acid (IAA), abscisic acid (ABA) were up-regulated by chilling treatment but inhibited by AVG. The contents of ETH, ABA and IAA also paralleled with the transcriptome data, which suggests that the response of ABA and IAA during chilling stress may regulate by ETH signaling, and together may belong to an integrated network of hormonal signaling pathways underpinning chilling stress response in grapevine leaves. Together, these findings provide new clues for further studying the complex regulatory mechanism of ETH under low-temperature stress in plants more generally and new opportunities for breeding cold-resilient grapevines.

Nitrogen application improves salt tolerance of grape seedlings via regulating hormone metabolism.

Salt stress is a dominant environmental factor that restricts the growth and yield of crops. Nitrogen is an essential mineral element for plants, regulates various physiological and biochemical processes, and has been reported to enhance salt tolerance in plants. However, the crosstalk between salt and nitrogen in grapes is not well understood. In this study, we found that nitrogen supplementation (0.01 and 0.1 mol L-1 NH4 NO3 ) significantly increased the accumulation of proline, chlorophyll, Na+ , NH4 + , and NO3 - , while it reduced the malondialdehyde content and inhibited photosynthetic performance under salt stress conditions (200 mmol L-1 NaCl). Further transcriptome and metabolome analyses showed that a total of 4890 differentially expressed genes (DEGs) and 753 differently accumulated metabolites (DAMs) were identified. Joint omics results revealed that plant hormone signal transduction pathway connected the DEGs and DAMs. In-depth analysis revealed that nitrogen supplementation increased the levels of endogenous abscisic acid, salicylic acid, and jasmonic acid by inducing the expression of 11, 4, and 13 genes related to their respective biosynthesis pathway. In contrast, endogenous indoleacetic acid content was significantly reduced due to the remarkable regulation of seven genes of its biosynthetic pathway. The modulation in hormone contents subsequently activated the differential expression of 13, 10, 12, and 29 genes of the respective downstream hormone signaling transduction pathways. Overall, all results indicate that moderate nitrogen supplementation could improve salt tolerance by regulating grape physiology and endogenous hormone homeostasis, as well as the expression of key genes in signaling pathways, which provides new insights into the interactions between mineral elements and salt stress.

Root exudate concentrations of indole-3-acetic acid (IAA) and abscisic acid (ABA) affect maize rhizobacterial communities at specific developmental stages.

Root exudates shape the rhizosphere microbiome, but little is known about the specific compounds in root exudates that are important. Here, we investigated the impacts of the plant-synthesized phytohormones indole-3-acetic acid (IAA) and abscisic acid (ABA) exuded by roots on the maize rhizobacterial communities. To identify maize genotypes that differed in the root exudate concentrations of IAA and ABA, we screened hundreds of inbred lines using a semi-hydroponic system. Twelve genotypes with variable exudate concentrations of IAA and ABA were selected for a replicated field experiment. Bulk soil, rhizosphere, and root endosphere samples were collected at two vegetative and one reproductive maize developmental stage. IAA and ABA concentrations in rhizosphere samples were quantified by liquid chromatography-mass spectrometry. The bacterial communities were analyzed by V4 16S rRNA amplicon sequencing. Results indicated that IAA and ABA concentrations in root exudates significantly affected the rhizobacterial communities at specific developmental stages. ABA impacted the rhizosphere bacterial communities at later developmental stages, whereas IAA affected the rhizobacterial communities at the vegetative stages. This study contributed to our knowledge about the influence that specific root exudate compounds have on the rhizobiome composition, showing that the phytohormones IAA and ABA exuded by roots have a role in the plant-microbiome interactions.

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.

Indole-3-acetic acid, a hormone potentially involved in chilling-induced seed browning of pepper (Capsicum annuum L.) fruit during cold storage

Pepper (Capsicum annuum L.) fruit is affected by chilling temperatures below 7–10 °C; thus, there are limitations to maintaining postharvest freshness during its cold storage and distribution. Here, the six endogenous hormones, abscisic acid, gibberellic acid, indole-3-acetic acid (IAA), jasmonic acid, jasmonoyl-isoleucine, and salicylic acid, were quantitatively analyzed, and the genes and amino acids associated with them were investigated under the hypothesis that hormones are primarily involved in chilling injury (CI) of pepper fruit. Pepper fruit of two different genotypes, ‘Takanotsume’ (‘TK’) and ‘Gyeonggiyangpyeong’ (‘GG’), were harvested at the mature-green stage and stored at 2 °C for 21 d. Seed browning was the most visible symptom of CI during storage. Seed browning was rarely observed for ‘TK’; however, it was observed for ‘GG’ with a higher production of reactive oxygen species. Thus, ‘TK’ was less sensitive to chilling than ‘GG’, as demonstrated by the completely different CI levels. IAA levels substantially increased in ‘GG’ on 3 d of cold storage; however, it did not change in ‘TK’ during the entire storage period. Since the pattern between the expression level of CaAMI1 and the IAA content was similar, the IAM pathway was probably involved in the IAA production in ‘GG’. The content of individual amino acids substantially changed in ‘GG’ compared to ‘TK’ but the initial proline content was highest in ‘TK’. ‘GG’ showed a more complex correlation between the analyzed factors compared to ‘TK’. The CI level of ‘TK’ positively correlated with gamma-aminobutyric acid (GABA) and auxin response factor 19 (CaARF19). The CI level of ‘GG’ had a positive, and negative correlation with GABA and alanine, and CaARF6, respectively. These results might help elucidate the mechanism of chilling-induced seed browning in pepper fruit and develop pepper cultivars that are resistant to CI during cold storage and distribution.

Optimization of Morphogenesis and In Vitro Production of Five Hyacinthus orientalis Cultivars

To maximize the economic benefits of Hyacinthus orientalis L., the micropropagation and morphogenesis induction of five Hyacinthus cultivars were investigated under four different concentrations of indole acetic acid (IAA) with two cytokinins, benzyl adenine (BA), or kinetin (Kin). Days for morphogenesis initiation and shoot formation in the red cultivars were fewer than in the blue and white cultivars. Blue cultivars showed an increase in fresh weight and chlorophyll content under either BA or Kin, but they showed an increase in shoot height in the BA treatments only. IAA at 1.5 mg/L caused a time reduction in days for morphogenesis induction and shoot formation and enhanced shoot height and fresh weight. Kin had a lesser impact than BA on all parameters at all concentrations. The number of shoots differed significantly among the cultivars. The Murashige and Skoog (MS) medium supplemented with 3.0 mg/L indole-3-butyric acid (IBA) produced the highest percentage of root formation (93.3%), number of roots/plantlet (5.26), and root length (1.10 cm). The Jan Bos cultivar at 3.0 mg/L IBA had the highest mean rooting percentage (100%) and number of roots per plantlet (6.66), while Pink Pearl had the highest root length (1.39 cm).

Identification of the phytohormones indole‐3‐acetic acid and trans‐zeatin in microalgae

AbstractBACKGROUNDMicroalgae can biosynthesize phytohormones that promote plant growth and development. These compounds can potentially replace synthetic agricultural inputs that are harmful to the environment. The main plant growth‐promoting phytohormones present in microalgae are auxins and cytokinins. The objective of this study was to evaluate the influence of culture conditions (autotrophic and heterotrophic) on the concentrations of the endogenous phytohormones indole‐3‐acetic acid (IAA) and trans‐zeatin (tZ) in the microalgae Chlorella fusca LEB 111, Chlorella vulgaris LEB 112, Scenedesmus obliquus LEB 117, Synechococcus nidulans LEB 115 and Spirulina sp. LEB 18.RESULTSAll microalgae produced IAA and tZ under the three evaluated conditions (autotrophic light/dark (12/12 h), autotrophic continuous light (24 h) and heterotrophic). The IAA concentrations ranged from 1.94 to 56.45 nmol g−1, whereas those of tZ ranged from 0.06 to 35.52 pmol g−1. The cultivation conditions increased the carbohydrate and protein concentrations. Continuous light favored the production of carbohydrates in the studied cyanobacteria (Synechococcus nidulans LEB 115 and Spirulina sp. LEB 18). However, the light/dark condition (12/12 h) afforded the highest protein concentrations for green algae and cyanobacteria. There were no statistically significant differences in the lipid content of the strains studied.CONCLUSIONSThe results of this study are valuable and indicate that the cultivation conditions and species used in this study may be applied in sustainable agriculture, providing alternatives that may contribute to minimizing the environmental impact of synthetic chemical inputs in agriculture. © 2023 Society of Chemical Industry.