Endogenous Indole-3-acetic Acid Research Articles

Dynamic changes of endogenous phytohormones and carbohydrates during spontaneous morphogenesis of Centaurium erythraea Rafn

Common centaury (Centaurium eryhtraea Rafn) is a medicinal plant species with vigorous morphogenic potential in vitro. The process of spontaneous shoot regeneration in a solid root culture is characteristic for this plant species. In this context, the aim of this work was to investigate the dynamic changes of endogenous phytohormones and carbohydrates content in root explants at different time points (0, 2, 4, 7, 14, 21, 28, and 60 days) during spontaneous centaury morphogenesis in vitro. Detailed analysis of cytokinins (CKs) showed that trans-zeatin (tZ) was the major bioactive CK at all time points. The corresponding riboside, tZ9R, was also determined in the majority of the identified transport forms, at all time-points. Further analysis of endogenous auxin revealed a significant increase in endogenous indole-3-acetic acid (IAA) after 21 days, when a huge jump in the ratio of IAA/bioactive CKs was also observed. The maximum total soluble sugar content was measured after 14 days, while a significant decrease was determined after 21 days, when the first regenerated adventitious shoots appeared. This undoubtedly indicates an increased energy requirement prior to the actual regeneration of the shoots. The obtained results indicate that the period from day 14 to day 21 involves the most dramatic disturbances in endogenous bioactive CKs, IAA and carbohydrate balance, which are very important and valuable factors for the onset of shoot regeneration.

Endogenous phytohormone analysis during sequential stages of somatic embryogenesis in Musa AAA cv. Grand Naine (subgroup Cavendish)

Abstract This is the first initiative study to provide quantified levels of four endogenous phytohormones during the induction, regeneration, maturation and germination stages of somatic embryogenesis (SE) in banana, using immature male bud explants, in the popular commercial triploid cultivar Grand Naine (AAA). Phytohormones are known to play a major role in the regulation of SE and most protocols have been developed for various cultivars of banana following empirical approaches. Although, several reports are available with regard to the impact of growth regulators exogenously supplemented to the media, the vital role of endogenous growth hormones in various developmental stages of SE remain unclear in banana. Reverse Phase High Performance Liquid Chromatography (RP-HPLC) was used to analyze endogenous status of indole acetic acid (IAA), zeatin, gibberellic acid (GA) and abscisic acid (ABA). Results from this study revealed that endogenous IAA and GA along with exogenous auxin play a major role in the induction of embryogenic competence of male bud explants. The levels of endogenous IAA and zeatin were found to be higher in embryogenic calli than non-embryogenic calli, although three different types of exogenous auxins were supplemented in callogenesis medium, but not cytokinin. Higher level of ABA and GA was observed in early and late developmental stages of somatic embryo, respectively. GA also played a predominant role in germination of somatic embryos. These findings will be applied for improvement of SE protocol in recalcitrant banana cultivars by suitably altering or supplementing exogenous growth hormones.

Identification and Fine Mapping of a Mutant pv‐nts Gene Responsible for Dwarf and Thin Stem of Snap Bean (Phaseolus vulgaris L.)

ABSTRACTPlant height is one of the most important traits in the breeding of snap bean, which determines the planting density and the resistance to failure, which in turn affects its yield and quality. Therefore, studying the molecular mechanism of plant height in snap bean is an important measure to realize the improvement of snap bean. We obtained a dwarf, thin‐stemmed mutant nts (normal to slim) from a dwarf variety of snap bean A18 via 60CO‐γ‐ray treatment. We conducted phenotypic observations, endogenous hormone content measurements and genetic analyses of the dwarfing thin‐stemmed mutant nts and explored gene localization and candidate gene screening for the mutant trait in snap bean. Compared with wild‐type A18, nts mutant exhibited various abnormal phenotypes such as dwarfing, reduced branching, thinner top stem, reduced plant width, reduced number of leaf area and thousand grain weight and increased content of hormones such as indole‐3‐acetic acid (IAA) in the top stem. Genetic analysis indicated that the mutant trait was controlled by a single recessive nuclear gene, and the mutant gene was named pv‐nts. pv‐nts was localized to a 361.1‐kb segment on chromosome 8 as revealed by bovine serum albumin (BSA) hybrid pool sequencing and simple sequence repeat (SSR) molecular markers. Phvul.008G106300 (encoding LAX2 protein) was identified as a candidate gene corresponding to pv‐nts via gene function annotation. Phvul.008G106300 was significantly upregulated in nts mutant compared with wild‐type A18, which was consistent with the results of endogenous IAA levels. Sequence analysis showed that the Phvul.008G106300 gene in nts had a base mutation that altered the protein structure, thus causing the dwarfed, thin‐stemmed phenotype of cauliflower. Taken together, these results contribute to a better understanding of the genetic basis of dwarfing traits in snap bean.

Paclobutrazol Enhanced Stem Lodging Resistance of Direct-Seeded Rice by Affecting Basal Internode Development.

The objectives of this study were to explore the mechanism of stem mechanical strength in direct-seeded rice (DSR) as affected by paclobutrazol, especially its related endogenous hormone and cell wall component changes in culm tissue and response to the application of paclobutrazol. Field experiments were conducted in Changchun County, Jilin Province, China, by using two japonica rice varieties, Jiyujing and Jijing305, with soaking seeds in paclobutrazol at concentrations of (0 mg L-1, S0; 50 mg L-1; S1; 100 mg L-1; S2; 150 mg L-1, S3; 200 mg L-1, S4) in 2021 and 2022. The results suggest that the application of paclobutrazol increased the grain yield and reduced the lodging rate of DSR. Compared with the S0 treatments, soaking the seeds in paclobutrazol treatments rapidly shortened the length of the basal internode by decreasing the endogenous indole acetic acid (IAA) and gibberellin A3 (GA3) contents in culm tissue. The larger breaking strength (M) was attributed to a higher section modulus (SM) and bending stress (BS). The higher mechanical tissue thickness in culm tissue under paclobutrazol treatments, which was raised by higher endogenous zeatin and zeatin riboside (Z+ZR) content in culm tissue, increased the culm diameter, culm wall thickness, and section modulus (SM) of the internode. Compared with the S0 treatments, soaking the seeds in paclobutrazol treatments increased the cellulose content, lignin content, activities of lignin-related enzymes, and expression of key genes in lignin biosynthesis, as well as resulted in a higher bending stress (BS) to enhance the culm breaking strength (M).

Chitosan and its Nanoform Regulates Physiological Processes and Antioxidant Mechanisms to Improve Drought Stress Tolerance of Vicia faba Plant

Purpose: Drought stress is an important challenge to global food security and agricultural output. Dramatic and quick climate change has made the problem worse. It caused unexpected impacts on the growth, development, and yield of different plants. Hence, the ultimate yield does not fulfill the required demand. Understanding the biochemical, ecological, and physiological reactions to these pressures is essential for improved management. Chitosan applications have a wide prospect of addressing abiotic issues. Moreover, chitosan and chitosan nanoparticles have a positive impact on increasing plant tolerance to abiotic stress, like drought stress. The current research investigated the consequences of drought stress on the morpho-physiological and biochemical parameters of Vicia faba plants, a comparison of chitosan and chitosan nanoparticles, and their ameliorating capacity towards drought stress. Methods: A pot experiment was conducted to evaluate the beneficial role of either chitosan (0.5, 1.0, and 2.0 gL− 1) or chitosan NPs (10, 20, and 30 mgL− 1) in inducing the Vicia faba tolerance to drought stress (60% water field capacity). Results: Drought stress significantly affected vegetative growth parameters of the shoot system, photosynthetic pigments, and indole acetic acid, accompanied by significant increases in vegetative growth parameters of the root system, some chemical composition of dry leaf tissues (total soluble sugar, soluble protein, proline, phenolic compound, glutathione, α tocopherol), hydrogen peroxide, malonialdehyde, lipoxygenase, and antioxidant enzyme activities (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, glutathione reductase). All applied treatments. chitosan and chitosan nanoparticles, at all concentrations, improved plant tolerance to drought stress via increasing vegetative growth parameters, photosynthetic pigments, indole acetic acid, total soluble sugar, soluble protein, proline, phenolic compound, glutathione, α tocopherol, and antioxidant enzyme activities, accompanied by decreases in hydrogen peroxide, malondialdehyde, and lipoxygenase enzyme. It is worthy to mention that 20 mgL− 1 chitosan nanoparticles was the most optimal treatment either under well water conditions (90% water field capacity) or drought stress conditions (60% water field capacity). Moreover, it is obvious from these results that the response of bean plants grown under well watered conditions was more pronounced than that of those plants grown under drought stress conditions to 20 mgL− 1 chitosan nanoparticles. Conclusions: Hence, it can be concluded that chitosan and chitosan nanoparticles can mitigate the negative impacts of drought stress by improving the photosybthetic pigments, endogenous indole acetic acid, and osmolyte contents, as well as the non-enzymatic and enzymatic antioxidant compounds of the Vicia faba plant.

Involvement of Auxin, Flavonoids and Strigolactones in the Different Rooting Ability of European Chestnut (Castanea sativa) and Hybrids (Castanea crenata × Castanea sativa).

The aim of this study was to investigate the differences between Castanea sativa Mill. and Castanea crenata Siebold & Zucc. × Castanea sativa Mill. in rooting ability in relation to endogenous levels of auxin, auxin cofactors and inhibitors that influence rooting success. Leafy cuttings of the two commercial cultivars 'Marsol' and 'Maraval' (Castanea crenata × Castanea sativa) and the native accession 'Kozjak' (Castanea sativa) were analyzed. Endogenous indole-3-acetic acid (IAA) concentration was assessed at the beginning of propagation (day 0); in addition, strigolactones, flavonoids, rooting ability and quality were assessed 120 days after. The concentration of endogenous IAA in 'Maraval' (324.34 ± 28.66 ng g-1) and 'Marsol' (251.60 ± 35.44 ng g-1) was significantly higher than in 'Kozjak' (112.87 ± 35.44 ng g-1). The best rooting result was observed with the genotypes 'Maraval' (100.00 ± 0.00%) and 'Marsol' (90.48 ± 6.15%). A significantly lower strigol concentration was observed in the roots of 'Maraval' (75.54 ± 17.93 ng g-1) compared with other genotypes. The total flavonoid concentration in 'Maraval' was significantly higher (2794.99 ± 187.13 μg g-1) than in 'Kozjak' (1057.38 ± 61.05 μg g-1). Our results indicate that the concentration of endogenous IAA has a significant influence on rooting success. The results further indicate that in the case of flavonoids and strigolactones, not only the individual compounds but also their ratio is important for rooting success. Correlation coefficients calculated between analyzed compounds and rooting success point toward specific functions of flavonoids and strigolactones in the rooting of Castanea that need to be functionally analyzed.

Effect of seed priming with auxin on ROS detoxification and carbohydrate metabolism and their relationship with germination and early seedling establishment in salt stressed maize

As crucial stages in the plant ontogeny, germination and seedling establishment under adverse conditions greatly determine staple crop growth and productivity. In the context of green technologies aiming to improve crop yield, seed priming is emerging as an effective approach to enhance seed vigor and germination performance under salt stress. In this study, we assess the efficiency of seed priming with indole-3-acetic acid (IAA) in mitigating the adverse effects of salt stress on maize (Zea mays L.) seedlings during germination and early seedling stages. In unprimed seeds, salt stress reduced germination indices, and seedling (both radicle and coleoptile) growth, together with decreased tissue hydration. However, seed priming using IAA significantly improved maize salt response, as reflected by the increased seed germination dynamics, early seedling establishment, and water status. Besides, seedlings from IAA-primed seeds showed a higher activity of α-amylase, resulting in increased sugar contents in roots and coleoptiles of salt-stressed plants. Further, IAA-seed priming stimulated the accumulation of endogenous IAA in salt-stressed seedlings, in concomitance with a significant effect on reactive oxygen species detoxification and lipid peroxidation prevention. Indeed, our data revealed increased antioxidant enzyme activities, differentially regulated in roots and coleoptiles, leading to increased activities of the antioxidant enzymes (SOD, CAT and GPX). In summary, data gained from this study further highlight the potential of IAA in modulating early interactions between multiple signaling pathways in the seed, endowing maize seedlings with enhanced potential and sustained tolerance to subsequent salt stress.

Salt stress alleviation in Calendula officinalis L. by potassium nanoparticles application and Streptomyces bacteria inoculation

The current study was conducted to mitigate salt stress on Calendula officinalis L. plants using Streptomyces (Sm) bacteria alone or in combination with potassium nanoparticles (K NPs). Based on the results, morphometric characters, leaf SPAD and relative water content in plants treated with Sm bacteria and K NPs increased compared to the nontreated control under salinity stress. However, leaf ionic leakage, malondialdehyde (MDA) and hydrogen peroxide (H2O2) content decreased considerably in these treated plants. Also, under salt stress, the activity of antioxidant enzymes was higher in Sm bacteria + K NPs -treated plants than in controls. In all plants, endogenous indole acetic acid (IAA) content increased compared to plants grown in non-saline conditions. Inoculated plants reflected a relative increase in IAA by about 28% over the uninoculated plants. The highest amount of abscisic acid (ABA) and putrescine (Put) was related to those plants treated with Sm bacteria + K NPs, which the amounts were 43% and 47% higher than in control plants, respectively. Application of Sm bacteria + K NPs had a helpful outcome on both macronutrients (N-NO- 3, P, K and Mg) and micronutrients (Fe, Zn, and Mn) of vines leaves. In general, the inoculation of Sm bacteria + K NPs application by improving the uptake of nutrients, regulating phytohormones and increasing the antioxidant enzymes activity resulted in salinity tolerance improvement in calendula plants.

Exogenous Indole-3-Acetic Acid Suppresses Rice Infection of Magnaporthe oryzae by Affecting Plant Resistance and Fungal Growth.

Auxin is an important phytohormone that regulates diverse biologic processes, including plant growth and immunity. Indole-3-acetic acid (IAA), known as one of the main forms of auxin, is able to activate plant immunity. However, it is unknown whether IAA enhances plant resistance and/or suppresses the growth of the fungal pathogen Magnaporthe oryzae. Here, we found that IAA could induce expression levels of pathogenesis-related genes to enhance disease resistance and could control the development of blast disease through inhibiting M. oryzae infection. Exogenous IAA suppressed mycelial growth and delayed spore germination by inhibiting fungal endogenous IAA biosynthesis and impairing redox homeostasis, respectively. When applied to a field test, two IAA analogues, 1-naphthaleneacetic acid and 2,4-dichlorophenoxy acetic acid, can effectively control rice blast disease. Our study advances the understanding of IAA in controlling rice blast disease through suppressing pathogen growth and enhancing plant resistance.

Endogenous IAA affected fluoranthene accumulation by regulating H+-ATPase and SOD activity in ryegrass

This study explores the role of endogenous indole-3-acetic acid (IAA) in modulating plant responses to pollution stress and its effect on pollutant accumulation, with a focus on fluoranthene (Flu) in ryegrass. To elucidate the mechanism, we employed an IAA promoter (α-aminobutyric acid [α-AB]) and an IAA inhibitor (naphthylphthalamic acid [NPA]) to regulate IAA levels and analyze Flu uptake characteristics. The experimental setup included a Flu treatment group (ryegrass with Flu addition) and a control group (ryegrass without Flu). Our findings demonstrate that Flu treatment enhanced IAA content and plant growth in ryegrass compared to the control. The Flu+AB treatment further enhanced these effects, while the Flu+NPA treatment exhibited a contrasting trend. Moreover, Flu+AB treatment led to increased Flu accumulation, in contrast to the inhibitory effect observed with Flu+NPA treatment. Flu treatment also enhanced the activities of key antioxidant enzymes (SOD, POD, CAT) and increased soluble sugar and protein levels, indicative of enzymatic and nonenzymatic defense responses, respectively. The Flu+AB treatment amplified these responses, whereas the Flu+NPA treatment attenuated them. Significantly, Flu treatment raised H+-ATPase activity compared to the control, an effect further elevated by Flu+AB treatment and diminished by Flu+NPA treatment. A random forest analysis suggested that Flu accumulation dependency varied under different treatments: it relied more on H+-ATPase activity under Flu+AB treatment and more on SOD activity under Flu+NPA treatment. Additionally, Flu+AB treatment boosted the transpiration rate in ryegrass, thereby increasing the Flu translocation factor, a trend reversed by Flu+NPA treatment. This research highlights crucial factors influencing Flu accumulation in ryegrass, offering potential new avenues for controlling the gathering of contaminants within plant systems.

S-ABA Enhances Rice Salt Tolerance by Regulating Na+/K+ Balance and Hormone Homeostasis.

In order to explore the regulating role and the physiological and biochemical mechanisms of trans-abscisic acid (hereinafter referred as S-ABA) in the process of rice growth and development under salt stress, we took Chaoyou 1000 and Yuxiangyouzhan as materials and set up three salt concentration treatments, CK0 (Control treatment), N1 (50 mmol L-1 NaCl), and N2 (100 mmol L-1 NaCl), in potted trials; we aimed to study the mechanism of rice's response to salt stress from the perspective of agricultural traits and physiological biochemicals and to improve rice's resistance to salt stress through exogenously applying the regulating technology of S-ABA. The following results were obtained: Under salt stress, the growth of rice was significantly suppressed compared to CK0, exhibiting notable increases in agricultural indicators, photosynthesis efficiency, and the NA+ content of leaves. However, we noted a significant decrease in the K+ content in the leaves, alongside a prominent increase in NA+/K+ and a big increase in MDA (malondialdehyde), H2O2 (hydrogen peroxide), and O2- (superoxide anion). This caused the cytomembrane permeability to deteriorate. By applying S-ABA under salt stress (in comparison with salt treatment), we promoted improvements in agronomic traits, enhanced photosynthesis, reduced the accumulation of NA+ in leaves, increased the K+ content and the activity of antioxidant enzymes, and reduced the active oxygen content, resulting in a sharp decrease in the impact of salt stress on rice's development. The application of S-ABA decreased the endogenous ABA (abscisic acid) content under salt stress treatment but increased the endogenous GA (gibberellin) and IAA (indole acetic acid) contents and maintained the hormonal homeostasis in rice plants. To summarize, salt stress causes damage to rice growth, and the exogenous application of S-ABA can activate the pouring system mechanism of rice, suppress the outbreak of active oxygen, and regulate NA+/K+ balance and hormone homeostasis in the blades, thus relieving the salt stress.

Analysis of the regulatory mechanism of exogenous IAA-mediated tryptophan accumulation and synthesis of endogenous IAA in Chlorococcum humicola

The activated sludge method is widely used for the treatment of phenol-containing wastewater, which gives rise to the problem of toxic residual sludge accumulation. Indole-3-acetic acid (IAA), a typical phytohormone, facilitates the microalgal resistance to toxic inhibition while promoting biomass accumulation. In this study, Chlorococcum humicola (C. humicola) was cultured in toxic sludge extract and different concentrations of IAA were used to regulate its physiological properties and enrichment of high value-added products. Ultimately, proteomics analysis was used to reveal the response mechanism of C. humicola to exogenous IAA. The results showed that the IAA concentration of 5 × 10−6 mol/L (M) was most beneficial for C. humicola to cope with the toxic stress in the sludge extract medium, to promote the activity of rubisco enzyme, to enhance the efficiency of photosynthesis, and, finally, to accumulate protein as a percentage of specific dry weight 1.57 times more than that of the control group. Exogenous IAA altered the relative abundance of various amino acids in C. humicola cells, and proteomic analyses showed that exogenous IAA stimulated the algal cells to produce more indole-3-glycerol phosphate (IGP), indole, and serine by up-regulating the enzymes. These precursors are converted to tryptophan under the regulation of tryptophan synthase (A0A383V983), and tryptophan can be metabolized to endogenous IAA to promote the growth of C. humicola. These findings have important implications for the treatment of toxic residual sludge while enriching for high-value amino acids.

Genome-Wide Identification and Expression Analysis Reveal bZIP Transcription Factors Mediated Hormones That Functions during Early Somatic Embryogenesis in Dimocarpus longan.

The basic leucine zip (bZIP) transcription factors (TFs) are a group of highly conserved gene families that play important roles in plant growth and resistance to adversity stress. However, studies on hormonal regulatory pathways and functional analysis during somatic embryogenesis (SE) in Dimocarpus longan is still unavailable. In this study, a total of 51 bZIP family members were systematically identified in the whole genome of longan, a comprehensive bioinformatics analysis of DlbZIP (bZIP family members of D. longan) was performed, and subcellular localization and profiles patterns after transiently transformed DlbZIP60 were analyzed. The combined analysis of RNA-seq, ATAC-seq and ChIP-seq showed that four members have different H3K4me1 binding peaks in early SE and differentially expressed with increased chromatin accessibility. Comparative transcriptome analysis of bZIPs expression in early SE, different tissues and under 2,4-D treatment revealed that DlbZIP family might involved in growth and development during longan early SE. The qRT-PCR results implied that DlbZIP family were subjected to multiple hormonal responses and showed different degrees of up-regulated expression under indole-3-acetic acid (IAA), abscisic acid (ABA) and methyl jasmonate (MeJA) treatments, which indicated that they played an important role in the hormone synthesis pathways associated with the early SE of longan. Subcellular localization showed that DlbZIP60 was located in the nucleus, and the contents of endogenous IAA, MeJA and ABA were up-regulated in transiently DlbZIP60 overexpressed cell lines. These results suggest that DlbZIP60 may mediate hormones pathways that functions the development during early SE in longan.

Integrated metabolomics and transcriptomics analysis highlight key pathways involved in the somatic embryogenesis of Darjeeling tea.

Darjeeling tea is a globally renowned beverage, which faces numerous obstacles in sexual reproduction, such as self-incompatibility, poor seed germination, and viability, as well as issues with vegetative propagation. Somatic embryogenesis (SE) is a valuable method for rapid clonal propagation of Darjeeling tea. However, the metabolic regulatory mechanisms underlying SE in Darjeeling tea remain largely unknown. To address this, we conducted an integrated metabolomics and transcriptomics analysis of embryogenic callus (EC), globular embryo (GE), and heart-shaped embryo (HE). The integrated analyses showed that various genes and metabolites involved in the phenylpropanoid pathway, auxin biosynthesis pathway, gibberellin, brassinosteroid and amino acids biosynthesis pathways were differentially enriched in EC, GE, and HE. Our results revealed that despite highly up-regulated auxin biosynthesis genes YUC1, TAR1 and AAO1 in EC, endogenous indole-3-acetic acid (IAA) was significantly lower in EC than GE and HE. However, bioactive Gibberellin A4 displayed higher accumulation in EC. We also found higher BABY BOOM (BBM) and Leafy cotyledon1 (LEC1) gene expression in GE along with high accumulation of castasterone, a brassinosteroid. Total flavonoids and phenolics levels were elevated in GE and HE compared to EC, especially the phenolic compound chlorogenic acid was highly accumulated in GE. Integrated metabolome and transcriptome analysis revealed enriched metabolic pathways, including auxin biosynthesis and signal transduction, brassinosteroid, gibberellin, phenylpropanoid biosynthesis, amino acids metabolism, and transcription factors (TFs) during SE in Darjeeling tea. Notably, EC displayed lower endogenous IAA levels, conducive to maintaining differentiation, while higher IAA concentration in GE and HE was crucial for preserving embryo identity. Additionally, a negative correlation between bioactive gibberellin A4 (GA4) and IAA was observed, impacting callus growth in EC. The high accumulation of chlorogenic acid, a phenolic compound, might contribute to the low success rate in GE and HE formation in Darjeeling tea. TFs such as BBM1, LEC1, FUS3, LEA, WOX3, and WOX11 appeared to regulate gene expression, influencing SE in Darjeeling tea.

Exogenous gibberellin suppressed taproot secondary thickening by inhibiting the formation and maintenance of vascular cambium in radish (Raphanus sativus L.).

The thickening of radish taproots is primarily determined by secondary growth driven by the vascular cambium and is a highly intricate process regulated by plant hormones, transcription factors, and many metabolic pathways. Gibberellin (GA), a plant hormone associated with cell elongation, is essential in secondary growth. However, the mechanism through which exogenous GA3 regulates secondary taproot growth in radishes remains unclear. Integrated morphological, anatomical, hormonal, and transcriptomic analyses of taproots in radishes treated with GA3 and its biosynthesis inhibitor paclobutrazol (PBZ) were performed to explore their effects on taproot secondary growth and key regulatory pathways. GA3 significantly hindered taproot thickening by inhibiting the formation and maintenance of the vascular cambium, and PBZ promoted root development by increasing root length rather than root diameter. Transcriptome analysis revealed 2,014, 948, and 1,831 differentially expressed genes identified from the control vs. GA3, control vs. PBZ, and GA3 vs. PBZ comparisons, respectively. Kyoto Encyclopedia of Genes and Genome pathway enrichment analysis revealed that differentially expressed genes were primarily involved in the biosyntheses of secondary metabolites and metabolic pathways. GA3 significantly increased the levels of endogenous indole-acetic acid and the expression of auxin synthesis and signal transduction genes. Exogenous GA3 significantly inhibited the expression of genes involved in the maintenance and differentiation of vascular cambium, including WOX14, ER/ERL1, and XCP2. Exogenous GA3 affects root thickening in radishes primarily by regulating hormone signal transduction pathways, vascular cambium activity, and substance and energy metabolisms. Our findings provide insights into the mechanisms underlying taproot thickening in radishes and provide a valuable gene database for future studies.

Plant Regeneration via Organogenesis in Jerusalem Artichokes and Comparative Analysis of Endogenous Hormones and Antioxidant Enzymes in Typical and Atypical Shoots.

The Jerusalem artichoke (Helianthus tuberosus) is a tuberous plant with considerable nutrient and bioactive compounds. The optimization of the in vitro clonal propagation protocol is critical for large-scale reproduction and biotechnological applications of Jerusalem artichoke production. In this work, in vitro plant regeneration from the stem nodes of the Jerusalem artichoke via direct organogenesis is presented. In the shoot induction stage, the stem segments produced more shoots with vigorous growth on MS medium containing 0.5 mg/L 6-benzylaminopurine (6-BA). The concentrations of 6-BA and gibberellic acid (GA3) were both optimized at 0.5 mg/L for shoot multiplication, and the combination of 0.05 mg/L indole-3-butyric acid (IBA) and 0.05 mg/L 1-naphthylacetic acid (NAA) was the most responsive for root induction, yielding the largest number of roots. The regenerated plantlets were successfully hardened at a 96% survival rate and vigorously grew in the field. The genetic stability of the regenerated plants was confirmed by flow cytometry and simple sequence repeat (SSR) analysis. However, 17.3% of shoots on the optimum shoot induction medium had withered leaves and excessive callus (atypical shoots), which greatly reduced the induction efficiency. Enzyme activity in the typical and atypical shoots was compared. The atypical shoots had significantly higher levels of endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA), as well as increased activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), whereas the content of 6-BA, zeatin (ZT), and GA3 was significantly reduced. The activity of the three enzymes was positively correlated with the content of IAA and ABA, while being negatively correlated with that of 6-BA, ZT, and GA3. The results suggest that the poor growth of the atypical shoots might be closely related to the significant accumulation of endogenous IAA and ABA, thus significantly increasing antioxidant enzyme activity.

Exogenous IAA enhances low potassium tolerance of sweetpotato by regulating root response strategy

ABSTRACT Plant roots are sensitive to potassium (K+) deficiency signals. Therefore, regulating root growth by exogenous methods is a vital strategy to improve low K+ tolerance of sweetpotato. We studied the effects of exogenous indole-3-acetic acid (IAA) on growth, K+ absorption, and root characteristics in sweetpotato exposed to low K+ treatment (LK). LK significantly inhibited dry mass, K+ concentration and accumulation, as well as the root elongation (length) and branching (forks and crossings) in sweetpotato seedlings. However, exogenous IAA increased the length, ratio, and density of lateral roots and promoted absorption and accumulation of K+, which effectively alleviated the inhibitory effect of low K+. Exogenous IAA also increased the expression levels of auxin synthesis (IbYUC6 and IbTAR2) and transport (IbPIN1, IbPIN3, and IbPIN8) genes in leaves and roots, which promoted the increase of endogenous IAA content. Furthermore, exogenous IAA was more effective on low-K-tolerant variety (XS32) than low-K-sensitive variety (NZ1) under LK stress, depending on their different IAA synthesis and transport strategies. These results indicated that exogenous IAA enhanced root responsiveness of sweetpotato to low K+ stress by modulating auxin biosynthesis and transport, thereby improving the tolerance of sweetpotato to low K+ stress.

Induction of Tolerance in Groundnut Plants Against Drought Stress and Cercospora Leaf Spot Disease with Exogenous Application of Arginine and Sodium Nitroprusside Under Field Conditions

Naturally, under field conditions, plants are regularly experienced by a mixture of two or more stress factors. Drought is a major abiotic stress, and fungal pathogens characterize a main biotic stress challenge faced by plants and impact negatively on plant development and productivity. We propose that foliar application of nitric oxide (NO) donors can have positive effects on the induction of tolerance to biotic and abiotic stress on groundnut plants. This investigation was carried out to study the changes in growth, some biochemical aspects, and yield and quality of groundnut plants as well as induction of resistance to Cercospora leaf spot disease in response to nitric oxide (NO) donors, sodium nitroprusside (SNP), and arginine (Arg) (2.5, 5.0, and 7.5 mM) under two water irrigation levels 100% and 75% of water irrigation requirements (WIR), in two field experiments through two successive growing seasons of 2021 and 2022. Decreasing irrigation water significantly reduced shoot length, branches numberplant-1, shoot fresh and dry weight, photosynthetic pigments components, endogenous indole acetic acid (IAA) contents, and yield components. Furthermore, root fresh and dry weight, phenols, total soluble sugars (TSS), proline contents, and the accumulation of hydrogen peroxide (H2O2) and lipid peroxidation of groundnut leaves increased significantly. Contrarily, foliar application with Arg and SNP alleviated the negative influences of drought on growth and productivity of groundnut plants via enhancing photosynthetic pigments, IAA, phenolic compounds, TSS, and proline contents. Additionally, SNP and Arg significantly decreased oxidative damage through decreasing H2O2 and lipid peroxidation by the induction of antioxidant enzymes. Remarkably, the increase of drought level led to a reduction in Cercospora leaf spot (CLS) disease with the use of high concentrations of both Arg and SNP. Interestingly, in both stressed and unstressed plants, SNP treatment at 7.5 mM was the most effective in reducing the incidence and severity of disease, while Arg at 2.5 mM recorded the lowest reduction compared to other treatments. In conclusion, foliar treatment of either SNP or Arg is a profound effect on modulating the drought stress and induction of resistance to Cercospora leaf spot disease of groundnut plants throughout regulating physiological and biochemical processes associated with photosynthesis and oxidative responses.

Transcriptomic and Hormone Analyses Provide Insight into the Regulation of Axillary Bud Outgrowth of Eucommia ulmoides Oliver.

An essential indicator of Eucommia ulmoides Oliver (E. ulmoides) is the axillary bud; the growth and developmental capacity of axillary buds could be used to efficiently determine the structural integrity of branches and plant regeneration. We obtained axillary buds in different positions on the stem, including upper buds (CK), tip buds (T1), and bottom buds (T2), which provided optimal materials for the study of complicated regulatory networks that control bud germination. This study used transcriptomes to analyze the levels of gene expression in three different types of buds, and the results showed that 12,131 differentially expressed genes (DEGs) were discovered via the pairwise comparison of transcriptome data gathered from CK to T2, while the majority of DEGs (44.38%) were mainly found between CK and T1. These DEGs were closely related to plant hormone signal transduction and the amino acid biosynthesis pathway. We also determined changes in endogenous hormone contents during the process of bud germination. Interestingly, except for indole-3-acetic acid (IAA) content, which showed a significant upward trend (p < 0.05) in tip buds on day 4 compared with day 0, the other hormones showed no significant change during the process of germination. Then, the expression patterns of genes involved in IAA biosynthesis and signaling were examined through transcriptome analysis. Furthermore, the expression levels of genes related to IAA biosynthesis and signal transduction were upregulated in tip buds. Particularly, the expression of the IAA degradation gene Gretchen Hagen 3 (GH3.1) was downregulated on day 4, which may support the concept that endogenous IAA promotes bud germination. Based on these data, we propose that IAA synthesis and signal transduction lead to morphological changes in tip buds during the germination process. On this basis, suggestions to improve the efficiency of the production and application of E. ulmoides are put forward to provide guidance for future research.

A New Function of MbIAA19 Identified to Modulate Malus Plants Dwarfing Growth.

The primary determinants of apple (Malus) tree architecture include plant height and internode length, which are the significant criteria for evaluating apple dwarf rootstocks. Plant height and internode length are predominantly governed by phytohormones. In this study, we aimed to assess the mechanisms underlying dwarfism in a mutant of Malus baccata. M. baccata dwarf mutant (Dwf) was previously obtained through natural mutation. It has considerably reduced plant height and internode length. A comparative transcriptome analysis of wild-type (WT) and Dwf mutant was performed to identify and annotate the differentially expressed genes responsible for the Dwf phenotype using RNA-seq and GO and KEGG pathway enrichment analyses. Multiple DEGs involved in hormone signaling pathways, particularly auxin signaling pathways, were identified. Moreover, the levels of endogenous indole-3-acetic acid (IAA) were lower in Dwf mutant than in WT. The Aux/IAA transcription factor gene MbIAA19 was downregulated in Dwf mutant due to a single nucleotide sequence change in its promoter. Genetic transformation assay demonstrated strong association between MbIAA19 and the dwarf phenotype. RNAi-IAA19 lines clearly exhibited reduced plant height, internode length, and endogenous IAA levels. Our study revealed that MbIAA19 plays a role in the regulation of dwarfism and endogenous IAA levels in M. baccata.