Exogenous Indole-3-butyric Acid Research Articles

Exogenous IBA stimulatory effects on root formation of Actinidia deliciosa rootstock and Actinidia arguta male scion stem cuttings

Recalcitrance to root of kiwifruit (Actinidia spp.) stem cuttings (SCs) is a restriction for its commercial production. Exogenous hormone is the key factor to regulate root formation, but the research on exogenous hormone stimulatory effects on Actinidia spp. is still lagging. Kiwifruit plants had been mostly propagated by seeds. However, vegetative propagation offers several advantages over sexual propagation, among them being crop homogeneity, practicability, and simplicity of the technique. A study was therefore conducted to investigate the potential responses of kiwifruit SCs from Actinidia deliciosa rootstock and Actinidia arguta male scion SCs treated with indole-3-butyric acid (IBA) concentrations at low (10, 100 ppm), medium (1,000, 10,000 ppm) and high (100,000 ppm) levels. Parallel experiments for A. deliciosa and A. arguta’s treatments were arranged in a randomized complete block design, with 12 replications. Treatments comprised different IBA concentrations, namely, 0 (control), 10, 100, 1,000, 10,000 and 100,000 ppm. At 103 days, rooting percentage, number of roots, root length, dry root mass, size of callus formation and callus percentage were determined. In A. deliciosa SCs, treatments had high significant (p ≤ 0.05) effects in rooting percentage, number of roots, root length, size of callus formation and callus percentage, except for dry root mass. In A. arguta male SCs, treatments also, showed high significant (p ≤ 0.05) effects in the number of roots, root length and dry root mass, except for the rooting percentage. No callus formation was observed in A. arguta male SCs. Relative to the control, in A. deliciosa SCs, the highest (42%) rooting percentage and lengthy (0.3 cm) roots, both were observed at the medium (10,000 ppm) IBA concentration, whereas the most (0.29) number of roots were produced at the highest (100,000 ppm) IBA concentration. Calli percentage (94%) was highest at low (100 ppm) IBA, while the biggest (2.8) size of callus formation was at the highest IBA concentration of 100,000 ppm, when compared to the control. In A. arguta male SCs, the greatest number of roots (1.08) and root mass (0.07 g) were attained at the medium IBA concentration of 10,000 ppm. The longest (0.94 cm) root length was achieved at the low IBA concentration of 100 ppm. The SCs of A. arguta male scion required low to medium (100 to 10,000 ppm) concentrations of IBA for proper roots stimulation and development, whereas in SCs of A. deliciosa, highest rooting percentage paired with callus formation, was achieved at medium to higher (10,000 to 100,000 ppm) IBA concentrations. Principal component analysis (PCA) revealed that PC1 and PC2 accounted for 99% of the entire variation. While PC1 accounted for 94% of the total variation, PC2 accounted for 5% of the total variation in A. deliciosa. However, in A. arguta PCA revealed that PC1 and PC2 accounted for 93% of the entire variation. While PC1 accounted for 72% of the total variation, PC2 accounted for 21% of the total variation. The use of exogenous application of IBA was effective for adventitious root formation in SCs of A. deliciosa rootstock and A. arguta male scion. IBA showed its effectiveness in stimulating root development at 10000 ppm IBA.

Responses of isolated balsam-fir stem segments to exogenous ACC, IAA, and IBA.

In this investigation, the effects of exogenous indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and 1-aminocyclopropane-1-carboxylic acid (ACC) on anatomical development within cultured segments of Abies balsamea (L.) Mill. were compared, using debudded and defoliated leaders produced in the preceding year as bioassay material. In stem apical regions, IAA promoted radial enlargement of pre-existing cortical resin ducts and attending parenchyma enlargement, whereas IBA promoted cell division and expansion of parenchyma on the outer edge of phloem without altering cortical duct shape. Cortical woody ducts, each partially surrounded by cambium, were observed as a novel but infrequent feature. A single cortical woody duct was spatially associated with each mature leaf as its vascular trace, and they were not encountered elsewhere in the cortex, nor were they induced to form in response to any hormone application. An unknown leaf factor induces the development of cortical woody ducts. Both IAA and IBA promoted cell division in the vascular cambium. The common cellular response at the interface between the latewood boundary and cambial zone was the radial expansion of primary-walled fusiform cambial cell derivatives with little if any ensuing tracheary element (TE) differentiation. Enhanced TE production at basal stem positions occurred when ACC was provided with IAA and/or IBA, and an IAA + IBA + ACC combination produced a basal stem response similar to that in untreated segments having intact leaves. The data support the conclusion that IAA, IBA, and ACC have distinct but complementary roles in the overall regulation of the types of cellular differentiation that contribute to cortex histogenesis and diameter growth of balsam-fir leaders.

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 interaction between exogenous IBA with sucrose, light and ventilation alters the expression of ARFs and Aux/IAA genes in Carica papaya plantlets.

The interaction between exogenous IBA with sucrose, light and ventilation, alters the expression of ARFs and Aux/IAA genes in in vitro grown Carica papaya plantlets. In vitro papaya plantlets normally show low rooting percentages during their ex vitro establishment that eventually leads to high mortality when transferred to field conditions. Indole-3-butyric acid (IBA) auxin is normally added to culture medium, to achieve adventitious root formation on in vitro papaya plantlets. However, the molecular mechanisms occurring when IBA is added to the medium under varying external conditions of sugar, light and ventilation have not been studied. Auxin response factors (ARF) are auxin-transcription activators, while auxin/indole-3-acetic acid (Aux/IAA) are auxin-transcription repressors, that modulate key components involved in auxin signaling in plants. In the present study, we identified 12 CpARF and 18 CpAux/IAA sequences in the papaya genome. The cis-acting regulatory elements associated to those CpARFs and CpAux/IAA gene families were associated with stress and hormone responses. Furthermore, a comprehensive characterization and expression profiling analysis was performed on 6 genes involved in rhizogenesis formation (CpARF5, 6, 7 and CpAux/IAA11, 13, 14) from in vitro papaya plantlets exposed to different rhizogenesis-inducing treatments. In general, intact in vitro plantlets were not able to produce adventitious roots, when IBA (2mg L-1) was added to the culture medium; they became capable to produce roots and increased their ex-vitro survival. However, the best rooting and survival % were obtained when IBA was added in combination with adequate sucrose supply (20g L-1), increased light intensity (750µmol photon m-2s-1) and ventilation systems within the culture vessel. Interestingly, it was precisely under those conditions that promoted high rooting and survival %, where the highest expression of CpARFs, but the lowest expression of CpAux/IAAs occurred. One interesting case occurred when in vitro plantlets were exposed to high levels of light in the absence of added IBA, as high rooting and survival occurred, even though no exogenous auxin was added. In fact, plantlets from this treatment showed the right expression profile between auxin activators/repressors genes, in both stem base and root tissues.

An HD-ZIP transcription factor, MxHB13, integrates auxin-regulated and juvenility-determined control of adventitious rooting in Malus xiaojinensis.

Adventitious root (AR) formation is a critical factor in the vegetative propagation of forestry and horticultural plants. Competence for AR formation declines in many species during the miR156/SPL-mediated vegetative phase change. Auxin also plays a regulatory role in AR formation. In apple rootstock, both high miR156 expression and exogenous auxin application are prerequisites for AR formation. However, the mechanism by which the miR156/SPL module interacts with auxin in controlling AR formation is unclear. In this paper, leafy cuttings of juvenile (Mx-J) and adult (Mx-A) phase Malus xiaojinensis were used in an RNA-sequencing experiment. The results revealed that numerous genes involved in phytohormone signaling, carbohydrate metabolism, cell dedifferentiation, and reactivation were downregulated in Mx-A cuttings in response to indole butyric acid treatment. Among the differentially expressed genes, an HD-ZIP transcription factor gene, MxHB13, was found to be under negative regulation of MdSPL26 by directly binding to MxHB13 promoter. MxTIFY9 interacts with MxSPL26 and may play a role in co-repressing the expression of MxHB13. The expression of MxTIFY9 was induced by exogenous indole butyric acid. MxHB13 binds to the promoter of MxABCB19-2 and positively affects the expression. A model is proposed in which MxHB13 links juvenility-limited and auxin-limited AR recalcitrance mechanisms in Mx-A.

Morpho-anatomical and biochemical changes associated with rooting of micropropagated ninebark cuttings

Ninebark (Physocarpus opulifolius) is an attractive ornamental shrub with poor rooting characteristics in some cultivars, which is a limiting factor in commercial production This study was designed to optimize rooting conditions of ninebark cuttings and to observe the effect of exogenous auxin IBA on some morpho-anatomical and biochemical changes associated with rhizogenesis in the in vitro conditions. Both auxins under study: the indole-3-butyric acid (IBA) and 1-naphthalene acetic acid (NAA) gave comparable effects but the combination of ½ MS + 1 mg·L−1 IBA was the most cost effective for all rooting parameters. Anatomical changes at the cuttings’ bases during root formation were typical for woody plants and they were accelerated by auxin in the culture medium. High levels of the endogenous indole acid and hydrogen peroxide were temporarily associated with intensive cell divisions in cuttings, and the polyphenolic acid contents kept increasing during rooting above the initial levels and those in controls.

\u03b3-Aminobutyric Acid Participates in the Adult-Phase Adventitious Rooting Recalcitrance

In many tree species especially the rooting-recalcitrant woody perennials, the adventitious root (AR) in the juvenile phase can be easily induced by exogenous auxin, but AR formation becomes recalcitrant in the adult phase. Also, it is reported that the γ-aminobutyric acid (GABA) inhibits primary root growth in Arabidopsis and the AR formation in poplar (Populus ssp). So far, how GABA affects or is affected by the ontogenetic phase or auxin remains unclear. Here, we used an apple rootstock, Malus xiaojinensis, and tobacco (Nicotiana benthamiana) to investigate this question. We first analyzed the content of GABA, the activity of GABA synthetic enzyme GAD, and the expression of the coding gene MxGADs, respectively, in leafy cuttings of juvenile and adult phase. Next, the effect of exogenous GABA on AR formation was examined in in vitro shoots of M. xiaojinensis and tobacco. Interestingly, significant and consistent increases in GABA concentration, GAD activity, and expression of MxGAD genes in response to exogenous indole butyric acid (IBA) were detected in adult-phase cuttings, but not in juvenile-phase cuttings. Exogenous GABA application inhibited the AR formation by delaying rooting time and reducing root number and the total root length in in vitro shoots of both M. xiaojinensis and tobacco. The expression of MxPIN members increased in response to IBA application, but these changes were restrained by the addition of GABA. These results indicate that both the loss of juvenility and IBA are required to trigger GABA accumulation. GABA may affect the AR formation as a co-actor by inhibiting polar auxin transport. Together, these findings facilitate the understanding of the regulatory network among GABA, juvenility, and auxin signaling on the AR formation.

Mdm-miR160 Participates in Auxin-Induced Adventitious Root formation of apple rootstock

Adventitious root (AR) formation is an essential process for the vegetative propagation of apple rootstocks. However, the mechanisms of miR160 mediate AR formation in apple remains to be seen. In this study, five mdm-miR160 family members were identified in apple rootstocks and two AUXIN RESPONSIVE FACTOR (MdARF16 and MdARF17) were found as the targets of mdm-miR160. Furthermore, the sequences of mdm-miR160 family members’ precursors were cloned from four different AR rooting ability apple rootstocks, whereas, mdm-miR160a, mdm-miR160c and mdm-miR160e were highly conserved than mdm-miR160b and mdm-miR160d. Mdm-miR160 and their targets expression patterns showed obviously negative relationship in different stages during AR formation. In addition, the transcript level of mdm-miR160 was higher in ‘SH6’ and lower in ‘MP’, where it responds to exogenous indole-3-butyric acid (IBA). Mdm-miR160a was cloned from ‘M26’ and used for further experiments. The result of over-expressed mdm-miR160a in tobacco (Nicotiana tabacum L.cv.SR1) inhibited AR formation in 35S:MdMIR160a transgenic lines as compared with WT, whereas, exogenous IBA treatment could promote AR formation in 35S:MdMIR160a transgenic lines. Expression of five endogenous miRNAs: miR167c, miR393a, miR396a, miR396b, and miR156 in transgenic lines were lower than in WT. Moreover, the targets of endogenous miRNAs in transgenic lines showed different expression patterns with WT. In consistent, mdm-miR160 was an auxin responsive factor and participated in AR formation in apple rootstock, however, over-expressed mdm-miR160a has inhibitory effect on AR formation while exogenous IBA treatment could raise the rooting ability of transgenic lines.

A glutathione-dependent control of the indole butyric acid pathway supports Arabidopsis root system adaptation to phosphate deprivation.

Root system architecture results from a highly plastic developmental process to adapt to environmental conditions. In particular, the development of lateral roots and root hair growth are constantly optimized to the rhizosphere properties, including biotic and abiotic constraints. The development of the root system is tightly controlled by auxin, the driving morphogenic hormone in plants. Glutathione, a major thiol redox regulator, is also critical for root development but its interplay with auxin is scarcely understood. Previous work showed that glutathione deficiency does not alter root responses to indole acetic acid (IAA), the main active auxin in plants. Because indole butyric acid (IBA), another endogenous auxinic compound, is an important source of IAA for the control of root development, we investigated the crosstalk between glutathione and IBA during root development. We show that glutathione deficiency alters lateral roots and root hair responses to exogenous IBA but not IAA. Detailed genetic analyses suggest that glutathione regulates IBA homeostasis or conversion to IAA in the root cap. Finally, we show that both glutathione and IBA are required to trigger the root hair response to phosphate deprivation, suggesting an important role for this glutathione-dependent regulation of the auxin pathway in plant developmental adaptation to its environment.

Exploring Vegetative Propagation Techniques for the Threatened Pteroceltis tatarinowii Maxim Using Stem Cuttings

Pteroceltis tatarinowii Maxim, the only species of the genus Pteroceltis (family Ulmaceae), is an endemic rare tree species in China. This study was performed to explore vegetative propagation techniques for P. tatarinowii using stem cuttings. First, the effects of exogenous indole-3-butyric acid (IBA) and cutting positions on rooting performance were investigated to screen the appropriate exogenous auxin treatment and to determine the proper cuttings type. The results showed that the control cuttings pretreated with no exogenous IBA, irrespective of whether the stem cuttings were terminal, middle, or basal, rooted in a manner significantly inferior to that of cuttings pretreated with IBA. Their rooting percentage was less than 50%. Among the IBA-treated cuttings, the middle cuttings pretreated with 1000 mg·L−1 IBA rooted best, with the shortest number of days until rooting emergence (20 days), the highest rooting percentage (84.0%), the lowest mortality rate (4.0%), the greatest root number (average of 6.7 per cutting), and the longest roots per cutting (44.4 cm per cutting). Terminal cuttings pretreated with 1000 mg·L−1 IBA acquired satisfactory rooting traits and had the same shortest rooting duration (20 days) and the following parameters: rooting, 70.7%; mortality, 10.7%; average roots per cutting, 5.2; and longest root, 29.1 cm. To further determine the optimum cutting propagation time for this plant, a second experiment was performed and the cuttings were collected beginning in early June, when the growth of the current season was feasible for harvesting cuttings. Stem cuttings collected in late June and middle July had significantly higher rooting percentages (≥80%) compared with those collected in early June (66.7%). The other three rooting parameters were not significantly affected by the collection date. However, according to the overall rooting traits, the cuttings collected in both late June and middle July remarkably outperformed those collected in early June regarding the number of roots and the total root length per cutting. The initial nutrient reserves in the cuttings were also determined. A significant difference in the soluble carbohydrate level was found among collection times, but the nitrogen level in the cuttings was similar. The study revealed that stem cutting propagation of P. tatarinowii was achievable, and it was best achieved with cuttings collected from the terminal and middle positions of the branches of the current season from late June to middle July and treated with 1000 mg·L−1 IBA using the quick dip method.

Expressional and Functional Verification of the Involvement of CmEXPA4 in Chrysanthemum Root Development

Expansin (EXP) plays an important role in plant root formation. The EXP genes associated with chrysanthemum roots have not yet been reported. Here we isolated a root-specific EXP gene in chrysanthemum (Chrysanthemum morifolium), namely CmEXPA4. Bioinformatics analysis showed that CmEXPA4-encoded protein has a conserved DPPB (Double-Psi Beta-Barrel) domain in the N-terminal with a series of Cys residues, an HFD (His-Phe-Asp) motif in the central region, and a pollen allergen domain in the C-terminal. The protein also has a specific α-insertion of WCNP (Trp-Cys-Asn-Pro), which suggests that it belongs to the A-subgroup of the EXP family. In the present study, we cloned the 1,129 bp promoter region upstream of CmEXPA4, and the analysis revealed an abundance of cis-acting elements associated with hormones, light and stress-related responses, and some root-specific regulatory elements in particular. Subcellular localization results indicated that CmEXPA4 locates in the cell wall. Exogenous indole butyric acid induced the up-regulation of CmEXPA4 expression, whereas exogenous abscisic acid inhibited its expression. Tissue expression analysis showed that CmEXPA4 was preferentially expressed in the roots and was synchronized with the rapid emergence of the root. These results suggested that CmEXPA4 may act on the growth and development of chrysanthemum roots. The function of CmEXPA4 was further tested by virus-induced gene silencing, and the results showed that CmEXPA4 silencing inhibited the normal development of the chrysanthemum root system. The roots appeared thinner and shorter, and several important root parameters, including total length, average diameter, surface area, total volume, and root tip number, decreased significantly. The cortical cells of the transgenic plant roots were significantly smaller and shorter than those of the control. Collectively, our results demonstrated that CmEXPA4 gene plays a key role in the growth and development of chrysanthemum roots and affects the root system by acting on the individual cells.

ITRAQ-Based Proteomic Analysis Reveals Potential Regulation Networks of IBA-Induced Adventitious Root Formation in Apple.

Adventitious root (AR) formation, which is controlled by endogenous and environmental factors, is indispensable for vegetative asexual propagation. However, comprehensive proteomic data on AR formation are still lacking. The aim of this work was to study indole-3-butyric acid (IBA)-induced AR formation in the dwarf apple rootstock ‘T337’. In this study, the effect of IBA on AR formation was analysed. Subsequent to treatment with IBA, both the rooting rate and root length of ‘T337’ increased significantly. An assessment of hormone levels in basal stem cuttings suggested that auxin, abscisic acid, and brassinolide were higher in basal stem cuttings that received the exogenous IBA application; while zeatin riboside, gibberellins, and jasmonic acid were lower than non-treated basal stem cuttings. To explore the underlying molecular mechanism, an isobaric tags for relative and absolute quantification (iTRAQ)-based proteomic technique was employed to identify the expression profiles of proteins at a key period of adventitious root induction (three days after IBA treatment). In total, 3355 differentially expressed proteins (DEPs) were identified. Many DEPs were closely related to carbohydrate metabolism and energy production, protein homeostasis, reactive oxygen and nitric oxide signaling, and cell wall remodeling biological processes; as well as the phytohormone signaling, which was the most critical process in response to IBA treatment. Further, RT-qPCR analysis was used to evaluate the expression level of nine genes that are involved in phytohormone signaling and their transcriptional levels were mostly in accordance with the protein patterns. Finally, a putative work model was proposed. Our study establishes a foundation for further research and sheds light on IBA-mediated AR formation in apple as well as other fruit rootstock cuttings.

Rooting Ability of Hardwood Cuttings in Highbush Blueberry (Vaccinium corymbosum L.) Using Different Indole-butyric Acid Concentrations

Vegetative propagation by cuttings is a very popular method. However, blueberry propagation using cuttings is still a main factor limiting its expansion because its results can vary according to the blueberry cultivar and environmental factors. This study aimed to evaluate the rooting abilities of hardwood cuttings for six blueberry cultivars (O’Neal, Misty, Diana, Biloxi, Bluebeauty, and Coville) using three different exogenous indole-butyric acid (IBA) concentrations (1000, 2000, and 3000 ppm), and to determine if the cutting position (basal, central, apical) affects rooting performance. A control treatment (0 ppm IBA) was also performed. After 90 days of each treatment, rooting percentage, average root length, and average root number per cutting were assessed and used to calculate rooting index, which is a measure of rooting ability. The rooting percentages of hardwood cuttings differed largely among cultivars and were highest for ‘Bluebeauty’ (68.55%), followed by ‘Biloxi’ (68.01%). The rooting index values of these two cultivars (33.59 and 35.18, respectively) were significantly higher than those of the other four cultivars. The rooting response of blueberry hardwood cuttings to IBA concentrations was quadratic, and 1000 and 2000 ppm IBA were sufficient to express the maximum rooting percentage in most cultivars. The rooting abilities of basal, central, and apical cuttings were similar with treatments with high IBA concentrations. The effects of the cultivar, IBA concentration, and interaction between them on rooting percentage, average root length, and average root number were significant; however, the effects of the cutting position on the rooting percentage and average root length were not. This suggested that the rooting abilities of blueberry hardwood cuttings were significantly influenced by the cultivar and IBA concentration rather than by the cutting position.

Indole-3-butyric acid promotes adventitious rooting in Arabidopsis thaliana thin cell layers by conversion into indole-3-acetic acid and stimulation of anthranilate synthase activity

BackgroundIndole-3-acetic acid (IAA), and its precursor indole-3-butyric acid (IBA), control adventitious root (AR) formation in planta. Adventitious roots are also crucial for propagation via cuttings. However, IBA role(s) is/are still far to be elucidated. In Arabidopsis thaliana stem cuttings, 10 μM IBA is more AR-inductive than 10 μM IAA, and, in thin cell layers (TCLs), IBA induces ARs when combined with 0.1 μM kinetin (Kin). It is unknown whether arabidopsis TCLs produce ARs under IBA alone (10 μM) or IAA alone (10 μM), and whether they contain endogenous IAA/IBA at culture onset, possibly interfering with the exogenous IBA/IAA input. Moreover, it is unknown whether an IBA-to-IAA conversion is active in TCLs, and positively affects AR formation, possibly through the activity of the nitric oxide (NO) deriving from the conversion process.ResultsRevealed undetectable levels of both auxins at culture onset, showing that arabidopsis TCLs were optimal for investigating AR-formation under the total control of exogenous auxins. The AR-response of TCLs from various ecotypes, transgenic lines and knockout mutants was analyzed under different treatments. It was shown that ARs are better induced by IBA than IAA and IBA + Kin. IBA induced IAA-efflux (PIN1) and IAA-influx (AUX1/LAX3) genes, IAA-influx carriers activities, and expression of ANTHRANILATE SYNTHASE -alpha1 (ASA1), a gene involved in IAA-biosynthesis. ASA1 and ANTHRANILATE SYNTHASE -beta1 (ASB1), the other subunit of the same enzyme, positively affected AR-formation in the presence of exogenous IBA, because the AR-response in the TCLs of their mutant wei2wei7 was highly reduced. The AR-response of IBA-treated TCLs from ech2ibr10 mutant, blocked into IBA-to-IAA-conversion, was also strongly reduced. Nitric oxide, an IAA downstream signal and a by-product of IBA-to-IAA conversion, was early detected in IAA- and IBA-treated TCLs, but at higher levels in the latter explants.ConclusionsAltogether, results showed that IBA induced AR-formation by conversion into IAA involving NO activity, and by a positive action on IAA-transport and ASA1/ASB1-mediated IAA-biosynthesis. Results are important for applications aimed to overcome rooting recalcitrance in species of economic value, but mainly for helping to understand IBA involvement in the natural process of adventitious rooting.

Interaction of stockplants shading and exogenous auxin on the propagation of Cola anomala K. Schum (Malvaceae) by cuttings

The establishment of an efficient protocol for vegetative propagation is still a challenge for Cola anomala, a priority target for domestication in West and Central Africa. The present study examined the rooting ability of C. anomala leafy stem cuttings in response to different levels of stockplants shading and different concentrations of exogenously applied indole 3-butyric acid (IBA). 900 cuttings were set in three blocks of a split plot experimental design in non-mist propagators. Each main plot contained three shading levels (0%, 50% and 75%), whereas five exogenous IBA concentrations (0, 1000, 2000, 5000 and 10,000mg/l) were tested at the subplot level. At each level, treatments were assigned at random to experimental units so as to have 3 blocks×3 levels of shading×5 IBA concentrations×20 cuttings. After 16weeks, cuttings were assessed for mortality and rooting. Results showed that stockplants grown under 50% and 75% shade resulted in a subsequent significantly lower cutting's mortality rate as well as significantly higher percentage of rooted cuttings and number of roots per rooted cutting, compared to stockplants grown under 0% shade. Although IBA concentration had no effect on mortality rate, it significantly affected rooting ability. Considering all levels of shading together, the percentage of rooted cuttings as well as the number of roots per rooted cutting increased with exogenous IBA concentration and reached their maximum values (100% and 6 respectively) at 10000mg/l IBA. With stockplants grown under high irradiance (0% shade), the maximum rooting percentage (100%) was obtained when cuttings were treated with 10,000mg/l IBA, whereas with stockplants grown under shade (50% and 75% shade) the IBA concentration necessary to achieve maximum rooting was reduced to 5000mg/l. These results indicate that stockplants shading increases the subsequent rooting ability as well as sensitivity to IBA of stem cuttings. This is valuable information to optimize the clonal propagation protocol for C. anomala and other species of the humid tropics of West and Central Africa, especially those considered to be difficult to propagate.

Impact of Indole-3-Butyric Acid on Adventitious Root Development from Cuttings of Tea

The objective of this study was to investigate the effects of the application of indole-3-butyric acid (IBA) at concentrations of 0, 30, 60, and 90 mg·L−1, for 24 hours, on rooting of softwood and semihardwood cuttings of tea (Camellia sinensis var. sinensis ‘Yabukita’ and C. sinensis var. assamica ‘IAC-259’) collected in winter and summer. In the summer, IBA increased root percentage of softwood cuttings from ‘Yabukita’ compared with the control. However, the rooting of semihardwood cuttings was unaffected by this growth regulator. In winter, application of 90 mg·L−1 IBA increased the rooting regardless of the type of ‘Yabukita’ cuttings. In addition, in ‘IAC-259’, there was an increase in dry weight, number of roots (NOR), and rooting percentage of softwood cuttings collected in summer with application of 90 mg·L−1 IBA compared with control. In contrast, during the same period of the year, the semihardwood cuttings of ‘IAC-259’ were unaffected by the IBA. In winter, the percentage of cutting survival, rooting, the number, and length of roots were unaffected by IBA in ‘IAC-259’. Overall, we would recommend the use of exogenous IBA for rooting of cuttings collected in the summer or winter.

Conversion of Indole-3-Butyric Acid to Indole-3-Acetic Acid in Shoot Tissue of Hazelnut (Corylus) and Elm (Ulmus)

Indole-3-butyric acid (IBA) is an endogenous compound that appears to regulate both lateral and adventitious root formation in many plant species and is also the auxin most available commercially for application to promote rooting. IBA is converted to indole-3-acetic acid (IAA) by β-oxidation in the peroxisomes. This process has been observed in a number of plant species and has been shown to be critical for normal root development in response to treatment with IBA. In this study, we investigated this process in hybrid hazelnut (Corylus americana × C. avellana), American elm (Ulmus americana), and Cathedral hybrid elm (U. pumila × U. davidiana var. japonica ‘Cathedral’), in which adventitious rooting is a major bottleneck for vegetative propagation, and the efficacy of IBA treatment is highly variable across different cultivars and at different collection times. Using differentially stable isotope-labeled IBA and IAA tracer and internal standard, respectively, and using gas chromatography coupled with selected reaction monitoring mass spectrometry, IBA-derived IAA was measured in shoot tissue treated with stable isotope-labeled IBA. In elm, higher levels of IBA-to-IAA conversion were generally observed in cultivars which formed adventitious roots most easily in softwood stem cutting trials. IBA-to-IAA conversion was observed in hazelnut genotypes with different rooting abilities and suggested a complex relationship exists between IBA conversion and root organogenesis. In both hazelnut and elm, endogenous free IAA levels were not significantly different across the genotypes examined. High rates of root formation is a key trait for establishment of large-scale production systems. Screening for optimal rates of IBA-to-IAA conversion may facilitate selection against genotypes which respond poorly to exogenous IBA and are thus difficult to propagate using hormone treatment.

Effect of growth hormones on some antioxidant parameters and gene expression in tomato

Bioregulators have a great effect on vital processes of plant growth and development. Known plant bioregulators include Naphthalene acetic acid (NAA), Indole-3-butyric acid (IBA) and Indole-3-acetic acid (IAA). Natural or synthetic plant bioregulators are organic compounds that affect the physiological processes in the plant, either to control some of these processes or to modify them. For example these bioregulators can affect the nature of the process, either by accelerating or decelerating plant growth, rates of maturation and also by altering the behavior of the plants or their products. Also, enhancement of important nutrients in human diet could be achieved by bioregulators. This study uses the model crop plant Tomato (Lycopersicon esculentum). Tomato is affected by a group of bioregulators, this group contains compounds which are powerful antioxidants in vitro. The current study aims to find out the effect of some plant bioregulators (IAA, IBA and NAA) on tomato growth, total protein content and enzyme activities of ascorbate peroxidase (APX), superoxide dismutase (SOD) and catalase (CAT). This study also investigates the effect of the above mentioned bioregulators on the level of RNA expression for SOD, CAT and TPX1 genes. The analytical quantification of target gene expression showed the induced effect of NAA on SOD expression and reducing effect of the other bioregulators (IAA and IBA) on CAT and TPX1 expression. However, at the protein level, we found that IBA and IAA caused a minor effect on total protein content while a significant effect was recorded on the total protein level using NAA. Upon measuring the enzyme activity of ascorbate peroxidase and catalase, we found that both the exogenous NAA and IBA stimulated ascorbate peroxidase activity in tomato while there was no considerable difference detected in IAA treated plants. Also, there was no considerable difference detected in catalase activity of all bioregulator-treated plants compared with the control.

Quantitation of endogenous levels of IAA, IAAsp and IBA in micro-propagated shoots of hybrid chestnut pre-treated with IBA

Endogenous levels of indole-3-acetic acid (IAA), indole-3-acetylaspartic acid (IAAsp) and indole-3-butyric acid (IBA) were measured during the first 8 d of in vitro rooting of rootstock from the chestnut ‘M3’ hybrid by high performance liquid chromatography (HPLC). Rooting was induced either by dipping the basal ends of the shoots into a 4.92-mM IBA solution for 1 min or by sub-culturing the shoots on solid rooting medium supplemented with 14.8-μM IBA for 5 d. For root development, the induced shoots were transferred to auxin-free solid medium. Auxins were measured in the apical and basal parts of the shoots by means of HPLC. Endogenous levels of IAA and IAAsp were found to be greater in IBA-treated shoots than in control shoots. In extracts of the basal parts of the shoots, the concentration of free IAA showed a significant peak 2 d after either root inductive method and a subsequent gradual decrease for the remainder of the time course. The concentration of IAAsp peaked at day 6 in extracts of the basal parts of shoots induced with 14.8-μM IBA for 5 d, whereas shoots induced by dipping showed an initial increase until day 2 and then remained stable. In extracts from basal shoot portions induced by dipping, IBA concentration showed a transient peak at day 1 and a plateau between day 2 and 4, in contrast to the profile of shoots induced on auxin-containing medium, which showed a significant reduction between 4 and 6 d after transferred to auxin-free medium. All quantified auxins remained at a relatively low level, virtually constant, in extracts from apical shoot portions, as well as in extracts from control non-rooting shoots. In conclusion, the natural auxin IAA is the signal responsible for root induction, although it is driven by exogenous IBA independently of the adding conditions.

Effects of Exogenous Indole Butyric Acid and Callus Formation on the Anti‐oxidant Activity, Total Phenolic, and Anthocyanin Constituents of Mulberry Cuttings

AbstractIn order to evaluate the effects of exogenous indole butyric acid (IBA) and callus formation on the anti‐oxidant activity, total phenolics, and anthocyanin constituents of Morus nigra L. and M. alba L. cuttings, we investigated the variations before and after the treatment. The results indicate that anti‐oxidant ability, total phenolic, and anthocyanin constituents of the callus stems of both Morus species were higher than those of non‐callus forming species. There were also increases observed in anti‐oxidant ability, total phenolic, and anthocyanin constituents of calli treated with IBA (1 000–3 000 mg/L).(Managing editor: Wei Wang)