Exogenous Auxin Research Articles

A DII Domain-Based Auxin Reporter Uncovers Low Auxin Signaling during Telophase and Early G1.

A sensitive and dynamically responsive auxin signaling reporter based on the DII domain of the INDOLE-3-ACETIC ACID28 (IAA28, DII) protein from Arabidopsis (Arabidopsis thaliana) was modified for use in maize (Zea mays). The DII domain was fused to a yellow fluorescent protein and a nuclear localization sequence to simplify quantitative nuclear fluorescence signal. DII degradation dynamics provide an estimate of input signal into the auxin signaling pathway that is influenced by both auxin accumulation and F-box coreceptor concentration. In maize, the DII-based marker responded rapidly and in a dose-dependent manner to exogenous auxin via proteasome-mediated degradation. Low levels of DII-specific fluorescence corresponding to high endogenous auxin signaling occurred near vasculature tissue and the outer layer and glume primordia of spikelet pair meristems and floral meristems, respectively. In addition, high DII levels were observed in cells during telophase and early G1, suggesting that low auxin signaling at these stages may be important for cell cycle progression.

Shading of stock plants and the use of auxin in red pitaya cuttings

Although there has been a significant expansion of red pitaya cultivation in Brazil and other countries around the world, its cultivation requires scientific expertise to identify the plant production systems best suited to Brazilian soils and climate. Therefore, this study aimed to evaluate the effect of exogenous auxin and shading of the parental stock plants on the subsequent quality of red pitaya cuttings. The use of a commercial rooting auxin (with and without) and five shading levels on stock plants (full sun, 35, 50, 65 and 80% shading) were tested via four randomized blocks in a factorial 2x5 scheme with two plants per plot. After 90 days, the following vegetative characteristics were evaluated: length of the longest root (LR), root dry mass (RDM), root width (RW), shoot fresh weight (SFW) and shoot dry weight (SDW), total dry weight (TDW), number of axillary shoots (NAS), sum of the length of the axillary shoots (SLAS), and shoot:root ratio (SRR). We concluded that for the production of high quality plants, collecting cuttings from stock plants grown in full sun or 80% shade is recommended, eliminating the need to use commercial rooting auxin.

EgHOX1, a HD-Zip II gene, is highly expressed during early oil palm (Elaeis guineensis Jacq.) somatic embryogenesis

The embryogenesis rate in oil palm tissue culture still averages at a low 6%. Hence, a better understanding of the regulatory mechanisms during somatic embryogenesis and identification of molecular markers may help to improve the oil palm cloning process. EgHOX1, a previously isolated cold plaque clone, was further characterized and identified to be a putative HD-Zip II gene. High levels of EgHOX1 transcripts were detected in early tissue culture stages involving embryogenesis induction. Transcripts accumulated preferentially in meristematic centers of embryogenic callus and then in the provascular regions of developing somatic embryos. EgHOX1 was modestly induced by exogenous auxin and highly induced by dehydration and osmotic stresses. However, its expression was down-regulated by light. Based on its expression patterns, this novel oil palm HD-Zip II gene may be involved during the acquisition of embryogenic competency in early somatic embryogenesis and in vascular development later on, similar to the roles of some HD-Zip genes in other plants.

Characterization and Expression Analysis of PbCS1 Gene Regulated by Iron Deficiency and Involved in Response to Auxin in Pyrus betulifolia

Iron (Fe) is an essential micronutrient required by all fruit trees. To elucidate the regulatory mechanism of auxin to the long-distance transport of Fe, a gene encoding a putative CS protein was isolated from Pyrus betulifolia. This gene was designated as PbCS1 containing 1 422 bp in length with an open reading frame encoding a protein of 473 amino acids with a predicted molecular mass of 52.69 ku and a theoretical isoelectric point of 6.91. The deduced PbCS1 protein contained a conserved CS domain and WPNVDAHS sequence existing in the PWPN-box. Based on its conserved domain and phylogenetic status, the PbCS1 should be grouped into type-Ⅰ subfamily of plant CS. Quantitative real-time PCR results indicated that the PbCS1 expression was enriched in leaves, roots and phloem, but relatively weak in xylem. Using split root systems, Fe deficiency in one portion of the root system could induce dramatic up-regulation of the PbCS1 expression in the Fe-sufficient part, suggesting that the PbCS1 expression was activated by systemic signals. In addition, supplying with NAA and exogenous auxin to the de-topped shoots could recover the Fe deficiency-induced up-regulation of the PbCS1 expression in the Fe-sufficient part of the root system. In contrast, NPA (an auxin transport inhibitor) application to the shoot tips arrested up-regulation of the PbCS1 expression in the untreated portion. The results suggested that Fe-deficiency-induced alterations of the PbCS1 expression were mediated by auxin.

Transcription of TIR1-Controlled Genes Can be Regulated within 10 Min by an Auxin-Induced Process. Can TIR1 be the Receptor?

ABP1 and TIR1/AFBs are known as auxin receptors. ABP1 is linked to auxin responses several of which are faster than 10 min. TIR1 regulates auxin-induced transcription of early auxin genes also within minutes. We use transcription of such TIR1-dependent genes as indicator of TIR1 activity to show the rapid regulation of TIR1 by exogenous auxin. To this end, we used quantification of transcription of a set of fifteen early auxin-induced reporter genes at t = 10 and t = 30 min to measure this as a TIR1-dependent auxin response. We conducted this study in 22 mutants of auxin transporters (pin5, abcb1, abcb19, and aux1/lax3), protein kinases and phosphatases (ibr5, npr1, cpk3, CPK3-OX, d6pk1, d6pkl1-1, d6pkl3-2, d6pkl1-1/d6pkl2-2, and d6pkl1-1/d6pkl3-2), of fatty acid metabolism (fad2-1, fad6-1, ssi2, lacs4, lacs9, and lacs4/lacs9) and receptors (tir1, tir1/afb2, and tir1/afb3) and compared them to the wild type. After 10 min auxin application, in 18 out of 22 mutants mis-regulated expression of at least one reporter was found, and in 15 mutants transcription of two-to-three out of five selected auxin reporter genes was mis-regulated. After 30 min of auxin application to mutant plants, mis-regulation of reporter genes ranged from one to 13 out of 15 tested reporter genes. Those genes chosen as mutants were themselves not regulated in their expression by auxin for at least 1 h, excluding an influence of TIR1/AFBs on their transcription. The expression of TIR1/AFB genes was also not modulated by auxin for up to 3 h. Together, this excludes a feedback or feedforward of these mutant genes/proteins on TIR1/AFBs output of transcription in this auxin-induced response. However, an auxin-induced response needed an as yet unknown auxin receptor. We suggest that the auxin receptor necessary for the fast auxin-induced transcription modulation could be, instead, ABP1. The alternative hypothesis would be that auxin-induced expression of a protein, initiated by TIR1/AFBs receptors, could initiate these responses and that this unknown protein regulated TIR1/AFB activities within 10 min.

Mutations in exocyst complex subunit SEC6 gene impaired polar auxin transport and PIN protein recycling in Arabidopsis primary root

Polar auxin transport, which is critical for land plant pattern formation and directional growth, is largely depended on asymmetric distribution of PIN proteins at the plasma membrane (PM). Endocytosis and recycling processes play important roles in regulating PIN protein distribution and abundance at the PM. Two subunits (SEC8, EXO70A1) of exocyst, an octameric vesicle-tethering complex, have been reported to be involved in PIN protein recycling in Arabidopsis. However, the function of exocyst complex in PIN protein recycling and polar auxin transport remains incompletely understood. In this study, we utilized two SEC6 down-regulation mutants (PRsec6-1 and PRsec6-2) to investigate the role of exocyst subunit SEC6 in the primary root development, polar auxin transport and PIN proteins recycling. We found that in PRsec6 mutants: 1. Primary root growth was retarded, and lateral root initiation were compromised. 2. Primary roots were sensitive to exogenous auxin 1-napthalene acetic acid (NAA) but not 2,4-dichlorophenoxy (2.4-D). 3. Recycling of PIN1 and PIN2 proteins from the Brefeldin A (BFA) compartment to the PM was delayed. 4. Vesicles accumulated in the primary root tip cells, especially accumulated in the cytosol closed to the PM. These results further demonstrated that the exocyst complex plays an important role in PIN protein recycling and polar auxin transport in Arabidopsis primary root.

1,3-di(benzo[d]oxazol-5-yl)urea acts as either adventitious rooting adjuvant or xylogenesis enhancer in carob and pine microcuttings depending on the presence/absence of exogenous indole-3-butyric acid

Asexual propagation in Ceratonia siliqua L. (carob), species of economic value, is difficult because of adventitious rooting recalcitrance. In Pinus radiata adventitious rooting of hypocotyl cuttings is enhanced by two urea-derivatives, 1,3-di(benzo[d]oxazol-5-yl)urea (5-BDPU) and 1,3-di(benzo[d]oxazol-6-yl)urea (6-BDPU), combined with exogenous indole-3-butyric acid (IBA). The research was aimed to define the role of these urea-derivatives in adventitious root (AR) formation of carob, and to identify morphogenic roles induced in carob, but also in pine, a distantly-related forest species. In carob, 5-BDPU (10 μM) highly promoted AR formation in combination with IBA (1 μM) when applied for 3 days, followed by a transfer onto hormone free medium (HF) up to culture end (4 weeks). IBA alone (1 μM) was more effective than IBA + kinetin (Kin, 10 nM), whereas Kin alone and 5-BDPU alone were not AR-inductive. The histological analysis showed that the cambial cells initiated the ARs, and similar numbers of AR-primordia were visible at day 12, independently of the AR-inductive treatment (i.e., IBA, IBA + 5-BDPU, IBA + Kin). No cutting treated with Kin alone, and rare HF (±5-BDPU)-treated ones, showed AR-primordia at day 12. The number of AR-forming explants increased under IBA + 5-BDPU. By contrast, the cambial cells were stimulated to initiate deuteroxylem instead of ARs under 5-BDPU alone. The histological analysis in pine microcuttings treated with IBA and/or 5-BDPU at the same concentrations confirmed that 5-BDPU applied alone enhanced xylogenesis, highlighting that this urea-derivative exhibits a dual morphogenic role being involved in the switching between adventitious rooting and xylogenesis depending on the presence of exogenous auxin in both species.

Comprehensive RNA-Seq Analysis on the Regulation of Tomato Ripening by Exogenous Auxin.

Auxin has been shown to modulate the fruit ripening process. However, the molecular mechanisms underlying auxin regulation of fruit ripening are still not clear. Illumina RNA sequencing was performed on mature green cherry tomato fruit 1 and 7 days after auxin treatment, with untreated fruit as a control. The results showed that exogenous auxin maintained system 1 ethylene synthesis and delayed the onset of system 2 ethylene synthesis and the ripening process. At the molecular level, genes associated with stress resistance were significantly up-regulated, but genes related to carotenoid metabolism, cell degradation and energy metabolism were strongly down-regulated by exogenous auxin. Furthermore, genes encoding DNA demethylases were inhibited by auxin, whereas genes encoding cytosine-5 DNA methyltransferases were induced, which contributed to the maintenance of high methylation levels in the nucleus and thus inhibited the ripening process. Additionally, exogenous auxin altered the expression patterns of ethylene and auxin signaling-related genes that were induced or repressed in the normal ripening process, suggesting significant crosstalk between these two hormones during tomato ripening. The present work is the first comprehensive transcriptome analysis of auxin-treated tomato fruit during ripening. Our results provide comprehensive insights into the effects of auxin on the tomato ripening process and the mechanism of crosstalk between auxin and ethylene.

Overexpression of wheat gene TaMOR improves root system architecture and grain yield in Oryza sativa.

Improved root architecture is an effective strategy to increase crop yield. We demonstrate that overexpression of transcription factor gene MORE ROOT (TaMOR) from wheat (Triticum aestivum L.) results in more roots and higher grain yield in rice (Oryza sativa). TaMOR, encoding a plant-specific transcription factor belonging to the ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) protein family, is highly conserved in wheat and its wild relatives. In this study, tissue expression patterns indicated that TaMOR mainly localizes to root initiation sites. The consistent gene expression pattern suggests that TaMOR is involved in root initiation. Exogenous auxin treatment induced TaMOR expression without de novo protein biosynthesis. Both in vivo and in vitro experiments demonstrated that TaMOR interacts with TaMOR-related protein TaMRRP, which contains a four-tandem-pentatricopeptide repeat motif. Overexpression of TaMOR led to more lateral roots in Arabidopsis thaliana, and TaMOR-overexpressing rice plants had more crown roots, a longer main panicle, a higher number of primary branches on the main panicle, a higher grain number per plant, and higher yield per plant than the plants of wild type. In general, TaMOR-D-overexpressing lines had larger root systems in Arabidopsis and rice, and produce a higher grain yield per plant. TaMOR therefore offers an opportunity to improve root architecture and increase yield in crop plants.

An Improved Method for Propagation of Seabuckthorn (Hippophae rhamnoides L.) by Cuttings

One year old growth stem cutting (2.9 ± 0.8 mm thickness), which is less than half of the conventional pencil thickness (7–8 mm) hardwood cutting, was studied for vegetative propagation of seabuckthorn (SBT). Rooting trial tested the effects of 14 media and 6 concentration of indole-3-butyric acid treatment. Over 94 % rooting was observed in all the media tested. The mean rooting percentage was 97.6 ± 2.2. Exogenous auxin treatments lack any benefit and rooting was over 97 % without hormonal treatment. Sevenfold more number of cuttings was obtained per plant as compared to pencil thickness hardwood cuttings, which is the conventional method of SBT propagation. The result of the present study could facilitate establishment of a vegetative propagation method wherein larger number of cuttings per plant can be propagated with higher rooting success rate without the need of exogenous application of rooting hormone.

English

The effect of exogenous auxins on the development of root system in cladodes of Opuntia ficus-indica was tested using different concentrations of indole butyric acid (lBA), naphthalene acetic acid (NAA) and a combination of IBA and NAA, and the control treated with 50% aqueous solution of ethanol. Results obtained showed that rooting in cladodes is most effective when treated with 2500 mg L-1 of IBA. A non-significant effect on rooting was observed when cladodes were treated with NAA alone or in combination with IBA. The development of O. ficus-indica in orchard and farmlands particularly in the dry Sudano-Sahelian zone of Nigeria would provide a valuable source of vegetarian food for humans and feed for livestock. Key words: Opuntia ficus-indica, rooting, cladodes, Indole butyric acid (IBA) Naphthalene acetic acid (NAA).

NCP1/AtMOB1A Plays Key Roles in Auxin-Mediated Arabidopsis Development

MOB1 protein is a core component of the Hippo signaling pathway in animals where it is involved in controlling tissue growth and tumor suppression. Plant MOB1 proteins display high sequence homology to animal MOB1 proteins, but little is known regarding their role in plant growth and development. Herein we report the critical roles of Arabidopsis MOB1 (AtMOB1A) in auxin-mediated development in Arabidopsis. We found that loss-of-function mutations in AtMOB1A completely eliminated the formation of cotyledons when combined with mutations in PINOID (PID), which encodes a Ser/Thr protein kinase that participates in auxin signaling and transport. We showed that atmob1a was fully rescued by its Drosophila counterpart, suggesting functional conservation. The atmob1a pid double mutants phenocopied several well-characterized mutant combinations that are defective in auxin biosynthesis or transport. Moreover, we demonstrated that atmob1a greatly enhanced several other known auxin mutants, suggesting that AtMOB1A plays a key role in auxin-mediated plant development. The atmob1a single mutant displayed defects in early embryogenesis and had shorter root and smaller flowers than wild type plants. AtMOB1A is uniformly expressed in embryos and suspensor cells during embryogenesis, consistent with its role in embryo development. AtMOB1A protein is localized to nucleus, cytoplasm, and associated to plasma membrane, suggesting that it plays roles in these subcellular localizations. Furthermore, we showed that disruption of AtMOB1A led to a reduced sensitivity to exogenous auxin. Our results demonstrated that AtMOB1A plays an important role in Arabidopsis development by promoting auxin signaling.

Improvement of adventitious root formation in flax using hydrogen peroxide

Flax (Linum usitatissimum L.) is an important crop for the production of oil and fiber. In vitro manipulations of flax are used for genetic improvement and breeding while improvements in adventitious root formation are important for biotechnological programs focused on regeneration and vegetative propagation of genetically valuable plant material. Additionally, flax hypocotyl segments possess outstanding morphogenetic capacity, thus providing a useful model for the investigation of flax developmental processes. Here, we investigated the crosstalk between hydrogen peroxide and auxin with respect to reprogramming flax hypocotyl cells for root morphogenetic development. Exogenous auxin induced the robust formation of adventitious roots from flax hypocotyl segments while the addition of hydrogen peroxide further enhanced this process. The levels of endogenous auxin (indole-3-acetic acid; IAA) were positively correlated with increased root formation in response to exogenous auxin (1-Naphthaleneacetic acid; NAA). Histochemical staining of the hypocotyl segments revealed that hydrogen peroxide and peroxidase, but not superoxide, were positively correlated with root formation. Measurements of antioxidant enzyme activities showed that endogenous levels of hydrogen peroxide were controlled by peroxidases during root formation from hypocotyl segments. In conclusion, hydrogen peroxide positively affected flax adventitious root formation by regulating the endogenous auxin levels. Consequently, this agent can be applied to increase flax regeneration capacity for biotechnological purposes such as improved plant rooting.

Physiological controls of chrysanthemum DgD27 gene expression in regulation of shoot branching.

DgD27 was cloned from D. grandiflorum for the first time and played an important role in shoot branching of chrysanthemum. Shoot branching plays an important role in determining plant architecture. D27 was previously proven to be involved in the strigolactone biosynthetic pathway in rice, Arabidopsis, and Medicago. To investigate the role of D27 in shoot branching of chrysanthemum, we isolated the D27 homolog DgD27. Functional analysis showed that DgD27 was a plastid-localized protein that restored the phenotype of Arabidopsis d27-1. Gene expression analysis revealed that DgD27 was expressed at the highest levels in stem, and was up-regulated by exogenous auxin. Decapitation could down-regulate DgD27 expression, but this effect could be restored by exogenous auxin. DgD27 expression was significantly down-regulated by dark treatment in axillary buds. In addition, DgD27 transcripts produced rapid responses in shoots and roots under conditions of phosphate absence, but only mild variation in responses in buds, stems, and roots with low nitrogen treatment. DgBRC1 transcripts also showed the same response in buds under low nitrogen conditions. Under phosphate deficiency, indole-3-acetic acid (IAA) levels increased, zeatin riboside levels decreased, and abscisic acid (ABA) levels increased in the shoot, while both IAA and ABA levels increased in the shoot under low nitrogen treatments. Gibberellin acid levels were unaffected by phosphate deficiency and low nitrogen treatments. Taken together, these results demonstrated the diverse roles of DgD27 in response to physiological controls in chrysanthemum shoot branching.

Overexpression of an F-box protein gene disrupts cotyledon vein patterning in Arabidopsis

Plant vascular patterning is complex. However, the detailed molecular mechanism of vascular patterning is still unknown. In this study, FBXL, an Arabidopsis F-box motif gene, was isolated by using 3′ rapid amplification of cDNA ends (RACE) technique. The gene contained a coding sequence of 1407 nucleotides coding 468 amino acid residues. Amino acid sequence analysis revealed that the gene encoded a protein harboring an F-box motif at the N terminus, an LRRs motif in the middle, and an FBD motif at the C terminus. FBXL promoter-β-glucuronidase (GUS) and 35S promoter–FBXL vectors were constructed and transformed into Arabidopsis thaliana to understand the function of the FBXL gene. GUS expression analysis indicated that FBXL was specifically expressed in the vascular tissues of the root, stem, leaf, and inflorescence. FBXL overexpression in Arabidopsis displayed an abnormal venation pattern in cotyledons. Furthermore, FBXL expression was not induced by exogenous auxin and its transcript accumulation did not overlap with the distribution of endogenous auxin. These results suggested that FBXL may be involved in cotyledon vein patterning via auxin-independent pathway.

Exogenous auxin regulates multi-metabolic network and embryo development, controlling seed secondary dormancy and germination in Nicotiana tabacum L.

BackgroundAuxin was recognized as a secondary dormancy phytohormone, controlling seed dormancy and germination. However, the exogenous auxin-controlled seed dormancy and germination remain unclear in physiological process and gene network.ResultsTobacco seeds soaked in 1000 mg/l auxin solution showed markedly decreased germination compared with that in low concentration of auxin solutions and ddH2O. Using an electron microscope, observations were made on the seeds which did not unfold properly in comparison to those submerged in ddH2O. The radicle traits measured by WinRHIZO, were found to be also weaker than the other treatment groups. Quantified by ELISA, there was no significant difference found in β-1,3glucanase activity and abscisic acid (ABA) content between the seeds imbibed in gradient concentration of auxin solution and those soaked in ddH2O. However, gibberellic acid (GA) and auxin contents were significantly higher at the time of exogenous auxin imbibition and were gradually reduced at germination. RNA sequencing (RNA-seq), revealed that the transcriptome of auxin-responsive dormancy seeds were more similar to that of the imbibed seeds when compared with primary dormancy seeds by principal component analysis. The results of gene differential expression analysis revealed that auxin-controlled seed secondary dormancy was associated with flavonol biosynthetic process, gibberellin metabolic process, adenylyl-sulfate reductase activity, thioredoxin activity, glutamate synthase (NADH) activity and chromatin regulation. In addition, auxin-responsive germination responded to ABA, auxin, jasmonic acid (JA) and salicylic acid (SA) mediated signaling pathway (red, far red and blue light), glutathione and methionine (Met) metabolism.ConclusionsIn this study, exogenous auxin-mediated seed secondary dormancy is an environmental model that prevents seed germination in an unfavorable condition. Seeds of which could not imbibe normally, and radicles of which also could not develop normally and emerge. To complete the germination, seeds of which would stimulate more GA synthesis to antagonize the stimulation of exogenous auxin. Exogenous auxin regulates multi-metabolic networks controlling seed secondary dormancy and germination, of which the most important thing was that we found the auxin-responsive seed secondary dormancy refers to epigenetic regulation and germination to enhance Met pathway. Therefore, this study uncovers a previously unrecognized transcriptional regulatory networks and physiological development process of seed dormancy and germination with superfluous auxin signal activate.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0724-5) contains supplementary material, which is available to authorized users.

Chrysanthemum transcription factor CmLBD1 direct lateral root formation in Arabidopsis thaliana.

The plant-specific LATERAL ORGAN BOUNDARIES DOMAIN (LBD) genes are important regulators of growth and development. Here, a chrysanthemum class I LBD transcription factor gene, designated CmLBD1, was isolated and its function verified. CmLBD1 was transcribed in both the root and stem, but not in the leaf. The gene responded to auxin and was shown to participate in the process of adventitious root primordium formation. Its heterologous expression in Arabidopsis thaliana increased the number of lateral roots formed. When provided with exogenous auxin, lateral root emergence was promoted. CmLBD1 expression also favored callus formation from A. thaliana root explants in the absence of exogenously supplied phytohormones. In planta, CmLBD1 probably acts as a positive regulator of the response to auxin fluctuations and connects auxin signaling with lateral root formation.

Involvement of three annexin genes in the ripening of strawberry fruit regulated by phytohormone and calcium signal transduction.

Three annexin genes may be involved in the ripening progress of strawberry fruit. Phytohormones and calcium regulate the expressions of three annexin genes during strawberry fruit ripening. Plant annexins are multi-functional membrane- and Ca(2+)-binding proteins that are involved in various developmental progresses and stress responses. Three annexins FaAnn5a, FaAnn5b and FaAnn8 cDNA obtained from strawberry fruit encode amino acid sequences of approximately 35 kDa containing four annexin repeats, Ca(2+)-binding site, GTP-binding motif, peroxidase residue, and conserved amino acid residues of tryptophan, arginine and cysteine. During fruit development, the transcript levels of FaAnn5a and FaAnn5b increased while FaAnn5b declined after 3/4R stage. The expression patterns of annexins suggested their potential roles in strawberry fruit development and ripening. Expressions of annexin genes were also highly correlated with hormone levels. In addition, exogenous abscisic acid (ABA) enhanced the expressions of FaAnn5a and FaAnn8 while exogenous auxin (IAA) retarded it. However, both ABA and IAA promoted the transcript levels of FaAnn5b, indicating the independent regulation of annexins in fruit likely due to multi-functions of their large family. The responses of annexin genes to exogenous ABA and IAA inhibitors verified the involvement of annexins in plant hormone signaling. Besides, calcium restrained the expressions of FaAnn5s (FaAnn5a and FaAnn5b) but promoted the expression of FaAnn8. Effects of calcium and ethylene glycol tetraacetic acid (EGTA) on the transcript levels of annexins confirmed that calcium likely mediated hormone signal transduction pathways, which helped to elucidate the mechanism of calcium in fruit ripening. Therefore, FaAnn5s and FaAnn8 might be involved in plant hormones' regulation in the development and ripening of strawberry fruit through calcium signaling in the downstream.

Rooting response of Prunus domestica L. microshoots in the presence of phytoactive medium supplements

The study aimed at evaluating the response of common plum (Prunus domestica L.) microshoots during in vitro rooting in the presence of two phytoactive medium supplements, i.e. a dialyzate of pineapple pulp and a conditioned medium containing green algae Desmodesmus subspicatus exudates. Rooting efficiency was evaluated after 4 weeks of culture. During the root induction phase the content of phenolic compounds in shoot bases was determined and anatomical studies were conducted. Medium supplements were analyzed for the content of carbohydrates and phenolic acids. Both supplements were efficient in rooting induction of shoots of a difficult-to-root cultivar ‘Wegierka Zwykla’. Medium supplementation allowed a significant reduction in the exogenous auxin content required for rooting. The highest rooting efficiencies on supplemented media were 28.9 and 27.8 %, in comparison with 33.3 % obtained in the control medium with doubled concentration of exogenous auxins. In the easy-to-root plum cultivar ‘Wegierka Dąbrowicka’ the rooting rate was slightly reduced in the presence of pineapple dialyzate, while in the presence of algal conditioned medium the rooting rate decreased substantially compared with the non-supplemented medium. Approximately 30 % of ‘Wegierka Dąbrowicka’ shoots rooted on supplemented auxin-free media. The content of phenolic compounds accumulated in shoot bases during the root induction stage reflected the differences in rooting ability between both plum cultivars, indicating potential stressful conditions of the culture generated by the presence of phytoactive natural supplements. Anatomical study allowed to recognize the mode of dedifferentiation leading to adventitious rhizogenesis in the common plum. The results are discussed in relation to the composition of medium supplements and their potential root-promoting activity.

Impact of Auxins on Vegetative Propagation through Stem Cuttings of Couroupita guianensis Aubl.: A Conservation Approach.

The present study explores the potential of exogenous auxins in the development of adventitious shoots and roots from shoot cuttings of Couroupita guianensis (Nagalingam), a threatened tree. Experiments were conducted to assess the effect of various concentrations of auxins on shoot and root morphological traits of stem cuttings in the greenhouse. Amongst the auxins tested, significant effects on number of shoot buds' induction and their growth were observed with α-Naphthalene Acetic Acid (NAA) treated nodal cuttings. Cent percentage of the stem cuttings of C. guianensis were rooted and shoots were induced when pretreated with 400 mg L−1 NAA for 5 min. Maximum 79% of stem cuttings responded to pretreatment of 300 mg L−1indole-3-butyric acid (IBA) for 5 min, and 75% of stem cuttings induced shoots with 400 mg L−1indole-3-acetic acid (IAA). Presence of at least 5 nodes on stem cuttings was found to be prerequisite for root and shoot induction. About 92% of plants were survived under natural soil conditions raised from the stem cuttings. This is the first report of vegetative propagation of C. guianensis through stem cuttings which could be used for conservation strategy and sustainable utilization of this threatened medicinal tree.