RESUMEN
Oxidative protein folding in the endoplasmic reticulum (ER) depends on the coordinated action of protein disulfide isomerases and ER oxidoreductins (EROs). Strict dependence of ERO activity on molecular oxygen as the final electron acceptor implies that oxidative protein folding and other ER processes are severely compromised under hypoxia. Here, we isolated viable Arabidopsis thaliana ero1 ero2 double mutants that are highly sensitive to reductive stress and hypoxia. To elucidate the specific redox dynamics in the ER in vivo, we expressed the glutathione redox potential (EGSH) sensor Grx1-roGFP2iL-HDEL with a midpoint potential of -240 mV in the ER of Arabidopsis plants. We found EGSH values of -241 mV in wild-type plants, which is less oxidizing than previously estimated. In the ero1 ero2 mutants, luminal EGSH was reduced further to -253 mV. Recovery to reductive ER stress induced by dithiothreitol was delayed in ero1 ero2. The characteristic signature of EGSH dynamics in the ER lumen triggered by hypoxia was affected in ero1 ero2 reflecting a disrupted balance of reductive and oxidizing inputs, including nascent polypeptides and glutathione entry. The ER redox dynamics can now be dissected in vivo, revealing a central role of EROs as major redox integrators to promote luminal redox homeostasis.
Asunto(s)
Arabidopsis , Proteína Disulfuro Isomerasas , Arabidopsis/genética , Arabidopsis/metabolismo , Ditiotreitol , Retículo Endoplásmico/metabolismo , Estrés del Retículo Endoplásmico/genética , Glutatión/metabolismo , Hipoxia , Oxidación-Reducción , Oxígeno/metabolismo , Proteína Disulfuro Isomerasas/metabolismo , Pliegue de ProteínaRESUMEN
A large portion of eukaryotic genes are associated with noncoding, natural antisense transcripts (NATs). Despite sharing extensive sequence complementarity with their sense mRNAs, mRNA-NAT pairs elusively often evade dsRNA-cleavage and siRNA-triggered silencing. More surprisingly, some NATs enhance translation of their sense mRNAs by yet unknown mechanism(s). Here, we show that translation enhancement of the rice (Oryza sativa) PHOSPHATE1.2 (PHO1.2) mRNA is enabled by specific structural rearrangements guided by its noncoding antisense RNA (cis-NATpho1.2). Their interaction in vitro revealed no evidence of widespread intermolecular dsRNA formation, but rather specific local changes in nucleotide base pairing, leading to higher flexibility of PHO1.2 mRNA at a key high guanine-cytosine�(GC) regulatory region inhibiting translation, â¼350-nt downstream of the start codon. Sense-antisense RNA interaction increased formation of the 80S complex in PHO1.2, possibly by inducing structural rearrangement within this inhibitory region, thus making this mRNA more accessible to 60S. This work presents a framework for nucleotide resolution studies of functional mRNA-antisense pairs.
Asunto(s)
Oryza/genética , ARN sin Sentido/genética , ARN Mensajero/genética , ARN no Traducido/genética , Regulación de la Expresión Génica de las Plantas , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Biosíntesis de Proteínas , ARN Bicatenario , ARN Mensajero/química , ARN Mensajero/metabolismo , ARN no Traducido/químicaRESUMEN
BACKGROUND: Plant immunity relies on the perception of immunogenic signals by cell-surface and intracellular receptors and subsequent activation of defense responses like programmed cell death. Under certain circumstances, the fine-tuned innate immune system of plants results in the activation of autoimmune responses that cause constitutive defense responses and spontaneous cell death in the absence of pathogens. RESULTS: Here, we characterized the onset of leaf death 12 (old12) mutant that was identified in the Arabidopsis accession Landsberg erecta. The old12 mutant is characterized by a growth defect, spontaneous cell death, plant-defense gene activation, and early senescence. In addition, the old12 phenotype is temperature reversible, thereby exhibiting all characteristics of an autoimmune mutant. Mapping the mutated locus revealed that the old12 phenotype is caused by a mutation in the Lectin Receptor Kinase P2-TYPE PURINERGIC RECEPTOR 2 (P2K2) gene. Interestingly, the P2K2 allele from Landsberg erecta is conserved among Brassicaceae. P2K2 has been implicated in pathogen tolerance and sensing extracellular ATP. The constitutive activation of defense responses in old12 results in improved resistance against Pseudomonas syringae pv. tomato DC3000. CONCLUSION: We demonstrate that old12 is an auto-immune mutant and that allelic variation of P2K2 contributes to diversity in Arabidopsis immune responses.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Lectinas/genética , Lectinas/metabolismo , Resistencia a la Enfermedad/fisiología , Hojas de la Planta/metabolismo , Mutación , Proteínas Portadoras/genética , Fenotipo , Receptores Mitogénicos/genética , Receptores Mitogénicos/metabolismo , Pseudomonas syringae/metabolismo , Enfermedades de las Plantas/genética , Regulación de la Expresión Génica de las PlantasRESUMEN
Plants are aerobic organisms relying on oxygen to serve their energy needs. The amount of oxygen available to sustain plant growth can vary significantly due to environmental constraints or developmental programs. In particular, flooding stress, which negatively impacts crop productivity, is characterized by a decline in oxygen availability. Oxygen fluctuations result in an altered redox balance and the formation of reactive oxygen/nitrogen species (ROS/RNS) during the onset of hypoxia and upon re-oxygenation. In this update, we provide an overview of the current understanding of the impact of redox and ROS/RNS on low-oxygen signaling and adaptation. We first focus on the formation of ROS and RNS during low-oxygen conditions. Following this, we examine the impact of hypoxia on cellular and organellar redox systems. Finally, we describe how redox and ROS/RNS participate in signaling events during hypoxia through potential post-translational modifications (PTMs) of hypoxia-relevant proteins. The aim of this update is to define our current understanding of the field and to provide avenues for future research directions.
Asunto(s)
Oxidación-Reducción , Estrés Oxidativo , Oxígeno/metabolismo , Fenómenos Fisiológicos de las Plantas , Plantas/metabolismo , Transducción de Señal , Estrés FisiológicoRESUMEN
Plant response to environmental stimuli involves integration of multiple signals. Upon low-oxygen stress, plants initiate a set of adaptive responses to circumvent an energy crisis. Here, we reveal how these stress responses are induced by combining (i) energy-dependent changes in the composition of the acyl-CoA pool and (ii) the cellular oxygen concentration. A hypoxia-induced decline of cellular ATP levels reduces LONG-CHAIN ACYL-COA SYNTHETASE activity, which leads to a shift in the composition of the acyl-CoA pool. Subsequently, we show that different acyl-CoAs induce unique molecular responses. Altogether, our data disclose a role for acyl-CoAs acting in a cellular signaling pathway in plants. Upon hypoxia, high oleoyl-CoA levels provide the initial trigger to release the transcription factor RAP2.12 from its interaction partner ACYL-COA BINDING PROTEIN at the plasma membrane. Subsequently, according to the N-end rule for proteasomal degradation, oxygen concentration-dependent stabilization of the subgroup VII ETHYLENE-RESPONSE FACTOR transcription factor RAP2.12 determines the level of hypoxia-specific gene expression. This research unveils a specific mechanism activating low-oxygen stress responses only when a decrease in the oxygen concentration coincides with a drop in energy.
Asunto(s)
Acilcoenzima A/metabolismo , Adenosina Trifosfato/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Estrés Fisiológico , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/fisiología , Hipoxia de la Célula , Inhibidor de la Unión a Diazepam/metabolismo , Regulación de la Expresión Génica de las Plantas , Modelos Biológicos , Oxígeno/metabolismo , Transducción de SeñalRESUMEN
Hypoxia regularly occurs during plant development and can be induced by the environment through, for example, flooding. To understand how plant tissue physiology responds to progressing oxygen restriction, we aimed to monitor subcellular physiology in real time and in vivo. We establish a fluorescent protein sensor-based system for multiparametric monitoring of dynamic changes in subcellular physiology of living Arabidopsis thaliana leaves and exemplify its applicability for hypoxia stress. By monitoring cytosolic dynamics of magnesium adenosine 5'-triphosphate, free calcium ion concentration, pH, NAD redox status, and glutathione redox status in parallel, linked to transcriptional and metabolic responses, we generate an integrated picture of the physiological response to progressing hypoxia. We show that the physiological changes are surprisingly robust, even when plant carbon status is modified, as achieved by sucrose feeding or extended night. Inhibition of the mitochondrial respiratory chain causes dynamics of cytosolic physiology that are remarkably similar to those under oxygen depletion, highlighting mitochondrial electron transport as a key determinant of the cellular consequences of hypoxia beyond the organelle. A broadly applicable system for parallel in vivo sensing of plant stress physiology is established to map out the physiological context under which both mitochondrial retrograde signalling and low oxygen signalling occur, indicating shared upstream stimuli.
Asunto(s)
Arabidopsis/metabolismo , Citosol/metabolismo , Mitocondrias/metabolismo , Células Vegetales/metabolismo , Adenosina Trifosfato/metabolismo , Arabidopsis/citología , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Calcio/metabolismo , Carbono/metabolismo , Transporte de Electrón , Glutatión/metabolismo , Concentración de Iones de Hidrógeno , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , NAD/metabolismo , Oxígeno/metabolismo , Hojas de la Planta/citología , Hojas de la Planta/metabolismo , Plantas Modificadas GenéticamenteRESUMEN
Plants often face combinatorial stresses in their natural environment. Here, arsenic (As) toxicity was combined with hypoxia (Hpx) in the roots of Arabidopsis thaliana as it often occurs in nature. Arsenic inhibited growth of both roots and leaves, whereas root growth almost entirely ceased in Hpx. Growth efficiently resumed, and Hpx marker transcripts decreased upon reaeration. Compromised recovery from HpxAs treatment following reaeration indicated some persistent effects of combined stresses despite lower As accumulation. Root glutathione redox potential turned more oxidized in Hpx and most strongly in HpxAs. The more oxidizing root cell redox potential and the lowered glutathione amounts may be conducive to the growth arrest of plants exposed to HpxAs. The stresses elicited changes in elemental and transcriptomic composition. Thus, calcium, magnesium, and phosphorous amounts decreased in rosettes, but the strongest decline was seen for potassium. The reorganized potassium-related transcriptome supports the conclusion that disturbed potassium homeostasis contributes to the growth phenotype. In a converse manner, photosynthesis-related parameters were hardly affected, whereas accumulated carbohydrates under all stresses and anthocyanins under Hpx exclude carbohydrate limitation. The study demonstrates the existence of both synergistic since mutually aggravating effects and antagonistic effects of single and combined stresses.
Asunto(s)
Arabidopsis/efectos de los fármacos , Arsénico/toxicidad , Raíces de Plantas/efectos de los fármacos , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Glutatión/metabolismo , Oxidación-Reducción/efectos de los fármacos , Oxígeno/metabolismo , Fotosíntesis/efectos de los fármacos , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/crecimiento & desarrollo , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Transcriptoma/efectos de los fármacosRESUMEN
Metabolomics is one omics approach that can be used to acquire comprehensive information on the composition of a metabolite pool to provide a functional screen of the cellular state. Studies of the plant metabolome include analysis of a wide range of chemical species with diverse physical properties, from ionic inorganic compounds to biochemically derived hydrophilic carbohydrates, organic and amino acids, and a range of hydrophobic lipid-related compounds. This complexitiy brings huge challenges to the analytical technologies employed in current plant metabolomics programs, and powerful analytical tools are required for the separation and characterization of this extremely high compound diversity present in biological sample matrices. The use of mass spectrometry (MS)-based analytical platforms to profile stress-responsive metabolites that allow some plants to adapt to adverse environmental conditions is fundamental in current plant biotechnology research programs for the understanding and development of stress-tolerant plants. In this review, we describe recent applications of metabolomics and emphasize its increasing application to study plant responses to environmental (stress-) factors, including drought, salt, low oxygen caused by waterlogging or flooding of the soil, temperature, light and oxidative stress (or a combination of them). Advances in understanding the global changes occurring in plant metabolism under specific abiotic stress conditions are fundamental to enhance plant fitness and increase stress tolerance. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 35:620-649, 2016.
Asunto(s)
Espectrometría de Masas , Metabolómica , Plantas , Aminoácidos , MetabolomaRESUMEN
BACKGROUND: Reactive oxygen species (ROS) have emerged in recent years as important regulators of cell division and differentiation. SCOPE OF REVIEW: The cellular redox state has a major impact on cell fate and multicellular organism development. However, the exact molecular mechanisms through which ROS manifest their regulation over cellular development are only starting to be understood in plants. ROS levels are constantly monitored and any change in the redox pool is rapidly sensed and responded upon. Different types of ROS cause specific oxidative modifications, providing the basic characteristics of a signaling molecule. Here we provide an overview of ROS sensors and signaling cascades that regulate transcriptional responses in plants to guide cellular differentiation and organ development. MAJOR CONCLUSIONS: Although several redox sensors and cascades have been identified, they represent only a first glimpse on the impact that redox signaling has on plant development and growth. GENERAL SIGNIFICANCE: We provide an initial evaluation of ROS signaling cascades involved in cell differentiation in plants and identify potential avenues for future studies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.
Asunto(s)
Diferenciación Celular/fisiología , Meristema/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/fisiología , Proliferación Celular , Meristema/citología , Meristema/crecimiento & desarrollo , Modelos Biológicos , Oxidación-Reducción , Raíces de Plantas/citología , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Brotes de la Planta/citología , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/metabolismoRESUMEN
Senescence represents the final developmental act of the leaf, during which the leaf cell is dismantled in a coordinated manner to remobilize nutrients and to secure reproductive success. The process of senescence provides the plant with phenotypic plasticity to help it adapt to adverse environmental conditions. Here, we provide a comprehensive overview of the factors and mechanisms that control the onset of senescence. We explain how the competence to senesce is established during leaf development, as depicted by the senescence window model. We also discuss the mechanisms by which phytohormones and environmental stresses control senescence as well as the impact of source-sink relationships on plant yield and stress tolerance. In addition, we discuss the role of senescence as a strategy for stress adaptation and how crop production and food quality could benefit from engineering or breeding crops with altered onset of senescence.
Asunto(s)
Adaptación Biológica , Producción de Cultivos , Hojas de la Planta/fisiología , Producción de Cultivos/métodos , Calidad de los Alimentos , Fitomejoramiento/métodosRESUMEN
Early detection of salt stress is vital for plant survival and growth. Still, the molecular processes controlling early salt stress perception and signaling are not fully understood. Here, we identified salt-responsive ERF1 (SERF1), a rice (Oryza sativa) transcription factor (TF) gene that shows a root-specific induction upon salt and hydrogen peroxide (H2O2) treatment. Loss of SERF1 impairs the salt-inducible expression of genes encoding members of a mitogen-activated protein kinase (MAPK) cascade and salt tolerance-mediating TFs. Furthermore, we show that SERF1-dependent genes are H2O2 responsive and demonstrate that SERF1 binds to the promoters of MAPK kinase kinase6 (MAP3K6), MAPK5, dehydration-responsive element bindinG2A (DREB2A), and zinc finger protein179 (ZFP179) in vitro and in vivo. SERF1 also directly induces its own gene expression. In addition, SERF1 is a phosphorylation target of MAPK5, resulting in enhanced transcriptional activity of SERF1 toward its direct target genes. In agreement, plants deficient for SERF1 are more sensitive to salt stress compared with the wild type, while constitutive overexpression of SERF1 improves salinity tolerance. We propose that SERF1 amplifies the reactive oxygen species-activated MAPK cascade signal during the initial phase of salt stress and translates the salt-induced signal into an appropriate expressional response resulting in salt tolerance.
Asunto(s)
Oryza/metabolismo , Proteínas de Plantas/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/efectos de los fármacos , Cloruro de Sodio/farmacología , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Peróxido de Hidrógeno/farmacología , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Quinasas Quinasa Quinasa PAM/genética , Quinasas Quinasa Quinasa PAM/metabolismo , Microscopía Confocal , Modelos Genéticos , Datos de Secuencia Molecular , Mutación , Oryza/genética , Oryza/crecimiento & desarrollo , Oxidantes/farmacología , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Regiones Promotoras Genéticas/genética , Unión Proteica , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Tolerancia a la Sal/genética , Estrés Fisiológico/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Growth regulation is an important aspect of plant adaptation during environmental perturbations. Here, the role of MULTIPASS (OsMPS), an R2R3-type MYB transcription factor of rice, was explored. OsMPS is induced by salt stress and expressed in vegetative and reproductive tissues. Over-expression of OsMPS reduces growth under non-stress conditions, while knockdown plants display increased biomass. OsMPS expression is induced by abscisic acid and cytokinin, but is repressed by auxin, gibberellin and brassinolide. Growth retardation caused by OsMPS over-expression is partially restored by auxin application. Expression profiling revealed that OsMPS negatively regulates the expression of EXPANSIN (EXP) and cell-wall biosynthesis as well as phytohormone signaling genes. Furthermore, the expression of OsMPS-dependent genes is regulated by auxin, cytokinin and abscisic acid. Moreover, we show that OsMPS is a direct upstream regulator of OsEXPA4, OsEXPA8, OsEXPB2, OsEXPB3, OsEXPB6 and the endoglucanase genes OsGLU5 and OsGLU14. The multiple responses of OsMPS and its target genes to various hormones suggest an integrative function of OsMPS in the cross-talk between phytohormones and the environment to regulate adaptive growth.
Asunto(s)
Adaptación Fisiológica/genética , Regulación de la Expresión Génica de las Plantas , Oryza/crecimiento & desarrollo , Reguladores del Crecimiento de las Plantas/metabolismo , Proteínas de Plantas/metabolismo , Factores de Transcripción/metabolismo , Ácido Abscísico/metabolismo , Brasinoesteroides/metabolismo , Pared Celular/fisiología , Citocininas/metabolismo , Perfilación de la Expresión Génica , Giberelinas/metabolismo , Ácidos Indolacéticos/metabolismo , Oryza/genética , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Transducción de Señal , Cloruro de Sodio , Esteroides Heterocíclicos/metabolismo , Factores de Transcripción/genéticaRESUMEN
The balance between cellular proliferation and differentiation is a key aspect of development in multicellular organisms. Recent studies on Arabidopsis roots revealed distinct roles for different reactive oxygen species (ROS) in these processes. Modulation of the balance between ROS in proliferating cells and elongating cells is controlled at least in part at the transcriptional level. The effect of ROS on proliferation and differentiation is not specific for plants but appears to be conserved between prokaryotic and eukaryotic life forms. The ways in which ROS is received and how it affects cellular functioning is discussed from an evolutionary point of view. The different redox-sensing mechanisms that evolved ultimately result in the activation of gene regulatory networks that control cellular fate and decision-making. This review highlights the potential common origin of ROS sensing, indicating that organisms evolved similar strategies for utilizing ROS during development, and discusses ROS as an ancient universal developmental regulator.
Asunto(s)
Evolución Biológica , Crecimiento y Desarrollo , Especies Reactivas de Oxígeno/metabolismo , Animales , Diferenciación Celular , Proliferación Celular , Glutarredoxinas/metabolismo , Homeostasis , NADPH Oxidasas/metabolismo , Plantas/metabolismo , Proteínas/metabolismo , Transducción de Señal , Tiorredoxinas/metabolismo , Levaduras/metabolismoRESUMEN
Fluctuations in oxygen (O2) availability occur as a result of flooding, which is periodically encountered by terrestrial plants. Plant respiration and mitochondrial energy generation rely on O2 availability. Therefore, decreased O2 concentrations severely affect mitochondrial function. Low O2 concentrations (hypoxia) induce cellular stress due to decreased ATP production, depletion of energy reserves and accumulation of metabolic intermediates. In addition, the transition from low to high O2 in combination with light changes-as experienced during re-oxygenation-leads to the excess formation of reactive oxygen species (ROS). In this review, we will update our current knowledge about the mechanisms enabling plants to adapt to low-O2 environments, and how to survive re-oxygenation. New insights into the role of mitochondrial retrograde signaling, chromatin modification, as well as moonlighting proteins and mitochondrial alternative electron transport pathways (and their contribution to low O2 tolerance and survival of re-oxygenation), are presented.
RESUMEN
Understanding gene expression will require understanding where regulatory factors bind genomic DNA. The frequently used sequence-based motifs of protein-DNA binding are not predictive, since a genome contains many more binding sites than are actually bound and transcription factors of the same family share similar DNA-binding motifs. Traditionally, these motifs only depict sequence but neglect DNA shape. Since shape may contribute non-linearly and combinational to binding, machine learning approaches ought to be able to better predict transcription factor binding. Here we show that a random forest machine learning approach, which incorporates the 3D-shape of DNA, enhances binding prediction for all 216 tested Arabidopsis thaliana transcription factors and improves the resolution of differential binding by transcription factor family members which share the same binding motif. We observed that DNA shape features were individually weighted for each transcription factor, even if they shared the same binding sequence.
Asunto(s)
Arabidopsis/metabolismo , ADN/metabolismo , Factores de Transcripción/metabolismo , Arabidopsis/genética , Sitios de Unión , Biología Computacional , ADN/genética , Unión Proteica , Factores de Transcripción/genéticaRESUMEN
Root architecture responds to environmental stress. Stress-induced metabolic and nutritional changes affect the endogenous root development program. Transcriptional and translational changes realize the switch between stem cell proliferation and cell differentiation, lateral root or root hair formation and root functionality for stress acclimation. The current work explores the effects of stress combination of arsenic toxicity (As) and hypoxia (Hpx) on root development in Arabidopsis thaliana. As revealed previously, combined As and Hpx treatment leads to severe nutritional disorder evident from deregulation of root transcriptome and plant mineral contents. Both As and Hpx were identified to pose stress-specific constraints on root development that lead to unique root growth phenotype under their combination. Besides inhibition of root apical meristem (RAM) activity under all stresses, As induced lateral root growth while root hair density and lengths were strongly increased by Hpx and HpxAs-treatments. A dual stimulation of phosphate (Pi)-starvation response was observed for HpxAs-treated plant roots; however, the response under HpxAs aligned more with Hpx than As. Transcriptional evidence along with biochemical data suggests involvement of PHOSPHATE STARVATION RESPONSE 1; PHR1-dependent systemic signaling. Pi metabolism-related transcripts in close association with cellular iron homeostasis modulate root development under HpxAs. Early redox potential changes in meristematic cells, differential ROS accumulation in root hair zone cell layers and strong deregulation of NADPH oxidases, NADPH-dependent oxidoreductases and peroxidases signify a role of redox and ROS signaling in root architecture remodeling under HpxAs. Differential aquaporin expression suggests transmembrane ROS transport to regulate root hair induction and growth. Reorganization of energy metabolism through NO-dependent alternate oxidase, lactate fermentation, and phosphofructokinase seems crucial under HpxAs. TOR and SnRK-signaling network components were potentially involved in control of sustainable utilization of available energy reserves for root hair growth under combined stress as well as recovery on reaeration. Findings are discussed in context of combined stress-induced signaling in regulation of root development in contrast to As and Hpx alone.
RESUMEN
Beta-type Ti-based alloys are promising new materials for bone implants owing to their excellent mechanical biofunctionality and biocompatibility. For treatment of fractures in case of systemic diseases like osteoporosis the generation of implant surfaces which actively support the problematic bone healing is a most important aspect. This work aimed at developing suitable approaches for electrodeposition of Sr-substituted hydroxyapatite (Srx-HAp) coatings onto Ti-45Nb. Potentiodynamic polarization measurements in electrolytes with 1.67â¯mmol/L Ca(NO3)2, which was substituted by 0, 10, 50 and 100% Sr(NO3)2, and 1â¯mmol/L NH4H2PO4 at 333â¯K revealed the basic reaction steps for OH- and PO43- formation needed for the chemical precipitation of Srx-HAp. Studies under potentiostatic control confirmed that partial or complete substitution of Ca2+- by Sr2+-ions in solution has a significant effect on the complex reaction process. High Sr2+-ion contents yield intermediate phases and a subsequent growth of more refined Srx-HAp coatings. Upon galvanostatic pulse-deposition higher reaction rates are controlled and in all electrolytes very fine needle-like crystalline coatings are obtained. With XRD the incorporation of Sr-species in the hexagonal HAp lattice is evidenced. Coatings formed in electrolytes with 10 and 50% Sr-nitrate were chemically analyzed with EDX mapping and GD-OES depth profiling. Only a fraction of the Sr-ions in solution is incorporated into the Srx-HAp coatings. Therein, the Sr-distribution is laterally homogeneous but non-homogeneous along the cross-section. Increasing Sr-content retards the coating thickness growth. Most promising coatings formed in the electrolyte with 10% Sr-nitrate were employed for Ca, P and Sr release analysis in Tris-Buffered Saline (150â¯mM NaCl, pHâ¯7.6) at 310â¯K. At a sample surface: solution volume ratio of 1:200, after 24â¯h the amount of released Sr-ions was about 30-35% of that determined in the deposited Srx-HAp coating. In vitro studies with human bone marrow stromal cells (hBMSC) revealed that the released Sr-ions led to a significantly enhanced cell proliferation and osteogenic differentiation and that the Sr-HAp surface supported cell adhesion indicating its excellent cytocompatibility.
Asunto(s)
Aleaciones/química , Durapatita/química , Galvanoplastia/métodos , Estroncio/química , Aleaciones/efectos adversos , Durapatita/efectos adversos , Humanos , Células Madre Mesenquimatosas/citología , Células Madre Mesenquimatosas/efectos de los fármacosRESUMEN
During their lifetime, plants are frequently exposed to a variety of stresses which negatively impact on growth and vitality. In order to respond specifically to a given stress situation, integration of multiple signal inputs is of utmost importance. Recently, we demonstrated that recognition and adaptation to low-oxygen stress requires integration of signals from energy metabolism, lipid metabolism and oxygen availability. Low oxygen which results in an energy crisis causes a shift in lipid intermediate ratios. Binding of C18:1-CoA by ACYL-COA BINDING PROTEIN 1 (ACBP1) at the plasma membrane concomitantly leads to release and nuclear accumulation of the ERFVII transcription factor RELATED TO APETALA 2.12 (RAP2.12) which is central to the activation of anaerobic metabolism during stress. Moreover, RAP2.12 protein stability is oxygen-dependently regulated and its oxidation results in degradation by the N-end rule pathway. Here, we illuminate the concept of multiple-signal integration under hypoxia and discuss signal inputs merging at the ACBP1-ERFVII signaling hub.