RESUMO
Drought stress is the most important stress factor for plants, being the main cause of agricultural crop loss in the world. Plants have developed complex mechanisms for preventing water loss and oxidative stress such as synthesis of abscisic acid (ABA) and non-enzymatic antioxidant compounds such as anthocyanins, which might help plants to cope with abiotic stress as antioxidants and for scavenging reactive oxygen species. A. chilensis (Mol.) is a pioneer species, colonizing and growing on stressed and disturbed environments. In this research, an integrated analysis of secondary metabolism in Aristotelia chilensis was done to relate ABA effects on anthocyanins biosynthesis, by comparing between young and fully-expanded leaves under drought stress. Plants were subjected to drought stress for 20 days, and physiological, biochemical, and molecular analyses were performed. The relative growth rate and plant water status were reduced in stressed plants, with young leaves significantly more affected than fully-expanded leaves beginning from the 5th day of drought stress. A. chilensis plants increased their ABA and total anthocyanin content and showed upregulation of gene expression when they were subjected to severe drought (day 20), with these effects being higher in fully-expanded leaves. Multivariate analysis indicated a significant positive correlation between transcript levels for NCED1 (9-cis-epoxycarotenoid dioxygenase) and UFGT (UDP glucose: flavonoid-3-O-glucosyltransferase) with ABA and total anthocyanin, respectively. Thus, this research provides a more comprehensive analysis of the mechanisms that allow plants to cope with drought stress. This is highlighted by the differences between young and fully-expanded leaves, showing different sensibility to stress due to their ability to synthesize anthocyanins. In addition, this ability to synthesize different and high amounts of anthocyanins could be related to higher NCED1 and MYB expression and ABA levels, enhancing drought stress tolerance.
Assuntos
Ácido Abscísico/biossíntese , Antocianinas/biossíntese , Magnoliopsida/metabolismo , Estresse Oxidativo , Folhas de Planta/metabolismo , Desidratação/metabolismoRESUMO
9-cis-epoxycarotenoid dioxygenase (NCED) encodes a key enzyme in abscisic acid (ABA) biosynthesis. Little is known regarding the regulation of stress response by NCEDs at physiological levels. In the present study, we generated transgenic tobacco overexpressing an NCED3 ortholog from citrus (CsNCED3) and investigated its relevance in the regulation of drought stress tolerance. Wild-type (WT) and transgenic plants were grown under greenhouse conditions and subjected to drought stress for 10 days. Leaf predawn water potential (Ψwleaf), stomatal conductance (gs), net photosynthetic rate (A), transpiration rate (E), instantaneous (A/E) and intrinsic (A/gs) water use efficiency (WUE), and in situ hydrogen peroxide (H2O2) and abscisic acid (ABA) production were determined in leaves of irrigated and drought-stressed plants. The Ψwleaf decreased throughout the drought stress period in both WT and transgenic plants, but was restored after re-watering. No significant differences were observed in gs between WT and transgenic plants under normal conditions. However, the transgenic plants showed a decreased (P ≤ 0.01) gs on the 4th day of drought stress, which remained lower (P ≤ 0.001) than the WT until the end of the drought stress. The A and E levels in the transgenic plants were similar to those in WT; therefore, they exhibited increased A/gs under drought conditions. No significant differences in A, E, and gs values were observed between the WT and transgenic plants after re-watering. The transgenic plants had lower H2O2 and higher ABA than the WT under drought conditions. Our results support the involvement of CsNCED3 in drought avoidance.
Assuntos
Dioxigenases/biossíntese , Nicotiana/fisiologia , Proteínas de Plantas/biossíntese , Ácido Abscísico/biossíntese , Adaptação Fisiológica , Citrus/enzimologia , Citrus/genética , Dioxigenases/genética , Dioxigenases/metabolismo , Secas , Folhas de Planta/enzimologia , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas/metabolismo , Estresse Fisiológico , Nicotiana/enzimologia , Nicotiana/genética , Nicotiana/metabolismoRESUMO
Plant responses to the environment and microorganisms, including arbuscular mycorrhizal fungi, involve complex hormonal interactions. It is known that abscisic acid (ABA) and ethylene may be involved in the regulation of arbuscular mycorrhiza (AM) and that part of the detrimental effects of ABA deficiency in plants is due to ethylene overproduction. In this study, we aimed to determine whether the low susceptibility to mycorrhizal colonization in ABA-deficient mutants is due to high levels of ethylene and whether AM development is associated with changes in the steady-state levels of transcripts of genes involved in the biosynthesis of ethylene and ABA. For that, tomato (Solanum lycopersicum) ethylene overproducer epinastic (epi) mutant and the ABA-deficient notabilis (not) and sitiens (sit) mutants, in the same Micro-Tom (MT) genetic background, were inoculated with Rhizophagus clarus, and treated with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The development of AM, as well as the steady-state levels of transcripts involved in ethylene (LeACS2, LeACO1 and LeACO4) and ABA (LeNCED) biosynthesis, was determined. The intraradical colonization in epi, not and sit mutants was significantly reduced compared to MT. The epi mutant completely restored the mycorrhizal colonization to the levels of MT with the application of 10 µM of AVG, probably due to the inhibition of the ACC synthase gene expression. The steady-state levels of LeACS2 and LeACO4 transcripts were induced in mycorrhizal roots of MT, whereas the steady-state levels of LeACO1 and LeACO4 transcripts were significantly induced in sit, and the steady-state levels of LeNCED transcripts were significantly induced in all genotypes and in mycorrhizal roots of epi mutants treated with AVG. The reduced mycorrhizal colonization in sit mutants seems not to be limited by ethylene production via ACC oxidase regulation. Both ethylene overproduction and ABA deficiency impaired AM fungal colonization in tomato roots, indicating that, besides hormonal interactions, a fine-tuning of each hormone level is required for AM development.
Assuntos
Ácido Abscísico/metabolismo , Etilenos/metabolismo , Fungos/crescimento & desenvolvimento , Micorrizas/crescimento & desenvolvimento , Solanum lycopersicum/metabolismo , Ácido Abscísico/biossíntese , Aminoácido Oxirredutases/antagonistas & inibidores , Etilenos/biossíntese , Glicina/análogos & derivados , Glicina/farmacologia , Liases/antagonistas & inibidores , Solanum lycopersicum/genética , Solanum lycopersicum/microbiologia , Micorrizas/metabolismo , Raízes de Plantas/microbiologiaRESUMO
The stress phytohormone abscisic acid (ABA) plays pivotal roles in plants' adaptive responses to adverse environments. Molybdenum cofactor sulfurases influence aldehyde oxidase activity and ABA biosynthesis. In this study, we isolated a novel EsMcsu1 gene encoding a molybdenum cofactor sulfurase from Eutrema salsugineum. EsMcus1 transcriptional patterns varied between organs, and its expression was significantly upregulated by abiotic stress or ABA treatment. Alfalfa plants that overexpressed EsMcsu1 had a higher ABA content than wild-type (WT) plants under drought stress conditions. Furthermore, levels of reactive oxygen species (ROS), ion leakage, and malondialdehyde were lower in the transgenic plants than in the WT plants after drought treatment, suggesting that the transgenic plants experienced less ROS-mediated damage. However, the expression of several stress-responsive genes, antioxidant enzyme activity, and osmolyte (proline and total soluble sugar) levels in the transgenic plants were higher than those in the WT plants after drought treatment. Therefore, EsMcsu1 overexpression improved drought tolerance in alfalfa plants by activating a series of ABA-mediated stress responses.
Assuntos
Ácido Abscísico/biossíntese , Adaptação Biológica , Brassicaceae/genética , Secas , Expressão Gênica , Medicago sativa/genética , Medicago sativa/metabolismo , Proteínas de Plantas/genética , Adaptação Biológica/genética , Sequência de Aminoácidos , Antioxidantes/metabolismo , Regulação da Expressão Gênica de Plantas , Dados de Sequência Molecular , Concentração Osmolar , Oxirredução , Fenótipo , Filogenia , Reguladores de Crescimento de Plantas/biossíntese , Proteínas de Plantas/química , Plantas Geneticamente Modificadas , Espécies Reativas de Oxigênio/metabolismo , Alinhamento de Sequência , Análise de Sequência de DNA , Estresse Fisiológico/genéticaRESUMO
The accumulation of putrescine (Put) and increased arginine decarboxylase (ADC, EC 4.1.1.19) activity levels in response to osmotic stress has been reported; however, the biological meaning of this increase remains unclear. To obtain new insights into these questions, we studied the drought response of a transgenic Lotus tenuis line that expresses the oat ADC gene, which is driven by the stress-inducible pRD29A promoter. This line contains high levels of Put with no changes in spermidine and spermine contents, even under water deficits. Our results indicate that the biochemical and morphological responses to dehydration correlate with the Put level and provide evidence that Put controls the ABA content in response to drought by modulating ABA biosynthesis at the transcriptional level.
Assuntos
Ácido Abscísico/biossíntese , Dioxigenases/metabolismo , Regulação da Expressão Gênica de Plantas , Lotus/metabolismo , Proteínas de Plantas/metabolismo , Putrescina/biossíntese , Transcrição Gênica , Arabidopsis/genética , Dioxigenases/genética , Secas , Potencial da Membrana Mitocondrial , Potenciais da Membrana , Osmose , Folhas de Planta/metabolismo , Proteínas de Plantas/genética , Raízes de Plantas/metabolismo , Caules de Planta/metabolismo , Plantas Geneticamente Modificadas , Prolina/química , Fatores de Tempo , ÁguaRESUMO
Aluminium (Al) toxicity and drought are two major factors limiting common bean (Phaseolus vulgaris) production in the tropics. Short-term effects of Al toxicity and drought stress on root growth in acid, Al-toxic soil were studied, with special emphasis on Al-drought interaction in the root apex. Root elongation was inhibited by both Al and drought. Combined stresses resulted in a more severe inhibition of root elongation than either stress alone. This result was different from the alleviation of Al toxicity by osmotic stress (-0.60 MPa polyethylene glycol) in hydroponics. However, drought reduced the impact of Al on the root tip, as indicated by the reduction of Al-induced callose formation and MATE expression. Combined Al and drought stress enhanced up-regulation of ACCO expression and synthesis of zeatin riboside, reduced drought-enhanced abscisic acid (ABA) concentration, and expression of NCED involved in ABA biosynthesis and the transcription factors bZIP and MYB, thus affecting the regulation of ABA-dependent genes (SUS, PvLEA18, KS-DHN, and LTP) in root tips. The results provide circumstantial evidence that in soil, drought alleviates Al injury, but Al renders the root apex more drought-sensitive, particularly by impacting the gene regulatory network involved in ABA signal transduction and cross-talk with other phytohormones necessary for maintaining root growth under drought.
Assuntos
Alumínio/toxicidade , Citocininas/biossíntese , Secas , Phaseolus/genética , Phaseolus/fisiologia , Estresse Fisiológico/efeitos dos fármacos , Estresse Fisiológico/genética , Ácido Abscísico/biossíntese , Vias Biossintéticas/efeitos dos fármacos , Vias Biossintéticas/genética , Parede Celular/efeitos dos fármacos , Parede Celular/genética , Colômbia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas/genética , Genótipo , Glucanos/metabolismo , Isopenteniladenosina/análogos & derivados , Isopenteniladenosina/metabolismo , Modelos Biológicos , Pressão Osmótica/efeitos dos fármacos , Phaseolus/efeitos dos fármacos , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/fisiologia , Plântula/efeitos dos fármacos , Plântula/crescimento & desenvolvimentoRESUMO
Isoprenoid compounds synthesised in the plastids are involved in plant response to water deficit. The functionality of the biosynthetic pathway of these compounds under drought stress has been analysed at the physiological and molecular levels in two related species of tomato (Solanum chilense and Solanum lycopersicum) that differ in their tolerance to abiotic challenge. Expression analysis of the genes encoding enzymes of these pathways (DXS, IPI, GGPPS, PSY1, NCED and HPT1) in plants at different RWC values shows significant differences for only GGPPS and HPT1, with higher expression in the tolerant S. chilense. Chlorophyll, carotenoids, α-tocopherol and ABA content was also determined in both species under different drought conditions. In agreement with HPT1 transcriptional activity, higher α-tocopherol content was observed in S. chilense than in S. lycopersicum, which correlates with a lower degree of lipoperoxidation in the former species. These results suggest that, in addition to lower stomatal conductance, α-tocopherol biosynthesis is part of the adaptation mechanisms of S. chilense to adverse environmental conditions.
Assuntos
Desidratação/fisiopatologia , Plastídeos/metabolismo , Solanum lycopersicum/genética , Solanum lycopersicum/metabolismo , alfa-Tocoferol/metabolismo , Ácido Abscísico/biossíntese , Adaptação Fisiológica , Carotenoides/biossíntese , Chile , Clorofila/biossíntese , Secas , Regulação da Expressão Gênica de Plantas , Genes de Plantas , Peroxidação de Lipídeos , Solanum lycopersicum/crescimento & desenvolvimento , Estômatos de Plantas/fisiologia , Plastídeos/genética , Solanum/genética , Solanum/metabolismo , Terpenos/metabolismo , Transcrição GênicaRESUMO
Glucose modulates plant metabolism, growth, and development. In Arabidopsis (Arabidopsis thaliana), Hexokinase1 (HXK1) is a glucose sensor that may trigger abscisic acid (ABA) synthesis and sensitivity to mediate glucose-induced inhibition of seedling development. Here, we show that the intensity of short-term responses to glucose can vary with ABA activity. We report that the transient (2 h/4 h) repression by 2% glucose of AtbZIP63, a gene encoding a basic-leucine zipper (bZIP) transcription factor partially involved in the Snf1-related kinase KIN10-induced responses to energy limitation, is independent of HXK1 and is not mediated by changes in ABA levels. However, high-concentration (6%) glucose-mediated repression appears to be modulated by ABA, since full repression of AtbZIP63 requires a functional ABA biosynthetic pathway. Furthermore, the combination of glucose and ABA was able to trigger a synergistic repression of AtbZIP63 and its homologue AtbZIP3, revealing a shared regulatory feature consisting of the modulation of glucose sensitivity by ABA. The synergistic regulation of AtbZIP63 was not reproduced by an AtbZIP63 promoter-5'-untranslated region::ß-glucuronidase fusion, thus suggesting possible posttranscriptional control. A transcriptional inhibition assay with cordycepin provided further evidence for the regulation of mRNA decay in response to glucose plus ABA. Overall, these results indicate that AtbZIP63 is an important node of the glucose-ABA interaction network. The mechanisms by which AtbZIP63 may participate in the fine-tuning of ABA-mediated abiotic stress responses according to sugar availability (i.e., energy status) are discussed.
Assuntos
Ácido Abscísico/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Fatores de Transcrição de Zíper de Leucina Básica/genética , Fatores de Transcrição de Zíper de Leucina Básica/metabolismo , Glucose/metabolismo , Regiões 5' não Traduzidas , Ácido Abscísico/biossíntese , Vias Biossintéticas , Regulação da Expressão Gênica de Plantas , Glucuronidase/genética , Glucuronidase/metabolismo , Hexoquinase/metabolismo , Regiões Promotoras Genéticas , Proteínas Serina-Treonina Quinases/metabolismo , Estabilidade de RNA , Transdução de Sinais , Transativadores/metabolismoRESUMO
This study was designed to isolate and characterize endophytic bacteria from sunflower (Helianthus annuus) grown under irrigation and water stress (drought) conditions, to analyze growth of isolated bacteria under drought condition, and to evaluate the ability of bacteria isolated from plants cultivated under drought to produce jasmonates (JAs) and abscisic acid (ABA). Bacteria were isolated from soil samples collected when sunflower plants were at the end of the vegetative stage. A total of 29 endophytic strains were isolated from plants grown under irrigation or drought condition. Eight strains (termed SF1 through SF8) were selected based on nitrogen-fixing ability. All eight strains showed positive catalase and oxidase activities; five strains (SF2, SF3, SF4, SF5, SF7) solubilized phosphates; none of the strains produced siderophores. Strains SF2, SF3, SF4, and SF5, the ones with the highest phosphate solubilization ability, strongly inhibited growth of the pathogenic fungi Verticillum orense and Sclerotinia sclerotiorum but had less inhibitory effect on Alternaria sp. Among the eight strains, SF2 showed 99.9% sequence homology with Achromobacter xiloxidans or Alcaligenes sp., while the other seven showed 99.9% homology with Bacillus pumilus. Strains SF2, SF3, and SF4 grown in control medium produced jasmonic acid (JA), 12-oxo-phytodienoic acid (OPDA), and ABA. These three strains did not differ in amount of JA or OPDA produced. ABA content was higher than that of JA, and production of both ABA and JA increased under drought condition. The characteristics of these isolated bacterial strains have technological implications for inoculant formulation and improved growth of sunflower crops.
Assuntos
Ácido Abscísico/biossíntese , Achromobacter/isolamento & purificação , Bacillus/isolamento & purificação , Ciclopentanos/metabolismo , Helianthus/microbiologia , Oxilipinas/metabolismo , Microbiologia do Solo , Ácido Abscísico/química , Achromobacter/classificação , Achromobacter/genética , Achromobacter/crescimento & desenvolvimento , Alternaria/crescimento & desenvolvimento , Alternaria/isolamento & purificação , Ascomicetos/crescimento & desenvolvimento , Bacillus/classificação , Bacillus/genética , Bacillus/crescimento & desenvolvimento , Biotecnologia/métodos , Meios de Cultura , Ciclopentanos/química , Desastres , Regulação da Expressão Gênica de Plantas , Helianthus/crescimento & desenvolvimento , Dados de Sequência Molecular , Oxilipinas/química , Controle Biológico de Vetores , Análise de Sequência de DNA , Verticillium/crescimento & desenvolvimentoRESUMO
The aim of this work was to evaluate phytohormone biosynthesis, siderophores production, and phosphate solubilization in three strains (E109, USDA110, and SEMIA5080) of Bradyrhizobium japonicum, most commonly used for inoculation of soybean and nonlegumes in USA, Canada, and South America. Siderophore production and phosphate solubilization were evaluated in selective culture conditions, which had negative results. Indole-3-acetic acid (IAA), gibberellic acid (GA(3)), and abscisic acid (ABA) production were analyzed by gas chromatography-mass spectrometry (GC-MS). Ethylene and zeatin biosynthesis were determined by GS-flame ionization detection and high-performance liquid chromatography (HPLC-UV), respectively. IAA, zeatin, and GA(3) were found in all three strains; however, their levels were significantly higher (p < 0.01) in SEMIA5080 (3.8 microg ml(-1)), USDA110 (2.5 microg ml(-1)), and E109 (0.87 microg ml(-1)), respectively. ABA biosynthesis was detected only in USDA110 (0.019 microg ml(-1)). Ethylene was found in all three strains, with highest production rate (18.1 ng ml(-1) h(-1)) in E109 cultured in yeast extract mannitol medium plus L-methionine. This is the first report of IAA, GA(3), zeatin, ethylene, and ABA production by B. japonicum in pure cultures, using quantitative physicochemical methodology. The three strains have differential capability to produce the five major phytohormones and this fact may have an important technological implication for inoculant formulation.