Β-aminobutyric Acid Research Articles

Field Evaluation of Plant Defense Inducers for the Control of Citrus Huanglongbing

Huanglongbing (HLB) is currently the most economically devastating disease of citrus worldwide and no established cure is available. Defense inducing compounds are able to induce plant resistance effective against various pathogens. In this study the effects of various chemical inducers on HLB diseased citrus were evaluated in four groves (three with sweet orange and one with mandarin) in Florida (United States) for two to four consecutive growing seasons. Results have demonstrated that plant defense inducers including β-aminobutyric acid (BABA), 2,1,3-benzothiadiazole (BTH), and 2,6-dichloroisonicotinic acid (INA), individually or in combination, were effective in suppressing progress of HLB disease. Ascorbic acid (AA) and the nonmetabolizable glucose analog 2-deoxy-D-glucose (2-DDG) also exhibited positive control effects on HLB. After three or four applications for each season, the treatments AA (60 to 600 µM), BABA (0.2 to 1.0 mM), BTH (1.0 mM), INA (0.1 mM), 2-DDG (100 µM), BABA (1.0 mM) plus BTH (1.0 mM), BTH (1.0 mM) plus AA (600 µM), and BTH (1.0 mM) plus 2-DDG (100 µM) slowed down the population growth in planta of 'Candidatus Liberibacter asiaticus', the putative pathogen of HLB and reduced HLB disease severity by approximately 15 to 30% compared with the nontreated control, depending on the age and initial HLB severity of infected trees. These treatments also conferred positive effect on fruit yield and quality. Altogether, these findings indicate that plant defense inducers may be a useful strategy for the management of citrus HLB.

Beta-aminobutyric acid priming of plant defense: the role of ABA and other hormones.

Plants are exposed to recurring biotic and abiotic stresses that can, in extreme situations, lead to substantial yield losses. With the changing environment, the stress pressure is likely to increase and sustainable measures to alleviate the effect on our crops are sought. Priming plants for better stress resistance is one of the sustainable possibilities to reach this goal. Here, we report on the effects of beta-aminobutyric acid, a priming agent with an exceptionally wide range of action and describe its way of preparing plants to defend themselves against various attacks, among others through the modulation of their hormonal defense signaling, and highlight the special role of abscisic acid in this process.

BABA-primed defense responses to Phytophthora infestans in the next vegetative progeny of potato.

The transcript of the PR1 gene accumulation as an informative marker of systemic acquired resistance (SAR) was analyzed in β-aminobutyric acid (BABA) primed potato in the short-lasting (3 days) and long-lasting (28 days) time periods after induction and in the vegetative descendants of primed plants derived from tubers and from in vitro seedlings. BABA pretreatment resulted either in minimal or no PR1 gene expression, but sequential treatment with BABA followed by virulent Phytophthora infestans provided data on the imprint of post-stress information and its duration until fertilization, in the form of an enhanced PR1 transcript accumulation and a transient increase of basal resistance to the late blight disease. The primed state for defense of the susceptible potato cultivar was transmitted to its vegetative progeny as a potentiated PR1 mRNA accumulation following challenge inoculation. However, variation was observed between vegetative accessions of the BABA-primed potato genotype in responsiveness to disease. In contrast to plants derived from tubers, potato propagated through in vitro seedlings largely lost inducible resistance traits, although itretained primed PR1 gene expression.

β-aminobutyric acid mediated drought stress alleviation in maize (Zea mays L.).

The present study highlights the role of β-aminobutyric acid (BABA) in alleviating drought stress effects in maize (Zea mays L.). Chemical priming was imposed by pretreating 1-week-old plants with 600 μM BABA prior to applying drought stress. Specific activities of key antioxidant enzymes and metabolites (ascorbate and glutathione) levels of ascorbate-glutathione cycle were studied to unravel the priming-induced modulation of plant defense system. Furthermore, changes in endogenous ABA and JA concentrations as well as mRNA expressions of key genes involved in their respective biosynthesis pathways were monitored in BABA-primed (BABA+) and non-primed (BABA-) leaves of drought-challenged plants to better understand the mechanistic insights into the BABA-induced hormonal regulation of plant response to water-deficit stress. Accelerated stomatal closure, high relative water content, and less membrane damage were observed in BABA-primed leaves under water-deficit condition. Elevated APX and SOD activity in non-primed leaves found to be insufficient to scavenge all H2O2 and O2 (·-) resulting in oxidative burst as evident after histochemical staining with NBT and DAB. A higher proline accumulation in non-primed leaves also does not give much protection against drought stress. Increased GR activity supported with the enhanced mRNA and protein expressions might help the BABA-primed plants to maintain a high GSH pool essential for sustaining balanced redox status to counter drought-induced oxidative stress damages. Hormonal analysis suggests that in maize, BABA-potentiated drought tolerance is primarily mediated through JA-dependent pathway by the activation of antioxidant defense systems while ABA biosynthesis pathway also plays an important role in fine-tuning of drought stress response.

Resistance to Spongospora subterranea induced in potato by the elicitor β-aminobutyric acid

Induction of resistance in potato to Spongospora subterranea (which causes powdery scab on tubers) was studied in two controlled glasshouse experiments. β-aminobutyric acid (BABA) was applied at different concentrations (1, 2 or 4 mM) to potato plants which were then inoculated with S. subterranea. Amounts of the pathogen in roots and intensity of Spongospora root galling were assessed. Infection was measured at different times during plant growth, at 3 or 6 weeks after inoculation (first experiment), and 2, 4 or 6 weeks after inoculation (second experiment). In the first experiment, growth of plants was reduced in proportion to the BABA application rate, and the plants had high levels of S. subterranea infection. In the second experiment, at 4 weeks after inoculation, plants treated with BABA had less S. subterranea in their roots and fewer root galls compared with non-treated plants. Six weeks after inoculation, plants treated with 1 mM BABA developed S. subterranea infection, almost to the level of non-treated plants. In contrast, 2 and 4 mM BABA treatments greatly reduced the amount of S. subterranea in roots and numbers of root galls compared with non-treated plants. Repeated applications (at 2 weeks intervals) increased the effectiveness of BABA. A third test indicated that BABA was not directly toxic to S. subterranea resting spores. These results demonstrate that chemically induced resistance reduces host root infection by S. subterranea, and may have disease management potential. This is the first report of chemically induced host resistance to Spongospora.

Comparative effect of Nickel and beta-aminobutiric Acid on some Secondary Metabolits of Echium amoenum

Plants have a wonderful variety of secondary metabolites which may be change due to environmental factors and stress conditions. Considering the importance of Echium amoenum in Iranian traditional medicine, this study aimed to investigate the effect of abiotic stresses on the possibility of further production of secondary metabolites in the plant. In general, according our research findings, beta-aminobutyric acid increased growth indexes. Effect of BABA on secondary metabolites was different. BABA increased plant flavonoids but reduced the tannins. Numerous studies have pointed to the stress effects of this material at high concentrations but the concentrations used in this study increased the plant growth. Nickel in applied concentrations had no significant reduction in plant dry weight but increased the photosynthetic pigments. Ni increased plant flavonoids but reduced the tannins. Nickel and beta-aminobutyric acid at low concentrations, is recommended to use for greater production of secondary metabolites in Echium cultivation.DOI: http://dx.doi.org/10.3126/ijls.v9i5.12687

Priming for enhanced defense.

When plants recognize potential opponents, invading pathogens, wound signals, or abiotic stress, they often switch to a primed state of enhanced defense. However, defense priming can also be induced by some natural or synthetic chemicals. In the primed state, plants respond to biotic and abiotic stress with faster and stronger activation of defense, and this is often linked to immunity and abiotic stress tolerance. This review covers recent advances in disclosing molecular mechanisms of priming. These include elevated levels of pattern-recognition receptors and dormant signaling enzymes, transcription factor HsfB1 activity, and alterations in chromatin state. They also comprise the identification of aspartyl-tRNA synthetase as a receptor of the priming activator β-aminobutyric acid. The article also illustrates the inheritance of priming, exemplifies the role of recently identified priming activators azelaic and pipecolic acid, elaborates on the similarity to defense priming in mammals, and discusses the potential of defense priming in agriculture.

BABA and Phytophthora nicotianae Induce Resistance to Phytophthora capsici in Chile Pepper (Capsicum annuum).

Induced resistance in plants is a systemic response to certain microorganisms or chemicals that enhances basal defense responses during subsequent plant infection by pathogens. Inoculation of chile pepper with zoospores of non-host Phytophthora nicotianae or the chemical elicitor beta-aminobutyric acid (BABA) significantly inhibited foliar blight caused by Phytophthora capsici. Tissue extract analyses by GC/MS identified conserved change in certain metabolite concentrations following P. nicotianae or BABA treatment. Induced chile pepper plants had reduced concentrations of sucrose and TCA cycle intermediates and increased concentrations of specific hexose-phosphates, hexose-disaccharides and amino acids. Galactose, which increased significantly in induced chile pepper plants, was shown to inhibit growth of P. capsici in a plate assay.

Activity of the phenolic pathway’s enzymes influenced by resistance-inducing chemicals in tomato plant

Chemical elicitors, namely salicylic acid (SA), β-amino butyric acid (BABA), chitosan (CHT) and 2,6-dicholoroisonicotinic acid (INA), are known to play a role in the induction of plant resistance to pathogens by increasing the activity of enzymes of phenolic synthesis pathways such as peroxidase, polyphenol oxidase and phenyl alanine ammonia lyase. These chemical elicitors applied to tomato as an 8 h seed treatment, 2 h seedling treatment and seed plus seedling treatment increased the activity of peroxidase, polyphenol oxidase and phenyl alanine ammonia lyase. The highest increase in peroxidase and phenyl alanine ammonia lyase activity was induced by the seed plus seedling treatment with 15 mM β-amino butyric acid. The increase in these enzyme activities was 70.5% and 39.3% higher, respectively, over control, whereas the highest increase in polyphenol oxidase activity was induced by the seed plus seedling treatment with 1.5 mM salicylic acid. Polyphenol oxidase activity increased 137.9% compared to the non-treated control. Similarly, seed treatment as well as seedling treatment with the elicitors particularly salicylic acid, β-amino butyric acid and chitosan elicited increased activity of peroxidase, polyphenol oxidase and phenyl alanine ammonia lyase of the phenolic syntheses pathways, which are known to be the basic components of the resistance induction mechanism.

Transgenerational Inheritance in Plants of Acquired Defence Against Biotic and Abiotic Stresses: Implications and Applications

Angiosperm plants enjoy genetic mechanisms to establish and maintain the epigenetic methyl groups on cytosine residues at CG, CHG and CHH sites (where H = A, T or C) on genomic DNA. These epigenetic modifications are reversible and are erased and reset post-meiosis in gametes and post-fertilization in nascent embryos, at each generation. They control expression of genes for organ development and response to environment. Pathogens, sucking insects, temperature extremes, salinity, heavy metals, water or nutrient deficiency have been observed to cause genome-wide cytosine hypomethylation. The stress-primed DNA hypomethylation and so induced stress tolerant phenotype(s) are transmitted to subsequent generation(s). Like the biotic and abiotic stresses, certain plant metabolites, salicylic acid and β-aminobutyric acid, and DNA hypomethylation-inducing synthetic chemical azacytidine, are known to prime transgenerational systemic acquired stress resistance/tolerance. Genetic deficiency in RNA-dependent DNA methylation pathway, that establishes methylation marks on DNA, confers on the mutant plants pleiotropic phenotypes, including wide tolerance to stresses. Observations of resistance to priming by stress or non-transfer of the acquired adaptive phenotype to all the descendants or some of the descendants in the first and/or second generation progeny are explained. This may be genotype-specific effect or on account of insufficiency in exposure of gametes to stress or endogenous chemical signal(s) based on stress perception. Need for discovery of new chemicals for priming of stress resistance and of crop variety-wise priming procedures to elicit transgenerational stress resistance to produce epigenetically protected seeds is also emphasized.

β-Aminobutyric Acid-Induced Resistance Against Root-Knot Nematodes in Rice Is Based on Increased Basal Defense.

The nonprotein amino acid β-aminobutyric acid (BABA) is known to protect plants against various pathogens. The mode of action is relatively diverse and specific in different plant-pathogen systems. To extend the analysis of the mode of action of BABA to plant-parasitic nematodes in monocot plants, we evaluated the effect of BABA against the root-knot nematode (RKN) Meloidogyne graminicola in rice. BABA treatment of rice plants inhibited nematode penetration and resulted in delayed nematode and giant cell development. BABA-induced resistance (BABA-IR) was still functional in mutants or transgenics defective in salicylic acid biosynthesis and response or abscisic acid (ABA) response. Pharmacological inhibition of jasmonic acid (JA) and ethylene (ET) biosynthesis indicated that BABA-IR against rice RKN likely occurs independent of JA and ET. However, histochemical and biochemical quantification in combination with quantitative real-time reverse transcription-polymerase chain reaction data suggest that BABA protects rice against RKN through the activation of basal defense mechanisms of the plant, such as reactive oxygen species accumulation, lignin formation, and callose deposition.

Seed priming with BABA (β-amino butyric acid): a cost-effective method of abiotic stress tolerance in Vigna radiata (L.) Wilczek.

The effects of β-amino butyric acid (BABA) on abiotic stress tolerance potential of three Vigna radiata varieties were studied. The reduction in the growth of seedlings subjected to NaCl/polyethylene glycol (PEG) stress is alleviated by BABA seed priming, which also enhanced photosynthetic pigment content and photosynthetic and mitochondrial activities, and also modified the chlorophyll a fluorescence-related parameters. Moreover, BABA seed priming reduced malondialdehyde content in the seedlings and enhanced the accumulation of proline, total protein, total carbohydrate, nitrate reductase activity, and activities of antioxidant enzymes like guaiacol peroxidase and superoxide dismutase. Most of these positive features of BABA priming were predominantly exhibited when the plants were encountered with stress (NaCl/PEG). The BABA content in the BABA-treated green gram seeds and seedlings was also detected and quantified with high-performance thin layer chromatography (HPTLC), and it revealed that the priming effect of BABA initiated in seeds and further gets carried over to the seedlings. It was concluded that BABA seed priming improved the drought and salinity stress tolerance potential of all the three green gram varieties, and it was evident in the NaCl-tolerant variety Pusa Vishal as compared to Pusa Ratna (abiotic stress sensitive) and Pusa 9531(drought tolerant). Dual mode in cost effectiveness of BABA priming is evident from: (1) the positive features of priming are being exhibited more during the exposure of plants to stress, and (2) priming of seedlings can be carried out by BABA application to seeds at very low concentration and volume.

β-Aminobutyric acid increases drought tolerance and reorganizes solute content and water homeostasis in flax (Linum usitatissimum)

β-Aminobutyric acid (BABA) is a non-protein amino acid that induces drought tolerance in plants. The mechanisms involved in this tolerance are still poorly understood. In the present study, metabolomic and ionomic profiling performed in flax (Linum usitatissimum) leaves revealed that BABA induces a major reorganization in solute content. This reorganization resulted in increased accumulation of non-structural carbohydrates and proline and a decrease in inorganic solutes. This response has high similarities with that obtained when flax is exposed to an osmotic stress. BABA treatment also induced a decrease in osmotic potential and a change in water status of flax leaves. These modifications are accompanied by an improvement in drought tolerance.

Development of β-Amino Acid Dehydrogenase for the Synthesis of β-Amino Acids via Reductive Amination of β-Keto Acids

An l-erythro-3,5-diaminohexanoate dehydrogenase from Candidatus Cloacamonas acidaminovorans (3,5-DAHDHcca) was engineered to β-amino acid dehydrogenase (β-AADH) by screening a domain scanning mutagenesis library. The best β-AADH mutant displayed about 200-fold activity toward (R)-β-homomethionine compared with the wild-type enzyme. (R)-β-Homomethionine, (R)-β-phenylalanine, and (S)-β-aminobutyric acid were obtained via β-AADH-catalyzed reductive amination of the corresponding β-keto acids, which were generated from β-keto-nitriles or β-keto-esters with nitrilase or lipase. This is the first example of the direct reductive amination of β-keto acids catalyzed by β-AADH to give β-amino acids, opening a new venue for the synthesis of chiral β-amino acids.

Enhanced resistance of jujube (Zizyphus jujuba Mill. cv. Dongzao) fruit against postharvest Alternaria rot by β-aminobutyric acid dipping

Considerable losses of jujube (Zizyphus jujuba Mill. cv. Dongzao) fruit caused by Alternaria rot often occurred during storage. In order to evaluate effects of β-aminobutyric acid (BABA) on the infection on jujubes by Alternaria alternata, the fruit were dipped in BABA solutions and then inoculated with the pathogen. Results showed that BABA dipping at concentrations of 0.5, 1.0 and 2.0gL−1 significantly (P<0.05) reduced disease incidence and lesion area on the fruit inoculated with A. alternata, whereas BABA did not affect conidial germination and mycelial growth of the pathogen in vitro. In addition, BABA reduced natural infection and postharvest softening of jujubes during the storage at 0°C and 85–95% relative humidity. Biochemical evaluations revealed that BABA enhanced activities of defence-related enzymes including peroxidase, phenylalanine ammonia-lyase and chitinase of the fruit. BABA altered antioxidant metabolism to trigger disease resistance by significantly (P<0.05) decreasing catalase activity but increasing superoxide dismutase activity and ascorbic acid content in jujubes. These results suggested that the protective effects of BABA dipping on jujubes might be due to its ability on activating several highly coordinated defence-related responses of the fruit against infection, instead of its direct antifungal activity on the pathogen. These findings suggested that application of BABA would offer a promising approach for controlling postharvest disease and improving storage quality of horticultural products.

Proteomic analysis of elicitation of downy mildew disease resistance in pearl millet by seed priming with β-aminobutyric acid and Pseudomonas fluorescens.

The study is based on the comparative proteomic analysis between BABA and P. fluorescens mediated resistance in pearl millet, in response to downy mildew causing biotroph - S. graminicola. To our knowledge, this article is the first to report on seedling proteome of pearl millet whose genome is not yet sequenced. In addition, the study also provides clue for the plausible antagonistic cross-talk that might exist between jasmonic acid signaling and salicylic acid signaling in SAR and ISR mediated resistance by BABA and P. fluorescens against the downy mildew pathogen. Furthermore, pearl millet seedling proteome being perturbed by pathogen inoculation was more apparent than that caused by elicitor treatment, as revealed by multivariate statistics like PCA. Analysis by gene enrichment tools further revealed that the glucose metabolism pathway was majorly being affected in our study. This could be attributed to the essential balance that is being maintained in energy diversion towards stress and normal physiological process due to the priming effect of the elicitors against biotic stress.

The effect of β-aminobutyric acid (BABA) on root knot nematode and soft rot pathogen disease complexes in Solanum tuberosum plants

The efficacy of three elicitors, DL-β-aminobutyric acid (BABA), Acibenzolar-S-methyl (Bion) and Messenger (Harpin) on potato plants inoculated with Meloidogyne incognita second stage juveniles (J2s) was investigated in this study. The efficacy of each elicitor was evaluated based on galling index, egg numbers, total root knot nematode (RKN) population numbers, number of juveniles and the percentage of females in respective extracted populations per treatment at 28 and 56 dpi. There was a significant decrease in galling indices of all treated compared to untreated control plants. The highest percentage reduction was observed for 20 mM BABA-treated plants (33 %) followed by 5 mM BABA (23 %), 50 mg/l Bion (18 %), 100 mg/l Bion (15 %) and Messenger (8 %). The number of eggs extracted from plants treated with 20 mM BABA was significantly lower (66 %) compared to untreated controls. Furthermore, treating plants with 20 mM BABA decreased the total RKN population numbers by 55 % whilst the decrease observed for Bion and Messenger was between 24 and 39 %. Of the three tested elicitors, 20 mM BABA was found to be the most effective elicitor at both 28 and 56 dpi. Hence, it was selected for further testing against RKN and Pectobacterium carotovorum subsp. brasiliense (Pcb) disease complex. Efficacy was tested by comparing the colony forming units (cfu) of Pcb from treated and untreated control plants inoculated with M. incongita and Pcb simultaneously. The concentration of Pcb from untreated plants inoculated with both pathogens was significantly higher (3.3 × 103 cfu/ml) compared to their treated counterparts (8.71 × 102 cfu/ml). This suggests that BABA has the potential to decrease soft rot bacterial infections in RKN disease complexes by decreasing the rate of RKN infection. This is the first report where BABA is shown to decrease the infection rate of RKN as a primary causal agent in combination with a secondary pathogen.

B-Amino Butyric Acid ? Resistance Inducing Agent in Pearl Millet

β-amino butyric acid (BABA), applied as inducer of resistance to the seeds of susceptible cultivar of pearl millet [Pennisetum glaucum (L) R Br] against downy mildew [Sclerospora graminicola (Sacc) Schroet]. Infection offered protection to the host operative through vegetative and reproductive growth. Biochemical studies identified a close association between BABA-treatment and accumulation of defence-related proteins like phenylalanine ammonia lyase, peroxidise and β-1,3-glucanase. Studies on phenotypic host defence identified modifications in host cell wall leading to papillae formation with hydroxyproline-rich glycoproteins (HRGPs) as its major constituent. The HRGPs were identified as extensions by use of MAC 265 monoclonal antibodies. PgMPK4 (mitogen-activated protein kinase) was identified as the crucial signal transduction module signalling of pathogen cues. This increased accumulation of PgMPK4 mRNA and kinase activity in BABA-treated samples and further kinase inhibitor treatments providing critical evidence of PgMPK4 involvement in the JA- and SA mediated expression of defence genes, it may be assumed that BABA-induced resistance could be a JA/SA mediated phenomenon.

The pearl millet mitogen-activated protein kinase PgMPK4 is involved in responses to downy mildew infection and in jasmonic- and salicylic acid-mediated defense.

Plant mitogen-activated protein kinases (MPKs) transduce signals required for the induction of immunity triggered by host recognition of pathogen-associated molecular patterns. We isolated a full-length cDNA of a group B MPK (PgMPK4) from pearl millet. Autophosphorylation assay of recombinant PgMPK4 produced in Escherichia coli confirmed it as a kinase. Differential accumulation of PgMPK4 mRNA and kinase activity was observed between pearl millet cultivars 852B and IP18292 in response to inoculation with the downy mildew oomycete pathogen Sclerospora graminicola. This increased accumulation of PgMPK4 mRNA, kinase activity as well as nuclear-localization of PgMPK protein(s) was only detected in the S. graminicola resistant cultivar IP18292 with a ~tenfold peak at 9h post inoculation. In the susceptible cultivar 852B, PgMPK4 mRNA and immuno-detectable nuclear PgMPK could be induced by application of the chemical elicitor β-amino butyric acid, the non-pathogenic bacteria Pseudomonas fluorescens, or by the phytohormones jasmonic acid (JA) or salicylic acid (SA). Furthermore, kinase inhibitor treatments indicated that PgMPK4is involved in the JA- and SA-mediated expression of three defense genes, lipoxygenase, catalase 3 and polygalacturonase-inhibitor protein. These findings indicate that PgMPK/s contribute to pearl millet defense against the downy mildew pathogen by activating the expression of defense proteins.

Effect of β-aminobutyric acid on cell wall modification and senescence in sweet cherry during storage at 20 °C

The effects of postharvest β-aminobutyric acid (BABA) treatment on fruit firmness, pectin degrading enzymes, cell wall constituents and microstructural alterations of pericarp in sweet cherry fruit were investigated. BABA significantly delayed the decline of fruit firmness and inhibited the increase of membrane permeability and the accumulation of malondialdehyde in cherries. The BABA-treated fruit exhibited significantly higher contents of water-soluble pectin, CDTA-soluble pectin, Na2CO3-soluble pectin, total pectin, cellulose and hemicellulose than the control during storage. Activities of pectin degrading enzymes including polygalacturonase and pectinmethylesterase were markedly reduced by BABA treatment. Observations by scanning electron microscopy showed BABA maintained smooth cuticle and integrated structure of subepidermal cell in sweet cherry. These results suggest that the delay in fruit senescence by BABA may be due to depressed membrane permeability and malondialdehyde content, reduced activities of polygalacturonase and pectinmethylesterase, enhanced cell wall polysaccharides content, and integrated subepidermal cell structure in sweet cherry.