Search

Drought is a major environmental stress factor that affects the growth and development of plants. All plants have to maintain the reactive oxygen species within certain levels for normal cellular homeostasis by means of their antioxidant systems, which can be classified as enzymatic and non-enzymatic. Plants under drought stress generate an excess production of reactive oxygen species. At high concentrations, this can be detrimental by producing damage to the protein structures and inhibiting enzymes, as well as oxidizing macromolecules, which may eventually lead to cell death. There has been increasing attention paid to the antioxidant capacity of aromatic/medicinal plants, with a high antioxidant content having been reported in some plant extracts, such as in Mentha piperita (peppermint). Peppermint plants cultivated under drought stress also present high levels of phenolic compounds, peroxidase enzyme activity and lipid peroxidation of membranes. A simple and inexpensive laboratory class is proposed for teaching some mechanisms that plants have evolved to avoid reactive oxygen species damage. The series of lab experiments described is aimed at demonstrating the antioxidant status in aromatic plants subjected to drought stress, by measuring total phenolic compound content (non-enzymatic antioxidant compound), peroxidase activity (enzymatic antioxidant) and malondialdehyde, as convenient biomarkers for lipid peroxidation. The proposed class will be carried out by undergraduate students of the advanced biochemistry course, as part of our biology and agronomy studies. The experiment presented is intended to be used as a vehicle to emphasize the concepts that students have learned in their lectures. This lab exercise to be carried out by the students has dual goals: to apply a methodology only learned superficially on previous courses, and also to increase their understanding of how plants developed resistance mechanisms in order to tolerate drought stress.

Secondary metabolites commonly play important physiological roles in plants and can be modified quantitatively and qualitatively by exposure to biotic and abiotic interactions. Plant growth promoting rhizobacteria (PGPR) and herbivory induce systemic resistance. In the present study, we analyzed the induction of secondary metabolites in peppermint plants in response to chewing insect herbivory on PGPR-inoculated Mentha piperita plants. The secondary metabolites of M. piperita plants were increased when plants were inoculated with PGPR and also exposed to caterpillar herbivory. It was found that the total essential oil yield in inoculated plants with insect damage was ~2.6-fold higher than in controls. The yield was similar to that of plants either damaged by insects or inoculated, indicating that there was no synergism. The same trend was observed for phenolic compounds. In contrast, VOC emissions were significantly higher in plants infested by insects, independent of whether they were inoculated. Insect damaged plants had 5.5 times higher monoterpene emissions than control plants, and ~ 2-fold higher emissions than on PGPR-inoculated plants without insects. To gain a better understanding of how herbivory on PGPR-inoculated plants can cause an increase in secondary metabolites of peppermint, we examined changes in plant defense hormones in inoculated plants after herbivory. We found that the combination of both treatments increased the endogenous jasmonic and salicylic acid levels to the same extent as in plants only inoculated or only insect-damaged. Because different interactions can alter the phytochemistry of plants such as M. piperita, this topic is both ecologically and economically relevant.

Plant growth-promoting rhizobacteria (PGPR) has a significant role in plant-insect interaction. However, the extent of their impact on insects is still not well understood. This investigation was designed to evaluate the role of inoculation with Bacillus amyloliquefaciens GB03 on sweet basil (Ocimum basilucum L.) in the development and nutritional parameters of Spodoptera frugiperda. In addition, the feeding preferences on inoculated and non-inoculated plants were assessed.Spodoptera frugiperda larvae reared with inoculated sweet basil leaves had a strong negative effect on the development of the insect, resulting in lower larval and pupal weights, and a longer period for larval-adult development. Moreover, adult emergence was reduced, but the relative consumption rate (RCR) value was unaffected, thereby revealing no alteration of the palatability. Growth rate and nutritional indicators, such as the efficiency of conversion of ingested food (ECI) and the efficiency of conversion of digested food (ECD), were reduced in larvae reared from treated plants. In the choice test, larvae avoided feeding on inoculated leaves.The higher occurrence of secondary metabolites in inoculated plants could have been the reason for the reduction of the plant nutritional rate and also for the food selection, since it has been previously reported that GB03 inoculated sweet basil increased the essential oil yield. Therefore, PGPR inoculation could be used as a growth promoter, making it a promising candidate for plant protection programs against insects in aromatic plant production. © 2021 Society of Chemical Industry.

We investigated the effects of microbial volatile organic compounds (mVOC) emitted by Bacillus amyloliquefaciens GB03on Mentha piperita growing under different levels of NaCl stress, by evaluating their growth-promoting potential and abilityto increase salt tolerance effects. Plants were exposed to bacterial VOCs without having any physical contact with therhizobacteria. The VOCs emitted by the rhizobacteria (mVOCs) were analyzed using SPME fibers. An increase in the levelof salt concentration led to a decrease in plant growth. However, these negative effects of salinity were inhibited in theplants exposed to mVOCs. Plants grown in a saline media and exposed to GB03 VOCs had significantly better morphologicalcharacteristics and higher total chlorophyll content compared to controls. The level of endogenous jasmonic acid (JA),salicylic acid, and abscisic acid increased in salt-stressed plants compared to controls. The level of JA did not show anychange in plants grown in a saline media either exposed to mVOCs or not. In contrast, the amount of salicylic acid increasedremarkably in salt-stressed plants exposed to mVOCs compared to controls (salt-stressed plants not exposed to mVOCs),but the levels of abscisic acid decreased in salt-stressed plants exposed to mVOCs. The chromatographic analyses of themVOCs produced by salt-stressed GB03 bacteria were similar, regardless of the concentration of salt in the media wherethe bacteria were grown, although it was observed that the relative percentage of acetoin increased with salt concentration.After determining that acetoin was the main VOCs compound, we exposed plants to acetoin, which demonstrated that acetoincaused similar effects on plants grown under salt stress conditions as those exposed to GB03 mVOCs. Based on these results,the use of mVOCs from PGPR is suggested as a useful technological innovation to facilitate the growth of M. piperita insalt-stressed environments. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Biotecnología Ambiental y Salud - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Cordoba. Instituto de Biotecnología Ambiental y Salud; Argentina Fil: Banchio, Erika. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Biotecnología Ambiental y Salud - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Cordoba. Instituto de Biotecnología Ambiental y Salud; Argentina

Salinity is a major abiotic stress factor that affects crops and has an adverse effect on plant growth. In recent years, there has been increasing evidence that microbial volatile organic compounds (mVOC) play a significant role in microorganism plant interactions. In the present study, we evaluated the impact of microbial volatile organic compounds (mVOC) emitted by Bacillus amyloliquefaciens GB03 on the biosynthesis of secondary metabolites and the antioxidant status in Mentha piperita L. grown under 0, 75 and 100 mM NaCl. Seedlings were exposed to mVOCs, avoiding physical contact with the bacteria, and an increase in NaCl levels produced a reduction in essential oil (EO) yield. Nevertheless, these undesirable effects were mitigated in seedlings treated with mVOCs, resulting in an approximately a six-fold increase with respect to plants not exposed to mVOCs, regardless of the severity of the salt stress. The main components of the EOs, menthone, menthol, and pulegone, showed the same tendency. Total phenolic compound (TPC) levels increased in salt-stressed plants but were higher in those exposed to mVOCs than in stressed plants without mVOC exposure. To evaluate the effect of mVOCs on the antioxidant status from salt-stressed plants, the membrane lipid peroxidation was analyzed. Peppermint seedlings cultivated under salt stress and treated with mVOC showed a reduction in malondialdehyde (MDA) levels, which is considered to be an indicator of lipid peroxidation and membrane damage, and had an increased antioxidant capacity in terms of DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity in relation to plants cultivated under salt stress but not treated with mVOCs. These results are important as they demonstrate the potential of mVOCs to diminish the adverse effects of salt stress. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Chiappero, Julieta. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Palermo, Tamara Belen. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Giordano, Walter Fabian. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Banchio, Erika. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina

The effects of plant inoculation with plant growth-promoting rhizobacteria (PGPR) and those resulting from the exogenous application of salicylic acid (SA) or methyl jasmonte (MeJA) on total phenolic content (TPC) and monoterpenes in Mentha x piperita plants were investigated. Although the PGPR inoculation response has been studied for many plant species, the combination of PGPR and exogenous phytohormones has not been investigated in aromatic plant species. The exogenous application of SA produced an increase in TPC that, in general, was of a similar level when applied alone as when combined with PGPR. This increase in TPC was correlated with an increase in the activity of the enzyme phenylalanine ammonia lyase (PAL). Also, the application of MeJA at different concentrations in combination with inoculation with PGPR produced an increase in TPC, which was more relevant at 4 mM, with a synergism effect being observed. With respect to the main monoterpene concentrations present in peppermint essential oil (EO), it was observed that SA or MeJA application produced a significant increase similar to that of the combination with rhizobacteria. However, when plants were exposed to 2 mM MeJA and inoculated, an important increase was produced in the concentration on menthol, pulegone, linalool, limonene, and menthone concentrations. Rhizobacteria inoculation, the treatment with SA and MeJA, and the combination of both were found to affect the amount of the main monoterpenes present in the EO of M. piperita. For this reason, the expressions of genes related to the biosynthesis of monoterpene were evaluated, with this expression being positively affected by MeJA application and PGPR inoculation, but was not modified by SA application. Our results demonstrate that MeJA or SA application combined with inoculation with PGPR constitutes an advantageous management practice for improving the production of secondary metabolites from M. piperita. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Santoro, Valeria Maricel. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Schmidt, Axel. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Gershenzon, Jonathan. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Banchio, Erika. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina

The effects of plant inoculation with plant growth-promoting rhizobacteria (PGPR) and those resulting from the exogenous application of salicylic acid (SA) or methyl jasmonte (MeJA) on total phenolic content (TPC) and monoterpenes in Mentha x piperita plants were investigated. Although the PGPR inoculation response has been studied for many plant species, the combination of PGPR and exogenous phytohormones has not been investigated in aromatic plant species. The exogenous application of SA produced an increase in TPC that, in general, was of a similar level when applied alone as when combined with PGPR. This increase in TPC was correlated with an increase in the activity of the enzyme phenylalanine ammonia lyase (PAL). Also, the application of MeJA at different concentrations in combination with inoculation with PGPR produced an increase in TPC, which was more relevant at 4 mM, with a synergism effect being observed. With respect to the main monoterpene concentrations present in peppermint essential oil (EO), it was observed that SA or MeJA application produced a significant increase similar to that of the combination with rhizobacteria. However, when plants were exposed to 2 mM MeJA and inoculated, an important increase was produced in the concentration on menthol, pulegone, linalool, limonene, and menthone concentrations. Rhizobacteria inoculation, the treatment with SA and MeJA, and the combination of both were found to affect the amount of the main monoterpenes present in the EO of M. piperita. For this reason, the expressions of genes related to the biosynthesis of monoterpene were evaluated, with this expression being positively affected by MeJA application and PGPR inoculation, but was not modified by SA application. Our results demonstrate that MeJA or SA application combined with inoculation with PGPR constitutes an advantageous management practice for improving the production of secondary metabolites from M. piperita.

Environmental stress represents a major limitation for increasing crop productivity and the use of natural resources. Most plants are exposed to various types of stress to different degrees and have an inherent ability to adapt to seasonal variations, but when they are subjected to drought and salinity stress, a series of morphological, physiological, biochemical and molecular changes occur. Moreover, both drought and salinity result in osmotic stress, which inhibits growth and causes disturbances at metabolic level. An effect of osmotic stress is the production of high levels of reactive oxygen species (ROS). At low concentrations, ROS are essential participants in cell signaling, but an excess generation of ROS results in toxicity, damaging macromolecules leading to cell death. To avoid the deleterious effects of ROS and adjust this imbalance, plants have evolved antioxidant systems that can be classified as enzymatic and non-enzymatic, and together, these preserve homeostasis in all cell compartments. In addition, oxidative stress can be measured indirectly following the formation of oxidative by-products of lipids, proteins, or nucleic acids, with malondialdehyde (MDA) being one of the most widely used markers. It has been observed that the negative effects on plant development caused by water stress can be mitigated by the use of PGPR (Plant Growth Promoting Rhizobacteria) microorganisms, which is an alternative technology for improving the capacity of tolerance to abiotic stress in plants. In the present review, by considering enzymatic and non-enzymatic responses, we elaborate on the role of PGPR in helping medicinal and aromatic plants to cope with osmotic stress through antioxidant defenses. This review paper also emphasizes a future research requirement involving investigating the combined utilization of osmotic stress and PGPR in order to enhance the content of secondary metabolites. In addition, this present review examines the antioxidant responses in MAPs subjected to osmotic stress and inoculated with PGPR, which have not been extensively reviewed before.

Plant growth-promoting rhizobacteria (PGPR) work primarily by improving the nutrient status of plants and increasing plants’ phytohormone production. Although this response has been demonstrated in many plant species, it is not well understood in aromatic plant species. To examine the effect of PGPR strains on the emission of volatile organic compounds (VOCs), total phenolic production and phenylalanine ammonia-lyase (PAL) activity, shoots of peppermint (Mentha piperita) plants were inoculated or co-inoculated with strains of beneficial rhizobacteria.VOC emissions for the inoculated groups were ∼3-fold higher than for controls. Co-inoculated plants produced the greatest increase in VOC emission in comparison to singly inoculated and control plants. The synthesis of phenolic compounds in leaves of all the treated plants was enhanced in comparison with controls; and higher activity of the PAL enzyme was observed in inoculated plants. In view of the economic importance of VOCs and phenolic compounds for a variety of applications in the food and cosmetic industries, P. fluorescens, B. subtilis and P. putida SJ04 have the potential to improve the productivity of cultivated aromatic plants. Better understanding of the processes that affect secondary metabolites accumulation will lead to increased yields of these commercially valuable natural products.

Plant growth promoting bacteria (PGPB)are agriculturally important soil bacteria that increase plant growth. We subjected peppermint to inoculation with three species of PGPB. After inoculation, the plants were sprayed with methyl jasmonate solution (MeJA)or SA (salicylic acid). Then, the plants were harvested and the plant growth parameters, trichome density, EO content and endogenous phytohormones were measured. Shoot fresh weight was reduced in plants inoculated and treated with MeJA whereas EO content varied depending on the MeJA concentration applied. Plants inoculated and treated with MeJA 2 mM showed the maximum increase in EO production, revealing a synergism between PGPB and MeJA. SA treatments also enhanced EO yield. The increased growth and EO production observed upon PGPB application were at least partly due to an increase in the JA and SA concentrations in the plant, as well as to an associated rise in the glandular trichome density. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Biotecnología Ambiental y Salud - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Cordoba. Instituto de Biotecnología Ambiental y Salud; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina Fil: Santoro, Valeria Maricel. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Schmidt, Axel. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Gershenzon, Jonathan. Instituto Max Planck Institut für Chemische Okologie; Alemania Fil: Banchio, Erika. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Biotecnología Ambiental y Salud - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Cordoba. Instituto de Biotecnología Ambiental y Salud; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina

Rhizobacteria that colonize plant roots and promote plant growth are referred to as plant growth-promoting rhizobacteria, and this can stimulate plant growth either indirectly or directly. Volatile organic compounds (VOCs) emitted by rhizobacteria have the capacity to promote plant growth as well as perform biocontrol of fungal pathogens. The microbial volatile organic compounds (mVOCs) are characterized by a low molecular weight and a high vapor pressure, which facilitate evaporation and diffusion at normal temperatures and at above-ground and below-ground pressures. mVOCs can travel far from the point of production through the atmosphere, porous soils and liquids, thereby making them ideal infochemicals for mediating interspecific interactions. However, knowledge about the biological and ecological roles of microbial VOCs is still limited compared with that of plant VOCs. Here, we describe a simple and inexpensive laboratory class aimed at biotechnology or soil microbiology students, which uses techniques to increase their understanding of the mechanisms of plant growth promoting rhizobacteria and also illustrate the effects of mVOCs emitted by rhizobacteria on plant growth promotion, as well as evaluating their potential as a biocontrol. The laboratory class is divided into two sessions: an initial 3-hour experimental session and a second 2-hour analytical one. The experimental session involves two separate experiments: one of which is dedicated to illustrating the effect of mVOCs on plant growth parameters, while the second explores the capacity of VOCs as a biocontrol. Also, the class provides students with an opportunity to perform useful assays, draw conclusions from their results, and discuss possible extensions of the study. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Chiappero, Julieta. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Banchio, Erika. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina

An experiment was conducted to investigate the effects of plant growth promoting rhizobacteria (PGPR) on Mentha piperita grown under drought stress. We performed root inoculation with strains of two PGPR species (Pseudomonas fluorescens WCS417 r and Bacillus amyloliquefaciens GB03) on peppermint plants and subjectedthem to moderate (MS) or severe drought stress (SS). To determine the growth-promoting potential and ability of PGPR to increase the drought tolerance in peppermint, different plant growth parameters were measured, along with the activities of antioxidant enzymes such as peroxidase (PX) and superoxide dismutase (SOD), as well as the non-enzymatic antioxidant proline and total phenolic content (TPC). In addition, to determine whether drought stress induces oxidative damage in peppermint, membrane lipid peroxidation was analyzed. An increment in the level of drought stress produced a reduction in plant growth, fresh weight, leaf number and leaf area. However, these negative effects of drought were mitigated in plants exposed to PGPR inoculation, resultingin significantly less reduction in the above growth traits related to plants not treated with PGPR, regardless of the severity of the drought treatment. In addition, drought-stressed plants treated with PGPR had a significantlyhigher total phenolic content than water-stressed plants without PGPR. Higher enzymatic activities were also observed in drought-stressed plants inoculated with PGPR. The proline content did not change in stressed plants, but inoculation reduced the amount of proline in the different stressed conditions tested. Membrane lipid peroxidation was also decreased in inoculated plants grown under drought conditions.These results are important as they illustrate the potential of PGPR to mitigate the adverse consequences of drought stress, and offer a way of increasing the tolerance of peppermint plants grown and TPC under water deficit conditions. Fil: Chiappero, Julieta. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Sosa Alderete, Lucas Gastón. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Palermo, Tamara Belen. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina Fil: Banchio, Erika. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Biotecnologia Ambiental y Salud. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Biotecnologia Ambiental y Salud.; Argentina

The effects of single inoculation and co-inoculation of two plant growth-promoting rhizobacteria (PGPR) (Pseudomonas fluorescens, Azospirillum brasilense) on growth and essential oil (EO) composition and phenolic content were evaluated in marigold (Tagetes minuta). Plant growth parameters (shoot fresh weight, root dry weight, leaf number, node number) were measured. EO yield increased 70% in P. fluorescens-inoculated and co-inoculated plants in comparison with control (non-inoculated) plants, without altering EO composition. The biosynthesis of the major EO components was increased in the inoculated plants. Shoot fresh weight and EO yield were significantly higher in P. fluorescens-inoculated and in co-inoculated plants than in control plants. The total phenolic content was 2-fold higher in singly-inoculated or co-inoculated treatments than in controls. In view of the economic importance of monoterpenes and phenolic compounds for a variety of applications in the food and cosmetic industries, P. fluorescens and other PGPR have clear potential for improving the productivity of cultivated aromatic plants. Better understanding of the processes that affect the accumulation of secondary metabolites will lead to increased yields of these commercially valuable natural products. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Santoro, Valeria Maricel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Nievas, Fiorela Lujan. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Giordano, Walter Fabian. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Banchio, Erika. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Many species or strains of the genus Pseudomonas have been characterized as plant growth promoting rhizobacteria (PGPR). We used a combination of phenotypic and genotypic techniques to analyze the community of fluorescent Pseudomonas strains in the rhizosphere of commercially grown Mentha piperita (peppermint). Biochemical techniques, Amplified rDNA Restriction Analysis (ARDRA), and 16S rRNA gene sequence analysis revealed that the majority of the isolated native fluorescent strains were P. putida. Use of two Repetitive Sequence-based PCR (rep-PCR) techniques, BOX-PCR and ERIC-PCR, allowed us to evaluate diversity among the native strains and to more effectively distinguish among them. PGPR activity was tested for the native strains and reference strain P. fluorescens WCS417r. Micropropagated M. piperita plantlets were exposed to microbial volatile organic compounds (mVOCs) emitted by the bacterial strains, and plant biomass parameters and production of essential oils (EOs) were measured. mVOCs from 11 of the native strains caused an increase in shoot fresh weight. mVOCs from three native strains (SJ04, SJ25, SJ48) induced changes in M. pierita EO composition. The mVOCs caused a reduction of metabolites in the monoterpene pathway, for example menthofuran, and an increase in menthol production. Menthol production is the primary indicator of EO quality. The mVOCs produced by native strains SJ04, SJ25, SJ48, and strain WCS417r were analyzed. The obtained mVOC chromatographic profiles were unique for each of the three native strains analyzed, containing varying hydrocarbon, aromatic, and alogenic compounds. The differential effects of the strains were most likely due to the specific mixtures of mVOCs emitted by each strain, suggesting a synergistic effect occurs among the compounds present.

Bacteria affect plant growth through several mechanisms. A recently described mechanism involves the production of microbial volatile organic compounds (mVOCs), which are gaseous molecules capable of interacting with plants in the soil environment. mVOCs may promote plant growth directly, through induced resistance systemic (ISR), or indirectly through suppression of phytopathogens (biocontrol). In this chapter, we describe several experimental designs for evaluation of mVOCs effects on plant growth, ISR or biocontrol mechanisms; potential problems with the methodologies and possible solutions. To date, relatively few mVOCs have been identified and their effects on plant growth characterized. Generally, the effect observed on a particular plant–bacterium interaction was attributed to the pool of mVOCs produced, like an evidence of synergism among chemical compounds.

Plant growth-promoting rhizobacteria (PGPR) are increasingly accepted and important in agricultural production worldwide. There is rising demand for food produced without synthetic chemical products, for sustainable agricultural methods, and for a holistic vision of development associated with environmental protection. In this study, we found that the effects of PGPR inoculation and volatile organic compound (VOC) emission on various aromatic plant species (Origanum majorana [sweet marjoram], Origanum x majoricum [Italian oregano], Ocimum basilicum [sweet basil], Tagetes minuta [wild marigold], Mentha x piperita [peppermint]) varied depending on the inoculated strain (Pseudomonas fluorescens WCS417r, Azospirillum brasilense Sp7, Bacillus subtilis GB03, or their combination). PGPR-inoculated plant species display host response specificity. The responses we observed were diverse. In most cases, the growth parameters evaluated (leaf number, shoot fresh weight, root dry weight) were significantly increased by P. fluorescens inoculation. Essential oil (EO) yield was increased to varying degrees in O. majorana, O. x majoricum, and T. minuta inoculated with P. fluorescens. Monoterpene accumulation was increased ~2-fold in most cases and 24-fold in O. majorana.

Plant growth-promoting rhizobacteria (PGPR) affect growth of host plants through various direct and indirect mechanisms. Three native PGPR (Pseudomonas putida) strains isolated from rhizospheric soil of a Mentha piperita (peppermint) crop field near Córdoba, Argentina, were characterised and screened in vitro for plant growth-promoting characteristics, such as indole-3-acetic acid (IAA) production, phosphate solubilisation and siderophore production, effects of direct inoculation on plant growth parameters (shoot fresh weight, root dry weight, leaf number, node number) and accumulation and composition of essential oils. Each of the three native strains was capable of phosphate solubilisation and IAA production. Only strain SJ04 produced siderophores. Plants directly inoculated with the native PGPR strains showed increased shoot fresh weight, glandular trichome number, ramification number and root dry weight in comparison with controls. The inoculated plants had increased essential oil yield (without alteration of essential oil composition) and biosynthesis of major essential oil components. Native strains of P. putida and other PGPR have clear potential as bio-inoculants for improving productivity of aromatic crop plants. There have been no comparative studies on the role of inoculation with native strains on plant growth and secondary metabolite production (specially monoterpenes). Native bacterial isolates are generally preferable for inoculation of crop plants because they are already adapted to the environment and have a competitive advantage over non-native strains. Fil: Santoro, Valeria Maricel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina Fil: Giordano, Walter Fabian. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina Fil: Banchio, Erika. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina

Plant growth-promoting rhizobacteria (PGPR) generally exert their effects through enhancement of plant nutrient status and/or phytohormone production. The effects of PGPR on aromatic plant species are poorly known. We measured plant growth parameters, chlorophyll content, trichome density, stomatal density, and levels of secondary metabolites in peppermint (Mentha piperita) seedlings inoculated with PGPR strains Bacillus subtilis GB03, Pseudomonas fluorescens WCS417r, P. putida SJ04, or a combination of WCS417r + SJ04. The treated plants, in comparison with controls, showed increases in shoot biomass, root biomass, leaf area, node number, trichome density, and stomatal density, and marked qualitative and quantitative changes in monoterpene content. Improved knowledge of the factors that control or affect biosynthesis of secondary metabolites and monoterpene accumulation will lead to strategies for improved cultivation and productivity of aromatic plants and other agricultural crops without the use of chemical fertilizers or pesticides. Fil: Cappellari, Lorena del Rosario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Santoro, Valeria Maricel. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Reinoso, Herminda Elmira. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Ciencias Naturales; Argentina Fil: Travaglia, Claudia Noemi. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Giordano, Walter Fabian. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Banchio, Erika. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina