Plant Exudates Research Articles

Poor-Soil Rhizosphere Enriched with Different Microbial Activities Influence the Availability of Base Elements

Understanding the ecology of soil rhizosphere is essential to enhancing soil ecosystem and plants productivity. Poor-soil properties can limit rhizosphere microbial composition, interactions and plants productivity. Furthermore, the presence of plant exudates and microbial interation can change the rhizosphere dynamic. In the current study, we used two types of soils, rich nutrient soil represented by potting-soil and poor-soil represented with nutrient-deprived poor-soil. The two types of soil were inoculated with five microbial combinations using plant growth promoting bacteria (PGPB, Pseudomonas fluorescens) and mycorrhiza, and planted with two-day-old sorghum bicolor and Setaria italica (Foxtail millet) seedlings. Soil elements analyses were conducted 60 days after planting. The availability of exchangeable base alkali elements (Ca, Mg, Na) were measured and compared. Na was exclusively affected by PGPB inoculation in both soil types. Ca and Mg increased highest when associated with arbuscular inoculation, exclusively, in comparison to association with PGPB or Ectomycorrhiza in both soil types when planted with sorghum. Whereas, the same elements Ca and Mg, increased highest when associated with arbuscular mycorrhiza inoculation whether combined with PGPB or ectomycorrhiza when in soil planted with Setaria italica. The mycorrhiza increased Ca and Mg availability when combined with PGPB. Naincrease was associated only with PGPB inoculation solely in both soil types. The use of arbuscular mycorrhiza inoculation combined with PGPB is ecofriendly method to enrich rhizosphere in poor-soil and eliminate the need to use any chemical fertilizers.

Indole-3-acetic acid in plant–pathogen interactions: a key molecule for in planta bacterial virulence and fitness

The plant pathogenic bacterium Pseudomonas savastanoi, the causal agent of olive and oleander knot disease, uses the so-called “indole-3-acetamide pathway” to convert tryptophan to indole-3-acetic acid (IAA) via a two-step pathway catalyzed by enzymes encoded by the genes in the iaaM/iaaH operon. Moreover, pathovar nerii of P. savastanoi is able to conjugate IAA to lysine to generate the less biologically active compound IAA-Lys via the enzyme IAA-lysine synthase encoded by the iaaL gene. Interestingly, iaaL is now known to be widespread in many Pseudomonas syringae pathovars, even in the absence of the iaaM and iaaH genes for IAA biosynthesis.Here, two knockout mutants, ΔiaaL and ΔiaaM, of strain Psn23 of P. savastanoi pv. nerii were produced. Pathogenicity tests using the host plant Nerium oleander showed that ΔiaaL and ΔiaaM were hypervirulent and hypovirulent, respectively and these features appeared to be related to their differential production of free IAA. Using the Phenotype Microarray approach, the chemical sensitivity of these mutants was shown to be comparable to that of wild-type Psn23. The main exception was 8 hydroxyquinoline, a toxic compound that is naturally present in plant exudates and is used as a biocide, which severely impaired the growth of ΔiaaL and ΔiaaM, as well as growth of the non-pathogenic mutant ΔhrpA, which lacks a functional Type Three Secretion System (TTSS). According to bioinformatics analysis of the Psn23 genome, a gene encoding a putative Multidrug and Toxic compound Extrusion (MATE) transporter, was found upstream of iaaL. Similarly to iaaL and iaaM, its expression appeared to be TTSS-dependent. Moreover, auxin-responsive elements were identified for the first time in the modular promoters of both the iaaL gene and the iaaM/iaaH operon of P. savastanoi, suggesting their IAA-inducible transcription. Gene expression analysis of several genes related to TTSS, IAA metabolism and drug resistance confirmed the presence of a concerted regulatory network in this phytopathogen among virulence, fitness and drug efflux.

Influence of pulsing biocides on vase life of cut roses (<i>Rosa hybrida</i> L.)

The effects of pulsing solutions comprising biocides (1g Al2 (SO 4 ) 3 l-1, 0.4 ml HQS l-1, 0.6 ml NaOCl l-1, 0.6g Ca(ClO) 2 l-1), and tap water as control) on the vase life of rose ( Ro s a hybrida L. ) cut flower variety Upper Class which is Red colored intermediate flower was evaluated in laboratory experiment. The pulsing treatments were arranged in a CRD with four replications. The results depicted that treatments comprised NaOCl and HQS were able to prolong the vase life of the cut flower stalks up to 15.80 and 15.40 days respectively while Al 2 (SO 4 ) 3 did not offer statistically significant advantage over the use of ordinary tap water. Spectrometric analysis on solution turbidity of the vase solutions depicted the smallest value in cut flower stalks pulsed with NaOCl while the highest values were recorded in water, which is an indication of more bacterial proliferation or accumulation of plant exudates in the later cases. The amount of water passed through 5 cm long excised stem sections was the highest in stalks pulsed with Ca(ClO) 2 and NaOCl while the lowest was in those pulsed with Al| 2 (SO 4 ) 3 and water. Pulsing of the cut flower stalks with biocides also significantly increased vase solution uptake, and total soluble solid during vase life. The results of the present study clearly indicated significant improvement of the vase life of cut flower stalks by biocide pulsing treatment especially NaOCl and HQS. K e y words: Cut Flowers, Intermediate Rose, Hydraulic Conductance, Solution Uptake, Physiological Characteristics

Systemic enrichment of antifungal traits in the rhizosphere microbiome after pathogen attack

Summary Plant‐associated microbial communities are crucial for plant growth and play an important role in disease suppression. Community composition and function change upon pathogen attack, yet to date, we do not know whether these changes are a side effect of the infection or actively driven by the plant. Here, we used a split‐root approach to test whether barley plants recruit bacteria carrying antifungal traits upon infestation with Fusarium graminearum. Split‐root systems allow disentangling local infection effects, such as root damage, from systemic, plant‐driven effects on microbiome functionality. We assessed the recruitment of fluorescent pseudomonads, a taxon correlated with disease suppression, and of two well‐described antifungal genes (phlD coding for 2,4‐DAPG and hcnAB coding for HCN). We show an enrichment of fluorescent pseudomonads, phlD and hcnAB, upon pathogen infection. This effect was only measurable in the uninfected root compartment. We link these effects to an increased chemotaxis of pseudomonads towards exudates of infected plants. Synthesis. We conclude that barley plants selectively recruited bacteria carrying antifungal traits upon pathogen attack and that the pathogen application locally interfered with this process. By disentangling these two effects, we set the base for enhancing strategies unravelling how pathogens and plant hosts jointly shape microbiome functionality.

Does the combination of citrate and phytase exudation in Nicotiana tabacum promote the acquisition of endogenous soil organic phosphorus?

Plant acquisition of endogenous forms of soil phosphorus (P) could reduce external P requirements in agricultural systems. This study investigated the interaction of citrate and phytase exudation in controlling the accumulation of P and depletion of soil organic P by transgenic Nicotiana tabacum plants. N. tabacum plant lines including wild-type, vector controls, transgenic plants with single-trait expression of a citrate transporter (A. thaliana frd3) or fungal phytases (phyA: A. niger, P. lycii) and crossed plant lines expressing both traits, were characterized for citrate efflux and phytase exudation. Monocultures and intercropped combinations of single-trait plants were grown in a low available P soil (12 weeks). Plant biomass, shoot P accumulation, rhizosphere soil pH and citrate-extractable-P fractions were determined. Land Equivalent Ratio and complementarity effect was determined in intercropped treatments and multiple-linear-regression was used to predict shoot P accumulation based on plant exudation and soil P depletion. Crossed plant lines with co-expression of citrate and phytase accumulated more shoot P than single-trait and intercropped plant treatments. Shoot P accumulation was predicted based on phytase-labile soil P, citrate efflux, and phytase activity (Rsq=0.58, P < .0001). Positive complementarity occurred between intercropped citrate- and phytase-exuding plants, with the greatest gains in shoot P occurring in plant treatments with A. niger phyA expression. We show for the first time that trait synergism associated with the exudation of citrate and phytase by tobacco can be linked to the improved acquisition of P and the depletion of soil organic P.

Effects of Pyrene on Low Molecule Weight Organic Compounds in the Root Exudates of Five Species of Festuca

Phytoremediation is an important measure to remove organic pollutants from contaminated soil, and the root secretion of plant is considered to be closely related to the mechanisms of phytoremediation of organic pollutants. It is in favor of revealing the mechanisms of remediation by studying the characteristics of root exudates of plants with phytoremediation potential under the stress of pollutants. In the present research, pyrene and five species of Festuca which have been testified to be tolerant to pyrene stress were selected as studied objects. A soil-cultivating experiment with rhizobag technique was conducted to investigate the effects of pyrene on low molecule weight organic compounds in the root exudates of plant species under five concentration levels of pyrene (10.19, 20.32, 40.36, 79.94,and 160.68 mg·kg-1,denoted by C1, C2, C3, C4 and C5,respectively) on day 30, 40, 50, 60 and 70 of experiments. The results showed that the presence of vegetation significantly enhanced the dissipation of pyrene in the soil environment. This effect was especially marked with Festuca arundinacea, followed by those with Festuca mazzetiana, Festuca pubiglumis, and Festuca longiglumis, and that with Festuca stapfii was the lowest. During the whole experiments, the amounts of soluble sugar excreted by the five species of Festuca tested in root exudates were promoted with pyrene stress, then fluctuated with a stable trend along with the increase of stress concentration or the extension of stress period, which appeared to rise appreciably at relative low pyrene spiked (C1-C3) or earlier stress stage (30-40 d) and reduce at relative high pyrene spiked level (C3-C5) or later stress stage (40-70 d), and the highest amount of soluble sugars in root exudates occurred on day 50 of experiments with 40.36 mg·kg-1 pyrene treatment. The greater the phytoremediation potential of the plant species tested, the more obvious this trend wads. Compared with the control treatment (CK), pyrene stress promoted the root system of all five species of Festuca tested to release more low molecular weight organic acids, the stronger the restoration potential of plant species, the higher the concentration of pyrene stress under which the amount of organic acids in root exudates was increased to the peak value. Among the five species of Festuca tested, oxlic acid, acetic acid, lactic acid and malic acid were the main components of organic acids in root exudates, with a percentage of greater than 98.15% in all pyrene stress treatments, but there were traces of fumaric acid in the roots secretion of plant species with the stronger restoration potential. Data also indicated that 19 types of amino acids were found in root exudates of Festuca and the composition of amino acids in root exudates of Festuca was stable under all pyrene stress treatments, but the amino acid amount was different in root exudates under pyrene stress. The amount of all amino acids in those root exudates increased with increasing pyrene concentration, especially, the amount of threonine, serine, glycine, and alanine increased significantly among the 19 types of amino acids and the differences were significant among different treatments with different pyrene concentrations (P<0.05). However, proline, hydroxy proline and aspartic acid were always released in the form of functional group as a response to the pyrene stress, their contents soared quickly with the increase of stress concentration in soils, and the difference was significant among different treatments with different pyrene concentrations (P<0.05); the more the components of functional group participated in stress response, the stronger the restoration potential of plant species. These results indicated secretion characteristics of soluble sugar, low molecular weight organic acids and amino acids in the root system were closely related to their phytoremediation potential under the pyrene stress, the greater the phytoremediation potential, the more the amount of these low molecular weight secretions and the more complex these components, and the stronger the adaptability to polluted environment and the physiological plasticity to adapt to these contaminants.

Behavior and Ecology of the White-Footed Tamarin (Saguinus Leucopus) in a Fragmented Landscape of Colombia: Small Bodied Primates and Seed Dispersal in Neotropical Forests

Tamarins are small-bodied Neotropical primates that mainly feed on ripe fruits and insects, and supplement their diet with plant exudates, nectar, fungi and vertebrate prey. They are important seed dispersers in Neotropical forests as they are able to disperse a large number of small and medium-sized seeds from parental trees. In this paper, we describe the diet of the white-footed tamarin ( Saguinus leucopus) and its role as seed disperser in a fragmented landscape in Colombia. During a twelve month period, we collected data on activity patterns, ranging behavior and feeding ecology, as well as on habitat-wide forest productivity. S. leucopus fed from &gt;95 plant species and spent 17% of their time feeding. We found a positive relationship between fruit consumption and ripe-fruit availability. Dietary diversity increased during periods of fruit scarcity, when the tamarins fed more on insects and exudates. During periods of fruit scarcity, they relied more heavily on the borders of forest fragments and made occasional incursions into adjacent fragments across a matrix of pastures. They used larger areas and had larger overlapping home ranges during periods of fruit scarcity. We recovered at least 44 species of seeds effectively dispersed by tamarins, including small and medium-sized seeds (range &lt;1–26 mm). Seeds were dispersed up to 500m from parent trees across a wide diversity of habitat types. This study provides further evidence on the important role small-bodied frugivorous primates play in the recovery of forest connectivity and in the maintenance of tropical forest diversity in human-impacted landscapes.

Unusual chemical composition of a Mexican propolis collected in Quintana Roo, Mexico

Propolis is a resinous natural substance collected by honey bees from buds and exudates of various trees and plants. It is widely accepted that the composition of propolis depends on the phytogeographic characteristics of the site of collection. In this study, we have analyzed the chemical composition of a propolis collected in Quintana Roo, Mexico, and evaluated its antioxidant, antifungal, and antibacterial activities. Unexpectedly, the chemical analysis showed that the main components of the ethanolic extract of this Mexican propolis appeared to be pentacyclic triterpenoids, such as α and β-amyrin derivatives, and sterols. The crude extract did not show antioxidant activity when tested using the DPPH-reduction assay, and it also proved inactive when tested for antifungal and antibacterial activities using microdilution and agar diffusion assays, respectively. The fact that the presence of both α and β-amyrins and their derivatives have been reported from the resin of Bursera simaruba, one of the plants used by the bees for propolis production in Quintana Roo, Mexico, confirms the relationship that exists between the flora available to bees in a given region and the chemical composition of the propolis that they produce.

Paenibacillus polymyxa BFKC01 enhances plant iron absorption via improved root systems and activated iron acquisition mechanisms

Despite the high abundance of iron (Fe) in most earth's soils, Fe is the major limiting factor for plant growth and development due to its low bioavailability. With an increasing recognition that soil microbes play important roles in plant growth, several strains of beneficial rhizobactria have been applied to improve plant nutrient absorption, biomass, and abiotic or biotic stress tolerance. In this study, we report the mechanisms of microbe-induced plant Fe assimilation, in which the plant growth promoting rhizobacteria (PGPR) Paenibacillus polymyxa BFKC01 stimulates plant's Fe acquisition machinery to enhance Fe uptake in Arabidopsis plants. Mechanistic studies show that BFKC01 transcriptionally activates the Fe-deficiency-induced transcription factor 1 (FIT1), thereby up-regulating the expression of IRT1 and FRO2. Furthermore, BFKC01 has been found to induce plant systemic responses with the increased transcription of MYB72, and the biosynthetic pathways of phenolic compounds are also activated. Our data reveal that abundant phenolic compounds are detected in root exudation of the BFKC01-inoculated plants, which efficiently facilitate Fe mobility under alkaline conditions. In addition, BFKC01 can secret auxin and further improved root systems, which enhances the ability of plants to acquire Fe from soils. As a result, BFKC01-inoculated plants have more endogenous Fe and increased photosynthetic capacity under alkaline conditions as compared to control plants. Our results demonstrate the potential roles of BFKC01 in promoting Fe acquisition in plants and underline the intricate integration of microbial signaling in controlling plant Fe acquisition.

Stem‐galling moths provide cetoniine beetles with feeding sites via sap exudation of invasive alien plants

AbstractThe alien moth Epiblema sugii (Lepidoptera: Tortricidae) induces stem galls on an invasive alien weed, Ambrosia trifida. During summer, along riverbanks in central Japan, the native insects Protaetia brevitarsis, P. orientalis submarumorea (Coleoptera: Scarabaeidae: Cetoniinae), and Camponotus vitiosus (Hymenoptera: Formicidae) feed on the sap exuded from the galls. The cetoniine beetles are highly aggregated among the galls and make wounds on the galls to facilitate sap exudation. Feeding on gall sap may be beneficial to the beetles due to the efficient intake of water and sugar, and the beetles’ inflicting wounds and feeding on the sap seem to have little effect on the gallers. This is a unique finding, where alien plant–galler interaction provides a feeding site for native insects.

Environmental Metabolomics of the Tomato Plant Surface Provides Insights on Salmonella enterica Colonization.

Foodborne illness-causing enteric bacteria are able to colonize plant surfaces without causing infection. We lack an understanding of how epiphytic persistence of enteric bacteria occurs on plants, possibly as an adaptive transit strategy to maximize chances of reentering herbivorous hosts. We used tomato (Solanum lycopersicum) cultivars that have exhibited differential susceptibilities to Salmonella enterica colonization to investigate the influence of plant surface compounds and exudates on enteric bacterial populations. Tomato fruit, shoot, and root exudates collected at different developmental stages supported growth of S. enterica to various degrees in a cultivar- and plant organ-dependent manner. S. enterica growth in fruit exudates of various cultivars correlated with epiphytic growth data (R(2) = 0.504; P = 0.006), providing evidence that plant surface compounds drive bacterial colonization success. Chemical profiling of tomato surface compounds with gas chromatography-time of flight mass spectrometry (GC-TOF-MS) provided valuable information about the metabolic environment on fruit, shoot, and root surfaces. Hierarchical cluster analysis of the data revealed quantitative differences in phytocompounds among cultivars and changes over a developmental course and by plant organ (P < 0.002). Sugars, sugar alcohols, and organic acids were associated with increased S. enterica growth, while fatty acids, including palmitic and oleic acids, were negatively correlated. We demonstrate that the plant surface metabolite landscape has a significant impact on S. enterica growth and colonization efficiency. This environmental metabolomics approach provides an avenue to understand interactions between human pathogens and plants that could lead to strategies to identify or breed crop cultivars for microbiologically safer produce. In recent years, fresh produce has emerged as a leading food vehicle for enteric pathogens. Salmonella-contaminated tomatoes represent a recurrent human pathogen-plant commodity pair. We demonstrate that Salmonella can utilize tomato surface compounds and exudates for growth. Surface metabolite profiling revealed that the types and amounts of compounds released to the plant surface differ by cultivar, plant developmental stage, and plant organ. Differences in exudate profiles explain some of the variability in Salmonella colonization susceptibility seen among tomato cultivars. Certain medium- and long-chain fatty acids were associated with restricted Salmonella growth, while sugars, sugar alcohols, and organic acids correlated with larger Salmonella populations. These findings uncover the possibility of selecting crop varieties based on characteristics that impair foodborne pathogen growth for enhanced safety of fresh produce.

Foliage-dwelling ants in a neotropical savanna: effects of plant and insect exudates on ant communities

Ant dominance in tropical ecosystems can be explained by a capacity to exploit liquid foods such as extrafloral nectaries (EFNs) and secretions from honeydew-producing hemipterans (HPHs). Such nutritious exudates may determine ant distribution in space and shape specialization in ant–plant interactions. We provide a first assessment of how EFNs and HPHs mediate the structure of ant assemblages, ant visitation intensity, and characteristics of ant–plant interaction networks across space in Brazilian “cerrado” savanna. We used arboreal pitfall traps to sample visiting ants in four cerrado localities and recorded the presence of lepidopteran larvae to determine their possible response to ant visitation. Ant species composition and richness did not differ regardless of the presence of liquid rewards on plants, and most network patterns did not show consistent differences. However, in two of the four sites, ant densities were higher on plants with HPHs or EFNs due to increased activity by Camponotus and Pseudomyrmex ants. At these two sites, plants with liquid food sources had a more specific ant assemblage (higher specialization d′) than did plants without resources, and caterpillars were more frequently found on plants with fewer workers of Camponotus and Pseudomyrmex. Plants with HPHs had increased ant visitation and accumulated more ant species than did plants with EFNs or without liquid foods. Ant response to such food sources may thus depend on local conditions and identity of ant species, and may determine how ant assemblages are structured. Results highlight how different patterns of ant visitation to liquid resources can produce distinctive effects on herbivore infestation.

Honey-derived Flavonoids: Natural Products for the Prevention of Atherosclerosis and Cardiovascular Diseases

The ancient product honey produced by honeybees, particularly the species Apis mellifera from the nectar blossoms or from exudates of trees and plants. Honey contains a very high content of carbohydrates, mostly monoand disaccharides but it also contains many members of the family of antioxidant flavonoids. Over the last several decade of studies on human disease processes it has become recognized that an elevated, unfavourable oxidation status and a states of chronic inflammation underlies multiple diseases most notably, cardiovascular disease (CVD). The underlying cause of most CVD is atherosclerosis, the trapping of lipids in the vessel wall by modified proteoglycans, followed by oxidation, a chronic immune response and the development and rupture of atherosclerotic plaques. Many of the flavonoids present in honey have actions which impact on the oxidative and other processes of atherosclerosis. In this review we describe the actions of many of the flavonoids present in honey and speculate on the manner in which these might aggregate to produce a favorable CVD protective effect of honey per se.

Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.

Resinas naturales de especies vegetales mexicanas: usos actuales y potenciales

Se revisa el estado actual de la información sobre la flora mexicana productora de resinas, así como sus aplicaciones actuales y potenciales. Los exudados vegetales están recuperando su lugar en el mercado internacional y México posee una amplia flora de coníferas, latifoliadas tropicales y de clima templado, árboles, arbustos y trepadoras, las cuales en mayor o menor cantidad producen resinas que tienen una amplia aplicación en actividades humanas. Los exudados vegetales son considerados productos forestales menores (PFM) o productos forestales no maderables (PFNM), y pudieran alcanzar o tal vez superar el valor económico de la producción maderera. Las 28 familias botánicas mencionadas en esta revisión están representadas ampliamente en la flora mexicana, en ellas están incorporados 79 géneros, los cuales incluyen especies que está documentado en la literatura botánica que producen resinas. Es necesario conocerlas profundamente para identificar nichos de oportunidad sea en la industria alimentaria, el curtido de pieles, la elaboración de barnices, la de preservadores o de aditivos de maderas, ya que pueden ser alternativas viables para el manejo sostenible de bosques y selvas, siempre y cuando se aprovechen para mejorar las condiciones de los productores y de aquellos trabajadores que participan en su transformación.

Effect of propolis extracts against methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is a human pathogen that causes a wide range of infections worldwide. In this study, 40 clinical isolates of S. aureus were tested for their susceptibility to oxacillin and to different classes of antibiotics by disc diffusion method. Data revealed that out of these 40 isolates, 28 were MRSA. Most isolates were not only resistant to oxacillin but also found resistant to a number of other antibiotics. Propolis is a mixture of beeswax and resins collected by the honeybee from plant buds, leaves, and exudates. It has been used for centuries in folk medicine. The antimicrobial activity of ethanolic extract of propolis alone or in combination with antimicrobial drugs against MRSA isolates was evaluated. The results showed that the propolis extract was found to exhibit antimicrobial activity against all tested isolates. Also the results demonstrated the combination between propolis and some tested antimicrobial drugs in vitro is effective against multi-drug resistance MRSA.

Evaluation of the effects of propolis extracts and their constituents against the ticks Rhipicephalus sanguineus, Rhipicephalus microplus and Amblyomma cajennense

Propolis is a resinous substance produced by bees Apis mellifera, containing mainly plant exudates and bee waxes. Propolis is important to the bees, as it is responsible for the maintenance of the hive as a sterile environment, acting against bacteria, fungus and even invading larvae. It has been extensively used in alternative medicine. However, few studies have been developed concerning the use of propolis to animal health. Thus, new strategies are of great importance for tick control. Hence, the aim of this project was to determine the activity of crude extracts of Brazilian propolis and their constituents for the control of specific and generalist ticks. Chloroform extracts were prepared from samples of green propolis from Lavras (state of Minas Gerais) and black propolis from Picos (state of Piauí), previously analyzed chemically. The bioassays were carried out in vitro to verify the effectiveness of the extracts using the larval package test. Bioassays-guided isolations were carried out to obtain active constituents presented in the studied samples. The crude extract of the propolis sample from Picos did not show any acaricide activity. On the other hand, the sample of propolis from Lavras showed high activity, and was fractionated by column chromatography in silica gel. A subfraction with acaricide activity was obtained and analyses by high performance liquid chromatography (HPLC) were developed. The majority compounds were isolated using preparative HPLC and identified by means of current spectroscopic analysis in chemistry of natural products (IR, UV, mass and NMR) (2,2-dimethyl-cromene-6-propenoic-dicafeoyl glucoside acid, artepillin-C, baccarin and 2,2-dimethyl-cromene-8-prenyl-6-propenoic acid). Finally, new bioassays were carried out, but no effect was observed testing the isolated compounds. Thus, probably the high acaricidal activity observed in the active subfraction was due to a synergism among the subfraction constituents.

Leachability of volatile fuel compounds from contaminated soils and the effect of plant exudates: A comparison of column and batch leaching tests

Volatile fuel compounds such as fuel oxygenates (FO) (MTBE and ETBE) and BTEX (benzene, toluene, ethylbenzene and xylene) are some of the most soluble components of fuel. Characterizing the leaching potential of these compounds is essential for predicting their mobility through the soil profile and assessing the risk of groundwater contamination. Plant root exudates can play an important role in the modification of contaminant mobility in soil–plant systems, and such effects should also be considered in leaching studies. Artificially spiked samples of A and B horizons from an alumi-umbric Cambisol were leached in packed-columns and batch experiments using Milli-Q water and plant root exudates as leaching agents. The leaching potential and rate were strongly influenced by soil-contaminant interactions and by the presence of root exudates. Organic matter in A horizon preferably sorbed the most non-polar contaminants, lowering their leaching potential, and this effect was enhanced by the presence of root exudates. On the other hand, the inorganic components of the B horizon, showed a greater affinity for polar molecules, and the presence of root exudates enhanced the desorption of the contaminants. Column experiments resulted in a more realistic protocol than batch tests for predicting the leaching potential of volatile organic compounds in dissimilar soils.

RhizoFlowCell system reveals early effects of micropollutants on aquatic plant rhizosphere

In aquatic systems, one of the non-destructive ways to quantify toxicity of contaminants to plants is to monitor changes in root exudation patterns. In aquatic conditions, monitoring and quantifying such changes are currently challenging because of dilution of root exudates in water phase and lack of suitable instrumentation to measure them. Exposure to pollutants would not only change the plant exudation, but also affect the microbial communities that surround the root zone, thereby changing the metabolic profiles of the rhizosphere. This study aims at developing a device, the RhizoFlowCell, which can quantify metabolic response of plants, as well as changes in the microbial communities, to give an estimate of the stress to which the rhizosphere is exposed. The usefulness of RhizoFlowCell is demonstrated using naphthalene as a test pollutant. Results show that RhizoFlowCell system is useful in quantifying the dynamic metabolic response of aquatic rhizosphere to determine ecosystem health.

Genes related to antioxidant metabolism are involved in Methylobacterium mesophilicum-soybean interaction.

The genus Methylobacterium is composed of pink-pigmented methylotrophic bacterial species that are widespread in natural environments, such as soils, stream water and plants. When in association with plants, this genus colonizes the host plant epiphytically and/or endophytically. This association is known to promote plant growth, induce plant systemic resistance and inhibit plant infection by phytopathogens. In the present study, we focused on evaluating the colonization of soybean seedling-roots by Methylobacterium mesophilicum strain SR1.6/6. We focused on the identification of the key genes involved in the initial step of soybean colonization by methylotrophic bacteria, which includes the plant exudate recognition and adaptation by planktonic bacteria. Visualization by scanning electron microscopy revealed that M. mesophilicum SR1.6/6 colonizes soybean roots surface effectively at 48 h after inoculation, suggesting a mechanism for root recognition and adaptation before this period. The colonization proceeds by the development of a mature biofilm on roots at 96 h after inoculation. Transcriptomic analysis of the planktonic bacteria (with plant) revealed the expression of several genes involved in membrane transport, thus confirming an initial metabolic activation of bacterial responses when in the presence of plant root exudates. Moreover, antioxidant genes were mostly expressed during the interaction with the plant exudates. Further evaluation of stress- and methylotrophic-related genes expression by qPCR showed that glutathione peroxidase and glutathione synthetase genes were up-regulated during the Methylobacterium-soybean interaction. These findings support that glutathione (GSH) is potentially a key molecule involved in cellular detoxification during plant root colonization. In addition to methylotrophic metabolism, antioxidant genes, mainly glutathione-related genes, play a key role during soybean exudate recognition and adaptation, the first step in bacterial colonization.