Gilson Dahmer
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Root exudates mediated interactions belowground

Root exudates mediated interactions belowground | Gilson Dahmer | Scoop.it

The root exudate composition reflects the contradictory-concomitantly attractive and repulsive-behaviour of plants towards soil microorganisms. Plants produce antimicrobial, insecticide and nematicide compounds to repel pathogens and invaders. They also produce border cells that detach from roots and play an important role as biological and physical barrier against aggressors. Plants produce also metabolites used as carbon source resulting in the attraction of phytobeneficial soil microorganisms that help plants in controlling diseases directly via the production of antimicrobial compounds or indirectly via the induction of plant systemic resistance. The root exudates may have a direct impact on carbon and nitrogen cycling, as they exhibit a rhizosphere priming effect towards soil organic matter degraders, and may inhibit nitrification process by soil nitrifying microorganisms. They also contain signalling molecules required for the establishment of ‘plant-microorganisms’ interactions. The composition of root exudates is therefore broad ranging, consisting of feeding, antimicrobial and signalling molecules. We thus focused this review on current research concerning the role of the root exudate composition in ‘plant-microorganisms’ interactions and functioning of the rhizosphere.


Via Jean-Michel Ané
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Using root form to improve our understanding of root function -

Using root form to improve our understanding of root function - | Gilson Dahmer | Scoop.it

It has been said – and even written – that the ‘fine roots of perennial plants are a royal pain to study’ (Pregitzer, 2002). This is because the complex branching architecture of ephemeral roots leads to changes in root form and function across sub-millimeter scales (Fig. 1). While painful to consider, the variation in traits from short-lived, absorptive root tips to more proximal, transportive roots, may be our best hope of quantifying and understanding the functional role of living roots throughout the soil profile. Further, inherent variation in root functional traits across plant species may allow us to scale root function from the rhizosphere to the biosphere in order to understand global biogeochemical cycling under current and future climatic conditions. This issue of New Phytologist contains two papers that approach the linkages between root form and function from different, but complementary, directions. Kong et al. (pp. 863–872) take a broad geographic approach, describing patterns of trait variation across the distal root tips of 96 subtropical and tropical tree species in southern China, while Smith et al. (pp. 851–862) worked at the scale of a single site to investigate the relationships among root traits and root decomposition rates of graminoid species across a gradient of soil moisture in grazed ecosystems in central Scotland.

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A review of the effects of soil organisms on plant hormone signalling pathways

A review of the effects of soil organisms on plant hormone signalling pathways | Gilson Dahmer | Scoop.it

Plants interact with a large number of soil organisms. For a long time, these interactions have been the research area of soil ecologists and trophic relationships and physico-chemical modifications of the soil matrix were generally proposed as mechanisms underlying plant-soil organism interactions. However, some specific symbioses and diseases have been well characterized at the molecular level by plant biologists and microbiologists. These interactions involve a physical contact between soil organism and plant. They are mediated through signal molecules that play upon the different plant hormonal signalling pathways, leading to modifications in plant development and defence. Nowadays, the role of signal molecules emerges as an important feature of interactions between plants and free-living soil organisms. In this review we discuss genetic and physiological evidences of hormone signalling involvement in plant response to physically associated but also free-living soil organisms, for very different taxa ranging from the micrometer to the centimetre scales. The same hormone signalling pathways seems to be activated by very different kinds of soil organisms such as bacteria, nematodes, collembola and even earthworms, with common consequences on plant growth, development and defence. Plant hormonal homeostasis appears to be the corner stone to understand and predict the issue of the multiple interactions that plants entertain with the community of soil organisms.


Via Jean-Michel Ané, Mary Williams
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CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication

CHOLINE TRANSPORTER-LIKE1 is required for sieve plate development to mediate long-distance cell-to-cell communication | Gilson Dahmer | Scoop.it

Phloem, a plant tissue responsible for long-distance molecular transport, harbours specific junctions, sieve areas, between the conducting cells. To date, little is known about the molecular framework related to the biogenesis of these sieve areas. Here we identify mutations at theCHER1/AtCTL1 locus of Arabidopsis thaliana. The mutations cause several phenotypic abnormalities, including reduced pore density and altered pore structure in the sieve areas associated with impaired phloem function. CHER1 encodes a member of a poorly characterized choline transporter-like protein family in plants and animals. We show that CHER1 facilitates choline transport, localizes to the trans-Golgi network, and during cytokinesis is associated with the phragmoplast. Consistent with its function in the elaboration of the sieve areas, CHER1 has a sustained, polar localization in the forming sieve plates. Our results indicate that the regulation of choline levels is crucial for phloem development and conductivity in plants.

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Metabolites | Metabolite Profiling of Root Exudates of Common Bean under Phosphorus Deficiency

Root exudates improve the nutrient acquisition of plants and affect rhizosphere microbial communities. The plant nutrient status affects the composition of root exudates. The purpose of this study was to examine common bean (Phaseolus vulgaris L.) root exudates under phosphorus (P) deficiency using a metabolite profiling technique. Common bean plants were grown in a culture solution at P concentrations of 0 (P0), 1 (P1) and 8 (P8) mg P L−1 for 1, 10 and 20 days after transplanting (DAT). Root exudates were collected, and their metabolites were determined by capillary electrophoresis time-of-flight mass spectrometry (CE-TOF MS). The shoot P concentration and dry weight of common bean plants grown at P0 were lower than those grown at P8. One hundred and fifty-nine, 203 and 212 metabolites were identified in the root exudates, and 16% (26/159), 13% (26/203) and 9% (20/212) of metabolites showed a P0/P8 ratio higher than 2.0 at 1, 10 and 20 DAT, respectively. The relative peak areas of several metabolites, including organic acids and amino acids, in root exudates were higher at P0 than at P8. These results suggest that more than 10% of primary and secondary metabolites are induced to exude from roots of common bean by P deficiency.
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Biswapriya B Misra's curator insight, September 10, 2014 10:55 PM
Root exudates improve the nutrient acquisition of plants and affect rhizosphere microbial communities. The plant nutrient status affects the composition of root exudates. The purpose of this study was to examine common bean (Phaseolus vulgaris L.) root exudates under phosphorus (P) deficiency using a metabolite profiling technique. Common bean plants were grown in a culture solution at P concentrations of 0 (P0), 1 (P1) and 8 (P8) mg P L−1 for 1, 10 and 20 days after transplanting (DAT). Root exudates were collected, and their metabolites were determined by capillary electrophoresis time-of-flight mass spectrometry (CE-TOF MS). The shoot P concentration and dry weight of common bean plants grown at P0 were lower than those grown at P8. One hundred and fifty-nine, 203 and 212 metabolites were identified in the root exudates, and 16% (26/159), 13% (26/203) and 9% (20/212) of metabolites showed a P0/P8 ratio higher than 2.0 at 1, 10 and 20 DAT, respectively. The relative peak areas of several metabolites, including organic acids and amino acids, in root exudates were higher at P0 than at P8. These results suggest that more than 10% of primary and secondary metabolites are induced to exude from roots of common bean by P deficiency.
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Bananas galore

Bananas galore | Gilson Dahmer | Scoop.it

Rosa would certainly have welcomed a great new catalogue of some 50 banana varieties from the Solomon Islands by Gabriel Sachter-Smith, put out by ProMusa. The varieties on the cover are Broken Heart, Ruhuvia Chichi and Ba’u Lalao.

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Functional soil microbiome: Belowground solutions to an aboveground problem

Functional soil microbiome: Belowground solutions to an aboveground problem | Gilson Dahmer | Scoop.it

There is considerable evidence in the literature that beneficial rhizospheric microbes can alter plant morphology, enhance plant growth, and increase mineral content. Of late, there is a surge to understand the impact of the microbiome on plant health. Recent research shows the utilization of novel sequencing techniques to identify the microbiome in model systems such as Arabidopsis and Maize. However, it is not known how the community of microbes identified may play a role to improve plant health and fitness. There are very few detailed studies with isolated beneficial microbes showing the importance of the functional microbiome in plant fitness and disease protection. Some recent work on the cultivated microbiome in rice shows a wide diversity of bacterial species is associated with the roots of field-grown rice plants. However, biological significance and potential effects of the microbiome on the host plants are completely unknown. Work performed with isolated strains showed various genetic pathways that are involved in recognition of host-specific factors that are involved in the beneficial host-microbe interactions. The composition of the microbiome in plants is dynamic and controlled by multiple factors. In the case of the rhizosphere, temperature, pH, and the presence of chemical signals from bacteria, plants, and nematodes all shape the environment and influence which organisms will flourish. This provides a basis for plants and their microbiomes to selectively associate with one another. This update addresses the importance of the functional microbiome to identify phenotypes that may provide a sustainable and effective strategy to increase crop yield and food security.

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What! Organic Agriculture Isn't Sustainable? - Kansas City infoZine

What! Organic Agriculture Isn't Sustainable? - Kansas City infoZine | Gilson Dahmer | Scoop.it
Dear EarthTalk: Do You Agree with the Recent Claim in the Wall Street Journal That Organic Agriculture Isn

 

 

http://www.infozine.com/news/stories/op/storiesView/sid/58971/

 

 


Via Giri Kumar
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Plant root exudates mediate neighbour recognition and trigger complex behavioural changes

Plant root exudates mediate neighbour recognition and trigger complex behavioural changes | Gilson Dahmer | Scoop.it

Some plant species are able to distinguish between neighbours of different genetic identity and attempt to pre-empt resources through root proliferation in the presence of unrelated competitors, but avoid competition with kin. However, studies on neighbour recognition have met with some scepticism because the mechanisms by which plants identify their neighbours have remained unclear.In order to test whether root exudates could mediate neighbour recognition in plants, we performed a glasshouse experiment in which plants of Deschampsia caespitosa were subjected to root exudates collected from potential neighbours of different genetic identities, including siblings and individuals belonging to the same or a different population or species.Our results show that root exudates can carry specific information about the genetic relatedness, population origin and species identity of neighbours, and trigger different responses at the whole root system level and at the level of individual roots in direct contact with locally applied exudates. Increased root density was mainly achieved through changes in morphology rather than biomass allocation, suggesting that plants are able to limit the energetic cost of selfish behaviour.This study reveals a new level of complexity in the ability of plants to interpret and react to their surroundings.

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Is there an association between root architecture and mycorrhizal growth response?

Is there an association between root architecture and mycorrhizal growth response? | Gilson Dahmer | Scoop.it
The symbiosis between arbuscular mycorrhizal (AM) fungi and plants is evolutionarily widespread. The response of plant growth to inoculation by these fungi (mycorrhizal growth response; MGR) is highly variable, ranging from positive to negative. Some of this variation is hypothesized to be associated with root structure and function. Specifically, species with a coarse root architecture, and thus a limited intrinsic capacity to absorb soil nutrients, are expected to derive the greatest growth benefit from inoculation with AM fungi.To test this hypothesis, previously published literature and phylogenetic information were combined in a meta-analysis to examine the magnitude and direction of relationships among several root architectural traits and MGR.Published studies differed in the magnitude and direction of relationships between root architecture and MGR. However, when combined, the overall relationship between MGR and allocation to roots, root diameter, root hair length and root hair density did not differ significantly from zero.These findings indicate that possessing coarse roots is not necessarily a predictor of plant growth response to AM fungal colonization. Root architecture is therefore unlikely to limit the evolution of variation in MGR.
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Comparison of the Rhizosphere Bacterial Communities of Zigongdongdou Soybean and a High-Methionine Transgenic Line of This Cultivar

Comparison of the Rhizosphere Bacterial Communities of Zigongdongdou Soybean and a High-Methionine Transgenic Line of This Cultivar | Gilson Dahmer | Scoop.it

Previous studies have shown that methionine from root exudates affects the rhizosphere bacterial population involved in soil nitrogen fixation. A transgenic line of Zigongdongdou soybean cultivar (ZD91) that expresses Arabidopsis cystathionine γ-synthase resulting in an increased methionine production was examined for its influence to the rhizosphere bacterial population. Using 16S rRNA gene-based pyrosequencing analysis of the V4 region and DNA extracted from bacterial consortia collected from the rhizosphere of soybean plants grown in an agricultural field at the pod-setting stage, we characterized the populational structure of the bacterial community involved. In total, 87,267 sequences (approximately 10,908 per sample) were analyzed. We found that Acidobacteria, Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, Planctomycetes, Gemmatimonadetes, Firmicutes, and Verrucomicrobia constitute the dominant taxonomic groups in either the ZD91 transgenic line or parental cultivar ZD, and that there was no statistically significant difference in the rhizosphere bacterial community structure between the two cultivars.

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Interessantíssimo!

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The H+-ATPase HA1 of Medicago truncatula Is Essential for Phosphate Transport and Plant Growth during Arbuscular Mycorrhizal Symbiosis

The H+-ATPase HA1 of Medicago truncatula Is Essential for Phosphate Transport and Plant Growth during Arbuscular Mycorrhizal Symbiosis | Gilson Dahmer | Scoop.it

A key feature of arbuscular mycorrhizal symbiosis is improved phosphorus nutrition of the host plant via the mycorrhizal pathway, i.e., the fungal uptake of Pi from the soil and its release from arbuscules within root cells. Efficient transport of Pi from the fungus to plant cells is thought to require a proton gradient across the periarbuscular membrane (PAM) that separates fungal arbuscules from the host cell cytoplasm. Previous studies showed that the H+-ATPase gene HA1 is expressed specifically in arbuscule-containing root cells of Medicago truncatula. We isolated a ha1-2 mutant of M. truncatula and found it to be impaired in the development of arbuscules but not in root colonization by Rhizophagus irregularishyphae. Artificial microRNA silencing of HA1 recapitulated this phenotype, resulting in small and truncated arbuscules. Unlike the wild type, the ha1-2 mutant failed to show a positive growth response to mycorrhizal colonization under Pi-limiting conditions. Uptake experiments confirmed that ha1-2 mutants are unable to take up phosphate via the mycorrhizal pathway. Increased pH in the apoplast of abnormal arbuscule-containing cells of the ha1-2 mutant compared with the wild type suggests that HA1 is crucial for building a proton gradient across the PAMand therefore is indispensible for the transfer of Pi from the fungus to the plant.

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Organic food has real nutritional benefits

Organic food has real nutritional benefits | Gilson Dahmer | Scoop.it
When compared to conventional produce, organic has more antioxidants, fewer toxic metals, and less pesticide residue.
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Seeds: A Collective Voice - VPK - YouTube

SEEDS: A Collective Voice is a group of Artists, Seed Preservationists, Farmers, Educators and Activists joined together through the arts to raise awareness ...
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Identification and functional characterization of a sulfate transporter induced by both sulfur starvation and mycorrhiza formation in Lotus japonicus

Identification and functional characterization of a sulfate transporter induced by both sulfur starvation and mycorrhiza formation in Lotus japonicus | Gilson Dahmer | Scoop.it

Arbuscular mycorrhizas (AMs) are one of the most widespread symbioses in the world. They allow plants to receive mineral nutrients from the symbiotic fungus which in turn gets back up to 20% of plant carbon and completes its life cycle. Especially in low-nutrient conditions, AM fungi are capable of significantly improving plant phosphate and nitrogen acquisition, but fewer data are available about sulfur (S) nutrition.We focused on S metabolism in Lotus japonicus upon mycorrhizal colonization under sulfur starvation or repletion. We investigated both tissue sulfate concentrations and S-related gene expression, at cell-type or whole-organ level.Gene expression and sulfate tissue concentration showed that Rhizophagus irregularis colonization can improve plant S nutritional status under S starvation. A group 1 sulfate transporter, LjSultr1;2, induced by both S starvation and mycorrhiza formation, was identified. Its transcript was localized in arbuscule-containing cells, which was confirmed with a promoter-GUS assay, and its function was verified through phenotyping of TILLING mutants in nonmycorrhizal seedlings.LjSultr1;2 thus appears to encode a key protein involved in plant sulfate uptake. In contrast to phosphate transporters, a single gene,LjSultr1;2, seems to mediate both direct and symbiotic pathways of S uptake in L. japonicus.


Via Francis Martin
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