ER body-resident myrosinases and tryptophan specialized metabolism modulate root microbiota assembly.

Endoplasmic reticulum (ER) bodies are ER-derived structures that contain a large amount of PYK10 myrosinase, which hydrolyzes tryptophan (Trp)-derived indole glucosinolates (IGs). Given the well-described role of IGs in root-microbe interactions, we hypothesized that ER bodies in roots are important for interaction with soil-borne microbes at the root-soil interface. We used mutants impaired in ER bodies (nai1), ER body-resident myrosinases (pyk10bglu21), IG biosynthesis (myb34/51/122), and Trp specialized metabolism (cyp79b2b3) to profile their root microbiota community in natural soil, evaluate the impact of axenically collected root exudates on soil or synthetic microbial communities, and test their response to fungal endophytes in a mono-association setup. Tested mutants exhibited altered bacterial and fungal communities in rhizoplane and endosphere, respectively. Natural soils and bacterial synthetic communities treated with mutant root exudates exhibited distinctive microbial profiles from those treated with wild-type (WT) exudates. Most tested endophytes severely restricted the growth of cyp79b2b3, a part of which also impaired the growth of pyk10bglu21. Our results suggest that root ER bodies and their resident myrosinases modulate the profile of root-secreted metabolites and thereby influence root-microbiota interactions.

Unraveling the Roles of Neuropeptides in the Chemosensation of the Root-Knot Nematode Meloidogyne javanica.

The identification of novel drug targets in plant-parasitic nematodes (PPNs) is imperative due to the loss of traditional nematicides and a lack of replacements. Chemosensation, which is pivotal for PPNs in locating host roots, has become a focus in nematode behavioral research. However, its underlying molecular basis is still indistinct in such a diverse group of PPNs. To characterize genes participating in chemosensation in the Javanese root-knot nematode Meloidogyne javanica, RNA-sequencing of the second-stage juveniles (J2s) treated with tomato root exudate (TRE) for 1 h and 6 h was performed. Genes related to chemosensation in M. javanica mainly responded to TRE treatment at 1 h. Moreover, a gene ontology (GO) analysis underscored the significance of the neuropeptide G protein-coupled receptor signaling pathway. Consequently, the repertoire of putative neuropeptides in M. javanica, including FMRFamide-like peptides (FLPs), insulin-like peptides (ILPs), and neuropeptide-like peptides (NLPs), were outlined based on a homology analysis. The gene Mjflp-14a, harboring two neuropeptides, was significantly up-regulated at 1 h TRE treatment. Through peptide synthesis and J2 treatment, one of the two neuropeptides (MjFLP-14-2) was proven to influence the J2 chemotaxis towards tomato root tips. Overall, our study reinforces the potential of nematode neuropeptides as novel targets and tools for root-knot nematode control.

The Phosphorus-Iron Nexus: Decoding the Nutrients Interaction in Soil and Plant.

Phosphorus (P) and iron (Fe) are two essential mineral nutrients in plant growth. It is widely observed that interactions of P and Fe could influence their availability in soils and affect their homeostasis in plants, which has received significant attention in recent years. This review presents a summary of latest advances in the activation of insoluble Fe-P complexes by soil properties, microorganisms, and plants. Furthermore, we elucidate the physiological and molecular mechanisms underlying how plants adapt to Fe-P interactions. This review also discusses the current limitations and presents potential avenues for promoting sustainable agriculture through the optimization of P and Fe utilization efficiency in crops.

[Interaction between root exudates of medicinal plants and rhizosphere microorganisms and its application in ecological planting of Chinese medicinal materials].

The rhizosphere is an important place for material exchange between medicinal plants and soil. Root exudates are the medium of material and signal exchange between plants and soil and are the key factors in the regulation of rhizosphere microecology. Rhizosphere microorganisms are an important part of the rhizosphere microecology of medicinal plants, and the interaction between root exudates and rhizosphere microorganisms has an important influence on the growth and quality formation of medicinal plants. Rational utilization of the interaction between root exudates and rhizosphere microorganisms of medicinal plants is one of the important ways to ensure the healthy growth of medicinal plants and promote the development of ecological planting of Chinese medicinal materials. In the paper, the research status of root exudates and rhizosphere microorganisms of medicinal plants in recent years was summarized. The interaction mechanism between root exudates and rhizosphere microorganisms of medicinal plants, as well as the influence of rhizosphere microorganisms on the growth of medicinal plants, were analyzed. In addition, the advantages and promoting effects of intercropping ecological planting mode on rhizosphere microecology of medicinal plants and quality improvement of Chinese medicinal materials were explained, providing a good basis for the study of the interaction among medicinal plants, microorganisms, and soil. Furthermore, it could produce important theoretical and practical significance for the ecological planting and sustainable utilization of medicinal plants.

Extended automated quantification algorithm (AQuA) for targeted 1H NMR metabolomics of highly complex samples: application to plant root exudates.

INTRODUCTION: The Automated Quantification Algorithm (AQuA) is a rapid and efficient method for targeted NMR-based metabolomics, currently optimised for blood plasma. AQuA quantifies metabolites from 1D-1H NMR spectra based on the height of only one signal per metabolite, which minimises the computational time and workload of the method without compromising the quantification accuracy. OBJECTIVES: To develop a fast and computationally efficient extension of AQuA for quantification of selected metabolites in highly complex samples, with minimal prior sample preparation. In particular, the method should be capable of handling interferences caused by broad background signals. METHODS: An automatic baseline correction function was combined with AQuA into an automated workflow, the extended AQuA, for quantification of metabolites in plant root exudate NMR spectra that contained broad background signals and baseline distortions. The approach was evaluated using simulations as well as a spike-in experiment in which known metabolite amounts were added to a complex sample matrix. RESULTS: The extended AQuA enables accurate quantification of metabolites in 1D-1H NMR spectra with varying complexity. The method is very fast (< 1 s per spectrum) and can be fully automated. CONCLUSIONS: The extended AQuA is an automated quantification method intended for 1D-1H NMR spectra containing broad background signals and baseline distortions. Although the method was developed for plant root exudates, it should be readily applicable to any NMR spectra displaying similar issues as it is purely computational and applied to NMR spectra post-acquisition.

Effect of calcium and trace metals (Cd, Cu, Mn, Ni, Zn) on root iron uptake in relation to chemical properties of the root-excreted ligands.

Interferences of major cations (Ca2+, Mg2+) and trace metals (TM, i.e. Cd2+, Cu2+, Mn2+, Ni2+ and Zn2+) in root Fe uptake were evaluated. Root Fe uptake was modelled including the reactions of the root exuded ligand with the soil major and trace cations. Fe uptake was simulated with different ligands representing various affinities for the cations, the latter varying in concentration. The stability constant of Fe complexes (KFeL) does not influence Fe uptake, contrarily to the ligand parameters for Fe-hydroxide dissolution. Fe uptake decreases when KCaL or Ca2+ in solution increases. Presence of TM has nearly no influence on Fe uptake when the TM complexes have low stability constants (KML), as in the case of oxalate and citrate complexes. When ligands have high KML, like EDTA, DFO-B or mugineic acid (MA), TM reduces Fe uptake by 51-55%, and much more in the case of TM contamination. Exudation of Fe ligands with low KML has no negative effect on TM uptake, which can increase if the dissociation rate is high, as for Cu complexes. Ligands with high KML (EDTA, DFO-B, MA) greatly reduce TM uptake, only if their hydrated cations can be absorbed. Calcium does not significantly reduce Fe uptake when Ca-complexes have KCaL < 104. Consequently, ligands like oxalate or MA should be efficient in most soils. TM should perturbate Fe uptake mediated by ligands with high KML such as MA, but not oxalate. Plants exuding phytosiderophores should also absorb TM complexes to avoid micronutrient deficiencies.

Chemotaxis and Motility of Spongospora subterranea Zoospores in Response to Potato Root Exudate Constituents and pH.

Spongospora subterranea f. sp. subterranea is an important pathogen of potato responsible for major losses in most potato growing regions of the world. Infection is initiated by biflagellated motile zoospores released from long-lived resting spores. Zoospore chemotaxis to the host plant root is widely believed to be stimulated by host root exudate compounds, although direct evidence is lacking. This study refined the traditional chemotaxis capillary assay, with which we provided the first empirical evidence of S. subterranea zoospore chemotaxis. Individual potato root exudate metabolites were either taxis neutral, inhibitory, or attractant to the zoospores. L-Glutamine was the strongest chemoattractant, while spermine was the most inhibitory. Zoospore motility and chemotaxis were constrained by strongly acidic or alkaline solutions of pH < 5.3 and >8.5, respectively. Beyond pH, ionic constituents of the test solution affected zoospore motility as Sorensen's phosphate buffer stalled zoospore motility, but HEPES buffer at the same concentration and pH had little or no negative motility effect. Zoospore motility, as characterized by several parameters, influenced chemotaxis. Among the parameters measured, total distance traveled was the best predictor of zoospore chemotaxis. The characterization of environmental and ecological effects on zoospore motility and chemotaxis highlights useful targets for S. subterranea disease control through manipulation of zoospore taxis or selection of host resistance traits.

Amino acid fertilizer strengthens its effect on crop yield and quality by recruiting beneficial rhizosphere microbes.

BACKGROUND: There is currently an increase in the use of new types of fertilizers in modern agriculture. Studies have shown that amino acid fertilizers can improve crop yield and quality. However, their effects on crop rhizosphere ecology and their ecological impacts on crop yield are largely unknown. This study evaluated the effects of a water-soluble amino acid fertilizer (WAAF) on tomatoes and its ecological effects on rhizosphere bacterial communities using greenhouse pot experiments. RESULTS: The results showed that WAAF could promote the growth of tomatoes and improve the quality of fruits more effectively than water-soluble chemical fertilizer controls. Interestingly, WAAF showed a different regulating pattern on root exudates and increased the secretion of 17 major water-soluble root exudates, including hexadecanoic acid and 3-hydroxy-γ-butyrolactone. Water-soluble amino acid fertilizer also affected noticeably the composition, abundance, and beta-diversity of rhizosphere bacterial communities, and strengthened the potential relationships between community members. Water-soluble amino acid fertilizer showed a significant selective enrichment ability and recruited some members of the genera such as Cupriavidus, Ralstonia, Chitinophaga, Gemmatimonas, Mitsuaria, Mucilaginibacter, Paracoccus, Sphingopyxis, and Variovorax. Network analysis and functional prediction implied that, besides fertilizer effects, the recruiting of beneficial microbes involved in chemotaxis and biofilm formation was also a considerable factor in tomato yield and quality improvement. CONCLUSION: Our study revealed ecological and recruiting effects of WAAF on rhizosphere microbes and potentially beneficial microbiota, and provided a basis for the amino acid fertilizer regulation of rhizosphere ecology to improve soil health and further improve crop yield and quality. © 2023 Society of Chemical Industry.

Meloidogyne enterolobii-induced Changes in Guava Root Exudates Are Associated With Root Rotting Caused by Neocosmospora falciformis.

Despite the worldwide importance of disease complexes involving root-feeding nematodes and soilborne fungi, there have been few in-depth studies on how these organisms interact at the molecular level. Previous studies of guava decline have shown that root exudates from Meloidogyne enterolobii-parasitized guava plants (NP plants), but not from nematode-free plants (NF plants), enable the fungus Neocosmospora falciformis to rot guava roots, leading to plant death. To further characterize this interaction, NP and NF root exudates were lyophilized; extracted with distinct solvents; quantified regarding amino acids, soluble carbohydrates, sucrose, phenols, and alkaloids; and submitted to a bioassay to determine their ability to enable N. falciformis to rot the guava seedlings' roots. NP root exudates were richer than NF root exudates in amino acids, carbohydrates, and sucrose. Only the fractions NP-03 and NP-04 enabled fungal root rotting. NP-03 was then sequentially fractionated through chromatographic silica columns. At each step, the main fractions were reassessed in bioassay. The final fraction that enabled fungal root rotting was submitted to analysis using high performance liquid chromatography, nuclear magnetic resonance, mass spectrometry, energy-dispersive X-ray fluorescence, and computational calculations, leading to the identification of 1,5-dinitrobiuret as the predominant substance. In conclusion, parasitism by M. enterolobii causes an enrichment of guava root exudates that likely favors microorganisms capable of producing 1,5-dinitrobiuret in the rhizosphere. The accumulation of biuret, a known phytotoxic substance, possibly hampers root physiology and the innate immunity of guava to N. falciformis.

Linking root exudation to belowground economic traits for resource acquisition.

The concept of a root economics space (RES) is increasingly adopted to explore root trait variation and belowground resource-acquisition strategies. Much progress has been made on interactions of root morphology and mycorrhizal symbioses. However, root exudation, with a significant carbon (C) cost (c. 5-21% of total photosynthetically fixed C) to enhance resource acquisition, remains a missing link in this RES. Here, we argue that incorporating root exudation into the structure of RES is key to a holistic understanding of soil nutrient acquisition. We highlight the different functional roles of root exudates in soil phosphorus (P) and nitrogen (N) acquisition. Thereafter, we synthesize emerging evidence that illustrates how root exudation interacts with root morphology and mycorrhizal symbioses at the level of species and individual plant and argue contrasting patterns in species evolved in P-impoverished vs N-limited environments. Finally, we propose a new conceptual framework, integrating three groups of root functional traits to better capture the complexity of belowground resource-acquisition strategies. Such a deeper understanding of the integrated and dynamic interactions of root morphology, root exudation, and mycorrhizal symbioses will provide valuable insights into the mechanisms underlying species coexistence and how to explore belowground interactions for sustainable managed systems.

Relationship between nitrifying microorganisms and other microorganisms residing in the maize rhizosphere.

The microbial network of rhizosphere is unique as a result of root exudate. Insights into the relationship that exists with the energy metabolic functional groups will help in biofertilizer production. We hypothesize that there exists a relationship between nitrifying microorganisms and other energy metabolic functional microbial groups in the maize rhizosphere across different growth stages. Nucleospin soil DNA extraction kit was used to extract DNA from soil samples collected from maize rhizosphere. The 16S metagenomics sequencing was carried out on Illumina Miseq. The sequence obtained was analyzed on MG-RAST. Nitrospira genera were the most abundant in the nitrifying community. Nitrifying microorganisms were more than each of the studied functional groups except for nitrogen-fixing bacteria. Also, majority of the microorganisms were noticed at the fruiting stage and there was variation in the microbial structure across different growth stages. The result showed that there exists a substantial amount of both negative and positive correlation within the nitrifying microorganisms, and between them and other energy metabolic functional groups. The knowledge obtained from this study will help improve the growth and development of maize through modification of the rhizosphere microbial community structure.

Maize Root Exudates Recruit Bacillus amyloliquefaciens OR2-30 to Inhibit Fusarium graminearum Infection.

Bacillus spp. can exert plant growth-promoting effects and biocontrol effects after effective colonization, and bacterial chemotaxis toward plant root exudates is the initial step to colonize. Under biotic stress, plants are able to alter their root exudates to attract or avoid different types of microbes. Hence, Bacillus chemotaxis toward root exudates after pathogen infection is crucial for exerting their beneficial effects. In this study, the Bacillus amyloliquefaciens OR2-30 strain, which exhibited greater chemotaxis ability toward maize root exudates after Fusarium graminearum infection, was screened from 156 rhizosphere microorganisms. The infected maize root exudates were further confirmed to improve the swarming and biofilm formation ability of the OR2-30 strain. Chemotaxis, swarming, and biofilm formation ability were able to influence bacterial colonization. Indeed, the the OR2-30 strain displayed more effective colonization ability in the maize rhizosphere after F. graminearum inoculation. Moreover, lipopeptides produced by OR2-30 were identified as iturins and responsible for suppressing F. graminearum growth. Further study showed that lipopeptides suppressed the growth of F. graminearum by inhibiting conidia formation and germination, inducing reactive oxygen species production and causing cell death in mycelium. Eventually, the OR2-30 strain increased maize resistance against F. graminearum. These results suggested that maize root exudates could recruit B. amyloliquefacines OR2-30 after F. graminearum infection, and that OR2-30 then suppresses the F. graminearum by producing lipopeptides, such as iturins, to protect maize.

Isoflavone malonyl-CoA acyltransferase GmMaT2 is involved in nodulation of soybean by modifying synthesis and secretion of isoflavones.

Malonyl-CoA:flavonoid acyltransferases (MaTs) modify isoflavones, but only a few have been characterized for activity and assigned to specific physiological processes. Legume roots exude isoflavone malonates into the rhizosphere, where they are hydrolyzed into isoflavone aglycones. Soybean GmMaT2 was highly expressed in seeds, root hairs, and nodules. GmMaT2 and GmMaT4 recombinant enzymes used isoflavone 7-O-glucosides as acceptors and malonyl-CoA as an acyl donor to generate isoflavone glucoside malonates. GmMaT2 had higher activity towards isoflavone glucosides than GmMaT4. Overexpression in hairy roots of GmMaT2 and GmMaT4 produced more malonyldaidzin, malonylgenistin, and malonylglycitin, and resulted in more nodules than control. However, only GmMaT2 knockdown (KD) hairy roots showed reduced levels of malonyldaidzin, malonylgenistin, and malonylglycitin, and, likewise, reduced nodule numbers. These were consistent with the up-regulation of only GmMaT2 by rhizobial infection, and higher expression levels of early nodulation genes in GmMaT2- and GmMaT4-overexpressing roots, but lower only in GmMaT2-KD roots compared with control roots. Higher malonyl isoflavonoid levels in transgenic hairy roots were associated with higher levels of isoflavones in root exudates and more nodules, and vice versa. We suggest that GmMaT2 participates in soybean nodulation by catalyzing isoflavone malonylation and affecting malonyl isoflavone secretion for activation of Nod factor and nodulation.

Multiple analysis of root exudates and microbiome in rice (Oryza sativa) under low P conditions.

Plants release various metabolites from roots and root exudates contribute to differences in stress tolerance among plant species. Plant and soil microbes have complex interactions that are affected by biotic and abiotic factors. The purpose of this study was to examine the differences in metabolites in root exudates of rice (Oryza sativa) cultivars and their correlation with bacterial populations in the rhizosphere. Two rice cultivars (O. sativa cv. Akamai and O. sativa cv. Koshihikari) were grown in soils fertilized with 0 g P kg-1 (- P) or 4.8 g P kg-1 (+ P). Root exudates and root-attached soil were collected at 13 and 20 days after transplanting (DAT) and their metabolites and bacterial community structure were determined. The exudation of proline, serine, threonine, valine and 4-coumarate were increased under low P conditions in both cultivars. There was a positive correlation between the concentration of pantothenate in root exudates and the representation of members of the genera Clostridium and Sporosarcina, which were negatively correlated with root dry weight. Gracilibacter, Opitutus, Pelotomaculum, Phenylobacterium and Oxobacter were positively correlated with root dry weight and presence of allantoin, 2-aminobtyrate and GlcNac. This study provides new information about the response of plants and rhizosphere soil bacteria to low P conditions.

Bacterial rhizosphere community profile at different growth stages of Umorok (Capsicum chinense) and its response to the root exudates.

The role of microflora is an indispensable part of the living organisms. Plants actively recruit specific microbial community to establish favorable habitat with the distinct microbiome, essentially unique for each species, offering new opportunities for plant growth and productivity. Umorok, an indigenous chili variety of northeastern India, production is highly affected by various factors; therefore, rhizosphere bacteria and their relationship with the root exudates released were analyzed to demonstrate rhizosphere bacterial impact on plant growth and health. Culturable and metagenomic bacterial DNA was characterized and the chemical nature of the root exudate was analyzed using chemotaxis assay after its basic analysis in HPLC. Juvenile stage exhibited diverse bacterial species of gammaproteobacteria, alphaproteobacteria, and actinobacteria but lacked the betaproteobacteria while the microbial diversity was reduced in flowering and fruiting stages. However, every growth stage maintained a similar amount of bacterial population regardless of diversity. The population of Pseudomonas, Bacillus, and Burkholderia species was increased several folds in flowering and fruiting stage. Further, the chemotaxis assay unveiled the advantage of root exudate chemical composition for specific microbial recruitment. The chemical composition analysis of root exudates showed substantial variation in the concentration of organic acids, phenolics, and flavonoids that are favoring unique bacterial species. Thus, root exudates confer and limit the related microbial population besides typical plant-bacterial synergetic association. This study emphasized information about the type of microbial load present in each growth stage, which is essential to develop a microbial consortia package for Umorok overall crop improvement.

Oxalic Acid in Root Exudates Enhances Accumulation of Perfluorooctanoic Acid in Lettuce.

Perfluorooctanoic acid (PFOA) is bioaccumulative in crops. PFOA bioaccumulation potential varies largely among crop varieties. Root exudates are found to be associated with such variations. Concentrations of low-molecular-weight organic acids (LMWOAs) in root exudates from a PFOA-high-accumulation lettuce variety are observed significantly higher than those from PFOA-low-accumulation lettuce variety (p < 0.05). Root exudates and their LMWOAs components exert great influences on the linear sorption-desorption isotherms of PFOA in soils, thus activating PFOA and enhancing its bioavailability. Among root exudate components, oxalic acid is identified to play a key role in activating PFOA uptake, with >80% attribution. Oxalic acid at rhizospheric concentrations (0.02-0.5 mM) can effectively inhibit PFOA sorption to soils by decreasing hydrophobic force, electrostatic attraction, ligand exchange, and cation-bridge effect. Oxalic acid enhances dissolution of metallic ions, iron/aluminum oxides, and organic matters from soils and forms oxalate-metal complexes, based on nuclear magnetic resonance spectra, ultraviolet spectra, and analyses of metal ions, iron/aluminum organometallic complexes, and dissolved organic carbon. The findings not only reveal the activation process of PFOA in soils by root exudates, particularly oxalic acid at rhizospheric concentrations, but also give an insight into the mechanism of enhancing PFOA accumulation in lettuce varieties.

Changes in root-exudate-induced respiration reveal a novel mechanism through which drought affects ecosystem carbon cycling.

Root exudates play an important role in ecosystem response to climate change, but the functional consequences of drought-induced changes in the quality of root exudates are unknown. Here, we addressed this knowledge gap in a unique experimental approach. We subjected two common grassland species that differ widely in their growth strategies and root systems, the grass Holcus lanatus and the forb Rumex acetosa, to 2 wk of drought. We collected root exudates and soils at the end of the drought and after 2 wk of recovery and readded all root exudates to all soils in a fully reciprocal set-up to measure root-exudate-induced respiration. We found that soil treatment was unimportant for determining root-exudate-induced respiration. By contrast, root exudates collected from plants that had experienced drought clearly triggered more soil respiration than exudates from undroughted plants. Importantly, this increased respiration compensated for the lower rates of root exudation in droughted plants. Our findings reveal a novel mechanism through which drought can continue to affect ecosystem carbon cycling, and a potential plant strategy to facilitate regrowth through stimulating microbial activity. These findings have important implications for understanding plant and ecosystem response to drought.

Autotoxicity of root exudates varies with species identity and soil phosphorus.

Root exudate autotoxicity (i.e. root exudates from a given plant have toxic effects on itself) has been recognized to be widespread. Here we examined how plant species identity and soil phosphorus (P) availability influenced this autotoxicity and the possible stoichiometric mechanisms. We conducted an experiment with three species (Luctuca sativa, Sesbania cannabina, and Solidago canadensis), which were subject to four treatments consisting of activated carbon (AC) and soil P. AC addition increased the whole-plant biomass of each species under high P conditions and this AC effect varied strongly with species identity. For Solidago, the relative increase in whole-plant biomass due to AC addition was larger in the low P than in the high P. Root exudate autotoxicity differed between roots and shoots. AC addition decreased root N:P ratios but failed to influence shoot N:P ratios in three species. These findings suggest that soil P enrichment might mediate root exudate autotoxicity and that this P-mediated autotoxicity might be related to root N and P stoichiometry. These patterns and their implications need to be addressed in the context of plant communities.

Non-Targeted Metabolomics Reveals Sorghum Rhizosphere-Associated Exudates are Influenced by the Belowground Interaction of Substrate and Sorghum Genotype.

Root exudation is an important plant process by which roots release small molecules into the rhizosphere that serve in overall plant functioning. Yet, there is a major gap in our knowledge in translating plant root exudation in artificial systems (i.e., hydroponics, sterile media) to crops, specifically for soils expected in field conditions. Sorghum (Sorghum bicolor L. Moench) root exudation was determined using both ultra-performance liquid chromatography and gas chromatography mass spectrometry-based non-targeted metabolomics to evaluate variation in exudate composition of two sorghum genotypes among three substrates (sand, clay, and soil). Above and belowground plant traits were measured to determine the interaction between sorghum genotype and belowground substrate. Plant growth and quantitative exudate composition were found to vary largely by substrate. Two types of changes to rhizosphere metabolites were observed: rhizosphere-enhanced metabolites (REMs) and rhizosphere-abated metabolites (RAMs). More REMs and RAMs were detected in sand and clay substrates compared to the soil substrate. This study demonstrates that belowground substrate influences the root exudate profile in sorghum, and that two sorghum genotypes exuded metabolites at different magnitudes. However, metabolite identification remains a major bottleneck in non-targeted metabolite profiling of the rhizosphere.

Influence of aspartic acid and lysine on the uptake of gold nanoparticles in rice.

The interactions between plants and nanomaterials (NMs) can shed light on the environmental consequences of nanotechnology. We used the major crop plant rice (Oryza sativa L.) to investigate the uptake of gold nanoparticles (GNPs) coated with either negatively or positively charged ligands, over a 5-day period, in the absence or presence of one of two amino acids, aspartic acid (Asp) or lysine (Lys), acting as components of rice root exudates. The presence of Asp or Lys influenced the uptake and distribution of GNPs in rice, which depended on the electrical interaction between the coated GNPs and each amino acid. When the electrical charge of the amino acid was the same as that of the surface ligand coated onto the GNPs, the GNPs could disperse well in nutrient solution, resulting in increased uptake of GNPs into rice tissue. The opposite was true where the charge on the surface ligand was different from that on the amino acid, resulting in agglomeration and reduced Au uptake into rice tissue. The behavior of GNPs in the hydroponic nutrient solution was monitored in terms of agglomeration, particle size distribution, and surface charge in the presence and absence of Asp or Lys, which depended strongly on the electrostatic interaction. Results from this study indicated that the species of root exudates must be taken into account in assessing the bioavailability of nanomaterials to plants.