Trends in Plant Science
Volume 27, Issue 1,
, Pages 80-91
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Plant root exudates serve pivotal roles in supporting plant development and interactions with the physicochemical and biological factors in the rhizosphere. Under stress conditions, root exudation is involved in enhancing plant resource-use efficiency and facilitating the crosstalk between plant and soil microbes to ameliorate stress. Although there are a large number of root exudates that remain to be characterized, recent technological advancements have allowed for the function of many exudate compounds to be elucidated. In this review, we discuss current knowledge about the key root exudates that modulate plant resource-use efficiency under various abiotic stresses including drought, aluminum toxicity, phosphorus, nitrogen, and iron deficiency. The role that key root exudates play in shaping microbial communities in the rhizosphere under stress conditions is also an important consideration addressed in this review.
What are root exudates?
Root exudation (see Glossary) processes are a strong carbon sink for plants, accounting for up to 21% of plant net photosynthates depending on the plant species, growth stage, and nutrient status . A large proportion of plant root exudates are comprised of high-molecular-weight compounds such as proteins and mucilage while the lower molecular weight compounds are more diverse. These low-molecular-weight compounds encompass a wide range of primary metabolites (amino acids, sugars,
Rhizosheath, mycorrhizal fungi, abscisic acid, and osmolytes influence plant performance under drought stress
Drought has many deleterious effects on plants including but not limited to decreasing growth and increasing oxidative stress . The formation of a rhizosheath around roots helps plants cope with drought and has been reported in desert plants and many crops including maize, sorghum, oat, and barley . Although the exact mechanism by which the rhizosheath ameliorates plant drought stress is unknown, it has been suggested to reduce root water loss by increasing the contact between soil and
Mycorrhiza, carboxylates, and acid phosphatases enhance plant P acquisition
P deficiency can severely impair plant development because it is essential in many biological molecules (phospholipid, ATP, and nucleic acid) and cellular activities such as protein regulation and energy transduction . While many soils contain a tremendous amount of P, the majority of soil P is immobilized in organic and inorganic forms that are not available for plant uptake. The important mechanisms that plants use to cope with P deficiency include establishing symbiosis with mycorrhizal
Root exudates mediate belowground N cycle for plant N acquisition
N is an essential constituent in chlorophyll, nucleic acids, and proteins. N stress affects many fundamental processes in plants such as amino acid biosynthesis, photosynthesis, and the tricarboxylic acid cycle . As a result, the root exudation profiles of N-stressed plants commonly display a marked decrease in amino acids, carboxylates, and sugars [39,55]. However, many secondary metabolites have been shown to be induced by N stress and function to modulate microbial activity involved in
Coumarins, flavins, and phytosiderophores in plant Fe acquisition
Fe is an essential micronutrient involved in many cellular activities including photosynthesis and DNA biosynthesis . Despite being very abundant in the soil, Fe largely exists in the ferric form (Fe3+), which forms highly insoluble oxide and hydroxide minerals, making Fe unavailable for plant uptake. Lower soil pH helps reduce Fe3+ to ferrous forms (Fe2+) that are more available for plant uptake, but the Fe2+ is prone to oxidation to Fe3+ in the presence of oxygen. There are two strategies
Carboxylates confer tolerance to Al toxicity
Due to the abundance and high solubility of Al at low pH, Al toxicity has become a major constraint for crop production, especially in tropical countries where acidic soils are prevalent. Upon exposure to Al, root growth is rapidly inhibited . Long term exposure to Al not only puts plants under significant amounts of oxidative stress, but also damages the root systems, disrupting the uptake of water and nutrients . The secretion of carboxylates plays a crucial role in enhancing plant
The roles of root exudates for enhancing plant performance under drought and various abiotic stresses are critical for plant growth and productivity. It is promising that plant resource-use efficiency can be improved by altering root exudation processes through breeding or genetic engineering. For example, the wheat Al-activated malate transporter (TaALMT1) that confers Al-tolerance in wheat genotype CAR3911 has been successfully introgressed into the Al-sensitive, high-yielding winter wheat
This work is supported by the Agricultural Research Division (ARD) of the Institute of Agriculture and Natural Resources. We thank the James Schnable, Sydney Everhart, Yufeng Ge, and the anonymous reviewers for their input in this work. Work on this topic in the Schachtman Lab has been supported by United States Department of Agriculture (USDA)-National Institute of Food and Agriculture (NIFA) award 2020-67019-31796 and the National Science Foundation EPSCOR to fund The Center for Root and
Declaration of interests
No interests to declare.
- Primary metabolites
- metabolites that are essential for cell growth and functioning.
- the region around the root that is characterized by the firm adhesion of soil aggregates to the root tissue that remains attached even after vigorous agitation.
- the layer of root-surrounding soil that is under the direct influence of root exudates.
- Root exudation
- the process in which plants release carbon and other compounds from the roots to the surrounding soil.
- Secondary metabolites
- Y. Ma
A new allele for aluminium tolerance gene in barley (Hordeum vulgare L.)
- J.F. Ma
Aluminium tolerance in plants and the complexing role of organic acids
Trends Plant Sci.
(2001)(Video) Biological Pathways to Carbon- Rich Soils - Webinar with Dr. Christine Jones
- H.H. Tsai et al.
Mobilization of iron by plant-borne coumarins
Trends Plant Sci.
- D. Coskun
How plant root exudates shape the nitrogen cycle
Trends Plant Sci.
- S. Zhu
Nitrogen fertilizer rate affects root exudation, the rhizosphere microbiome and nitrogen-use-efficiency of maize
Appl. Soil Ecol.
- C. Staudinger
Evidence for a rhizobia-induced drought stress response strategy in Medicago truncatula
- R.D. Sleator et al.
Bacterial osmoadaptation: the role of osmolytes in bacterial stress and virulence
FEMS Microbiol. Rev.
- A. Canarini
Drought effects on Helianthus annuus and Glycine max metabolites: from phloem to root exudates
- Y. Kaci
Isolation and identification of an EPS-producing Rhizobium strain from arid soil (Algeria): characterization of its EPS and the effect of inoculation on wheat rhizosphere soil structure
- R.L. Berendsen
The rhizosphere microbiome and plant health
Trends Plant Sci.
Root exudation and rhizosphere biology
The role of root exudates in rhizosphere interactions with plants and other organisms
Annu. Rev. Plant Biol.
Influence of low-molecular-weight organic acids on the solubilization of phosphate
Biol. Fertil. Soils
Benzoxazinoids in root exudates of maize attract Pseudomonas putida to the rhizosphere
Response of plants to water stress
Front. Plant Sci.
The rhizosheath: from desert plants adaptation to crop breeding
Unwrapping the rhizosheath
Disruption of the Paenibacillus polymyxa levansucrase gene impairs its ability to aggregate soil in the wheat rhizosphere
Role of arbuscular mycorrhizal fungi in plant growth regulation: implications in abiotic stress tolerance
Front. Plant Sci.
Drought-induced accumulation of root exudates supports post-drought recovery of microbes in mountain grassland
Front. Plant Sci.
Harnessing rhizosphere microbiomes for drought-resilient crop production
Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi
Strigolactones stimulate arbuscular mycorrhizal fungi by activating mitochondria
Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato
Plant Cell Environ.
Flavonoids in plant rhizospheres: secretion, fate, and their effects on biological communication
Atmospheric CO2 enrichment and drought stress modify root exudation of barley
Glob. Chang. Biol.
Abscisic acid and cytokinins in the root exudates and leaves and their relationship to senescence and remobilization of carbon reserves in rice subjected to water stress during grain filling
Root exudate metabolomes change under drought and show limited capacity for recovery
Abscisic acid and abiotic stress tolerance in crop plants
Front. Plant Sci.
Exogenous application of abscisic acid (ABA) increases root and cell hydraulic conductivity and abundance of some aquaporin isoforms in the ABA-deficient barley mutant Az34
Root ABA accumulation enhances rice seedling drought tolerance under ammonium aupply: interaction with aquaporins
Front. Plant Sci.
Phytohormones regulate accumulation of osmolytes under abiotic stress
Sinorhizobium meliloti chemoreceptor McpU mediates chemotaxis toward host plant exudates through direct proline sensing
Appl. Environ. Microbiol.
Reduced ABA accumulation in the root system is caused by ABA exudation in upland rice (Oryza sativa L. var. Gaoshan1) and this enhanced drought adaptation
Plant Cell Physiol.
Osmolyte accumulation: can it really help increase crop yield under drought conditions?
Plant Cell Environ.
Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource
Moderating mycorrhizas: Arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries
Plant Cell Environ.
Carbon trading for phosphorus gain: the balance between rhizosphere carboxylates and arbuscular mycorrhizal symbiosis in plant phosphorus acquisition
Plant Cell Environ.
Tradeoffs among root morphology, exudation, and mycorrhizal symbioses for phosphorus-acquisition strategies of 16 crop species
Mycorrhizal associations and phosphorus acquisition: from cells to ecosystems
Annu. Plant Rev. Phosphorus Metab. Plants
How belowground interactions contribute to the coexistence of mycorrhizal and non-mycorrhizal species in severely phosphorus-impoverished hyperdiverse ecosystems
Root structure and functioning for efficient acquisition of phosphorus: matching morphological and physiological traits
Can citrate efflux from roots improve phosphorus uptake by plants? Testing the hypothesis with near-isogenic lines of wheat
Root exudation of sugars, amino acids, and organic acids by maize as affected by nitrogen, phosphorus, potassium, and iron deficiency
J. Plant Nutr. Soil Sci.
Exudation of carboxylates in Australian Proteaceae: chemical composition
Plant Cell Environ.
Quantifying citrate-enhanced phosphate root uptake using microdialysis
Analysis of phosphate acquisition efficiency in different Arabidopsis accessions
Function and mechanism of organic anion exudation from plant roots
Annu. Rev. Plant Physiol.
Characterisation of Al-stimulated efflux of malate from the apices of Al-tolerant wheat roots
Root excretion of carboxylic acids and protons in phosphorus-deficient plants
Cited by (46)
Direct introduction MALDI FTICR MS based on dried droplet deposition applied to non-targeted metabolomics on Pisum Sativum root exudates
Non-targeted metabolomic approaches based on direct introduction (DI) through a soft ionization source are nowadays used for large-scale analysis and wide cover-up of metabolites in complex matrices. When coupled with ultra-high-resolution Fourier-Transform ion cyclotron resonance (FTICR MS), DI is generally performed through electrospray (ESI), which, despite the great analytical throughput, can suffer of matrix effects due to residual salts or charge competitors. In alternative, matrix assisted laser desorption ionization (MALDI) coupled with FTICR MS offers relatively high salt tolerance but it is mainly used for imaging of small molecule within biological tissues. In this study, we report a systematic evaluation on the performance of direct introduction ESI and MALDI coupled with FTICR MS applied to the analysis of root exudates (RE), a complex mixture of metabolites released from plant root tips and containing a relatively high salt concentration. Classic dried droplet deposition followed by screening of best matrices and ratio allowed the selection of high ranked conditions for non-targeted metabolomics on RE. Optimization of MALDI parameters led to improved reproducibility and precision. A RE desalted sample was used for comparison on ionization efficiency of the two sources and ion enhancement at high salinity was highlighted in MALDI by spiking desalted solution with inorganic salts. Application of a true lyophilized RE sample exhibited the complementarity of the two sources and the ability of MALDI in the detection of undisclosed metabolites suffering of matrix effects in ESI mode.
Cadmium tolerance and accumulation from the perspective of metal ion absorption and root exudates in broomcorn millet
2023, Ecotoxicology and Environmental Safety
Cadmium (Cd) is a persistent heavy metal that poses environmental and public health concerns. This study aimed to identify the potential biomarkers responsible for Cd tolerance and accumulation by investigating the response of the content of essential metal elements, transporter gene expression, and root exudates to Cd stress in broomcorn millet (Panicum miliaceum). A hydroponics experiment was conducted using two broomcorn millet cultivars with distinct Cd tolerance levels and accumulation phenotypes (Cd-tolerant and Cd-sensitive cultivars). Cd stress inhibited lateral root growth, especially in the Cd-sensitive cultivar. Furthermore, Cd accumulation was significantly greater in the Cd-tolerant cultivar than in the Cd-sensitive cultivar. Cd stress significantly inhibited the absorption of essential metal elements and significantly increased the calcium concentration. Differentially expressed genes involved in metal ion transport were identified via transcriptome analysis. Cd stress altered the composition of root exudates, thus increasing lipid species and decreasing alkaloid, lignan, sugar, and alcohol species. Moreover, Cd stress significantly reduced most alkaloid, organic acid, and phenolic acid exudates in the Cd-tolerant cultivar, while it increased most lipid and phenolic acid exudates in the Cd-sensitive cultivar. Some significantly changed root exudates (ferulic acid, O-coumaric acid, and spermine) are involved in the phenylalanine biosynthesis, and arginine and proline metabolic pathways, thus, may be potential biomarkers of Cd stress response. Overall, metal ion absorption and root exudates are critical for Cd tolerance and accumulation in broomcorn millet. These findings provide valuable insights into improving Cd phytoremediation by applying mineral elements or metabolites.
Nontargeted metabolomic analysis to unravel alleviation mechanisms of carbon nanotubes on inhibition of alfalfa growth under pyrene stress
2022, Science of the Total Environment
Carbon nanotubes have displayed great potential in enhancing phytoremediation of PAHs polluted soils. However, the response of plants to the coexistence of carbon nanotubes and PAHs and the associated influencing mechanisms remain largely unknown. Here, the effect of carbon nanotubes on alfalfa growth and pyrene uptake under exposure to pyrene was evaluated through sand culture experiment and gas chromatography time-of-flight mass spectrometer (GC-TOF-MS) based metabolomics. Results showed that pyrene at 10 mg kg−1 obviously reduced the shoot fresh weight of alfalfa by 18.3 %. Multiwall carbon nanotubes (MWCNTs) at 25 and 50 mg kg−1 significantly enhanced the shoot fresh weight in a dose-dependent manner, nearly by 80 % at 50 mg kg−1. Pyrene was mainly accumulated in alfalfa roots, in which the concentration was 35 times as much as that in shoots. MWCNTs greatly enhanced the accumulation of pyrene in alfalfa roots, almost by two times at 50 mg kg−1, while decreased pyrene concentration in shoots, from 0.11 mg kg−1 to 0.044 mg kg−1 at MWCNTs concentration of 50 mg kg−1. Metabolomics data revealed that pyrene at 10 mg kg−1 trigged significant metabolic changes in alfalfa root exudates, downregulating 27 metabolites. MWCNTs generated an increase in the contents of some downregulated metabolites caused by pyrene stress, which were restored to the original level or even higher, mainly including organic acids and amino acids. MWNCTs significantly enriched some metabolic pathways positively correlated with shoot growth and pyrene accumulation in shoots under exposure to pyrene, including TCA cycle, glyoxylate and dicarboxylate metabolism, cysteine and methione metabolism as well as alanine, aspartate and glutamate metabolism. This work highlights the regulation effect of MWCNTs on the metabolism of root exudates, which are helpful for alfalfa to alleviate the stress from pyrene contamination.
Characterization of copper-induced-release of exudates by Citrus sinensis roots and their possible roles in copper-tolerance
Copper (Cu) excess is often observed in old Citrus orchards. Little information is available on the characterization of Cu-induced-release of root exudates and their possible roles in plant Cu-tolerance. Using sweet orange [Citrus sinensis (L.) Osbeck cv. Xuegan] seedlings as materials, we investigated the impacts of 0, 0.5, 25, 150, 350, 550, 1000, 2000 or 5000μM CuCl2 (pH 4.8) on Cu uptake, root exudates [malate, citrate, total phenolics (TP), total soluble sugars (TSS) and total free amino acids (TFAA)], electrolyte leakage and malondialdehyde, and solution pH under hydroponic conditions; the time-course of root exudates and solution pH in response to Cu; and the impacts of protein synthesis and anion-channel inhibitors, and temperature on Cu-induced-secretion of root exudates and solution pH. About 70% of Cu was accumulated in 0 and 0.5μM Cu-exposed roots, while over 97% of Cu was accumulated in ≥25μM Cu-exposed roots. Without Cu, the seedlings could alkalize the solution pH from 4.8 to above 6.0. Cu-stimulated-secretion of root exudates elevated with the increment of Cu concentration from 0 to 1000μM, then decreased or remained unchanged with the further increment of Cu concentration, while root electrolyte leakage and malondialdehyde (root-induced alkalization) increased (lessened) with the increment of Cu concentration from 0 to 5000μM. Further analysis indicated that Cu-stimulated-secretion of root exudates was an energy-dependent process and could repressed by inhibitors, and that there was no discernible delay between the onset of exudate release and the addition of Cu. To conclude, both root-induced alkalization and Cu-stimulated-release of root exudates played a key role in sweet orange Cu-tolerance via increasing root Cu accumulation and reducing Cu uptake and phytotoxicity.
Bricks out of the wall: polysaccharide extramural functions
2022, Trends in Plant Science
Plant polysaccharides are components of plant cell walls and/or store energy. However, this oversimplified classification neglects the fact that some cell wall polysaccharides and glycoproteins can localize outside the relatively sharp boundaries of the apoplastic moiety, where they adopt functions not directly related to the cell wall. Such polysaccharide multifunctionality (or ‘moonlighting’) is overlooked in current research, and in most cases the underlying mechanisms that give rise to unconventional ex muro trafficking, targeting, and functions of polysaccharides and glycoproteins remain elusive. This review highlights major examples of the extramural occurrence of various glycan cell wall components, discusses the possible significance and implications of these phenomena for plant physiology, and lists exciting open questions to be addressed by future research.
Foliar application of lambda-cyhalothrin modulates root exudate profile and the rhizosphere bacteria community of dioecious Populus cathayana
2022, Environmental Pollution
Dioecious plants show sexual differences in resistance traits to abiotic stresses. However, the effects of exogenous pesticide application on female and male plant growth and their associated adaptation mechanisms are unclear. Our study investigated the effects of the broad-spectrum pesticide lambda-cyhalothrin (λ-CY) on dioecious Populus cathayana growth and explored the factors through which λ-CY changed the rhizosphere bacterial community and physicochemical soil properties via sex-specific metabolomics. The sequential application of λ-CY significantly suppressed male shoot- and root biomass, with little effect on the growth of females. Females possessed a higher intrinsic chemo-diversity within their root exudates, and their levels of various metabolites (sugars, fatty acids, and small organic acids) increased after exposure to λ-CY with consequences on bacterial community composition. Maintaining high bacterial alpha diversity and recruiting specific bacterial groups slowed down the loss of rhizosphere nutrients in females. In contrast, the reduction in bacterial alpha diversity and network structure stability in males was associated with lower rhizosphere nutrient availability. Spearman's correlation analysis revealed that several bacterial groups were positively correlated with the root secretion of lipids and organic acids, suggesting that these metabolites can affect the soil bacterial groups actively involved in the nutrient pool. This study provided novel insights that root exudates and soil microbial interactions may mediate sex-specific differences in response to pesticide application.
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Plant health in natural environments depends on interactions with complex and dynamic communities comprising macro- and microorganisms. While many studies have provided insights into the composition of rhizosphere microbiomes (rhizobiomes), little is known about whether plants shape their rhizobiomes. Here, we discuss physiological factors of plants that may govern plant–microbe interactions, focusing on root physiology and the role of root exudates. Given that only a few plant transport proteins are known to be involved in root metabolite export, we suggest novel families putatively involved in this process. Finally, building off of the features discussed in this review, and in analogy to well-known symbioses, we elaborate on a possible sequence of events governing rhizobiome assembly.
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More than two-thirds of terrestrial plants acquire nutrients by forming a symbiosis with arbuscular mycorrhizal (AM) fungi. AM fungal hyphae recruit distinct microbes into their hyphosphere, the narrow region of soil influenced by hyphal exudates. They thereby shape this so-called second genome of AM fungi, which significantly contributes to nutrient mobilization and turnover. We summarize current insights into characteristics of the hyphosphere microbiome and the role of hyphal exudates on orchestrating its composition. The hyphal exudates not only contain carbon-rich compounds but also promote bacterial growth and activity and influence the microbial community structure. These effects lead to shifts in function and cause changes in organic nutrient cycling, making the hyphosphere a unique and largely overlooked functional zone in ecosystems.
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Root exudates are the main media of information communication and energy transfer between plant roots and the soil. Understanding the response of root exudates to contamination stress is crucial in revealing the rhizoremediation mechanisms. Here, we investigate the response of alfalfa root exudates to bis(2-ethylhexyl) phthalate (DEHP) stress based on nontargeted metabolomic analysis. Alfalfa root exudates were collected using greenhouse hydroponic culture and analysed by gas chromatography-time of flight mass spectrometry (GC-TOFMS). A total of 314 compounds were identified in alfalfa root exudates of which carbohydrates, acids and lipids accounted for 28.6, 15.58 and 13.87%, respectively. Orthogonal partial least squares discriminant analysis (OPLS-DA) shows that DEHP exerted an important influence on the composition and quantity of root exudates. Fifty metabolites were clearly changed even at lower concentrations of DEHP, including common carbohydrates, fatty acids and some special rhizosphere signal materials, such as 4′,5-dihyrroxy-7-methoxyisoflavone. DEHP stress significantly suppressed carbohydrate metabolism but promoted fatty acid metabolism. However, amino acid metabolism, lipid metabolism and the tricarboxylic acid (TCA) cycle showed little change in response to DEHP stress.
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Trends in Plant Science, Volume 25, Issue 12, 2020, pp. 1194-1202
Root–soil interactions in the rhizosphere are central to resource acquisition and crop production in agricultural systems. However, apart from studies in idealized experimental systems, rhizosphere processes in real agricultural soils in situ are largely uncharacterized. This limits the contribution of rhizosphere science to agriculture and the ongoing Green Revolution. Here, we argue that understanding plant responses to soil heterogeneity is key to understanding rhizosphere processes. We highlight rhizosphere sensing and root-induced soil modification in the context of heterogeneous soil structure, resource distribution, and root–soil interactions. A deeper understanding of the integrated and dynamic root–soil interactions in the heterogeneously structured rhizosphere could increase crop production and resource use efficiency towards sustainable agriculture.
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© 2021 Elsevier Ltd. All rights reserved.
How abiotic stress conditions affects plant roots? ›
Low soil temperature results in reduced tissue nutrient concentrations and as such decreases root growth Lahti et al. . Lateral root formation is inhibited by low temperature. Root growth and temperature generally increase together up to a point.What are the factors affecting root exudates? ›
Exudation from roots of organic substances is affected by a variety of factors, including soil water stress, temperature, light intensity, the age and species of plant, mineral nutrition, soil microorganisms, the degree of anaerobiosis, and the foliar application of chemicals.What is the abiotic stress response of plants? ›
Abiotic stress conditions, such as high light and osmotic stress, are known to trigger systemic stress signalling in plants, which leads to stress responses in unexposed distal tissues, resulting in systemic acquired acclimation. For instance, the activation of systemic acquired acclimation in A.What is the importance of plant root exudates? ›
For example, root exudates serve as signals that initiate symbiosis with rhizobia and mycorrhizal fungi. In addition, root exudates maintain and support a highly specific diversity of microbes in the rhizosphere of a given particular plant species, thus suggesting a close evolutionary link.What is the meaning of root exudates? ›
Root exudates refer to a suite of substances in the rhizosphere that are secreted by the roots of living plants and microbially modified products of these substances. They consist of low-molecular-weight organic compounds that are freely and passively released root-cell material and mucilage associated with roots.What causes exudate formation? ›
Exudate consists of fluid and leukocytes that move to the site of injury from the circulatory system in response to local inflammation. This inflammatory response leads to blood vessel dilatation and increased permeability, resulting in increased production of exudate.What factors affect root pressure? ›
- The quantity of xylem vessels in the root.
- The soil's water potential.
- The quantity of root hairs.
- The pace at which the roots absorb water.
- The stem's water potential.
- The rate of transpiration.
Primary root exudates include simple and complex sugars, amino acids, polypeptides and proteins, organic, aliphatic and fatty acids, sterols, and phenolics (Nguyen, 2003; Badri and Vivanco, 2009; Badri et al., 2009).What is the role of root exudates in rhizosphere interactions with plants and other organisms? ›
Roots produce chemical signals that attract bacteria and induce chemotaxis. Positive interactions mediated by root exudates also include growth facilitators or growth regulator mimics that support growth of other plants and also perform cross-species signaling with rhizospheric invertebrates.What is the composition of plant root exudates? ›
Root exudates are composed mainly of sugars, amino acids, organic acids, vitamins, and high molecular weight polymers, thus becoming a rich source of nutrients for the rhizospheric microbes .
What are examples of exudate? ›
Examples of plant exudates include saps, gums, resins, and latex. In humans, the exudate can be seen in a wound or even in the eye.What are the characteristics of exudate? ›
An exudate is defined by a high specific gravity (>1.020), fluid to serum total protein ratio less than 0.5, and fluid to serum LDH ratio greater than 0.6, with transudates having the opposite characteristics.What is the benefit of exudate? ›
The main role of exudate is in facilitating the diffusion of vital healing factors (eg growth and immune factors) and the migration of cells across the wound bed5. It also promotes cell proliferation, provides nutrients for cell metabolism, and aids autolysis of necrotic or damaged tissue.What is the main cause of root pressure in plants? ›
Root pressure is caused by active distribution of mineral nutrient ions into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis.What is the effect of root pressure in plants? ›
root pressure, in plants, force that helps to drive fluids upward into the water-conducting vessels (xylem). It is primarily generated by osmotic pressure in the cells of the roots and can be demonstrated by exudation of fluid when the stem is cut off just aboveground.Which of the following can be a cause of root pressure in plants? ›
So the correct answer is 'Osmosis'.What are the components of root exudate? ›
Root exudates are composed mainly of sugars, amino acids, organic acids, vitamins, and high molecular weight polymers, thus becoming a rich source of nutrients for the rhizospheric microbes .What are factors affecting rhizosphere? ›
The most important factors which affect / influence the microbial flora of the rhizosphere or rhizosphere effect are: soil type & its moisture, soil amendments, soil PH, proximity of root withsoil, plant species, and age of plant and root exudates.What are the main stimuli affecting the growth of the root? ›
Environmental factors, including light, chemical nutrients, water, and gravity are stimuli that can provoke tropisms in a plant. The plant grows in the direction of the stimulus as hormones inside the stem, root, and leaf systems in a plant aid in the elongation and growth process of the plant toward the stimuli.Which of the following factors affect the absorption of water by roots? ›
The quantity of water in the soil. Soil temperature. Concentration of soil solution. The quantity of air in the soil.