Physiology of organic nitrogen acquisition by ectomycorrhizal fungi and ectomycorrhizas

Chalot, Michel

doi:10.1016/s0168-6445(98)00004-7

Cited by 123 publications

(163 citation statements)

References 91 publications

(165 reference statements)

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“…Determination of free amino acid content in control roots and ectomycorrhizae grown on nitrate revealed higher levels of glutamate, glutamine and asparagine in symbiotic tissues compared with controls, thus leading us to hypothesize that in the T. platyphyllos-T. borchii ectomycorrhizal system these amino acids represent the N compounds by which serve to transfer nitrogen from the fungus to the host plant (Chalot and Brun 1998). After translocation into the root cells, the free glutamine level and the glutamine/glutamate ratio may be involved in governing the level of nitrate-reducing capacity in the plant partner (Campbell 1999).…”

Section: Discussionmentioning

confidence: 99%

Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae

et al. 2003

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The nitrate assimilation pathway represents a useful model system in which to study the contribution of a mycorrhizal fungus to the nitrogen nutrition of its host plant. In the present work we cloned and characterized the nitrate reductase gene (tbnr1) from Tuber borchii. The coding region of tbnr1 is 2,787 nt in length, and it encodes a protein of 929 amino acids. Biochemical and Northern-blot analyses revealed that nitrate assimilation in T. borchii is an inducible system that responds mainly to nitrate. Furthermore, we cloned a nitrate reductase cDNA (tpnr1) from Tilia platyphyllos to set up a quantitative real-time PCR assay that would allow us to determine the fungal contribution to nitrate assimilation in ectomycorrhizal tissue. Using this approach we demonstrated that the level of tbnr1 expression in ectomycorhizae is eight times higher than in free-living mycelia, whereas tpnr1 transcription was found to be down-regulated after the establishment of the symbiosis. Enzymatic assays showed that NADPH-dependent nitrite formation markedly increases in ectomycorrhizae. These findings imply that the fungal partner plays a fundamental role in nitrate assimilation by ectomycorrhizae. Amino acid determination by HPLC revealed higher levels of glutamate, glutamine and asparagine in symbiotic tissues compared with mycelial controls, thus suggesting that these amino acids may represent the compounds that serve to transfer nitrogen to the host plant.

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Section: Discussionmentioning

confidence: 99%

Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae

et al. 2003

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“…Mycorrhizal roots and axenic mycorrhizal fungi generally also absorb amino acids with high affinity, but the range of K m is not much lower than non-mycorrhizal plant roots. The effect of increased absorptive area and proteolytic activity may often be more important than uptake affinity in the improved acquisition of ON by mycorrhizal infection (Chalot and Brun 1998). Soil bacteria and fungi generally have very high affinities for amino acids, but the "K m " reported for soil microbial biomass absorbing amino acids from a slurry or soil solution are higher.…”

Section: Amino Acid Uptake Kinetics By Plants Mycorrhizae and Soil Mmentioning

confidence: 99%

“…While the role of ericoid and ectomycorrhizae in transferring ON to plants is well established (Read 1991;Marschner and Dell 1994;Chalot and Brun 1998), the relative contributions of mycorrhizal and non-mycorrhizal roots is still an open question for many ecosystems. Ecto-and ericoid mycorrhizae improve the surface area (Rousseau et al 1994) and affinity (Chalot et al 1996;Wallenda and Read 1999) of plant roots for ON, and many of the plant species studied are unable to grow on ON sources without their mycorrhizal symbiont (Stribley and Read 1980;Bajwa and Read 1985;Abuzinadah and Read 1989;Finlay et al 1992;Turnbull et al 1995).…”

Section: Plant-microbe Competition For Onmentioning

confidence: 99%

“…We also review the methodologies used to assess plant ON use in ecosystems, including the recent work on the use of natural abundance levels of 15 N to infer N sources for plant species. While some studies have shown that ericoid mycorrhizal fungi may allow their host plants access to N from amino sugars and nucleic acids (Chalot and Brun 1998), the majority of recent studies of ON uptake by plants have focused on amino acids. Therefore, this review will be restricted mainly to the discussion of amino acids as N sources for plants.…”

Section: Introductionmentioning

confidence: 99%

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The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems

2001

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The recently recognized importance of organic nitrogen (ON), particularly amino acids, to plant nutrition in many types of agricultural and natural ecosystems has raised questions about plant-microbe interactions, N availability in soils, and the ecological implications of ON use by plants in the light of climate change and N pollution. In this review we synthesize the recent work on availability and plant uptake of amino acids with classic work on ON in soils. We also discuss recent work on the use of natural abundance levels of (15)N to infer N sources for plants. Reliance on ON is widespread among plants from many ecosystems. Authors have reached this conclusion based on laboratory studies of amino acid uptake by plants in pure culture, amino acid concentrations in soils, plant uptake of isotopically labeled amino acids in the field and in plant-soil microcosms, and from plant natural abundance values of (15)N. The supply of amino acids to plants is determined mainly by the action of soil proteolytic enzymes, interactions between amino acids and the soil matrix, and competition between plants and microbes. Plants generally compete for a minor fraction of the total amino acid flux, but in some cases this forms a significant N resource, especially in ecosystems where microbial biomass undergoes large seasonal fluctuations and contributes labile ON to the soil. A quantitative understanding of ON use by plants is confounded by incomplete data on partitioning of ON between plants, mycorrhizal fungi, and competing soil microbes. Further research is needed to predict the ecological implications of ON use by plants given the influence of climatic change and N pollution.

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“…In other cases, some plants form mycorrhizas, symbiotic associations between mycorrhizal fungi and the roots of host plants, through which plants utilize organic nitrogenous compounds (e.g. proteins, peptides, and amino acids) as nitrogen sources (Read 1991;Chalot and Brun 1998).…”

Section: Introductionmentioning

confidence: 99%

Aspartic proteinases are expressed in pitchers of the carnivorous plant Nepenthes alata Blanco

Fukusaki

Kobayashi

2002

Planta

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Carnivorous plants acquire significant amounts of nitrogen from insects. The tropical carnivorous plant Nepenthes accumulates acidic fluid containing aspartic proteinase (AP) in its trapping organs (pitchers), suggesting that the plant utilizes insect protein as a nitrogen source. Aspartic proteinases have been purified and characterized from sterile pitcher fluid of several species of Nepenthes; however, there is, as of yet, no information about sequence and expression of Nepenthes AP genes. To identify the pitcher AP, we cloned plant AP homologs from N. alata and examined their expressions. Five AP homologs ( NaAP1-NaAP5) were obtained by reverse transcription-polymerase chain reaction with degenerate primers designed for the conserved sequences of plant APs. Alignment of deduced amino acid sequences with other plant APs demonstrated that NaAP1-NaAP4 contained a plant-specific insert (PSI), a unique sequence of plant AP. However, NaAP5 did not possess the insert, and had a shorter sequence (by >100 amino acids) than the other APs. Northern analysis using a part of the coding region of NaAP1 as a probe showed that bands of approx. 1.8 kb corresponding to the sizes of NaAP1-NaAP4 mRNA were present in roots, stems, leaves, tendrils, and lower part of the pitchers, but a band of approx. 1.3 kb corresponding to the size of NaAP5 mRNA was not observed in any organs. In pitchers, highest expressions of NaAP1-NaAP4 were seen in the lower part of open pitchers containing natural prey, suggesting that the expressions of NaAP1-NaAP4 are coupled with prey capture. Transcripts of NaAP2 and NaAP4 were detected in the digestive glands, where AP secretion may occur. This result suggests that NaAP2 and NaAP4 are the possible APs secreted into the pitcher of N. alata.

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Physiology of organic nitrogen acquisition by ectomycorrhizal fungi and ectomycorrhizas

Cited by 123 publications

References 91 publications

Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae

Characterization of the Tuber borchii nitrate reductase gene and its role in ectomycorrhizae

The unexpected versatility of plants: organic nitrogen use and availability in terrestrial ecosystems

Aspartic proteinases are expressed in pitchers of the carnivorous plant Nepenthes alata Blanco

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