The Influence of the Rhizosphere on Crop Productivity

Whipps, J. M.; Lynch, J. M.

doi:10.1007/978-1-4757-0611-6_5

Cited by 111 publications

(33 citation statements)

References 283 publications

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“…4). A 5-flM treatment in the experiment reported in Figure 4 did not increase growth rate above that for 2.5 uM, and other tests with saturating concentrations of luteolin (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) Mm in this medium, as determined by HPLC analysis) never increased the growth rate over the enhancement evident with 1 to 5 AM treatments in various experiments. Growth rates calculated for data in Figure 4 …”

Section: Biological Activity Of Flavonoidsmentioning

confidence: 57%

“…Plants certainly affect primary metabolism of soil microbes through carbon released from their roots (28), but specific molecules within that carbon mass can have unique effects on microbial growth. Luteolin and quercetin in seed exudate may play a critical role in structuring the microbial community around the developing root during the first few hours of germination by promoting growth of the N2-fixing alfalfa symbiont R. meliloti.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Flavonoids Released Naturally from Alfalfa Seeds Enhance Growth Rate of Rhizobium meliloti

Hartwig¹,

Joseph²,

Phillips³

1991

Plant Physiol.

192

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Alfalfa (Medicago sativa L.) releases different flavonoids from seeds and roots. Imbibing seeds discharge 3',4',5,7-substituted flavonoids; roots exude 5-deoxy molecules. Many, but not all, of these flavonoids induce nodulation (nod) genes in Rhizobium meliloti. The dominant flavonoid released from alfalfa seeds is identified here as quercetin-3-O-galactoside, a molecule that does not induce nod genes. Low concentrations (1-10 micromolar) of this compound, as well as luteolin-7-O-glucoside, another major flavonoid released from germinating seeds, and the aglycones, quercetin and luteolin, increase growth rate of R. meliloti in a defined minimal medium. Tests show that the 5,7-dihydroxyl substitution pattern on those molecules was primarily responsible for the growth effect, thus explaining how 5-deoxy flavonoids in root exudates fail to enhance growth of R. meliloti. Luteolin increases growth by a mechanism separate from its capacity to induce rhizobial nod genes, because it still enhanced growth rate of R. meliloti lacking functional copies of the three known nodD genes. Quercetin and luteolin also increased growth rate of Pseudomonas putida. They had no effect on growth rate of Bacillus subtilis or Agrobacterium tumefaciens, but they slowed growth of two fungal pathogens of alfalfa. These results suggest that alfalfa can create ecochemical zones for controlling soil microbes by releasing structurally different flavonoids from seeds and roots.

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Section: Biological Activity Of Flavonoidsmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 99%

Flavonoids Released Naturally from Alfalfa Seeds Enhance Growth Rate of Rhizobium meliloti

Hartwig¹,

Joseph²,

Phillips³

1991

Plant Physiol.

192

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“…The carbon sources selected for the enrichment media used in this study are major constituents of root exudates and internal carbon pools in a variety of grasses including Spartina alterniflora (Livingstone & Patriquin 1980, Boyle & Patriquin 1981, as well as in other plants (Street et al 1978, Bokhari et al 1979, Newman 1985, Whipps & Lynch 1986. Presumably, these carbon sources are important compounds in the root microenvironments of Salicornia as well.…”

Section: Resultsmentioning

confidence: 99%

Host-specific ecotype diversity of rhizoplane diazotrophs of the perennial glasswort Salicornia virginica and selected salt marsh grasses

Bagwell¹,

Dantzler²,

Bergholz³

et al. 2001

Aquat. Microb. Ecol.

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The degree of host specificity of most plant root associated bacteria is poorly understood. In this study we examined the physiological diversity of oxygen utilizing, culturable diazotrophs from the rhizoplane of the high marsh perennial glasswort Salicornia virginica and compared them to diazotrophs from other salt marsh plants (tall and short Spartina alterniflora, Juncus roemerianus, and Spartina patens) from the same ecosystem. Forty-six pure culture strains were recovered from the rhizoplane of S. virginica by stab inoculating freshly collected roots into combined nitrogen-free semi-solid media, followed by streak plating of clonal outgrowths. The majority of these strains were Gram-negative obligately aerobic or microaerophilic rods, but 3 Gram-positive strains were also isolated and characterized. API 20NE test strips were used for preliminary characterization of all strains, yielding 22 physiologically different API strain groups. One representative strain was selected from each API group and tested for the presence of nifH, denoting strains capable of N 2 -fixation. Seventeen strains (14 Gram-negative, 3 Gram-positive) were nifH-positive and were characterized further using BIOLOG test plates. Four well-supported strain clusters were identified by bootstrapped cluster analysis of the BIOLOG substrate utilization profiles. These clusters differed in utilization of carbohydrates, carboxylic acids, and amino acids. S. virginica diazotrophs were physiologically quite different from rhizoplane diazotrophs from the low marsh plants S. alterniflora and J. roemerianus, but much more similar to diazotrophs from another high marsh plant, S. patens. We hypothesize that the observed physiological differentiation between high marsh and low marsh diazotrophs reflects differences in selection pressures in the rhizoplane microenvironment produced by plants with differing abilities to ventilate the rhizosphere. In addition, high and low marsh branches were further resolved into host-specific strain clusters, which also implies a strong impact of other host features, such as the suite of carbon exudate compounds produced, on the distributions of specific diazotroph strains. These findings imply endemic, host-specific distributions of salt marsh diazotrophs and are consistent with the great diversity of diazotrophs that have been observed in this ecosystem to date. KEY WORDS: Diazotrophs · Rhizoplane · Physiological specialization · Rhizosphere ventilation Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 23: [293][294][295][296][297][298][299][300] 2001 1997, Stoffels et al. 1998, Fernandez et al. 1999, Nusslein & Tiedje 1999, suggesting that these organisms may have limited distribution patterns (i.e. endemism). Endemism would imply that microorganisms are physiologically restricted to defined niches in situ (e.g. Ferris et al. 1996, Moore et al. 1998, Bagwell & Lovell 2000a, with important implications for microbial diversity (Fenchel et al. 1997, Finlay et al....

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“…For cereals the range is 14 to 40% of the total fixed carbon, depending on plant age and growing conditions such as plant water status, soil aeration, soil strength and nutritional status of the plants (74). This organic carbon consists of low molecular weight organic solutes (,free exudates'), mucilage and sloughed off cells and tissues.…”

Section: Root Exudatesmentioning

confidence: 99%

Mechanisms of Manganese Acquisition by Roots from Soils

Marschner¹

1988

Manganese in Soils and Plants

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The Influence of the Rhizosphere on Crop Productivity

Cited by 111 publications

References 283 publications

Flavonoids Released Naturally from Alfalfa Seeds Enhance Growth Rate of Rhizobium meliloti

Flavonoids Released Naturally from Alfalfa Seeds Enhance Growth Rate of Rhizobium meliloti

Host-specific ecotype diversity of rhizoplane diazotrophs of the perennial glasswort Salicornia virginica and selected salt marsh grasses

Mechanisms of Manganese Acquisition by Roots from Soils

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