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PubMed1968

Contents and recovery of gibberellins in monoecious and gynoecious cucumber plants.

Diffusates from seedlings and root exudates from 6-week-old plants of a monoecious line of cucumber, Cucumis sativus L., contained considerably higher levels of gibberellin-(GA-) like substances than did those from plants of an isogenic gynoecious line. Most of the GA-like activity was found in a chromatogram region typical of GA(1) and GA(3); some activity, particularly in root exudates, appeared also at an R(F) similar to that of GA(4) and GA(7).When seedlings were treated with (3)H-labeled GA(1), more radioactivity was found in the diffusates from monoecious seedlings than from gynoecious ones. The same was true of biological activity in root diffusates from older plants which had been treated with gibberellin A(4+7).In conjunction with evidence present in literature, these results support the idea that endogenous GAs play a part in the regulation of sex expression in cucumber, relatively high levels favoring the formation of staminate flowers.

Journal Article↗

PubMed1989

A Chalcone and Two Related Flavonoids Released from Alfalfa Roots Induce nod Genes of Rhizobium meliloti.

Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Previous investigations identified the flavone luteolin as an active inducer in alfalfa seed extracts, but the nature of nod inducers released from roots has not been reported. Root exudate from 3-day-old alfalfa seedlings was purified and then assayed for biological activity with a nodABC-lacZ fusion in R. meliloti. Indentities of major nod inducers were established by spectroscopic analyses (ultraviolet/visible, proton nuclear magnetic resonance, and mass spectroscopy) and comparison with authentic standards. Major nod inducers, which were identified as 4',7-dihydroxyflavone, 4'-7-dihydroxyflavanone, and 4,4'-dihydroxy-2'-methoxychalcone, were released from seedling roots at 54, 22, and 20 picomole.plant(-1).day(-1), respectively. Luteolin was not found in these root exudates. The 4,4'-dihydroxy-2'-methoxychalcone induced nod genes at a concentration one order of magnitude lower than luteolin and is the first naturally released chalcone reported to have this function. Moderate and weak nod-inducing activity was associated, respectively, with 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone.

Journal Article↗

PubMed1999

A comparison of methods for detecting bacteria in root canal exudate.

This study compared the ability of bacterial detection from intracanal exudate by two different methods. One is a conventional method (i.e. the samples were transported into anaerobic chambers immediately after sampling and then moved to an outside laboratory for identification of bacteria). Another is a preculture method (i.e. the samples were inoculated into semisolid medium immediately after sampling, incubated for 24 h under anaerobic conditions, and then moved to the laboratory for bacterial identification). In 22 cases, the preculture method detected bacteria in 18 of 22 cases, whereas the conventional method detected bacteria in 6 of 22 cases. The preculture method showed significantly higher frequency of bacterial detection (p = 0.0003). Gram-positive cocci (alpha-Streptococcus, Enterococcus, etc.) were detected in many cases. These results suggested that the preculture method could be helpful in detecting root canal bacteria and enhance antibiotic treatment of endodontic disease.

Adult↗

PubMed1991

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

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.

Journal Article↗

PubMed1994

Iron Inefficiency in Maize Mutant ys1 (Zea mays L. cv Yellow-Stripe) Is Caused by a Defect in Uptake of Iron Phytosiderophores.

To determine the Fe inefficiency factors in the maize mutant ys1 (Zea mays L. cv Yellow Stripe), root exudates of Fe-inefficient ys1 and of two Fe-efficient maize cultivars (Alice, WF9) were collected in axenic nutrient solution cultures. Analysis by thin-layer chromatography and high-performance liquid chromatography revealed that under Fe deficiency ys1 released the phytosiderophore 2[prime]-deoxymugineic acid (DMA) in quantities similar to those of Alice and WF9. Under nonaxenic conditions, DMA released by plants of all three cultivars was rapidly decomposed by microorganisms in the nutrient solution. Uptake experiments with 59Fe-labeled DMA, purified from root exudates of either Fe-deficient Alice or ys1 plants, showed up to 20 times lower uptake and translocation of 59Fe in ys1 than in Alice or WF9 plants. The presence of microorganisms during preculture and short-term uptake experiments had no significant effect on uptake and translocation rates of 59Fe in Alice and ys1 plants. We conclude that Fe inefficiency in the maize mutant ys1 is the result of a defect in the uptake system for Fe-phytosiderophores.

Journal Article↗

PubMed1991

Role of Ethylene in the Germination of the Hemiparasite Striga hermonthica.

Seed germination of the hemiparasitic angiosperm Striga hermonthica (Del.) Benth is elicited by compounds present in the root exudates of the host plant. Although a variety of compounds can substitute for the host-derived signal, the mechanism through which these act is unknown. In the present study, an inhibitor of ethylene biosynthesis, aminoethoxyvinyl glycine, was found to inhibit germination. Addition of an intermediate in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid, was found to override this inhibition and to act as a substitute for the host-derived signal. 2,5-Norbornadiene, an inhibitor of ethylene action, was also found to inhibit germination. Ethylene is rapidly produced by Striga seeds after treatment with host root exudates. These results are consistent with a model for Striga seed germination in which host-derived signals and other compounds act by eliciting the synthesis of ethylene and in which ethylene itself initiates the biochemical changes leading to germination.

Journal Article↗

PubMed2002

Exudation of fluorescent beta-carbolines from Oxalis tuberosa L roots.

Root fluorescence is a phenomenon in which roots of seedlings fluoresce when irradiated with ultraviolet (UV) light. Soybean (Glycine max) and rye grass (Elymus glaucus) are the only plant species that have been reported to exhibit this occurrence in germinating seedling roots. The trait has been useful as a marker in genetic, tissue culture and diversity studies, and has facilitated selection of plants for breeding purposes. However, the biological significance of this occurrence in plants and other organisms is unknown. Here we report that the Andean tuber crop species Oxalis tuberosa, known as oca in the highlands of South America, secretes a fluorescent compound as part of its root exudates. The main fluorescent compounds were characterized as harmine (7-methoxy-1-methyl-beta-carboline) and harmaline (3, 4-dihydroharmine). We also detected endogenous root fluorescence in other plant species, including Arabidopsis thaliana and Phytolacca americana, a possible indication that this phenomenon is widespread within the plant kingdom.

Arabidopsis↗

PubMed2003

Characterization of the sodF gene region of Frankia sp. strain ACN14a and complementation of Escherichia coli sod mutant.

The Frankia sp. strain ACN14a superoxide dismutase SodF was previously shown to be induced in response to Alnus glutinosa root exudates, and its gene was sequenced. We report here the sequence of the 9-kb genomic segment surrounding the sodF gene and further characterize this gene and its product. Nine ORFs coding for various proteins, such as regulators, acetyl-CoA transferases, and a bacterioferritin A next to the sodF gene, were found. Northern blot analysis showed that the sodF gene was expressed as a major 1-kb transcript, which indicates that it has its own promoter. The sodF gene strongly complemented an Escherichia coli triple mutant (sodA sodB recA), restoring aerobic growth when the gene was expressed from the synthetic tac promoter but when expressed from its own promoter showed only slight rescue, suggesting that it was poorly recognized by the E. coli RNA polymerase. It is noteworthy that this is the first time that a Frankia gene has been reported to complement an E. coli mutant. The superoxide dismutase activity of the protein was inactivated by hydrogen peroxide, indicating that the metal ligand is iron, which is supported by analysis of the protein sequence. Thus, the SodF protein induced in Frankia by root exudates is an iron-containing enzyme similar to the one present in the nodules.

Base Composition↗

PubMed1988

Two host-inducible genes of Rhizobium fredii and characterization of the inducing compound.

Random transcription fusions with Mu d1(Kan lac) generated three mutants in Rhizobium fredii (strain USDA 201) which showed induction of beta-galactosidase when grown in root exudate of the host plants Glycine max, Phaseolus vulgaris, and Vigna ungliculata. Two genes were isolated from a library of total plasmid DNA of one of the mutants, 3F1. These genes, present in tandem on a 4.2-kilobase HindIII fragment, appear in one copy each on the symbiotic plasmid and do not hybridize to the Rhizobium meliloti common nodulation region. They comprise two separate transcriptional units coding for about 450 and 950 nucleotides, both of which are transcribed in the same direction. The two open reading frames are separated by 586 base pairs, and the 5H regions of the two genes show a common sequence. No similarity was found with the promoter areas of Rhizobium trifolii, R. meliloti, or Bradyrhizobium japonicum nif genes and with any known nodulation genes. Regions homologous to both sequences were detected in EcoRI digests of genomic DNAs from B. japonicum USDA 110, USDA 122, and 61A76, but not in genomic DNA from R. trifolii, Rhizobium leguminosarum, or Rhizobium phaseoli. Mass spectrometry and nuclear magnetic resonance analysis indicated that the inducing compound has properties of 4',7-dihydroxyisoflavone, daidzein. These results suggest that, in addition to common nodulation genes, several other genes appear to be specifically induced by compounds in the root exudate of the host plants.

Base Sequence↗

PubMed2003

Role of exudation of organic acids and phosphate in aluminum tolerance of four tropical woody species.

Responses of Melaleuca leucadendra (L.) L., Melaleuca cajuputi Powell, Acacia auriculiformis A. Cunn. ex Benth. and Eucalyptus camaldulensis Dehnh. to aluminum (Al) toxicity at low pH are poorly understood. We investigated effects of low pH and exudation of ligands by roots on Al tolerance of these species. Seedlings were grown hydroponically in nutrient solutions at pH 4.2 or 3.5 containing AlCl3 at concentrations ranging from 0 to 4 mM Al. The presence of 4 mM Al at pH 3.5 depressed growth in all species. Growth depression was greatest in E. camaldulensis, least in A. auriculiformis. In the low Al treatment (0.5 mM Al), roots of M. cajuputi tended to have the highest Al concentration among species, whereas in the 4 mM Al treatment, the highest Al concentration was found in roots of E. camaldulensis. Aluminum application enhanced root exudation of citrate in all species, with the enhancement in M. cajuputi, M. leucadendra and A. auriculiformis being similar and much greater than in E. camaldulensis. Exudation of oxalate and phenolic compounds was greater in E. camaldulensis than in the other species. The presence of Al enhanced phosphate exudation in all species, particularly in A. auriculiformis. Acacia auriculiformis was tolerant to low pH, probably because the presence of an unknown substance increased the pH. Application of 0.38 mM Al alleviated the toxicity of the pH 3.5 treatment in E. camaldulensis and M. cajuputi, whereas low pH alleviated Al toxicity in A. auriculiformis. We conclude that exudation of ligands such as citrate and phosphate only partly accounts for interspecific differences in Al tolerance among the tropical woody plants studied, whereas the reciprocal alleviation of Al toxicity and low pH differed considerably among the species.

Acacia↗

PubMed2006

Long- and short-chain plant-produced bacterial N-acyl-homoserine lactones become components of phyllosphere, rhizosphere, and soil.

Two N-acyl-homoserine lactone (acyl-HSL) synthase genes, lasI from Pseudomonas aeruginosa and yenI from Yersinia enterocolitica, were introduced into tobacco, individually and in combination. Liquid chromatograph-tandem mass spectrometry and thin-layer chromatography confirmed products of lasI and yenI activity in single and cotransformants. Cotransformants expressing plastid-localized LasI and YenI synthases produced the major acyl-HSLs for each synthase in all tissues tested. Total acyl-HSL signals accumulated in leaf tissue up to 3 pmol/mg of fresh weight, half as much in stem tissue, and approximately 10-fold less in root tissues. Acyl-HSLs were present in aqueous leaf washes from greenhouse-grown transgenic plants. Transgenic lines grown for 14 days under axenic conditions produced detectable levels of acyl-HSLs in root exudates. Ethyl acetate extractions of rhizosphere and nonrhizosphere soil from transgenically grown plants contained active acyl-HSLs, whereas plant-free soil or rhizosphere and nonrhizosphere soil from wild-type plants lacked detectable amounts of acyl-HSLs. This work shows that bioactive acyl-HSLs are exuded from leaves and roots and accumulate in the phytosphere of plants engineered to produce acyl-HSLs. These data further suggest that plants that are bioengineered to synthesize acyl-HSLs can foster beneficial plant-bacteria communications or deter deleterious interactions. Therefore, it is feasible to use bioengineered plants to supplement soils with specific acyl-HSLs to modulate bacterial phenotypes and plant-associated bacterial community structures.

4-Butyrolactone↗

PubMed1999

Allelopathic Substance Exuded from a Serious Weed, Germinating Barnyard Grass (Echinochloa crus-galli L.), Roots.

The allelopathy of a serious weed, barnyard grass (Echinochloa crus-galli L.), was investigated. Root exudates of young barnyard grass showed allelopathic effects and plant-selective activity and inhibited root elongation of all plants tested. With respect to shoot growth, the exudates did not show inhibition of barnyard grass only. The allelopathic substance was isolated and identified as p-hydroxymandelic acid by NMR. p-Hydroxymandelic acid strongly inhibited shoot growth and root elongation of all plants tested. The effects of three congeners of p-hydroxymandelic acid were tested on rice shoot growth. In the biological activity exhibited in rice, shoot growth was related to the hydroxyl groups.

Journal Article↗

PubMed1976

Effects of kinetin and root tip removal on exudation and potassium (rubidium) transport in roots of honey locust.

Exudation, (86)Rb transport, and water permeability were examined in excised roots of honey locust (Gleditsia triacanthos L.) treated by removing the tip 2 mm (tip-cut 2 mm) or tip 8 mm of the root, or by adding kinetin, or by both treatments. Tip removal increased the rate of exudation. Kinetin, 5 x 10(-6)m, inhibited exudation and Rb transport in tip-cut 2-mm roots; the inhibition was reversible. Kinetin inhibition of exudation was initially associated with lower K(Rb) transport and later with decreases in both ion transport and water permeability. Exudation was also inhibited at 10(-10) to 10(-7)m kinetin. Exudation from roots with intact tips was not altered by kinetin until after about 24 hours. Light during the exudation period had no significant (95%) influence on rate of exudation during the first 24 hours whether root tips were cut or kinetin applied.The results suggest the involvement of the root tip in regulating exudation in other parts of the root. This regulation might occur through cytokinin control of water permeability and the rate of ion transport.

Journal Article↗

PubMed2002

[Effect of phosphorus deficiency on activity of acid phosphatase exuded by wheat roots].

The activity of acid phosphatase exuded by roots, the tissue location of the enzyme, and the relationship between the enzyme activity and phosphorus efficiency of wheat were studied. The results showed that the activity of acid phosphatase exuded by wheat 81(85)5-3-3-3 and NC37 under P-sufficiency treat were lower than those under P-deficiency, and the enzyme activity of the former variety was significantly higher than that of the latter. There was a significant difference in the enzyme activity among 12 wheat genotypes grown under P-deficiency treat. Acid phosphatase was exuded by epidermis cell of root, especially by epidermal cell of root apex. Thus, there was a linear relationship between the enzyme activity and the surface area of root or the number of root apexes. It implied that the enzyme activity was markedly related to the size of root system. The linear relationship between relative grain yield and acid phosphatase activity was significant. It indicates that the enzyme activity could be used as an early indicator to select P-efficient wheat genotypes.

Acid Phosphatase↗

PubMed2004

Repression of Pseudomonas putida phenanthrene-degrading activity by plant root extracts and exudates.

The phenanthrene-degrading activity (PDA) of Pseudomonas putida ATCC 17484 was repressed after incubation with plant root extracts of oat (Avena sativa), osage orange (Maclura pomifera), hybrid willow (Salix alba x matsudana), kou (Cordia subcordata) and milo (Thespesia populnea) and plant root exudates of oat (Avena sativa) and hybrid poplar (Populus deltoides x nigra DN34). Total organic carbon content of root extracts ranged from 103 to 395 mg l(-1). Characterization of root extracts identified acetate (not detectable to 8.0 mg l(-1)), amino acids (1.7-17.3 mg l(-1)) and glucose (1.6-14.0 mg l(-1)), indicating a complex mixture of substrates. Repression was also observed after exposure to potential root-derived substrates, including organic acids, glucose (carbohydrate) and glutamate (amino acid). Carbon source regulation (e.g. catabolite repression) was apparently responsible for the observed repression of P. putida PDA by root extracts. However, we showed that P. putida grows on root extracts and exudates as sole carbon and energy sources. Enhanced growth on root products may compensate for partial repression, because larger microbial populations are conducive to faster degradation rates. This would explain the commonly reported increase in phenanthrene removal in the rhizosphere.

Acetates↗

PubMed2004

Manipulation of root hair development and sorgoleone production in sorghum seedlings.

Sorghum (Sorghum bicolor) roots exude a potent bioherbicide sorgoleone. Previous work indicates that sorgoleone is produced in living root hairs. We have developed a mist system that resulted in abundant production of root hairs exuding sorgoleone and a mat system that significantly inhibited root hair development and consequently sorgoleone production. Applying Ag+ (an ethylene action inhibitor) at 1.2 mM to the seedlings grown in the mist system also inhibited root hair formation and elongation. Hypoxic conditions in the mist system did not result in the inhibition of root hair growth as compared to the standard air atmosphere (20.8% O2). Applying ethephon (an ethylene-releasing agent) at 0.031 mM to the roots of seedlings grown in the mat system with water running at 1 ml/min reversed the inhibition of root hair development by water movement. These results indicate that either water movement or ethylene can be utilized to manipulate root hair development and sorgoleone production in sorghum seedlings. It is hypothesized that water movement reduced the local ethylene concentration on the root surface and consequently inhibited root hair development of sorghum seedlings grown in the mat system.

Benzoquinones↗

PubMed2005

Bacteria associated with spores of the arbuscular mycorrhizal fungi Glomus geosporum and Glomus constrictum.

Spores of the arbuscular mycorrhizal fungi (AMF) Glomus geosporum and Glomus constrictum were harvested from single-spore-derived pot cultures with either Plantago lanceolata or Hieracium pilosella as host plants. PCR-denaturing gradient gel electrophoresis analysis revealed that the bacterial communities associated with the spores depended more on AMF than host plant identity. The composition of the bacterial populations linked to the spores could be predominantly influenced by a specific spore wall composition or AMF exudate rather than by specific root exudates. The majority of the bacterial sequences that were common to both G. geosporum and G. constrictum spores were affiliated with taxonomic groups known to degrade biopolymers (Cellvibrio, Chondromyces, Flexibacter, Lysobacter, and Pseudomonas). Scanning electron microscopy of G. geosporum spores revealed that these bacteria are possibly feeding on the outer hyaline spore layer. The process of maturation and eventual germination of AMF spores might then benefit from the activity of the surface microorganisms degrading the outer hyaline wall layer.

Asteraceae↗

PubMed2004

[Research advances in mechanism of high phosphorus use efficiency of plants].

Phosphorus deficiency is one of the main factors influencing agricultural and forestry productions. Fertilization and soil improvement are the major measures to meet the demand of phosphorus for crops in traditional agriculture and forestry management. Recently, the plants with high phosphorus use efficiency have been discovered to replace the traditional measures to improve phosphorus use efficiency of crops. This paper reviewed the research advances in the morphological, physiological and genetics mechanisms of plants with high phosphorus use efficiency. There were three mechanisms for the plants with high phosphorus use efficiency to grow under phosphorus stress: (1) under low phosphorus stress, the root morphology would change (root system grew fast, root axes became small, the number and density of lateral root increased) and more photosynthesis products would transport from the crown to the root, (2) under low phosphorus stress, plant root exudation increased, mycorrhizae invaded into root system, the feature of root absorption kinetics changed, and the internal phosphorus cycling of plant reinforced to tolerate phosphorus deficiency, and (3) under long selection stress of low phosphorus, some plants would form the genetic properties of phosphorus nutrition that could exploit the hardly soluble phosphorus in the soil.

Fertilizers↗