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PubMed2005

The role of a salt marsh plant on trace metal bioavailability in sediments. Estimation by different chemical approaches.

GOAL, SCOPE AND BACKGROUND: The presence or absence of vegetation can condition sediment characteristics. The main aim of this work was to investigate the influence of the sea rush Juncus maritimus on metal (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) availability to organisms living on or in estuarine sediments, from Douro River (NW Portugal), by comparing the characteristics and chemical behaviour of rhizosediments (collected within the plant assemblage) and those of sediment (collected around the plant). In order to evaluate whether and how sediment characteristics condition the role of plants on metal availability, sandy and muddy sediments colonised by J. maritimus were studied in parallel. METHODS: Metal availability was estimated by enzymatic digestion with pepsin (ED), which may provide an estimate of metal availability to organisms living at estuarine sediments. Nevertheless, since no consensus exists yet on the most suitable methodologies to estimate metal bioavailability in sediments, two more conventional approaches, BCR sequential extraction (SE) and AVS/ SEM model, were also used, in parallel, and the information these approaches provided was compared with that provided by ED. Total-recoverable metal contents were determined by atomic absorption spectrophotometry after sediment digestion using a high-pressure microwave system. RESULTS AND DISCUSSION: Plants could concentrate metals around its roots and rhizomes. In addition, they were capable of oxidizing (release of oxygen by the roots) the anaerobic medium surrounding their roots in muddy sediment (reducing AVS). As sulphide oxidation renders metals (Cd, Cu, Ni, Pb and Zn) into more soluble forms, according to the AVS/SEM model, metals from muddy sites would be more available in rhizosediment than in sediment. The SE approach led to a similar conclusion. Nevertheless, the results provided by ED pointed at opposite conclusion, particularly for Cd and Zn, indicating less availability at rhizosediments than in the surrounding sediment. ED results were interpreted as a consequence of an enrichment of the rhizosediment in organic ligands exuded by the roots or liberated by dead plants. The effect of complexation of metals by organic compounds, which ED could not decompose/dissolve, seemed to overcome that caused by sediment oxidation. In general, a comparison of the informa tion about metal availability by ED, SE, AVS/SEM, showed that it did not always match and in few cases it was even contradictory. CONCLUSION AND OUTLOOK: Therefore, a thorough evaluation of the metal availability in sediments requires a combination of different chemical approaches, so as to take into consideration differences in ways of organism exposure (interstitial water and/or ingestion of sediment particles).

Bacteria, Anaerobic↗

PubMed1973

Organic acids and iron translocation in maize genotypes.

Translocation of Fe was studied in WF9 (Fe-efficient) and ys(1)/ys(1) (Fe-inefficient) maize (Zea mays L.) genotypes. Iron-deficient WF9 translocated more Fe to the tops than Fe-deficient ys(1)/ys(1). Malate and citrate contents of root saps increased nearly 2-fold and aconitate increased over 4-fold in both genotypes as Fe of nutrient solutions increased from 0.1 to 3 milligrams per liter. Relative acid contents in root saps were as follows: malate > aconitate > citrate. Citric acid concentrations in stem exudates were nearly the same as in root sap. Malic acid concentrations were considerably lower in exudates than in root saps, and only a trace of aconitic acid was detected in the exudates. The concentration of Fe was 7-fold higher in exudate of WF9 than in exudate of ys(1)/ys(1) and the concentration of exudate P was about the same for both genotypes.Electropherograms of WF9 stem exudates showed that (59)Fe moved toward the anode as (59)Fe-citrate. Exudates of ys(1)/ys(1) contained insufficient (59)Fe to produce radiographs. When (59)Fe was added in vitro to ys(1)/ys(1) stem exudate, the (59)Fe moved as (59)Fe-citrate, indicating that sufficient citric acid was present in the exudate to chelate the Fe. Effectiveness of citric, isocitric, trans-aconitic, and malic acids in moving (59)Fe electrophoretically in acetate, citrate, isocitrate, trans-aconitate, and malate buffers was studied. Malic, acetic, and trans-aconitic acids were ineffective in moving Fe from the origin. Citric acid moved Fe anodically whenever present on the electropherogram and successfully competed with the other acids for Fe.Results with ys(1)/ys(1) roots indicate an absence of an efficient mechanism for transporting Fe from cortical cells to the xylem. If Fe can reach the xylem stream, the ys(1)/ys(1) genotype should be as efficient as WF9 in moving Fe to the leaves.

Journal Article↗

PubMed1979

Protective effects of rat splenic lymphocytes and peritoneal exudate cells on herpes simplex virus infection of rat dorsal root ganglia in culture.

An in vitro model system was developed to study the effects that immune cells might have on herpes simplex virus (HSV) infection of rat dorsal root ganglia in culture. Our results demonstrate that rat splenic lymphocytes and peritoneal exudate cells are incapable of replicating HSV even if these cells come from sensitized animals and are stimulated in vitro. Both cell preparations can offer some protection to rat dorsal root ganglia from the effects of HSV infection. The data suggest that an immunologically non-specific (not mediated by sensitized cells) type of protection is important to neurons, while an immunologically specific (mediated by sensitized cells) protection is most beneficial to fibroblasts. This system can be utilized to study the mechanism of latency since the neurons of sensory ganglia are the natural site of latent herpes virus.

Animals↗

PubMed2005

The influence of organic ligands on the retention of lead in soil.

Organic acids are commonly produced and exuded by plant roots and soil microorganisms. Some of these organic compounds are effective chelating agents and have the potential to enhance metal mobility. The effect of citrate and salicylate on the leaching of lead in soil was investigated in a laboratory experiment. In short-term batch experiments, adsorption of lead to soil was slightly enhanced with increasing salicylate concentration (500-5000 microM) but decreased significantly in the presence of citrate. These observations suggested that citrate may enhance Pb leaching, but this was not observed in the column study. Soluble Pb in the presence and absence citrate or salicylate (up to 5000 microM) was added to soil columns at a moderate flow rate, but no Pb was observed to emerge from the soil in any of the soil columns. Rapid biodegradation of citrate in soil eliminated potential complexing ability. Breakthrough of Pb from soil was noted only when using small columns at high flow rates (>20 pore volumes per day). Under these conditions of physical and chemical non-equilibrium, citrate was not degraded and significantly enhanced Pb mobility. As in the batch adsorption experiments, the presence of salicylate reduced Pb leaching. Considering the extreme conditions required to induce Pb leaching, it is likely that Pb will remain relatively immobile in soil even in the presence of a strong complexing agent such as citrate.

Adsorption↗

PubMed2006

Seasonal variations in sugar contents and microbial community in a ryegrass soil.

The relationship among sugar concentrations, microbial community and physical variables (precipitation and soil temperature) was investigated in a ryegrass soil from January 2004 to January 2005. Mono- and disaccharide sugars were extracted using a mixture of dichloromethane and methanol and analyzed as their TMS derivatives by GC-MS. Changes in microbial community were assessed using phospholipid and neutral lipid fatty acids (PLFA and NLFA, respectively) analysis. The results of a one-year study showed that the seasonal variability of sugar contents found in the soil samples is mainly related to biomass or nutritional status of the fungal community. The increase in sucrose and fructose exudation by plant roots in the beginning of the growing season (early spring) may be responsible for the highest fungal biomass amount (PLFAs) observed in this study. Fungal storage lipid abundances (NLFAs) peaked in summer, during the same period that the highest concentrations of mannitol and trehalose were detected. This is consistent with these two sugars being stress-induced fungal metabolites, produced due to the low soil moisture observed during this season. In contrast, bacterial community growth seems to be more dependent on plant substrate than on physical variables, since the strongest decrease in bacterial biomass amounts (PLFAs) was found after cutting of the ryegrass field in early July.

Biomass↗

PubMed2005

Post-lumbar puncture arachnoiditis. The need for directed questioning.

The inflammation of the arachnoid mater may produce a fibrinous exudate around the roots that causes them to adhere to the dural sheath. We report the case of a man aged 23 years who suffered from acute inflammatory truncated sciatica. The diagnosis of adhesive arachnoiditis was made in front of clinical arguments associated to typical signs on Myelo CT Scan and MRI. The only explanation ever found was a traumatic lumbar puncture at the age of 6 years for suspected meningitis. Sequelae of arachnoiditis are difficult to diagnosis. When MRI or myelography suggests it as a possibility, precise directed questioning is necessary to seek a history, albeit distant, of spinal or meningeal events.

Adult↗

PubMed1999

A critical account on the inception of Striga seed germination.

The seeds of the parasitic weed Striga germinate in response to stimulants exuded by the roots of host plants and some nonhost plants. Literature data are summarized that support the view that strigolactones induce germination of parasitic weed seeds via a receptor-mediated mechanism. The suggestion by Lynn et al. that the strigol D-ring is solely responsible for germinating Striga seeds via a redox reaction was based on hypothesized structural similarities between the natural compound dihydrosorgoleone (SXSg) and the strigol D-ring. Experiments have shown that the mechanistic connection between SXSg and the strigol D-ring is not valid, and therefore the proposed redox mechanism for the induction of Striga seed germination by strigolactones does not hold.

Lactones↗

PubMed2002

Control of witchweed Striga hermonthica by intercropping with Desmodium spp., and the mechanism defined as allelopathic.

During investigations into the control of insect damage to maize crops in subsistence farming in Kenya, which involved intercropping with repellent plants, the fodder legumes silverleaf (Desmodium uncinatum) and greenleaf (D. intortum) were also found to reduce dramatically the infestation of maize by parasitic witchweeds such as Striga hermonthica. This effect was confirmed by further field testing and shown to be significantly greater than that observed with other legumes, e.g., cowpea, as were the concomitant yield increases. The mechanism was investigated, and although soil shading and addition of nitrogen fertilizer showed some benefits against S. hermonthica infestation, a putative allelopathic mechanism for D. uncinatum was observed. In screenhouse studies, a highly significant reduction in S. hermonthica infestation was obtained when an aqueous solution, eluting from pots in which D. uncinatum plants were growing, was used to irrigate pots of maize planted in soil seeded with high levels of S. hermonthica. Growth of the parasitic weed was almost completely suppressed. whereas extensive infestation occurred with the control eluate. Laboratory investigations into the allelopathic effect of D. uncinatum, using samples of water-soluble chemical components exuded from cleaned roots, demonstrated that this involved a germination stimulant for S. hermonthica and also an inhibitor for haustorial development.

Crops, Agricultural↗

PubMed2006

Sorptive behavior of sorgoleone in ultisol in two solvent systems and determination of its lipophilicity.

Sorgoleone (SGL) exuded by sorghum roots inhibits the development of some weeds. Due to its high hydrophobicity, it is expected that SGL presents low soil mobility and limited allelopathic activity in the field. This work aims to evaluate the sorptivity of sorgoleone in octanol-water and in soil under two solvent systems. The two solvent systems were methanol:water (60:40) (MeOH:H2O) and pure methanol (MeOH). These two solvent systems promote different conditions for SGL solubility. Treatments were arranged in a 2 x 6 factorial (solvent systems x equilibrium concentrations in the solution (EC)). For each solvent, the sorption was achieved by shaking 500 mg of soil with 10 ml of 0, 5, 10, 15, 25, 40, and 60 mg L-1 of SGL solution, during 24 h. After centrifugation, the supernatant was filtered and the SGL concentration was determined by high performance liquid chromatography (HPLC). Data of sorbed amount of SGL were submitted to variance analysis, using a hierarchic factorial model. The data of sorbed amount (x/m) and equilibrium concentration (C) were fitted to the linear (x/m = a + KdC) and to the Freundlich (x/m = KfC1/n) models. The isotherm obtained for the MeOH:H2O system presented linear shape, whereas for the MeOH system a two subsequent linear isotherm was fitted. Sorgoleone is a highly hydrophobic compound, presenting a log Kow of 6.1. The sorption of sorgoleone to the soil was very high. The organic environment stimulated the sorgoleone sorption to the soil.

Adsorption↗

PubMed1996

Aluminum Interactions with Voltage-Dependent Calcium Transport in Plasma Membrane Vesicles Isolated from Roots of Aluminum-Sensitive and -Resistant Wheat Cultivars.

The role of Al interactions with root-cell plasma membrane (PM) Ca2+ channels in Al toxicity and resistance was studied. The experimental approach involved the imposition of a transmembrane electrical potential (via K+ diffusion) in right-side-out PM vesicles derived from roots of two wheat (Triticum aestivum L.) cultivars (Al-sensitive Scout 66 and Al-resistant Atlas 66). We previously used this technique to characterize a voltage-dependent Ca2+ channel in the wheat root PM (J.W. Huang, D.L. Grunes, L.V. Kochian [1994] Proc Natl Acad Sci USA 91: 3473-3477). We found that Al3+ effectively blocked this PM Ca2+ channel; however, Al3+ blocked this Ca2+ channel equally well in both the Al-sensitive and -resistant cultivars. It was found that the differential genotypic sensitivity of this Ca2+ transport system to Al in intact roots versus isolated PM vesicles was due to Al-induced malate exudation localized to the root apex in Al-resistant Atlas but not in Al-sensitive Scout. Because malate can effectively chelate Al3+ in the rhizosphere and exclude it from the root apex, the differential sensitivity of Ca2+ influx to Al in intact roots of Al-resistant versus Al-sensitive wheat cultivars is probably due to the maintenance of lower Al3+ activities in the root apical rhizosphere of the resistant cultivar.

Journal Article↗

PubMed2000

Ecology. Plant invader may use chemical weapons.

On page 521, plant ecologists offer a novel explanation for the success of invasive plants. By comparing how one species of knapweed, Centaurea diffusa, behaves with its natural neighbors and with foreign plant species that evolved separately, they found that the invader apparently gains an edges in its adopted home not only by ditching its herbivores but by wielding weaponry: chemicals exuded from its roots that hamper its new neighbors' growth.

Asia↗

PubMed1991

Flavonoids released naturally from alfalfa promote development of symbiotic glomus spores in vitro.

Because flavonoids from legumes induce transcription of nodulation genes in symbiotic rhizobial bacteria, it is reasonable to test whether these compounds alter the development of vesicular-arbuscular mycorrhizal (VAM) fungi that infect those plants. Quercetin-3-O-galactoside, the dominant flavonoid released naturally from alfalfa (Medicago sativa L.) seeds, promoted spore germination of Glomus etunicatum and Glomus macrocarpum in vitro. Quercetin produced the maximum increases in spore germination, hyphal elongation, and hyphal branching in G. etunicatum at 1 to 2.5 muM concentrations. Two flavonoids exuded from alfalfa roots, 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone, also enhanced spore germination of this fungal species. Formononetin, an isoflavone that is released from stressed alfalfa roots, inhibited germination of both Glomus species. These in vitro results suggest that plant flavonoids may facilitate or regulate the development of VAM symbioses and offer new hope for developing pure, plant-free cultures of VAM fungi.

Journal Article↗

PubMed2005

Analysis of xylem sap proteins from Brassica napus.

BACKGROUND: Substance transport in higher land plants is mediated by vascular bundles, consisting of phloem and xylem strands that interconnect all plant organs. While the phloem mainly allocates photoassimilates, the role of the xylem is the transport of water and inorganic nutrients from roots to all aerial plant parts. Only recently it was noticed that in addition to mineral salts, xylem sap contains organic nutrients and even proteins. Although these proteins might have important impact on the performance of above-ground organs, only a few of them have been identified so far and their physiological functions are still unclear. RESULTS: We used root-pressure xylem exudate, collected from cut Brassica napus stems, to extract total proteins. These protein preparations were then separated by high-resolution two-dimensional gel electrophoresis (2-DE). After individual tryptic digests of the most abundant coomassie-stained protein spots, partial peptide sequence information was deduced from tandem mass spectrometric (MS/MS) fragmentation spectra and subsequently used for protein identifications by database searches. This approach resulted in the identification of 69 proteins. These identifications include different proteins potentially involved in defence-related reactions and cell wall metabolism. CONCLUSION: This study provides a comprehensive overview of the most abundant proteins present in xylem sap of Brassica napus. A number of 69 proteins could be identified from which many previously were not known to be localized to this compartment in any other plant species. Since Brassica napus, a close relative of the fully sequenced model plant Arabidopsis thaliana, was used as the experimental system, our results provide a large number of candidate proteins for directed molecular and biochemical analyses of the physiological functions of the xylem under different environmental and developmental conditions. This approach will allow exploiting many of the already established functional genomic resources, like i.e. the large mutant collections, that are available for Arabidopsis.

Brassica napus↗

PubMedDate not supplied

Methane emissions of rice increased by elevated carbon dioxide and temperature.

Methane (CH4) effluxes by paddy-culture rice (Oryza sativa L.) contribute about 16% of the total anthropogenic emissions. Since radiative forcing of CH4 at current atmospheric concentrations is 21 times greater on a per mole basis than that of carbon dioxide (CO2), it is imperative that the impact of global change on rice CH4 emissions be evaluated. Rice (cv. IR72) was planted in sunlit, closed-circulation, controlled-environment chambers in which CH4 efflux densities were measured daily. The CO2 concentration was maintained at either 330 or 660 micromol mol(-1). Air temperatures were controlled to daily maxima and minima of 32/23, 35/26, and 38/29 degrees C at each CO2 treatment. Emissions of CH4 each day were determined during a 4-h period after venting and resealing the chambers at 0800 h. Diurnal CH4 effluxes on 77, 98, and 119 d after planting (DAP) were obtained similarly at 4-h intervals. Emissions over four-plant hills and over flooded bare soil were measured at 53, 63, and 100 DAP. Emissions were negligible before 40 DAP. Thereafter, emissions were observed first in high-CO2, high-temperature treatments and reached a sustained maximum efflux density of about 7 mg m(-2) h(-1) (0.17 g m(-2) d(-1)) near the end of the growing season. Total seasonal CH4 emission was fourfold greater for high-CO2, high-temperature treatments than for the low-CO2, low-temperature treatment, probably due to more root sloughing or exudates, since about sixfold more acetate was found in the soil at 71 DAP. Both rising CO2 and increasing temperatures could lead to a positive feedback on global warming by increasing the emissions of CH4 from rice.

Air↗

PubMedDate not supplied

[Mathematic modeling of the dynamics of the interacting population of the rhizosphere microorganisms].

A quantitative model is proposed to describe the population dynamics of associative nitrogen-fixing microorganisms in the plant rhizosphere as dependent on the rate of carbon substrate exudation by plant roots. By changing the values of the basic model parameters, the effect of various factors on the behavior of two competing populations of rhizospheric microorganism can be studied.

Bacteria↗

PubMed2003

Degradation of crude oil in the rhizosphere of Sorghum bicolor.

Dissipation of petroleum contaminants in the rhizosphere is likely the result of enhanced microbial degradation. Plant roots may encourage rhizosphere microbial activity through exudation of nutrients and by providing channels for increased water flow and gas diffusion. Phytoremediation of crude oil in soil was examined in this study using carefully selected plant species monitored over specific plant growth stages. Four sorghum (Sorghum bicolor L.) genotypes with differing root characteristics and levels of exudation were established in a sandy loam soil contaminated with 2700 mg crude oil/kg soil. Soils were sampled at three stages of plant growth: five leaf, flowering, and maturity. All vegetated treatments were associated with higher remediation efficiency, resulting in significantly lower total petroleum hydrocarbon concentrations than unvegetated controls. A relationship between root exudation and bioremediation efficiency was not apparent for these genotypes, although the presence of all sorghum genotypes resulted in significant removal of crude oil from the impacted soil.

Biodegradation, Environmental↗

PubMed2004

[Research advance in cyclic hydroxamic acids, main allelochemicals of Zea mays].

The research advance in cyclic hydroxamic acids was reviewed in this paper. Cyclic hydroxamic acids are the important natural products of cereal crops. They and their respective derivatives are the constitutive compounds of a wide variety of gramineous plants and few dicot plants. They have structural diversity and different natural occurrences. Because of their phytotoxic properties, cyclic hydroxamic acids show a great variety of biological activities. They are the defensive agents against plant diseases, pests, nematodes and other plants. The distribution of cyclic hydroxamic acids in Zea mays and their variation in relation to the age were focused on in the paper. In Zea mays, there are structural diversity of cyclic hydroxamic acids and related benzoxazolinones. DIMBOA (1,4-benzoxazin-3(4H)-ones) is the most abundant derivative in Zea mays. The content of cyclic hydroxamic acids is strongly cultivar-dependent in Zea mays. Hydroxamic acids are not present in seeds. After germination, the level of DIMBOA increases, and the maximum level occurs in young seedlings a few days after germination. DIMBOA exists in all parts of plants, and its concentration is generally higher in shoots than in roots. In all stages, the young leaves of Zea mays have relatively high content of DIMBOA. The concentrations of these hydroxamic acids are highly dependent on environmental growth conditions. Under UV-light and water deficiencies, the levels of hydroxamic acids in plant increase rapidly. Cyclic hydroxamic acids exuded by Zea mays root can be quantitatively analyzed by HPLC. Supplying iron can significantly increase the exudation of DIMBOA from Zea mays root.

Benzoxazines↗

PubMed1966

Physiological basis of differential strontium accumulation in two barley genotypes.

Studies of rates of Sr transport from nutrient solutions containing 8 concentrations of Sr indicate a definite trend towards higher rates of Sr transport by roots of intact 12-day-old Regal barley (Hordeum vulgare, L.) seedlings as compared with Tregal. Differences in rates of Sr transport between the 2 varieties were also indicated by higher concentrations of Sr in fluids exuding from decapitated Regal roots as compared to fluids exuding from decapitated Tregal roots.No differences between Regal and Tregal were found in the physical factors of distance from epidermis to endodermis, number of cortical cell layers, or transpiration rate. Furthermore, no relationship was observed between transpiration rate and rate of Sr accumulation.Dependence of Sr transport on metabolic processes was indicated by marked effects of temperature, cyanide, and dinitrophenol on rates of Sr transport. Q(10) values for Sr transport by Regal and Tregal approached 2, thereby indicating that metabolic reactions were associated with this process. Strontium transport by both Regal and Tregal was markedly depressed in the presence of either cyanide or dinitrophenol. These results led to the conclusion that the Sr transport process is dependent on metabolic energy derived from respiration.

Journal Article↗