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PubMed1973

A chamber for applying pressure to roots of intact plants.

A chamber was designed to apply up to 20 bars pressure to roots of intact plants. The unique features of this chamber are a split top arrangement to permit enclosing roots of intact plants within the chamber, a circulation coil to control temperature of rooting media, and a valve arrangement to permit changing solution without disturbing the plant. Changes in transpiration in response to changes in the pressure applied to roots of intact pepper plants illustrate one use of the equipment. Well watered plants at low light (0.05 langley/min) were observed to exude water from the leaf margins when 5 bars pressure was applied to the roots. When roots were cut off, a 1 bar pressure caused exudation. Plants with cooled roots or plants in dry soil did not exude water when as much as 6 bars pressure was applied. Transient response of transpiration rates to sudden application and release of pressure was observed in pepper and bean plants but not in rhododendron. The magnitude of this transient response was highly dependent upon light intensity and CO(2) concentration in the aerial environment.

Journal Article↗

PubMedDate not supplied

Release into the environment of metals by two vascular salt marsh plants.

Metals in contaminated salt marshes are mainly locked in the anaerobic layer of sediments, where they are tightly bound as sulfides and organic complexes. Vascular plants survive in saturated soils in part by pumping O2 into their root zones, changing their microenvironment to an oxic one. This, along with chelating exudates, mobilizes metals, allowing uptake by the roots. We compared the common reed Phragmites australis and cordgrass Spartina alterniflora in lab and field studies for ways in which they handle trace metals. Both plants store most of their metal burden in their roots, but some is transported to aboveground tissues. Spartina leaves contain approximately 2-3 x more Cr, Pb, and Hg than Phragmites leaves, but equivalent Cu and Zn. Furthermore, Spartina leaves have salt glands, so leaf excretion of all metals is twice that of Phragmites. In-depth studies with Hg indicate that Hg excretion correlates with Na release but not with transpiration, which is 2.2 x higher in Phragmites; and that more Hg accumulates in early-appearing leaves than in upper (i.e. later) leaves in both species. Spartina thus makes more metals available to salt marsh ecosystems than Phragmites by direct excretion and via dead leaves which will enter the food web as detritus.

Ecosystem↗

PubMed1981

Transient susceptibility of root cells in four common legumes to nodulation by rhizobia.

Root cells of four common legumes were found to remain susceptible to nodulation by rhizobia for only a short period of time. Delayed inoculation experiments conducted with these legume hosts indicated that the initially susceptible region of the root became progressively less susceptible if inoculations were delayed by a few hours. Profiles of the frequency of nodule formation relative to marks indicating the regions of root and root hair development at the time of inoculation indicated that nodulation of Vigna sinensis (L.) Endl. cv California Black Eye and Medicago sativa L. cvs Moapa and Vernal roots was inhibited just below the region that was most susceptible at the time of inoculation. This result suggests the existence of a fast-acting regulatory mechanism in these hosts that prevents overnodulation. Nodulation in white clover may occur in two distinct phases. In addition to the transient susceptibility of preemergent and developing root hair cells, there appeared to be an induced susceptibility of mature clover root hair cells. A cell-free bacterial exudate preparation from Rhizobium trifolii cells was found to render mature root hair cells of white clover more rapidly susceptible to nodulation.

Journal Article↗

PubMed2001

Probing the role of calmodulin in Al toxicity in maize.

The role of calmodulin on Al toxicity was studied in two maize (Zea mays L.) inbred lines, Cat 100-6 (Al-tolerant) and S 1587-17 (Al-sensitive). Increasing levels of Al induced the release of malate at similar rate by roots of both genotypes, while the exudation of citrate, a stronger Al-binding compound, was 3.5 times higher in Cat 100-6 seedlings exposed to 16.2x10(-6) Al(3+) activity. The calmodulin inhibitor trifluoperazine significantly reduced the root growth in both genotypes, mimicking the main effect of Al. However, when Cat 100-6 and S 1587-17 seedlings were challenged with Al in conjunction with trifluoperazine, no further reduction in root growth or any other effect of Al toxicity was observed. The rate of Al-induced citrate exudation by both genotypes was not affected by treatment with trifluoperazine or calmidazolium, another calmodulin inhibitor. The Al(3+) interaction with cytoplasmic CaM was estimated using models for the binding of Al(3+) and Mg(2+) with CaM and physiological concentrations of citrate, CaM, InsP(3), ATP, ADP, Al(3+) and Mg(2+). In this simulation, Al(3+) associated with citrate and InsP(3), but not with CaM. We conclude that calmodulin is not relevant to the physiological processes leading to the Al tolerance in maize, nor is it a primary target for Al toxicity.

Adaptation, Physiological↗

PubMed2006

Effects of cadmium amendments on low-molecular-weight organic acid exudates in rhizosphere soils of tobacco and sunflower.

To recognize physiological response of plants to cadmium (Cd) toxicity in rhizosphere of plants, the pot experiments were employed to investigate how low-molecular-weight organic acids (LMWOAs) were exudated from tobacco and sunflower roots of Cd-amended soils. The aims of this study were to assess the effect of LMWOAs on uptake of Cd by tobacco and sunflower under pot experiments, thus comparing the ability of tobacco and sunflower for phytoremediation. Surface soils (0-20 cm) were collected from Taichung Experiment Station (TC) (silty loam). Cadmium chloride (CdCl(2)) was amended into TC soil, giving Cd concentrations of 1, 5, 10 mg kg(-1) soil. Soils with different concentrations of Cd were put into 12 cm (i.d.) pots for incubation, and then 2-week-old tobacco and sunflower seedlings were transplanted into the pots. Tobacco and sunflower were grown in greenhouse for 50 days, respectively. The rhizosphere and bulk soils, and fresh plant tissues were collected after harvest. The Cd concentrations in the plant and transfer factor values in the sunflower were higher than that in the tobacco. No LMWOAs were detected by gas chromatograph in bulk soils, and low amounts of LMWOAs were found in uncontaminated rhizosphere soils. Acetic, lactic, glycolic, malic, maleic, and succinic acids were found in the tobacco and sunflower rhizosphere soils. Concentrations of LMWOAs increased with increasing amendment of Cd concentrations in tobacco and sunflower rhizosphere soils. Correlation coefficient (r) of concentrations of Cd amendment versus LMWOAs exudates of tobacco and sunflower were 0.85 and 0.98, respectively. These results suggest that the different levels of LMWOAs present in the rhizosphere soil play an important role in the solubilization of Cd that bound with soil particle into soil solution and then uptake by plants.

Biomass↗

PubMed1998

Host mediators in endodontic exudates. II. Changes in concentration with sequential sampling.

Exudate is often found in the root canal of teeth requiring endodontic therapy. The aim of this study was to evaluate the relationship of sequential changes of different host mediators in endodontic exudates to clinical and radiographic findings. Thirty-two nonvital teeth with periapical symptoms were evaluated. Exudates were collected with filter paper strips every 3 min after opening of the pulp chamber. The concentrations of beta-glucuronidase, IgG, IgA, IgM, and interleukin-1 beta in the exudates were analyzed. In general, the concentration of the mediators in exudates from less involved lesions did not change over time. The exception was an increase in the IgM concentration when patients presented with percussion or palpation sensitivity. In contrast, in the more involved lesions, the concentrations of IgA and IgM increased as sampling progressed. The concentrations of beta-glucuronidase and interleukin-1 beta decreased over time in the more involved lesions. These data suggest that the amount of proinflammatory mediators in the canal and periapical lesion is limited. Furthermore, IgM seemed to be a marker for the severity of periapical lesions. This may relate to vascular permeability that allows passage of this larger molecule into the extravascular environment.

Exudates and Transudates↗

PubMed1971

Effect of iron on the transport of citrate into the xylem of soybeans and tomatoes.

Iron transport in soybeans (Glycine max [L] Merr.) and tomatoes (Lycopersicum esculentum) is controlled by factors that are altered manyfold as the plant experiences an iron stress (deficiency). Depending on their response to an Fe stress, plants in this study are classed (a) Fe-inefficient or (b) Fe-efficient. The Fe-efficient plants transport more Fe and concomitantly more citrate than the Fe-inefficient plants.An available supply of Fe added to the plant root will facilitate the release of citrate to the stem exudate in both soybeans and tomatoes. Also, when the iron supply is decreased by trapping Fe(2+) at the root, Fe transport decreases with a concomitant decrease of citrate in the stem exudate. Factors other than citrate appear to affect movement of Fe from the external solution into root cells where Fe is chelated with citrate and moves thereafter as Fe citrate. This makes some of the citrate that is transported in the stem exudate dependent on the amount of Fe made available at the root.

Journal Article↗

PubMed2006

Land plants equilibrate O2 and CO2 concentrations in the atmosphere.

The role of land plants in establishing our present day atmosphere is analysed. Before the evolution of land plants, photosynthesis by marine and fresh water organisms was not intensive enough to deplete CO(2) from the atmosphere, the concentration of which was more than the order of magnitude higher than present. With the appearance of land plants, the exudation of organic acids by roots, following respiratory and photorespiratory metabolism, led to phosphate weathering from rocks thus increasing aquatic productivity. Weathering also replaced silicates by carbonates, thus decreasing the atmospheric CO(2) concentration. As a result of both intensive photosynthesis and weathering, CO(2 )was depleted from the atmosphere down to low values approaching the compensation point of land plants. During the same time period, the atmospheric O(2) concentration increased to maximum levels about 300 million years ago (Permo-Carboniferous boundary), establishing an O(2)/CO(2) ratio above 1000. At this point, land plant productivity and weathering strongly decreased, exerting negative feedback on aquatic productivity. Increased CO(2) concentrations were triggered by asteroid impacts and volcanic activity and in the Mesozoic era could be related to the gymnosperm flora with lower metabolic and weathering rates. A high O(2)/CO(2) ratio is metabolically linked to the formation of citrate and oxalate, the main factors causing weathering, and to the production of reactive oxygen species, which triggered mutations and stimulated the evolution of land plants. The development of angiosperms resulted in a decrease in CO(2) concentration during the Cenozoic era, which finally led to the glacial-interglacial oscillations in the Pleistocene epoch. Photorespiration, the rate of which is directly related to the O(2)/CO(2) ratio, due to the dual function of Rubisco, may be an important mechanism in maintaining the limits of O(2) and CO(2) concentrations by restricting land plant productivity and weathering.

Atmosphere↗

PubMed2001

Differential aluminum tolerance in soybean: An evaluation of the role of organic acids.

The role of organic acids in aluminum (Al) tolerance has been the object of intensive research. In the present work, we evaluated the roles of organic acid exudation and concentrations at the root tip on Al tolerance of soybean. Exposing soybean seedlings to Al3+ activities up to 4.7 &mgr;M in solution led to different degrees of restriction of primary root elongation. Al tolerance among genotypes was associated with citrate accumulation and excretion into the external media. Citrate and malate efflux increased in all genotypes during the first 6 h of Al exposure, but only citrate efflux in Al-tolerant genotypes was sustained for an extended period. Tolerance to Al was correlated with the concentration of citrate in root tips of 8 genotypes with a range of Al sensitivities (r2=0.75). The fluorescent stain lumogallion indicated that more Al accumulated in root tips of the Al-sensitive genotype Young than the Al-tolerant genotype PI 416937, suggesting that the sustained release of citrate from roots of the tolerant genotype was involved in Al exclusion. The initial stimulation of citrate and malate excretion and accumulation in the tip of all genotypes suggested the involvement of additional tolerance mechanisms. The experiments included an examination of Al effects on lateral root elongation. Extension of lateral roots was more sensitive to Al than that of tap roots, and lateral root tips accumulated more Al and had lower levels of citrate.

Journal Article↗

PubMed2003

Do increases in xylem sap pH and/or ABA concentration mediate stomatal closure following nitrate deprivation?

Stomatal conductance (g(s)) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N-deprived plants was not associated with a decreased shoot water potential (Psi(shoot)); conversely Psi(shoot) was lower in N-supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2-0.3 pH units) xylem sap exuded from de-topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3-4-fold when measured on days 2 and 4. On day 2, leaves detached from N-deprived and N-supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10-100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N-deprived leaves relative to N-supplied leaves shows that factors residing within N-deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.

Abscisic Acid↗

PubMed2001

Interleukin-1beta production in periradicular lesions in a human immunodeficiency virus/acquired immune deficiency syndrome model compared with a noninfected host.

This study elucidates the role of interleukin-1 (IL-1) in developing periradicular lesions in immunocompetent and immunocompromised (human immunodeficiency virus/acquired immune deficiency syndrome) hosts. Eight cats were immunosuppressed with steroids before infection with feline immunodeficiency virus (FIV). Eight uninoculated cats served as controls. Periradicular lesions were induced around the canine teeth. At 1 and 4 wk periradicular exudate was sampled via the root canals. IL-1beta levels were measured with ELISA. Data were analyzed using the Mann-Whitney U test and the Wilcoxon signed rank test. Statistically significant differences existed in cytokine levels between the FIV and non-FIV groups (p < 0.001). Cytokines were below detectable levels in the FIV group. A significant decrease in IL-1beta levels at 4 wk compared with 1 wk occurred in the non-FIV group (p < 0.05). In conclusion decreased IL-1beta production was obtained in the FIV group. In the non-FIV group decreases in IL-1beta levels were encountered at the chronic stage of the periradicular lesion compared with the acute stage.

Acute Disease↗

PubMed1992

Rhizobium nodM and nodN genes are common nod genes: nodM encodes functions for efficiency of nod signal production and bacteroid maturation.

Earlier, we showed that Rhizobium meliloti nodM codes for glucosamine synthase and that nodM and nodN mutants produce strongly reduced root hair deformation activity and display delayed nodulation of Medicago sativa (Baev et al., Mol. Gen. Genet. 228:113-124, 1991). Here, we demonstrate that nodM and nodN genes from Rhizobium leguminosarum biovar viciae restore the root hair deformation activity of exudates of the corresponding R. meliloti mutant strains. Partial restoration of the nodulation phenotypes of these two strains was also observed. In nodulation assays, galactosamine and N-acetylglucosamine could substitute for glucosamine in the suppression of the R. meliloti nodM mutation, although N-acetylglucosamine was less efficient. We observed that in nodules induced by nodM mutants, the bacteroids did not show complete development or were deteriorated, resulting in decreased nitrogen fixation and, consequently, lower dry weights of the plants. This mutant phenotype could also be suppressed by exogenously supplied glucosamine, N-acetylglucosamine, and galactosamine and to a lesser extent by glucosamine-6-phosphate, indicating that the nodM mutant bacteroids are limited for glucosamine. In addition, by using derivatives of the wild type and a nodM mutant in which the nod genes are expressed at a high constitutive level, it was shown that the nodM mutant produces significantly fewer Nod factors than the wild-type strain but that their chemical structures are unchanged. However, the relative amounts of analogs of the cognate Nod signals were elevated, and this may explain the observed host range effects of the nodM mutation. Our data indicate that both the nodM and nodN genes of the two species have common functions and confirm that NodM is a glucosamine synthase with the biochemical role of providing sufficient amounts of the sugar moiety for the synthesis of the glucosamine oligosaccharide signal molecules.

Acetylglucosamine↗

PubMed1967

Day-night periodicity of exudation in detopped tobacco.

Exudate was collected periodically from the root systems of detopped tobacco plants. Volume, cations, and (42)K or (86)Rb transfer were measured. According to measurements of K by (42)K and by the flame photometer, when concentrations of KCl and KNO(3) were lower than 10(-2)m, the K in the exudate came mostly from a pool in the plant rather than from the external solution. With higher external KNO(3) solutions, within a few hours nearly all of the K in the exudate came directly from the external solutions. Studies with (86)Rb lead to the same conclusion. In contrast the maximum proportion of K in the exudate that came from KCl in the external solution was reached usually in many hours after detopping and amounted to from 50 to 75%. The higher the external concentration the faster it was reached. These data for KCl are indicative of the (42)K passing through a K pool in the root cells. K and Rb from high concentrations of KNO(3) and RbNO(3), however, may not pass through such a pool. The addition of 10(-2)m KNO(3) into the external solution during exudation essentially eliminated the effect of periodicity at least for a period of time and under the conditions of the experiments. Hydrochloric acid, mercuric chloride, anaerobiosis, and 2,4-dinitrophenol had the same effect and each resulted in a massive final exudation that usually persisted for 1 to 3 days before stopping. These results all lead to a hypothesis that periodicity is regulated at the tonoplast.

Journal Article↗

PubMedDate not supplied

Clinical significance of dental root canal microflora.

OBJECTIVES: Previous work by this group has shown that a significant association exists between pain and the presence of either Prevotella or Peptostreptococcus spp. in dental root canals. The aim of this study was to examine a more extensive series of canals microbiologically, to determine whether any other particular endodontic symptoms or clinical signs showed specific associations with individual bacterial species. METHODS: Seventy root canals were examined microbiologically and clinical data collected to investigate in detail such associations. RESULTS: Of the canals studied, 37 were associated with pain, 49 with tenderness to percussion, 23 with swelling, six with purulent exudate and 57 presented with wet root canals. Anaerobes were isolated from 70.3% of painful canals and from 29.7% of pain-free canals. Significant associations were found between (a) pain and either Prevotella spp. or peptostreptococci, both with P < 0.01; (b) tenderness to percussion and Prevotella spp. (P < 0.01) or anaerobes (P < 0.05); (c) swelling and Eubacterium spp. (P < 0.01), or with Prevotella spp. or Pstr. micros, both with P < 0.05; (d) purulent exudate and any one of F. necrophorum (P < 0.01), Prev. loescheii, Streptoccoccus constellatus or Bacteroides spp. (each P < 0.05); (e) wet canal and facultative anaerobes (P < 0.01), and any one of the genera of Eubacterium, Peptostreptococcus, Prevotella or Propionibacterium (each P < 0.05). CONCLUSION: It was concluded that several different endodontic clinical signs and symptoms are significantly associated with specific bacterial species.

Adult↗

PubMed1998

Host mediators in endodontic exudates. I. Indicators of inflammation and humoral immunity.

Exudate is often found in the root canal when entering the chamber and canal of teeth with periapical lesions. The aim of this study was to determine possible relationships between clinical or radiographic findings and the concentrations of different host mediators in endodontic exudates. Thirty-two nonvital teeth with periapical symptoms were included in the study. A Clinical Periapical Index was developed to quantify clinical findings. Endodontic exudates were collected with methylcellulose filter paper strips every 3 min, after opening of the pulp chamber. The concentrations of the lysosomal acid glycohydrolase beta-glucuronidase, IgG, IgA, IgM, and interleukin-1 beta in the endodontic exudates were analyzed. The results demonstrated that exudates collected from teeth with suppuration (cloudy exudates), and teeth with higher periapical index scores (Orstavik et al., 1986) contained higher concentrations of beta-glucuronidase and interleukin-1 beta. Furthermore, when the periapical index indicated severe involvement, higher IgG was observed in the first samples. The exudates from patients who presented with a sinus tract or swelling contained higher concentrations of IgM, compared with the patients with only periapical sensitivity. Data showed that endodontic exudates from patient with endodontic lesions can be analyzed for host mediators, and differences in the mediators were seen with different clinical and radiographic symptoms.

Adolescent↗

PubMed1979

Effect of temperature on water and ion transport in soybean and broccoli systems.

Steady-state flow rates and exudate osmotic potentials were measured from complete root systems from warm- (28/23 C) or cold-(17/11 C) grown soybean or broccoli (Brassica oleracea) plants at various pressures or different temperatures.In warm-grown soybean roots systems, a break occurred at 14.7 C in the Arrhenius plot of total flow at constant pressure. When plants were grown at lower temperatures, the break point shifted to 8 C. Broccoli, a chilling-resistant species, showed no break for the temperature range used, but cooler growth temperatures decreased the activation energy for water flow through the root system from 18 kilocalories per mole to 9 kilocalories per mole. In both broccoli and soybean, cold-grown plants had lower exudate potentials and greater flow rates at low hydrostatic pressures than the warm-grown plants.These observations indicate that the rate-limiting site for passive water transport is a membrane which may be modified as the plant acclimates to varying growth temperatures. An additional part of the acclimation process is an increase in activity of root ion pumps.

Journal Article↗

PubMed1970

Potassium Fluxes during Potassium Absorption by Intact Barley Plants of Increasing Potassium Content.

The presence of previously absorbed K in plants caused a marked reduction in the short term influx of (86)Rb-labeled K into roots of barley seedlings. The influx values agreed with net K absorption rates into intact plants, thus suggesting that K efflux was negligible in comparison with influx.Earlier interpretations of a large K efflux component from excised roots approaching equilibrium K concentrations are considered to be due to an underestimation of net K absorption rates resulting from xylem exudation as the K status of the roots increased.

Journal Article↗

PubMed1996

Demand-Driven Control of Root ATP Sulfurylase Activity and SO42- Uptake in Intact Canola (The Role of Phloem-Translocated Glutathione).

The activity of ATP sulfurylase extracted from roots of intact canola (Brassica napus L. cv Drakkar) increased after withdrawal of the S source from the nutrient solution and declined after refeeding SO42- to S-starved plants. The rate of SO42- uptake by the roots was similarly influenced. Identical responses were obtained in SO42- -fed roots when one-half of the root system was starved for S. The internal levels of SO42- and glutathione (GSH) declined after S starvation of the whole root system, but only GSH concentration declined in +S roots of plants from split root experiments. The concentration of GSH in phloem exudates decreased upon transfer of plants to S-free solution. Supplying GSH or cysteine to roots, either exogenously or internally via phloem sap, inhibited both ATP sulfurylase activity and SO42- uptake. Buthionine sulfoximine, an inhibitor of GSH synthesis, reversed the inhibitory effect of cysteine on ATP sulfurylase. It is hypothesized that GSH is responsible for mediating the responses to S availability. ATP sulfurylase activity and the SO42- uptake rate are regulated by similar demand-driven processes that involve the translocation of a phloem-transported message (possibly GSH) to the roots that provides information concerning the nutritional status of the leaves.

Journal Article↗