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PubMed2005

[Organic acid secretion and its detoxification mechanism in plant roots under aluminum stress].

Phytotoxicity of Al is becoming one of the most serious problems in limiting plant growth on acid soils. Under Al stress, a number of plant species, cultivars or genotypes exhibit inheritable tolerance by organic acid secretion which is specific to Al stress and localized to the root apex. Citric acid, oxalic acid and malic acid are thought to be the most effective organic acids in detoxifying Al. Organic acid detoxifies Al both extracellular and intracellular. Two exudation patterns and their related speculation are introduced in this review. The possible factors responsible for the organic acid secretion are discussed, which are also the research focuses in this field. At last, we put forward our perspective in the field.

Aluminum↗
PubMed2000

Growth, soluble carbohydrates, and aloin concentration of Aloe vera plants exposed to three irradiance levels.

Research was conducted on Aloe vera, a traditional medicinal plant, to investigate the effects of light on growth, carbon allocation, and the concentrations of organic solutes, including soluble carbohydrates and aloin. The plants were vegetatively propagated and grown under three irradiances: full sunlight, partial (30% full sunlight), and deep shade (10% full sunlight) for 12-18 months. After 1 year of growth, five plants from each treatment were harvested to determine total above- and below ground dry mass. Four plants from the full sunlight and the partial shade treatments were harvested after 18 months to assess the soluble carbohydrate, organic acid and aloin concentrations of the clear parenchyma gel and the yellow leaf exudate, separately. Plants grown under full sunlight produced more numerous and larger axillary shoots, resulting in twice the total dry mass than those grown under partial shade. The dry mass of the plants grown under deep shade was 8.6% that of plants grown under full sunlight. Partial shade increased the number and length of leaves produced on the primary shoot, but leaf dry mass was still reduced to 66% of that in full sunlight. In contrast, partial and deep shade reduced root dry mass to 28 and 13%, respectively, of that under full sunlight, indicating that carbon allocation to roots was restricted under low light conditions. When plants were sampled 6 months later, there were only minor treatment effects on the concentration of soluble carbohydrates and aloin in the leaf exudate and gel. Soluble carbohydrate concentrations were greater in the gel than in the exudate, with glucose the most abundant soluble carbohydrate. Aloin was present only in the leaf exudate and higher irradiance did not induce a higher concentration. Limitation in light availability primarily affected total dry mass production and allocation, without substantial effects on either primary or secondary carbon metabolites.

Journal Article↗
PubMed2001

Nitrogen-dependent accumulation of cytokinins in root and the translocation to leaf: implication of cytokinin species that induces gene expression of maize response regulator.

We have described the spatial and temporal accumulation pattern of various cytokinin species in roots, xylem sap and leaves during the resupply of nitrogen in maize. Upon addition of nitrate to nitrogen-depleted maize plants, isopentenyladenosine-5'-monophosphate (iPMP) started to accumulate in roots within 1 h preceding accumulation of trans-zeatin riboside-5'-monophosphate (ZMP), trans-zeatin riboside (ZR) and trans-zeatin (Z). In the xylem flow, both exudation rate of xylem sap and the concentration of the cytokinins increased, and ZR was the dominant species in the sap. In leaf tissue, the accumulation level of Z, which was the dominant form, started to increase 4 h after nitrate resupply to plants and the level was maintained for at least 24 h. Administration of a near physiological concentration of Z, ZR or ZMP (Z-type cytokinins) to detached leaves induced the accumulation of ZmRR1 transcript, that encode maize response regulators, but administration of isopentenyladenine, isopentenyladenosine or iPMP did not. These results strongly suggest that cytokinins are transported across the roots to shoots in response to nitrogen availability, and that, most probably, Z-type cytokinin(s), trigger the induction of ZmRR1.

Adenosine↗
PubMed1996

Immunolocalization of mannitol dehydrogenase in celery plants and cells.

Immunolocalization of mannitol dehydrogenase (MTD) in celery (Apium graveolens L.) suspension cells and plants showed that MTD is a cytoplasmic enzyme. MTD was found in the meristems of celery root apices, in young expanding leaves, in the vascular cambium, and in the phloem, including sieve-element/companion cell complexes, parenchyma, and in the exuding phloem sap of cut petioles. Suspension cells that were grown in medium with mannitol as the sole carbon source showed a high anti-MTD cross-reaction in the cytoplasm, whereas cells that were grown in sucrose-containing medium showed little or no cross-reaction. Gel-blot analysis of proteins from vascular and nonvascular tissues of mature celery petioles showed a strong anti-MTD sera cross-reactive band, corresponding to the 40-kD molecular mass of MTD in vascular extracts, but no cross-reactive bands in nonvascular extracts. The distribution pattern of MTD within celery plants and in cell cultures that were grown on different carbon sources is consistent with the hypothesis that the Mtd gene may be regulated by sugar repression. Additionally, a developmental component may regulate the distribution of MTD within celery plants.

Animals↗
PubMed1979

Allantoin and Allantoic Acid in Tissues and Stem Exudate from Field-grown Soybean Plants.

Samples of stem exudate and plant tissue collected from field-grown soybean (Glycine max [L.] Merr.) plants were analyzed for allantoin and allantoic acid. Nitrogen in nitrate plus amino acids exceeded ureide N concentration in stem exudate prior to flowering. During all of reproductive development (from about 40 days after planting until maturity), ureide N concentration was two to six times greater than amino acid plus nitrate N concentration. Allantoin and allantoic acid, not asparagine, are the principal forms of nitrogen transported from nodulated roots to shoots of the soybean plant. During pod and seed development ureide N comprised as high as 2.3, 37.7, and 15.8% of total N in leaf blades, stems + petioles, and fruits, respectively. The concentration of ureide in stems and fruits declined to nearly zero at maturity.Maximum ureide concentration of exudate collected from soybean nodules was 5.3 milligrams N per milliliter (94 micromoles allantoin per milliliter). This result supports evidence published by others that the site of allantoin synthesis is the nodule.

Journal Article↗
PubMed1994

The micromorphology in vivo of the buccocervical region of premolar teeth in young adults. A replica study by scanning electron microscopy.

The buccal surfaces of premolar teeth are common sites of gingival recession, generally attributed to overzealous oral hygiene. Scanning electron microscopy (SEM) of replicas made from dental impressions was applied to document the micromorphology of the buccocervical region of all premolar teeth in 27 dentally healthy, young adults. The SEM observations were correlated with clinical examination. Of the 216 sites, one-third, predominantly the maxillary first premolars, had gingival recession, but fewer than 50% were clinically discernible. The exposed roots were devoid of cementum, and the dentinal surface was smear-like or dotted with tubular apertures from which droplets of fluid extruded. SEM of replicas of gingiva, recorded as clinically healthy, frequently showed signs of inflammation: fluid exudate and distortion of gingival contour by swelling. The cervical enamel of healthy and affected sites showed characteristic periodic fissure-like cracks, probably enamel tufts. The high frequency of subclinical gingival recession, exposed cervical dentin, and gingival inflammation in dentally healthy young adults, in the absence of abrasion of hard or soft tissues, indicates the need to review conventional concepts of initiation of buccal recession and root exposure.

Adult↗
PubMed1983

Surface coatings on dental cementum incident to periodontal disease. I. A scanning electron microscopic study.

Root surfaces of extracted human teeth with advanced periodontal disease were studied by the apically migrated junctional epithelium, the topography characteristic of uninvolved cementum was frequently masked by a surface coating. The thickness of the coating increased in a coronal direction where it often blended with calculus. The observations indicate that this surface coating may originate from the inflammatory exudate and corresponds to the dental cuticle. The findings also indicate that the coating may be mineralized and may contain exogenous substances. These observations illustrate a need for further study and reexamination of the rationale for removal of tooth substance during scaling and root planing.

Dental Cementum↗
PubMed2024

Predictions of rhizosphere microbiome dynamics with a genome-informed and trait-based energy budget model.

Soil microbiomes are highly diverse, and to improve their representation in biogeochemical models, microbial genome data can be leveraged to infer key functional traits. By integrating genome-inferred traits into a theory-based hierarchical framework, emergent behaviour arising from interactions of individual traits can be predicted. Here we combine theory-driven predictions of substrate uptake kinetics with a genome-informed trait-based dynamic energy budget model to predict emergent life-history traits and trade-offs in soil bacteria. When applied to a plant microbiome system, the model accurately predicted distinct substrate-acquisition strategies that aligned with observations, uncovering resource-dependent trade-offs between microbial growth rate and efficiency. For instance, inherently slower-growing microorganisms, favoured by organic acid exudation at later plant growth stages, exhibited enhanced carbon use efficiency (yield) without sacrificing growth rate (power). This insight has implications for retaining plant root-derived carbon in soils and highlights the power of data-driven, trait-based approaches for improving microbial representation in biogeochemical models.

Rhizosphere↗
PubMed2006

Quantification and modeling of plasmid mobilization on seeds and roots.

Mobilization frequencies of the nonconjugative plasmid pMON5003 were quantified using Escherichia coli TB1(pRK2013) as donor of a helper plasmid, E. coli M182 (pMON5003) as donor of the nonconjugative plasmid, and Pseudomonas fluorescens as recipient. Initial mating experiments were conducted in nutrient and minimal salts media and pea seed exudates. Mobilization rates were higher during early stationary growth of donors, helpers, and recipients. Numbers of transconjugants were higher in biparental matings when donors contained both conjugative and nonconjugative plasmids, versus tri-parental matings. A mathematical model was developed to predict a nonconjugative plasmid transfer rate parameter (delta), estimating the proportion of conjugative matings in which a plasmid is mobilized. Values of delta ranged from 8 x 10(-3) to 7.9 x 10(-1). Transfer frequencies for pMON5003 from E. coli to P. fluorescens on pea seeds and roots were determined. Transconjugants (P. fluorescens 2-79 (pMON5003)) were isolated from seeds, roots, and soil, but mobilization frequencies were lower than in liquid media.

Conjugation, Genetic↗
PubMed1985

Studies on Genetic Male-Sterile Soybeans : IV. Effect of Male Sterility and Source of Nitrogen Nutrition on Accumulation, Partitioning, and Transport of Nitrogen.

Soybean (Glycine max [L.] Merr.) germplasm, isogenic except for loci controlling male sterility (ms(1)) and nodulation (rj(1)), was used to investigate the effects of reproductive tissue development and source of nitrogen nutrition on accumulation, transport, and partitioning of nitrogen in a greenhouse experiment. Nodulated plants were supplied nitrogen-free nutrient solution, and nonnodulated plants were supplied nutrient solution containing 20 millimolar KNO(3). Plants were sampled from flowering until maturity (77 to 147 days after transplanting).Accumulation rates of nitrogen in whole plants during reproductive growth were not significantly different among the four plant types. Nitrogen accumulation in the sterile, nonnodulated plants, however, ceased 2 weeks earlier than in fertile, nonnodulated or fertile and sterile, nodulated plants. This early cessation in nitrogen accumulation resulted in sterile, nonnodulated plants accumulating significantly less whole plant nitrogen by 133 days after transplanting (DAT) than fertile, nonnodulated plants. Thus, changing the site of nitrogen assimilation from nodules (N(2)-fixing plants) to roots and leaves (NO(3)-fed plants) resulted in similar whole-plant nitrogen accumulation rates in fertile and sterile plants, despite the absence of seed in the latter.Leaflet and stem plus petiole tissues of both types of sterile plants had significantly higher nitrogen concentrations after 119 DAT than both types of fertile plants. Significantly higher concentrations and exudation rates of nonureide, reduced-nitrogen in xylem sap of sterile than of fertile plants after 105 DAT were observed. These latter results indicated possible cycling of nonureide, reduced-nitrogen from the downward phloem translocation stream to the upward xylem translocation stream in roots of sterile plants. Collectively, these results suggest a lack of sinks for nitrogen utilization in the shoots of sterile plants. Hence, comparison of nitrogen accumulation rates for sterile and fertile plants does not provide a definitive test of the hypothesis that reproductive tissue development limits photosynthate availability for support of N(2) fixation and nitrate assimilation in determinate soybeans.Nitrogen assimilation during reproductive growth met a larger proportion of the reproductive-tissue nitrogen requirement of nitrate-dependent plants (73%) than of N(2)-fixing plants (63%). Hence, vegetative-tissue nitrogen mobilization to reproductive tissue was a more prominent process in N(2)-fixing than in nitrate-dependent plants. N(2)-fixing plants partitioned nitrogen to reproductive tissue more efficiently than nitrate-dependent plants as the reproductive tissues of the former and latter contained 65 and 55%, respectively, of the whole-plant nitrogen at the time that nitrogen accumulation in reproductive parts had ceased (133 DAT).

Journal Article↗
PubMed1993

Cariogenic potential of pooled plaque fluid from exposed root surfaces in humans.

The composition of pooled plaque fluid from exposed root surfaces of five population samples was determined before and at selected times (3, 7 and 15 min) after a 5 and 10% sucrose rinse. Subjects were 45-65 yr old, had exposed, sound root surfaces, and were grouped according to root caries status [caries-free (CF), no root caries history; caries-positive (CP), recorded root caries experience]. Samples were obtained only from the sound surfaces of the CF and CP subjects after overnight fasting. Plaque samples from each subgroup were pooled under mineral oil and maintained on ice. Plaque fluid was then isolated by centrifugation and analysed for organic acids and inorganic ions (ion chromatography), and pH (microelectrodes). From these data, the degree of saturation [DS(TM)] in plaque fluid with respect to tooth mineral (TM) was calculated. Before exposure to sucrose, plaque fluids from the CF and the CP subgroups had similar ionic compositions. These fluids were also found to be supersaturated with respect to tooth mineral. After exposure to sucrose, a rapid decrease in plaque fluid pH was observed, which corresponded primarily to lactic acid production. For all times examined, mean pH and DS(TM) values were lower and lactic acid concentrations were higher in the CP than the CF samples. Lower values of DS(TM) suggest that plaque fluid from CP subjects had a measurably greater cariogenic potential. Calcium concentrations also increased significantly and to comparable levels in all plaque fluid samples after sucrose exposure, despite lower acid production in CF samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗
PubMed2004

Rhizoremediation: a beneficial plant-microbe interaction.

Worldwide, contamination of soil and ground water is a severe problem. The negative effects of pollutants on the environment and on human health are diverse and depend on the nature of the pollution. The search for alternative methods for excavation and incineration to clean polluted sites resulted in the application of bioremediation techniques. In this review, we describe some generally accepted bioremediation tools and subsequently focus on the combination of two approaches, phytoremediation and bioaugmentation, resulting in rhizoremediation. During rhizoremediation, exudates derived from the plant can help to stimulate the survival and action of bacteria, which subsequently results in a more efficient degradation of pollutants. The root system of plants can help to spread bacteria through soil and help to penetrate otherwise impermeable soil layers. The inoculation of pollutant-degrading bacteria on plant seed can be an important additive to improve the efficiency of phytoremediation or bioaugmentation.

Biodegradation, Environmental↗
PubMed1981

Enzymes of Purine Biosynthesis and Catabolism in Glycine max: I. COMPARISON OF ACTIVITIES WITH N(2) FIXATION AND COMPOSITION OF XYLEM EXUDATE DURING NODULE DEVELOPMENT.

During the period examined from 12 to 63 days after planting, the ureides, allantoin and allantoic acid, were the predominant nitrogenous solutes in the xylem exudate of soybeans (Glycine max [L.]) growing solely on symbiotically fixed nitrogen, accounting for approximately 60% and greater than 95% of the total nitrogen in the xylem exudate before and after the onset of active nitrogen fixation, respectively. For plants between 18 and 49 days of age, the apparent rate of ureide export estimated from concentrations of ureides in xylem exudate collected over a period of one hour was closely related to the rate of nitrogen fixation estimated from measurements of C(2)H(2) reduction by nodulated root systems. After this time, the apparent rate of ureide export per plant continued to increase, reaching a maximum value at day 63 of 12 micromoles per plant per hour, even though the rate of C(2)H(2) reduction per plant declined approximately four-fold. The most probable pathway for the biosynthesis of ureides involves the catabolism of purines. The levels of phosphoribosylpyrophosphate (PRPP) synthetase, which catalyzes the formation of the PRPP required for purine synthesis, increased in parallel with the rates of nitrogen fixation (C(2)H(2)) from day 18 reaching a maximum value of 13.9 micromoles per plant per hour at day 49, and then both activities declined rapidly. During the period of active nitrogen fixation the ratio of PRPP synthesis estimated from measurements of PRPP synthetase activity in cell-free extracts to the apparent rate of ureide export was between 1 and 2. The activities of the enzymes of purine catabolism, xanthine dehydrogenase, uricase, and allantoinase, increased in parallel with the increases in nodule mass and the export of ureides with maximum activities of 13, 119, and 79 micromoles per plant per hour, corresponding with apparent rates of ureide export in the range of 9.5 to 11.9 micromoles per plant per hour. These results demonstrate that there is a close association between nitrogen fixation, PRPP synthetase activity, and ureide export in soybeans and support the proposal that recently-fixed nitrogen is utilized in the de novo synthesis of purines which are subsequently catabolized to produce the ureides.

Journal Article↗
PubMed1990

Morphologic and histochemical characteristics of the dental cuticle in teeth affected by prepubertal periodontitis.

A study was undertaken to determine the nature and composition of the cuticle found in teeth with generalized prepubertal periodontitis (PP). This was accomplished by using histological and histochemical methods on decalcified specimens. Forty-six permanent teeth which were extracted from three prepubertal periodontitis patients (siblings) were used. Nineteen of the 46 teeth were obtained with the facial or interdental gingiva. As a control, 20 healthy teeth extracted from 10 children for orthodontics reasons, and 22 teeth affected by terminal adult periodontitis (AP), were used. All the teeth with PP showed a thick coat covering the root surface from the cemento-enamel junction to the junctional epithelium. In some teeth the cuticle extended a few microns coronally to the cemento-enamel junction. The cuticle had a thickness which varied between 10 to 80 microns. It usually presented a very regular surface in the coronal portion of the root, and showed laminations suggesting appositional growth. In the middle and apical portions of the root exposed to the pocket, the cuticle was lobular with a very irregular surface and was covered with a thick microbial plaque. The staining reactions indicated that the cuticle was made of proteins probably derived from the inflammatory exudate. None of the healthy teeth examined nor those affected by AP showed a cuticle similar to those with PP. The cuticle formed on the teeth with PP appears to be an abnormal structure of proteinaceous nature, characteristic of these teeth, and may possibly play a role in the pathogenesis of the disease.

Adolescent↗
PubMed2003

Modulation of citrate metabolism alters aluminum tolerance in yeast and transgenic canola overexpressing a mitochondrial citrate synthase.

Aluminum (Al) toxicity is a major constraint for crop production in acid soils, although crop cultivars vary in their tolerance to Al. We have investigated the potential role of citrate in mediating Al tolerance in Al-sensitive yeast (Saccharomyces cerevisiae; MMYO11) and canola (Brassica napus cv Westar). Yeast disruption mutants defective in genes encoding tricarboxylic acid cycle enzymes, both upstream (citrate synthase [CS]) and downstream (aconitase [ACO] and isocitrate dehydrogenase [IDH]) of citrate, showed altered levels of Al tolerance. A triple mutant of CS (Deltacit123) showed lower levels of citrate accumulation and reduced Al tolerance, whereas Deltaaco1- and Deltaidh12-deficient mutants showed higher accumulation of citrate and increased levels of Al tolerance. Overexpression of a mitochondrial CS (CIT1) in MMYO11 resulted in a 2- to 3-fold increase in citrate levels, and the transformants showed enhanced Al tolerance. A gene for Arabidopsis mitochondrial CS was overexpressed in canola using an Agrobacterium tumefaciens-mediated system. Increased levels of CS gene expression and enhanced CS activity were observed in transgenic lines compared with the wild type. Root growth experiments revealed that transgenic lines have enhanced levels of Al tolerance. The transgenic lines showed enhanced levels of cellular shoot citrate and a 2-fold increase in citrate exudation when exposed to 150 micro M Al. Our work with yeast and transgenic canola clearly suggest that modulation of different enzymes involved in citrate synthesis and turnover (malate dehydrogenase, CS, ACO, and IDH) could be considered as potential targets of gene manipulation to understand the role of citrate metabolism in mediating Al tolerance.

Aluminum↗
PubMed2003

Subspecies-level variation in the phytoextraction of weathered p,p'-DDE by Cucurbita pepo.

Previous studies indicate that Cucurbita pepo can phytoextract highly weathered persistent organic pollutants (POPs) from soil and translocate large quantities to aerial tissues. To investigate intraspecific variability in uptake potential, a field study was conducted to quantify the phytoextraction of weathered p,p'-DDE by 21 cultivar varieties of summer squash from two distinct subspecies, C. pepo ssp texana and C. pepo ssp pepo. Significant differences exist between the two subspecies, with average root and stem to soil bioconcentration factors (BCF, dry weight ratio of contaminant concentration in the vegetation to that in the soil) of 7.22 and 5.40 for ssp pepo and of 2.37 and 0.454 for spp texana, respectively. The amounts of weathered p,p-DDE extracted from the soil by ssp pepo and ssp texana were 0.301 and 0.065%, respectively, with maximum values within each subspecies of 0.780 and 0.182%, respectively. The quantities of 14 inorganic elements were determined in both the soil and tissues (roots, stems, leaves, and fruit) of all 21 cultivar varieties. Phosphorus concentrations in the tissues of ssp pepo were 14 (fruit)-73% (stems) greater than those of ssp texana. These data support our hypothesis that the unique ability of certain cultivars of C. pepo to phytoextract highly weathered POPs from soil is the result of low molecular weight organic acid exudation as a unique phosphorus acquisition mechanism.

Biodegradation, Environmental↗
PubMed2004

Efficient micropropagation of Ensete ventricosum applying meristem wounding: a three-step protocol.

A highly efficient three-step protocol for in vitro propagation of Ensete ventricosum (enset) was developed that consisted of initiation, bud proliferation, and shoot elongation and rooting stages. At the initiation stage, it was crucial to use shoot tips (5-8 mm) with subtending corm tissues as explants to obtain growth. The addition of 0.5-1% (w/v) activated charcoal to the medium was essential to prevent phenol exudation which otherwise leads to the loss of cultures. During the bud proliferation stage, modified MS macronutrients and micronutrients together with a combination of cytokinins (1.6 microM naphthaleneacetic acid, 4.4 microM 6-benzylaminopurine, 23.2 microM kinetin, 22.6 microM N(6) 2-isopentyladenine) was used. This novel composition of macronutrients was based on the analysis of leaf nutrient content of glasshouse-grown enset sprouts. Multiple bud formation on the enlarged corm tissue was induced only when the meristem region was wounded before transfer to the bud proliferation medium. Up to 75 healthy shoots per explant were produced, whereas unwounded explants produced, only one to two shoots per explant. A third stage with a low concentration of cytokinin enabled shoot elongation as well as root development. The plantlets were acclimatized with 100% success and they showed no apparent phenotypical deviation.

Clone Cells↗