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  • 1
    Electronic Resource
    Electronic Resource
    Transport interactions between cadmium and zinc in roots of bread and durum wheat seedlings (2002)
    Oxford, UK : Blackwell Science, Ltd
    Physiologia plantarum 116 (2002), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Field studies have shown that the addition of Zn to Cd-containing soils can help reduce accumulation of Cd in crop plants. To understand the mechanisms involved, this study used 109Cd and 65Zn to examine the transport interactions of Zn and Cd at the root cell plasma membrane of bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum). Results showed that Cd2+ uptake was inhibited by Zn2+ and Zn2+ uptake was inhibited by Cd2+. Concentration-dependent uptake of both Cd2+ and Zn2+ consisted of a combination of linear binding by cell walls and saturable, Michaelis-Menten influx across the plasma membrane. Saturable influx data from experiments with and without 10 µm concentrations of the corresponding inhibiting ion were converted to double reciprocal plots. The results revealed a competitive interaction between Cd2+ and Zn2+, confirming that Cd2+ and Zn2+ share a common transport system at the root cell plasma membrane in both bread and durum wheat. The study suggests that breeding or agronomic strategies that aim to decrease Cd uptake or increase Zn uptake must take into account the potential accompanying change in transport of the competing ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2002.1160109.x
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for vacuolar sequestration of paraquat in roots of a paraquat-resistant Hordeum glaucum biotype (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Paraquat resistance in the grass weed Hordeum glaucum Steud. has been proposed to result from herbicide sequestration away from the growing points. In the present study, we used roots as a model system to investigate cellular transport of paraquat in resistant (R) and susceptible (S) H. glaucum biotypes. Both time- and concentration-dependent kinetics of paraquat influx across the root cell plasma membrane were similar in the S and R biotype. However, compartmentation analysis indicated greater herbicide accumulation in root vacuoles of the R seedlings. In contrast, the amount of paraquat accumulated in the cytoplasm of S was double that found in R biotype. While paraquat efflux from the cytoplasm back into the external solution was similar in the two biotypes, efflux across the tonoplast from the vacuole back into the cytoplasm was 5 times slower in the R than in the S biotype. At the end of a 48-h efflux period, nearly 7-fold more herbicide was retained in the roots of the R compared with those of the S biotype. These results suggest that paraquat resistance in H. glaucum may be due to the herbicide sequestration in the vacuole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb05410.x
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  • 3
    Electronic Resource
    Electronic Resource
    A gene in the multidrug and toxic compound extrusion (MATE) family confers aluminum tolerance in sorghum (2007)
    [s.l.] : Nature Publishing Group
    Nature genetics 39 (2007), S. 1156-1161 
    Details
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Crop yields are significantly reduced by aluminum toxicity on highly acidic soils, which comprise up to 50% of the world's arable land. Candidate aluminum tolerance proteins include organic acid efflux transporters, with the organic acids forming non-toxic complexes with rhizosphere aluminum. In ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/ng2074
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  • 4
    Electronic Resource
    Electronic Resource
    Ethylene involvement in the over-expression of Fe(III)-chelate reductase by roots of E107 pea [Pisum sativum L. (brz, brz)] and chloronerva tomato (Lycopersicon esculentum L.) mutant genotypes (1996)
    Springer
    BioMetals 9 (1996), S. 38-44 
    Details
    ISSN: 1572-8773
    Keywords: ethylene ; ethylene function ; inducible reductase ; iron-chelate reductase ; iron deficiency ; iron-deficiency ; roots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Recently, ethylene was reported to be involved in the regulation of Fe(III)-chelate reducing capacity by cucumber (Cucuinis sativus L.) roots. Here, we studied the effect of two ethylene inhibitors, aminooxyacetic acid (AOA) and cobalt, on the Fe(III) reducing capacity in roots of mutant genotypes [E107 pea [Pisum sativum L. (brz, brz)] and chloronerva tomato (Lycopersicon esculentum L.) that exhibit high rates of Fe(III)-chelate reduction and excessive iron accumulation. The ethylene inhibitors, AOA and cobalt, markedly inhibited Fe(III)-chelate reducing capacity in roots of both genotypes. Over-expression of root Fe(III) reductase activity by both mutants appears to be related to ethylene. Possibly, both mutants are genetically defective in their ability to regulate root ethylene production. The large inhibitory effect of both ethylene inhibitors on Fe(III)-chelate reducing capacity in roots of the mutant tomato genotype, chloronerva, disputes the contention that the nicotianamine-Fe(II) complex is the repressior of the gene responsible for Fe(III)-chelate reductase activity, as previously suggested by others. However, since nicotianamine shares the same biosynthetic precursor as ethylene, i.e. S-adenosyl methionine, nicotianamine may affect Fe(III)-chelate reductase activity in dicot and non-grass monocot roots by influencing ethylene biosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00188088
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  • 5
    Electronic Resource
    Electronic Resource
    Aluminum effects on the kinetics of calcium uptake into cells of the wheat root apex (1992)
    Springer
    Planta 188 (1992), S. 414-421 
    Details
    ISSN: 1432-2048
    Keywords: Aluminum toxicity ; Calcium (channel, transport) ; Microelectrode (calcium selective, vibrating) ; Triticum (calcium uptake)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of aluminum on the concentration-dependent kinetics of Ca2+ uptake were studied in two winter wheat (Triticum aestivum L.) cultivars, Al-tolerant Atlas 66 and Al-sensitive Scout 66. Seedlings were grown in 100 μM CaCl2 solution (pH 4.5) for 3 d. Subsequently, net Ca2+ fluxes in intact roots were measured using a highly sensitive technique, employing a vibrating Ca2+-selective microelectrode. The kinetics of Ca2+ uptake into cells of the root apex, for external Ca2+ concentrations from 20 to 300 μM, were found to be quite similar for both cultivars in the absence of external Al; Ca2+ transport could be described by Michaelis-Menten kinetics. When roots were exposed to solutions containing levels of Al that were toxic to Al-sensitive Scout 66 but not to Atlas 66 (5 to 20 μM total Al), a strong correlation was observed between Al toxicity and Al-induced inhibition of Ca2+ absorption by root apices. For Scout 66, exposure to Al immediately and dramatically inhibited Ca2+ uptake over the entire Ca2+ concentration range used for these experiments. Kinetic analyses of the Al-Ca interactions in Scout 66 roots were consistent with competitive inhibition of Ca2+ uptake by Al. For example, exposure of Scout 66 roots to increasing Al levels (from 0 to 10 μM) caused the K m for Ca2+ uptake to increase with each rise in Al concentration, from approx. 100 μM in the absence of Al to approx. 300 μM in the presence of 10 μM Al, while having no effect on the V max. The same Al exposures had little effect on the kinetics of Ca2+ uptake into roots of Atlas 66. The results of this study indicate that Al disruption of Ca2+ transport at the root apex may play an important role in the mechanisms of Al toxicity in Al-sensitive wheat cultivars, and that differential Al tolerance may be associated with the ability of Ca2+-transport systems in cells of the root apex to resist disruption by potentially toxic levels of Al in the soil solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192809
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  • 6
    Electronic Resource
    Electronic Resource
    Induction of iron(III) and copper(II) reduction in pea (Pisum sativum L.) roots by Fe and Cu status: Does the root-cell plasmalemma Fe(III)-chelate reductase perform a general role in regulating cation uptake? (1993)
    Springer
    Planta 190 (1993), S. 555-561 
    Details
    ISSN: 1432-2048
    Keywords: Cation absorption ; Copper (reduction, deficiency) ; Iron (reduction, deficiency) ; Pisum (cation uptake) ; Plasma membrane reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We investigated the effects of Fe and Cu status of pea (Pisum sativum L.) seedlings on the regulation of the putative root plasma-membrane Fe(III)-chelate reductase that is involved in Fe(III)-chelate reduction and Fe2+ absorption in dicotyledons and nongraminaceous monocotyledons. Additionally, we investigated the ability of this reductase system to reduce Cu(II)-chelates as well as Fe(III)-chelates. Pea seedlings were grown in full nutrient solutions under control, -Fe, and -Cu conditions for up to 18 d. Iron(III) and Cu(II) reductase activity was visualized by placing roots in an agarose gel containing either Fe(III)-EDTA and the Fe(II) chelate, Na2bathophenanthrolinedisulfonic acid (BPDS), for Fe(III) reduction, or CuSO4, Na3citrate, and Na2-2,9-dimethyl-4,7-diphenyl-1, 10-phenanthrolinedisulfonic acid (BCDS) for Cu(II) reduction. Rates of root Fe(III) and Cu(II) reduction were determined via spectrophotometric assay of the Fe(II)-BPDS or the Cu(I)-BCDS chromophore. Reductase activity was induced or stimulated by either Fe deficiency or Cu depletion of the seedlings. Roots from both Fe-deficient and Cu-depleted plants were able to reduce exogenous Cu(II)-chelate as well as Fe(III)-chelate. When this reductase was induced by Fe deficiency, the accumulation of a number of mineral cations (i.e., Cu, Mn, Fe, Mg, and K) in leaves of pea seedlings was significantly increased. We suggest that, in addition to playing a critical role in Fe absorption, this plasma-membrane reductase system also plays a more general role in the regulation of cation absorption by root cells, possibly via the reduction of critical sulfhydryl groups in transport proteins involved in divalent-cation transport (divalent-cation channels?) across the root-cell plasmalemma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00224795
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  • 7
    Electronic Resource
    Electronic Resource
    Al3+-Ca2+ interactions in aluminum rhizotoxicity (1993)
    Springer
    Planta 192 (1993), S. 104-109 
    Details
    ISSN: 1432-2048
    Keywords: Aluminum toxicity ; Calcium displacement ; Electrical potential ; Root ; Triticum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several mineral rhizotoxicities, including those induced by Al3+, H+, and Na+, can be relieved by elevated Ca2+ in the rooting medium. This leads to the hypothesis that the toxic cations displace Ca2+ from transport channels or surface ligands that must be occupied by Ca2+ in order for root elongation to occur. In this study with wheat (Triticum aestivum L.) seedlings, we have determined, in the case of Al3+, that (i) Ca2+, Mg2+, and Sr2+ are equally ameliorative, (ii) that root elongation does not increase as Ca2+ replaces Mg2+ or Sr2+ in the rooting media, and (iii) that rhizotoxicity is a function solely of Al3+ activity at the root-cell membrane surface as computed by a Gouy-Chapman-Stern model. The rhizotoxicity was indifferent to the computed membrane-surface Ca2+ activity. The rhizotoxicity induced by high levels of tris(ethylenediamine)cobaltic ion (TEC3+), in contrast to Al3+, was specifically relieved by Ca2+ at the membrane surface. The rhizotoxicity induced by H+ exhibited a weak specific response to Ca2+ at the membrane surface. We conclude that the Ca2+-displacement hypothesis fails in the case of Al3+ rhizotoxicity and that amelioration by cations (including monovalent cations) occurs because of decreased membrane-surface negativity and the consequent decrease in the membrane-surface activity of Al3+. However, TEC3+, but not Al3+, may be toxic because it inhibits Ca2+ uptake. The nature of the specific H+-Ca2+ interaction is uncertain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198699
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  • 8
    Electronic Resource
    Electronic Resource
    Organic acid exudation as an aluminum-tolerance mechanism in maize (Zea mays L.) (1995)
    Springer
    Planta 196 (1995), S. 788-795 
    Details
    ISSN: 1432-2048
    Keywords: Aluminum tolerance ; Citrate ; Malate ; Phosphate ; Root (apex, exudate) ; Zea (Al tolerance)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this study, the role of root organic acid synthesis and exudation in the mechanism of aluminum tolerance was examined in Al-tolerant (South American 3) and Al-sensitive (Tuxpeño and South American 5) maize genotypes. In a growth solution containing 6 μM Al3+, Tuxpeño and South American 5 were found to be two- and threefold more sensitive to Al than South American 3. Root organic acid content and organic acid exudation from the entire root system into the bulk solution were investigated via high-performance liquid chromatographic analysis while exudates collected separately from the root apex or a mature root region (using a dividedroot-chamber technique) were analyzed with a more-sensitive ion chromatography system. In both the Al-tolerant and Al-sensitive lines, Al treatment significantly increased the total root content of organic acids, which was likely the result of Al stress and not the cause of the observed differential Al tolerance. In the absence of Al, small amounts of citrate were exuded into the solution bathing the roots. Aluminum exposure triggered a stimulation of citrate release in the Al-tolerant but not in the Al-sensitive genotypes; this response was localized to the root apex of the Al-tolerant genotype. Additionally, Al exposure triggered the release of phosphate from the root apex of the Al-tolerant genotype. The same solution Al3+ activity that elicited the maximum difference in Al sensitivity between Al-tolerant and Al-sensitive genotypes also triggered maximal citrate release from the root apex of the Al-tolerant line. The significance of citrate as a potential detoxifier for aluminum is discussed. It is concluded that organic acid release by the root apex could be an important aspect of Al tolerance in maize.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197346
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  • 9
    Electronic Resource
    Electronic Resource
    Organic acid exudation as an aluminum-tolerance mechanism in maize (Zea mays L.) (1995)
    Springer
    Planta 196 (1995), S. 788-795 
    Details
    ISSN: 1432-2048
    Keywords: Aluminum tolerance ; Citrate ; Malate ; Phosphate ; Root (apex, exudate) ; Zea (Al tolerance)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this study, the role of root organic acid synthesis and exudation in the mechanism of aluminum tolerance was examined in Al-tolerant (South American 3) and Al-sensitive (Tuxpeño and South American 5) maize genotypes. In a growth solution containing 6 μM Al3+, Tuxpeño and South American 5 were found to be two- and threefold more sensitive to Al than South American 3. Root organic acid content and organic acid exudation from the entire root system into the bulk solution were investigated via high-performance liquid chromatographic analysis while exudates collected separately from the root apex or a mature root region (using a dividedroot-chamber technique) were analyzed with a more-sensitive ion chromatography system. In both the Al-tolerant and Al-sensitive lines, Al treatment significantly increased the total root content of organic acids, which was likely the result of Al stress and not the cause of the observed differential Al tolerance. In the absence of Al, small amounts of citrate were exuded into the solution bathing the roots. Aluminum exposure triggered a stimulation of citrate release in the Al-tolerant but not in the Al-sensitive genotypes; this response was localized to the root apex of the Al-tolerant genotype. Additionally, Al exposure triggered the release of phosphate from the root apex of the Al-tolerant genotype. The same solution Al3+ activity that elicited the maximum difference in Al sensitivity between Al-tolerant and Al-sensitive genotypes also triggered maximal citrate release from the root apex of the Al-tolerant line. The significance of citrate as a potential detoxifier for aluminum is discussed. It is concluded that organic acid release by the root apex could be an important aspect of Al tolerance in maize.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106775
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  • 10
    Electronic Resource
    Electronic Resource
    Use of an extracellular, ion-selective, vibrating microelectrode system for the quantification of K+, H+, and Ca2+ fluxes in maize roots and maize suspension cells (1992)
    Springer
    Planta 188 (1992), S. 601-610 
    Details
    ISSN: 1432-2048
    Keywords: Ion transport ; Microelectrode (ion-selective, vibrating) ; Suspension cell ; Zea (ion transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An ion-selective vibrating-microelectrode system, which was originally used to measure extracellular Ca2+ gradients generated by Ca2+ currents, was used to study K+, H+ and Ca2+ transport in intact maize (Zea mays L.) roots and individual maize suspension cells. Comparisons were made between the vibrating ion-selective microelectrode, and a technique using stationary ion-selective microelectrodes to measure ionic gradients in the unstirred layer at the surface of plant roots. The vibrating-microelectrode system was shown to be a major improvement over stationary ion-selective microelectrodes, in terms of sensitivity and temporal resolution. With the vibrating ion microelectrode, it was easy to monitor K+ influxes into maize roots in a background K+ concentration of 10 mM or more, while stationary K+ electrodes were limited to measurements in a background K+ concentration of 0.3 mM or less. Also, with this system it was possible to conduct a detailed study of root Ca2+ transport, which was previously not possible because of the small fluxes involved. For example, we were able to investigate the effect of the excision of maize roots on Ca2+ influx. When an intact maize root was excised from the seedling at a position 3 cm from the site of measurement of Ca2+ transport, a rapid fourfold stimulation of Ca2+ influx was observed followed by dramatic oscillations in Ca2+ flux, oscillating between Ca2+ influx and efflux. These results clearly demonstrate that wound or perturbation responses of plant organs involve transient alterations in Ca2+ transport, which had previously been inferred by demonstrations of touch-induced changes in cytoplasmic calcium. The sensitivity of this system allows for the measurement of ion fluxes in individual plant cells. Using vibrating K+ and H+electrodes, it was possible to measure H+efflux and both K+ influx and efflux in individual maize suspension cells under different conditions. The availability of this technique will greatly improve our ability to study ion transport at the cellular level, in intact plant tissues and organs, and in specialized cells, such as root hairs or guard cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197055
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