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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic evidence for the presence of an iron-sulfur center similar to Fx of Photosystem I inHeliobacillus mobilis (1994)
    Springer
    Photosynthesis research 41 (1994), S. 115-123 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; bacteriochlorophyll ; electron acceptor ; iron-sulfur center ; Photosystem I ; heliobacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Treatment of membranes ofHeliobacillus mobilis with high concentrations of the chaotropic agent urea resulted in the removal of the iron-sulfur centers FA and FB from the reaction center, as indicated by EPR spectra under strongly reducing conditions. In urea-treated membranes, transient absorption measurements upon a laser flash indicated a recombination between the photo-oxidized primary donor P798+ and a reduced acceptor with a time constant of 20 ms at room temperature. Benzylviologen, vitamin K-3 and methylene blue were found to accept electrons from the reduced acceptor efficiently. A differential extinction coefficient of 225–240 mM−1 cm−1 at 798 nm was determined from experiments in the presence of methylene blue. Transient absorption difference spectra between 400 and 500 nm in the presence and absence of artificial acceptors indicated that the electron acceptor involved in the 20 ms recombination has an absorption spectrum similar to that of an iron-sulfur center. This iron-sulfur center was assigned to be analogous to FX of Photosystem I. Our results provide evidence in support of the presence of FX in heliobacteria, which was proposed on the basis of the reaction center polypeptide sequence (Liebl et al. (1993) Proc. Natl. Acad. Sci. USA 90: 7124–7128). Implications for the electron transfer pathway in the reaction center of heliobacteria are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184151
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of ferulic acid on the mineral nutrition of grain sorghum (1987)
    Springer
    Plant and soil 98 (1987), S. 99-109 
    Details
    ISSN: 1573-5036
    Keywords: Allelopathy ; Ferulic acid ; Magnesium ; Mineral content ; Phosphorus ; PotassiumSorghum bicolor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two week old sorghum seedlings (Sorghum bicolor L. Moench) were treated with ferulic acid added to the nutrient solution. Effects on tissue concentration of P, K, Mg, Ca, Fe, and Zn were evaluated after 3 and 6 days. Treatemnts of 0.25 mM ferulic acid approximated the growth inhibition threshold, and after 6 days 0.5 mM treated plants weighed less than controls. Both treatments reduced the P content of the roots and shoots at the 3- and 6-day harvests in three replicate experiments. Roots of treated plants at both harvests had a lower concentration of K and Mg. These reductions in P, K, and Mg were most extensive from the 0.5 mM ferulic acid regime. In some cases at both harvests, shoot K was lower and Mg was higher than control tissue. Ferulic acid effects at the 3-day harvest included an elevation of Ca and depression of Fe in shoots. Changes in nutrient content preceded measurable differences in plant weight. These data indicate that one mechanism of growth inhibition by this allelochemical may be an alteration of nutrient balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02381731
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanisms of Hydroquinone-Induced Growth Reduction in Leafy Spurge (1999)
    Springer
    Journal of chemical ecology 25 (1999), S. 1611-1621 
    Details
    ISSN: 1573-1561
    Keywords: Hydroquinone ; allelopathy ; plant water balance ; photosynthesis ; chlorophyll fluorescence ; 13C isotopes ; leafy spurge ; Euphorbia esula ; small everlasting ; Antennaria microphylla Rydb
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Field observations indicate leafy spurge (Euphorbia esula) is inhibited by the presence of Antennaria microphylla. Hydroquinone (HQ), one of several compounds isolated from A. microphylla has been shown to inhibit leafy spurge seed germination, root elongation, and callus culture growth. The present study was designed to analyze the effects of HQ on water relations and photosynthesis of leafy spurge. Plants grown in 0.25 mM HQ had consistently higher leaf diffusive resistance and lower transpiration rates than control plants (P 〈 0.05). Chlorophyll fluorescence was significantly lower than controls (P 〈 0.05) towards the end of the treatment period. At the end of the treatment, tissue from 0.25 mM HQ plants had higher levels of 13C, indicating there had been a sustained interference with stomatal function. These data suggest that a disruption of the plant water balance is one mechanism of leafy spurge inhibition by A. microphylla.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020892917434
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of root exudate sorgoleone on photosynthesis (1993)
    Springer
    Journal of chemical ecology 19 (1993), S. 369-375 
    Details
    ISSN: 1573-1561
    Keywords: Sorgoleone ; allelochemical ; allelopathy ; photosynthesis ; chloroplast ; root exudate ; Sorghum bicolor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The aim of this investigation was to determine if sorgoleone (SGL), ap-benzoquinone inSorghum bicolor root exudate, is a photosynthesis inhibitor. Assays usingGlycine max leaf disks showed concentrations as low as 10μM SGL inhibited oxygen evolution more than 50%. Tests conducted on chloroplasts isolated fromPisum sativum showed that SGL is a powerful inhibitor of CO2-dependent oxygen evolution. Using a chloroplast suspension equivalent to 80–100μg chlorophyll, the I50 was approximately 0.2μM SGL. These data indicate inhibition of photosynthesis is part of the explanation for growth reduction caused by this allelochemical.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00993702
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of juglone on growth, photosynthesis, and respiration (1993)
    Springer
    Journal of chemical ecology 19 (1993), S. 559-568 
    Details
    ISSN: 1573-1561
    Keywords: Juglone ; allelopathy ; allelochemical ; photosynthesis ; chioroplast ; mitochondria ; Lemna minor ; Glycine max
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The impacts of juglone on plant growth and several other physiological functions were evaluated in this study. Juglone inhibitedLemna minor growth, chlorophyll content, and net photosynthesis at treatments between 10 and 40μM. Soybean leaf disks vacuum infiltrated with as little as 10μM juglone had reduced photosynthesis. Oxygen evolution by chloroplasts isolated fromPisum sativum was inhibited by juglone with an I50 of 2μM. Micromolar treatments of juglone stimulated oxygen uptake in mitochondria isolated fromGlycine max. These data suggest perturbations of chloroplast and mitochondrial functions may contribute to plant growth reductions observed in juglone-mediated allelopathy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994325
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  • 6
    Electronic Resource
    Electronic Resource
    Bioassay of naturally occurring allelochemicals for phytotoxicity (1988)
    Springer
    Journal of chemical ecology 14 (1988), S. 1821-1828 
    Details
    ISSN: 1573-1561
    Keywords: Allelopathy ; bioassay ; mechanism of action ; seed germination ; radicle growth ; seedling growth ; Lemna bioassay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The bioassay has been one of the most widely used tests to demonstrate allelopathic activity. Often, claims that a particular plant species inhibits the growth of another are based entirely on the seed germination response to solvent extracts of the suspected allelopathic plant; few of these tests are of value in demonstrating allelopathy under natural conditions. The veracity of the bioassay for evaluating naturally occurring compounds for phytotoxicity depends upon the physiological and biochemical response capacity of the bioassay organism and the mechanism(s) of action of the allelochemicals. The possibility that more than one allelochemical, acting in concert at very low concentrations, may be responsible for an observed allelopathic effect makes it imperative that bioassays be extremely sensitive to chemical growth perturbation agents. Among the many measures of phytotoxicity of allelochemicals, the inhibition (or stimulation) of seed germination, radicle elongation, and/or seedling growth have been the parameters of choice for most investigations. Few of these assays have been selected with the view towards the possible mechanism of the allelopathic effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01013479
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  • 7
    Electronic Resource
    Electronic Resource
    Prior cropping with grain sorghum inhibits weeds (1989)
    Springer
    Journal of chemical ecology 15 (1989), S. 951-960 
    Details
    ISSN: 1573-1561
    Keywords: Allelopathy ; grain sorghum ; Sorghum bicolor ; weed inhibition ; weed management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Three years of field data in northeastern Nebraska demonstrate that a grain sorghum crop reduces weediness in the following crop year. Weed growth was consistently lower in sorghum areas the year after strip-cropping fields with sequences of four-row bands of grain sorghum, soybeans, and corn. Percentage weed cover was significantly lower early in the year, and midsummer weed biomass was well below that found after corn and soybeans. Weed biomass in June and July following corn was two to four times that of grain sorghum strips. Inhibitory effects of grain sorghum were primarily on broadleaf weeds, often showing no action on grass weeds. No obvious differences were noted in the weed species present after the three crops. Allelopathy provides a logical explanation for the sorghum-mediated weed inhibition found in this study. The data have implications for weed management strategies in agriculture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01015190
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  • 8
    Electronic Resource
    Electronic Resource
    Caffeic Acid-Induced Changes in Plant–Water Relationships and Photosynthesis in Leafy Spurge Euphorbia esula (2000)
    Springer
    Journal of chemical ecology 26 (2000), S. 2095-2109 
    Details
    ISSN: 1573-1561
    Keywords: Caffeic acid ; allelopathy ; plant water balance ; photosynthesis ; chlorophyll fluorescence ; 13C carbon isotopes ; leafy spurge ; Euphorbia esula ; small everlasting ; Antennaria microphylla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Leafy spurge (Euphorbia esula), a native perennial weed introduced from Eurasia around the turn of the century, disrupts natural and agroecosystems across much of the Northern Great Plains. While leafy spurge displaces many native plant species, it has been demonstrated that small everlasting (Antennaria microphylla), a native perennial, is allelopathic to leafy spurge. Caffeic acid (CA), one of three compounds isolated from small everlasting, inhibits leafy spurge seed germination, root elongation, and callus culture growth. This study investigated the mechanism of this interference at the whole-plant level. Results indicate that inhibition of growth in leafy spurge after exposure to CA is primarily due to a disruption of plant–water relations. Leafy spurge cuttings were propagated in 0.5 strength Hoagland's nutrient solution for 30 days. For treatments, six plants were transferred into nutrient medium amended with either 0.1 or 0.25 mM CA for a period of 30 days. To determine the effect of pH, two additional groups of six plants were grown in nutrient medium adjusted with HCl corresponding to pH levels of plants treated with CA (pH 5.5–5.8 for 0.1 mM CA and pH 4.5–4.8 for 0.25 mM CA). By day 12 of the treatment period, plants treated with both levels of CA had significantly higher leaf diffusive resistances than control plants. Plants grown at the corresponding pH levels experienced higher diffusive resistances later in the treatment period (day 21). Transpiration was similarly affected with treated plants showing relatively higher transpiration rates compared to controls. Chlorophyll fluorescence was significantly lower than controls in all treated plants by end of the treatment period. The stable carbon isotope ratio (13C:12C) in these plants was higher than controls. These data show that a disruption of plant water relations is the primary mechanism of plant growth inhibition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005564315131
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