1,721,079 research outputs found
Calorimetric and UV spectroscopic study of the interaction of paraquat with phospholipids
No full textParaquat (PQ) is a popular herbicide and its main effect is the modification of the membrane integrity. The PQ-dipalmitoylphosphatidic acid (DPPA) and PQ-dipalmitoylphosphatydilcholine (DPPC) water suspension systems at pH 7 have been investigated in order to determine the kind of the molecular interaction that exists between PQ and phospholipids (PL) with different charges, and the influence of the presence of Ca++ ions on this interaction. The experimental results demonstrate that the interaction between PQ and PL is mainly electrostatic; PQ strongly binds to DPPA, which bears one negative charge at pH 7, but only weakly to DPPC, which, unlike DPPA, is uncharged. The presence of Ca++, in an amount sufficient to completely bind the lipid (1 M), strongly alters the DPPA-PQ interactions, thus inhibiting the binding of PQ to lipid. On the contrary, the DPPC-PQ interactions are not modified by the presence of calcium ions
Raman and fluorescence joint analyses of humic like substances extracted from earthworm faeces.
No full textInfluence of long-term residue and fertilizer applications on soil humic substances: A study by electrofocusing
No full textSoil samples were taken from the plots of an experimental field that had been treated continuously for 22 years with different residue and fertilizer applications (cereal residues, cattle manure, NH4NO3). The electrofocusing (EF) technique was used to characterize the humic substances extracted from these soils with 0.5 M NaOH. The EF patterns of the organic matter extracted from the soil which had received applications of cattle manure showed many bands focused in the typical pH gradient region of the most humified compounds. The EF patterns of the organic matter extracted from both unfertilized soil and from soils amended with straw appeared to be much less complex. The addition of NH4NO3 did not affect the soil organic matter characteristics investigated with the EF technique. The results obtained show that electrofocusing is a promising technique for the characterization of humic substances and may well be particularly useful in the evaluation of differences that occur in the humic substances in soil due to residue and organic fertilizer applications. © 1992 Williams and Wilkins
Sorption of atrazine and trifluralin in relation to the physio-chemical characteristics of selected soils
No full textThe sorption of two types of herbicide, atrazine (6-chloro-N2-ethyl-N4 - isopropyl-1,3,5-triazine-2,4-diamine) and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl- p-toluidine), was studied in four different soils representative of the intensively cultivated soils of the Po Valley (northern Italy). To study the effect of the organic matter content, experiments were carried out with one of the soils after the organic matter had been removed by a sodium hypochlorite treatment. The sorption ability for atrazine and trifluralin was decreased considerably when the soil with high organic matter content was treated with sodium hypochlorite; moreover, the sorption of trifluralin also seems to be influenced by the inorganic components of the soil. In comparison to atrazine, the sorption of trifluralin by the different soils was in all cases very high. Using increasing concentrations of herbicide the sorption coefficient (Kd) for each of the four soils was calculated together with the relative sorption constant (Koc) based on the organic carbon content of the soil. The values of Kf and 1/n in the Freundlich equation for atrazine and trifluralin adsorbed by the four soils were related to the characteristics of the soils. © 1992
The auxin-like activity of humic substances is related to membrane interactions in carrot cell cultures
No full textA detailed characterization of two humic fractions was performed: One with low
relative molecular mass (LMr<3,500 Da) and one with high relative molecular mass (HMr
>3,500 Da). Distinct 1H NMR spectroscopic patterns were observed for the two fractions.
HMr showed an aromatic proton region, an intense and broad region (3.0–5.0 ppm)
attributed to sugar-like and polyether components, and an intense doublet at 1.33 ppm
(identified as protons of the β-CH3 in lactate). In contrast, LMr did not show resonances
due to aromatic protons and was characterized by a broad unresolved region, assigned to
sugar-like components. The 13C NMR spectra showed that the LMr humic fraction was
richer in carboxylic and aliphatic C groups compared to HMr fraction. These substances
were fluorescein-labeled [fluorescein isothiocyanate (FITC)], and their interaction with
carrot cells in culture was monitored for 10 d, and compared to FITC–indole-3-acetic acid
(IAA) to clarify their mechanisms of biological activity. After different incubation times,
fluorescein staining of carrot cells and decrease of fluorescein concentration in the culture
medium were evaluated. Fluorescent membrane staining was only present in IAA and the
LMr humic fraction treated cell cultures. A consequential decrease of fluorescein
concentration in the culture media was also observed. Pretreatment of carrot cells with
unconjugated IAA or LMr humic fraction markedly reduced fluorescein staining of both
FITC–IAA and FITC–LMr humic fraction. Blocking tests gave indirect evidence ofpossible binding of the LMr humic fraction to IAA cell membrane receptors. These results
indicate that the two humic fractions behave differently. Only LMr humic fraction, like
IAA, interacts with cellular membranes in carrot cell cultures
Manure fertilization gives high-quality earthworm coprolites with positive effects on plant growth and N metabolism
Full text linkThermal analysis (TG-DTA) and isotopic characterization ( 13C-15N) of humic acids from different origins
No full textThermal analyses (TG-DTA), elemental composition and isotope analyses (13C and 15N) were performed on humic acids (HA) from peats, leonardites and lignites, in order to investigate their structure and the changes taking place during the humification process. Thermal analyses showed structural differences between HA samples in relation to their coalification rank. In particular the lignite HA were characterized by a more stable chemical composition at high temperatures. The δ13C and δ15N values can provide information on the biogeochemical processes involved in HA formation. In particular, peat HA were linked to anoxic environments that enable plant residues to persist in their structure. In contrast, leonardite and lignite HA formation seems to be governed by different biogeochemical processes from those responsible for peat diagenesis. However, the isotopic analyses did not provide any distinction between leonardite and lignite HA. On the basis of the data presented in this study, it may be concluded that TG-DTA and isotope ratio measurements are powerful tools for investigating the formation pathway of humic substances from coals. © 2004 Elsevier Ltd. All rights reserved
Influence of the content of heavy metals and molecular weight of humic acids fractions on the activity and stability of urease
No full textThe aim of this work was to evaluate the effect of two different humic acid (HA) fractions, high molecular weight (HMW 100-300 kDa) and low molecular weight (LMW 10-20 kDa), extracted from peat on the activity and stability of Jack Bean urease. HMW HA significantly inhibited urease activity at pH 6.0 but did not influence the activity at pH 7.0 and 8.0. HMW HA stabilised urease activity over a period of 11 days to treatments with protease and with Cu2+ and Hg2+ (two powerful inhibitors of soluble urease activity). The LMW HA inhibited urease activity at pH 6.0, 7.0 and 8.0, and did not stabilise urease activity in the presence of protease. The residual activity of urease, at pH 7.0 and 8.0 in the presence of LMW HA and Cu2+, was 90 and 69%; in the presence of LMW HA and Hg2+ it was 81 and 52%. The residual activity of urease, at pH 7.0 and 8.0, in the presence of HMW HA and Cu2+ was 99 and 88%; in the presence of HMW HA and Hg2+ it was 94 and 74%. These results showed that the two HA fractions influenced both the activity and stability of the urease differently. It is proposed that the inhibition of the urease by HMW and LMW HA is mainly due to the two heavy metals which, although immobilised on the HA, are still able to interact with the urease. © 2000 Elsevier Science Ltd
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