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1

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Macromolecular changes of humic substances induced by interaction with organic acids (1996)

PICCOLO, A. ; NARDI, S. ; CONCHERI, G.

Oxford, UK : Blackwell Publishing Ltd

European journal of soil science 47 (1996), S. 0

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ISSN: 1365-2389

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Two different humic materials, one from a forest soil and the other from wormcasts, were used to study the influence of mineral and organic acids on the conformational properties of humic substances. The macromolecular changes were followed by low pressure gel permeation chromatography after titrating humic material to low pHs with acids. All organic acids (mono-, di-, tri-carboxylic, and oxy-acids), added to humic solution prior to a gel permeation in an alkaline buffer, were able to shift the totality of absorbance of the humic chromatographic peak from high to low molecular sizes. Mineral acids, phenol, alcohols, dipolar aprotic solvents, could not produce the same shift and gave total absorbance at the column void volume as in the case of humic substances alone. The chromatographic peak shifted back to elution volumes proper of higher size molecules when the humic-organic acid mixture was back-titrated to high pHs before gel permeation. Elution in a much stronger alkaline buffer did not change the overall macromolecular behaviour.These results suggest that humic substances behave as micelles in solution and that hydrophobic bondings play an important role in holding humic molecules together. The organic acids enter the interior of the humic micelle-like aggregates and alter the stereochemical hydrophobic arrangement of the humic material. In alkaline conditions the negative charges developed disrupt the apparent high molecular size configuration and disperse the humic aggregates into small micelles. Such conformational properties of humic substances appear to be a function of pH and of the concentration of organic acid.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-2389.1996.tb01405.x

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Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase, glutamine synthetase, and phosphoenolpyruvate carboxylase in Daucus carota α II cells (1996)

Muscolo, A. ; Panuccio, M. R. ; Abenavoli, M. R. ; [et al.]

Springer

Biology and fertility of soils 22 (1996), S. 83-88

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ISSN: 1432-0789

Keywords: Key wordsDaucus carotaα II cell ; Tissue culture ; Humic fractions ; Auxin-like activity ; Earthworms ; Allolobophora caliginosa ; Allolophora rosea ; Nuclear magnetic resonance spectra

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (〈3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l–1) and the weakly acidic fraction (1 mg l–1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00384437

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3

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Effect of earthworm humic substances on esterase and peroxidase activity during growth of leaf explants of Nicotiana plumbaginifolia (1993)

Muscolo, A. ; Felici, M. ; Concheri, G. ; [et al.]

Springer

Biology and fertility of soils 15 (1993), S. 127-131

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ISSN: 1432-0789

Keywords: Nicotiana plumbaginifolia ; Tissue culture ; Esterase ; Peroxidase ; Humic fractions ; Earthworms

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary Leaf explants of Nicotiana plumbaginifolia were compared in cultures supplemented with hormones or humic substances (extracted from faeces of Allolobophora caliginosa) of various molecular complexity and concentration. The results showed that the humic substances (F1, F2, and T) at the concentration of 1 mg C l-1 produced greater leaf explants than those grown in the control. Furthermore, humic fractions like gibberellic alone induced a rhizogenic activity in leaf explants. Quantitative differences were also observed in the peroxidase activity induced in Nicotiana plumbaginifolia by humic matter (F2, F2, and T). In addition, the Nicotiana sp. tissue treated with humic fractions revealed, in the esterase enzyme pattern, the appearance of the 2a band, which was attributable to indoleacetic acid, since its profile was consistent with those obtained from tissues treated with indoleacetic acid. These differences demonstrate that humic substances exhibited a hormone-like behaviour, but no evidence of a relationship between biological activities and chemical characteristics of humus substances was found.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00336430

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4

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Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase, glutamine synthetase, and phosphoenolpyruvate carboxylase in Daucus carota α II cells (1996)

Muscolo, A. ; Panuccio, M. R. ; Abenavoli, M. R. ; [et al.]

Springer

Biology and fertility of soils 22 (1996), S. 83-88

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ISSN: 1432-0789

Keywords: Daucus carota α II cell ; Tissue culture ; Humic fractions ; Auxin-like activity ; Earthworms ; Allolobophora caliginosa ; Allolophora rosea ; Nuclear magnetic resonance spectra

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (〈3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l-1) and the weakly acidic fraction (1 mg l-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00384437

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5

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The effects of humic substances within the Ah horizon of a Calcic Luvisol on morphological changes related to invertase and peroxidase activities in wheat roots (1996)

Concheri, G. ; Nardi, S. ; Reniero, F. ; [et al.]

Springer

Plant and soil 179 (1996), S. 65-72

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ISSN: 1573-5036

Keywords: δ 13C ; humic fractions ; invertase and peroxidase activities ; NMR spectra ; root hairs ; scanning electron micrograph ; wheat roots

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The chemical and biological characteristics of humus within the Ah horizon (Calcic-Luvisol) have been studied. Attention was paid to variation in the NMR spectra of humic fractions and δ 13C values and to how these changes are related to different biological humic fraction activities. The chemical changes in particular involve the decrease of the aromatic component and the increase of the non-aromatic component within the horizon and the different δ 13C value not only within the horizon but also among the humic fractions distinctive of different molecular sizes. An attempt has been made to explain the vertical chemical changes in terms of processes affecting the biological characteristics of the high and low molecular size humic fractions. The main conclusions are that the low molecular size humic fractions, in the upper part of the horizon, are of greater importance with respect to the other humic fractions in influencing the enzyme activities linked to growth metabolism. The biological role of the high molecular size humic fractions characterised by a relevant content of peptidic- and carbohydratic-C is also presented.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00011643

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6

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EDXRF study of the effects of Cr on the growth of barley seedlingsPresented at the European Conference on EDXRS, Myconos, Greece, 30 May-6 June 1992. (1993)

Calliari, I. ; Concheri, G. ; Nardi, S.

New York, NY [u.a.] : Wiley-Blackwell

X-Ray Spectrometry 22 (1993), S. 332-337

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ISSN: 0049-8246

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Physics

Notes: Energy-dispersive x-ray fluorescence spectrometry was used to determine Cr and bioessential trace elements (Fe, Zn, Cu, Mn) in the leaves and roots of barley seedlings. The thin-film approach, secondary target excitation and microwave acid digestion were applied. The effects of Cr and other microelements on the growth of barley seedlings are discussed.

Additional Material: 9 Tab.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/xrs.1300220429

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