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Ciclo evolutivo della sostanza organica di alcuni terreni forestali dell'Aspromonte in relazione alla diversa copertura vegetale
No full textHumic substance: Relationship between structure and activity. deeper information suggests univocal findings.
No full textThe complexity of humic substances (HS) and their remarkable properties in agricultural applications has attracted and continue to attain the attention of many investigators, bringing over the years new knowledge on their structure, physicochemical and biological properties. Nevertheless, the numerous studies produced controversial results because of the difficulty to identify a precise relationship between the structure and the activity of these substances. Evidences presented here showed that the effects of HS on plant growth depends on the source, concentration and molecular weight of humic fractions and mainly on different chemical compounds contained into them. Humic matter appears also to display a hormone-like activity in particular an auxin like activity. It is not clear if this activity is strictly linked to the chemical structure of HS or whether it depends on hormones of microbial origin such as indole acetic acid entrapped into them. In any case, HS exhibit stimulatory effects on plant cell growth and development. In this review, the relationship between humic substance structure, chemical composition and physiological effects on plant growth and metabolism are examined. In particular, the responses of plants to humic substances are described, as well as the regulatory circuits that allow plants to cope with humus. Furthermore, how the present findings can add new information to the humic substances issue is widely discussed
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 of
possible 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
Ruolo dell alto e del basso peso molecolare nella attivita' biologica delle sostanze umiche
No full textAttivita' biologica e caratteristiche strutturali di sostanze umiche di origine forestale
No full textIsopentenyladenosine and cytokinin-like activity of different humic substances.
No full textIncreasing attention has been devoted in the last few years to the mechanisms by which humic substances (HS) influence plant growth. Nevertheless, amongst the biologically active compounds that might be present in HS, only indoleacetic acid has been identified. An enzyme-linked immunosorbent assay (ELISA) was applied to detect the presence of isopentenyladenosine (IPA), a cytokinin, in two lignosulphonate-humates, leonardite humic acid and in a high molecular weight humic fraction extracted from earthworm faeces. The IPA concentration ranged from 34 to 145pmolmg-1 humic C and was estimated by using a linear dose-response curve between the carbon (C) concentration and percentage of binding of an anti-IPA monoclonal antibody. The cytokinin-like activity of HS was evaluated by weighing small radish (Raphanus sativus L.) cotyledon leaves and measuring chlorophyll and protein contents, the activities of ATP sulfurylase and O-acetylserine sulfhydrylase on maize plants. It is noteworthy that, amongst the four HS, those from earthworm faeces showed the highest amount of IPA and the strongest cytokinin-like activity in both plants. The presence of IPA confirmed that HS influence plant metabolism at different levels. Our results open new perspectives in the plant-HS relationship and shed new light on the active components of HS
Effetto di humus forestali sulla morfologia della radice in relazione alle caratteristiche chimiche delle frazioni umiche
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