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Aranaz J, de Hita D, Olaetxea M, Urrutia O, Fuentes M, Baigorri R, Garnica M, Movila M, Zamarreño AM, Erro J, Baquero E, Gonzalez-Gaitano G, Alvarez JI, Garcia-Mina JM. The molecular conformation, but not disaggregation, of humic acid in water solution plays a crucial role in promoting plant development in the natural environment. FRONTIERS IN PLANT SCIENCE 2023; 14:1180688. [PMID: 37206971 PMCID: PMC10190593 DOI: 10.3389/fpls.2023.1180688] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 04/11/2023] [Indexed: 05/21/2023]
Abstract
Many studies have shown the capacity of soil humic substances (HS) to improve plant growth in natural ecosystems. This effect involves the activation of different processes within the plant at different coordinated molecular, biochemical, and physiological levels. However, the first event triggered by plant root-HS interaction remains unclear. Some studies suggest the hypothesis that the interaction of HS with root exudates involves relevant modification of the molecular conformation of humic self-assembled aggregates, including disaggregation, which might be directly involved in the activation of root responses. To investigate this hypothesis, we have prepared two humic acids. A natural humic acid (HA) and a transformed humic acid obtained from the treatment of HA with fungal laccase (HA enz). We have tested the capacity of the two humic acids to affect plant growth (cucumber and Arabidopsis) and complex Cu. Laccase-treatment did not change the molecular size but increased hydrophobicity, molecular compactness and stability, and rigidity of HA enz. Laccase-treatment avoided the ability of HA to promote shoot- and root-growth in cucumber and Arabidopsis. However, it does not modify Cu complexation features. There is no molecular disaggregation upon the interaction of HA and HA enz with plant roots. The results indicate that the interaction with plant roots induced in both HA and laccase-treated HA (HA enz), changes in their structural features that showed higher compactness and rigidity. These events might result from the interaction of HA and HA enz with specific root exudates that can promote intermolecular crosslinking. In summary, the results indicate that the weakly bond stabilized aggregated conformation (supramolecular-like) of HA plays a crucial role in its ability to promote root and shoot growth. The results also indicate the presence of two main types of HS in the rhizosphere corresponding to those non-interacting with plant roots (forming aggregated molecular assemblies) and those produced after interacting with plant root exudates (forming stable macromolecules).
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Affiliation(s)
- Javier Aranaz
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - David de Hita
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Maite Olaetxea
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Oscar Urrutia
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Marta Fuentes
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Roberto Baigorri
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Maria Garnica
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Maria Movila
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Angel M. Zamarreño
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Javier Erro
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | - Enrique Baquero
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
| | | | - Jose Ignacio Alvarez
- Department of Chemistry, Faculty of Sciences, University of Navarra, Pamplona, Spain
| | - Jose M. Garcia-Mina
- Institute for Biodiversity and Environment BIOMA, University of Navarra, Pamplona, Spain
- *Correspondence: Jose M. Garcia-Mina,
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Olaetxea M, Mora V, Baigorri R, Zamarreño AM, García-Mina JM. The Singular Molecular Conformation of Humic Acids in Solution Influences Their Ability to Enhance Root Hydraulic Conductivity and Plant Growth. Molecules 2020; 26:molecules26010003. [PMID: 33374946 PMCID: PMC7792592 DOI: 10.3390/molecules26010003] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 12/09/2020] [Accepted: 12/19/2020] [Indexed: 11/16/2022] Open
Abstract
Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed.
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Affiliation(s)
- Maite Olaetxea
- Department of Environmental Biology, BIOMA Institut, Sciences School, University of Navarra, 31007 Pamplona, Spain; (R.B.); (A.M.Z.)
- Correspondence: (M.O.); (J.M.G.-M.); Tel.: +34-680-70-82-59 (M.O.); +34-630-062-439 (J.M.G.-M.)
| | - Veronica Mora
- Plant Physiology and Plant-Microorganism Interaction Laboratory, Universidad Nacional de Río Cuarto, Córdoba 5800, Argentina;
| | - Roberto Baigorri
- Department of Environmental Biology, BIOMA Institut, Sciences School, University of Navarra, 31007 Pamplona, Spain; (R.B.); (A.M.Z.)
| | - Angel M. Zamarreño
- Department of Environmental Biology, BIOMA Institut, Sciences School, University of Navarra, 31007 Pamplona, Spain; (R.B.); (A.M.Z.)
| | - Jose M. García-Mina
- Department of Environmental Biology, BIOMA Institut, Sciences School, University of Navarra, 31007 Pamplona, Spain; (R.B.); (A.M.Z.)
- Correspondence: (M.O.); (J.M.G.-M.); Tel.: +34-680-70-82-59 (M.O.); +34-630-062-439 (J.M.G.-M.)
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Zanin L, Tomasi N, Cesco S, Varanini Z, Pinton R. Humic Substances Contribute to Plant Iron Nutrition Acting as Chelators and Biostimulants. FRONTIERS IN PLANT SCIENCE 2019; 10:675. [PMID: 31178884 PMCID: PMC6538904 DOI: 10.3389/fpls.2019.00675] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Accepted: 05/06/2019] [Indexed: 05/03/2023]
Abstract
Improvement of plant iron nutrition as a consequence of metal complexation by humic substances (HS) extracted from different sources has been widely reported. The presence of humified fractions of the organic matter in soil sediments and solutions would contribute, depending on the solubility and the molecular size of HS, to build up a reservoir of Fe available for plants which exude metal ligands and to provide Fe-HS complexes directly usable by plant Fe uptake mechanisms. It has also been shown that HS can promote the physiological mechanisms involved in Fe acquisition acting at the transcriptional and post-transcriptional level. Furthermore, the distribution and allocation of Fe within the plant could be modified when plants were supplied with water soluble Fe-HS complexes as compared with other natural or synthetic chelates. These effects are in line with previous observations showing that treatments with HS were able to induce changes in root morphology and modulate plant membrane activities related to nutrient acquisition, pathways of primary and secondary metabolism, hormonal and reactive oxygen balance. The multifaceted action of HS indicates that soluble Fe-HS complexes, either naturally present in the soil or exogenously supplied to the plants, can promote Fe acquisition in a complex way by providing a readily available iron form in the rhizosphere and by directly affecting plant physiology. Furthermore, the possibility to use Fe-HS of different sources, size and solubility may be considered as an environmental-friendly tool for Fe fertilization of crops.
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Affiliation(s)
- Laura Zanin
- Dipartimento di Scienze AgroAlimentari, Ambientali e Animali, Università degli Studi di Udine, Udine, Italy
| | - Nicola Tomasi
- Dipartimento di Scienze AgroAlimentari, Ambientali e Animali, Università degli Studi di Udine, Udine, Italy
| | - Stefano Cesco
- Faculty of Science and Technology, Free University of Bozen-Bolzano, Bolzano, Italy
| | - Zeno Varanini
- Dipartimento di Biotecnologie, Università di Verona, Verona, Italy
| | - Roberto Pinton
- Dipartimento di Scienze AgroAlimentari, Ambientali e Animali, Università degli Studi di Udine, Udine, Italy
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Involvement of Hormone- and ROS-Signaling Pathways in the Beneficial Action of Humic Substances on Plants Growing under Normal and Stressing Conditions. BIOMED RESEARCH INTERNATIONAL 2016; 2016:3747501. [PMID: 27366744 PMCID: PMC4913021 DOI: 10.1155/2016/3747501] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Revised: 04/10/2016] [Accepted: 05/03/2016] [Indexed: 12/24/2022]
Abstract
The importance of soil humus in soil fertility has been well established many years ago. However, the knowledge about the whole mechanisms by which humic molecules in the rhizosphere improve plant growth remains partial and rather fragmentary. In this review we discuss the relationships between two main signaling pathway families that are affected by humic substances within the plant: one directly related to hormonal action and the other related to reactive oxygen species (ROS). In this sense, our aims are to try the integration of all these events in a more comprehensive model and underline some points in the model that remain unclear and deserve further research.
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KIRISHIMA A, OHNISHI T, SATO N, TOCHIYAMA O. Simplified Modelling of the Complexation of Humic Substance for Equilibrium Calculations. J NUCL SCI TECHNOL 2010. [DOI: 10.1080/18811248.2010.9711669] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Mora V, Bacaicoa E, Zamarreño AM, Aguirre E, Garnica M, Fuentes M, García-Mina JM. Action of humic acid on promotion of cucumber shoot growth involves nitrate-related changes associated with the root-to-shoot distribution of cytokinins, polyamines and mineral nutrients. JOURNAL OF PLANT PHYSIOLOGY 2010; 167:633-42. [PMID: 20185204 DOI: 10.1016/j.jplph.2009.11.018] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Revised: 11/23/2009] [Accepted: 11/23/2009] [Indexed: 05/02/2023]
Abstract
Numerous studies have reported the ability of humic substances to increase shoot growth in different plant species cultivated under diverse growth conditions. However, the mechanism responsible for this effect of humic substances is poorly understood. It is possible that the shoot promoting effect of humic substances involves a primary effect on root H(+)-ATPase activity and nitrate root-shoot distribution that, in turn, causes changes in the root-shoot distribution of certain cytokinins, polyamines and abscisic acid, thus affecting shoot growth. We investigated this hypothesis in the present study. The results showed that the root application of a purified humic acid causes a significant increase in shoot growth that is associated with an enhancement in root H(+)-ATPase activity, an increase in nitrate shoot concentration, and a decrease in roots. These effects were associated with significant increases in the shoot concentration of several cytokinins and polyamines (principally putrescine), concomitant with decreases in roots. Likewise, these changes in the root-shoot distribution of diverse active cytokinins correlated well to significant changes in the root-shoot distribution of several mineral nutrients. These results, taken together, indicate that the beneficial effects of humic substances on shoot development in cucumber could be directly associated with nitrate-related effects on the shoot concentration of several active cytokinins and polyamines (principally putrescine).
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Affiliation(s)
- Verónica Mora
- Department of Chemistry and Soil Chemistry, Faculty of Sciences, University of Navarra, P.O. Box 273, 31080 Pamplona (Navarra), Spain
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Kirishima A, Ohnishi T, Sato N, Tochiyama O. Determination of the phenolic-group capacities of humic substances by non-aqueous titration technique. Talanta 2009; 79:446-53. [DOI: 10.1016/j.talanta.2009.04.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Revised: 04/03/2009] [Accepted: 04/03/2009] [Indexed: 10/20/2022]
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