Nuestros investigadores

Marta Fuentes Ramírez

Publicaciones científicas más recientes (desde 2010)

Autores: Fuentes, M, (Autor de correspondencia); González-Gaitano, Gustavo; et al.
ISSN 1439-0108  Vol. 18  Nº 4  2018  págs. 1389 - 1399
The traditional method to determine humic content (humic and fulvic acids) in commercial fertilizers, biostimulants, and organic materials is based on the oxidation of the organic carbon contained in the basic-soluble but acid-insoluble fraction (humic acids) and the basic-acid soluble fraction (fulvic acids) of their alkaline water extracts. This methodology, merely operational, makes it impossible to distinguish if the quantified carbon corresponds to substances with "humic" chemical nature or to non-humic organic matter but with similar solubility properties to those of humic matter. The aim of this work is to develop a new methodology that not only quantifies the humic content in commercial products (and raw materials) but also assesses the humic quality of the quantified organic matter. To this end, humic and fulvic (-like) fractions have been isolated/purified from several humic and non-humic materials and characterized by means of elemental analysis and UV-visible, fluorescence, and infrared spectroscopies, and these data have been used to perform a discriminant analysis (DA). The model obtained from the DA is able to discriminate humic and fulvic fractions from apparently humic or fulvic ones and provides discriminant classification functions that have proven to successfully predict the "humic quality" of the fractions isolated from commercial products, after their elemental and spectroscopic characterization. Therefore, the combination of the fractionation, characterization, and evaluation by the DA is proposed as an effective methodology for quantifying and assessing the quality of the humic content claimed in the labels of commercial products.
Autores: Olaetxea, Maite; Garcia, C. A.; et al.
ISSN 0929-1393  Vol. 123  2018  págs. 521 - 537
The ability of rhizospheric humic substances to improve plant growth has been well established by many studies carried out using diverse plant species cultivated under many different conditions. These beneficial effects of humic substances on plant development are expressed in both root and shoot. However, the mechanisms responsible for this action of humic substances are only partially known and poorly integrated. In fact, although the studies focused on plant root development are numerous, those dealing with plant shoot development are scarce. Likewise, studies integrating humic effects on root and shoot are also few. In this context, the main goal of this work is to summarize some of the results regarding the effects of humic substances on plant development within a hypothetical holistic framework that will allow us to interconnect these findings and disclose some features of the functional crosstalk between the effects on soil, root and shoot. Furthermore, the significance of all these mechanisms in plants growing in the field is also discussed.
Autores: Fuentes, M; Bacaicoa, E.; Rivero, M.; et al.
ISSN 1664-462X  Vol. 9  2018  págs. 351
Iron deficiency in plants is caused by a low availability of iron in the soil, and its main visual symptom is leaf yellowing due to a decrease in chlorophyll content, along with a reduction in plant growth and fruit quality. Foliar sprays with Fe compounds are an economic alternative to the treatment with expensive synthetic Fe-chelates applied to the soil, although the efficacy of foliar treatments is rather limited. Generally, plant response to Fe-foliar treatments is monitored by measuring chlorophyll content (or related parameters as SPAD index). However, different studies have shown that foliar Fe sprays cause a local regreening and that translocation of the applied Fe within the plant is quite low. In this context, the aim of this study was to assess the effects of foliar applications of different Fe compounds [FeSO4, Fe(III)-EDTA, and Fe(III)-heptagluconate] on Fe-deficient cucumber plants, by studying the main physiological plant root responses to Fe deficiency [root Fe(III) chelate reductase (FCR) activity; acidification of the nutrient solution; and expression of the Fe deficiency responsive genes encoding FCR, CsFRO1, Fe(II) root transporter CsIRT1, and two plasma membrane H+-ATPases, CsHA1 and CsHA2], along with SPAD index, plant growth and Fe content. The results showed that the overall assessment of Fe-deficiency root responses improved the evaluation of the efficacy of the Fe-foliar treatments compared to just monitoring SPAD indexes. Thus, FCR activity and expression of Fe-deficiency response genes, especially CsFRO1 and CsHA1, preceded the trend of SPAD index and acted as indicators of whether the plant was sensing or not metabolically active Fe due to the treatments. Principal component analysis of the data also provided a graphical tool to evaluate the evolution of plant responses to foliar Fe treatments with time.
Autores: Olaetxea, Maite; V.; García, A. C.; et al.
ISSN 1559-2316  Vol. 11  Nº 4  2016  págs. e1161878
Numerous studies have shown the ability of humic substances to improve plant development. This action is normally reflected in an enhancement of crop yields and quality. However, the mechanisms responsible for this action of humic substances remain rather unknown. Our studies have shown that the shoot promoting action of sedimentary humic acids is dependent of its ability to increase root hydraulic conductivity through signaling pathways related to ABA, which in turn is affected in roots by humic acids in an IAA-NO dependent way. Furthermore, these studies also indicate that the primary action of humic acids in roots might also be physical, resulting from a transient mild stress caused by humic acids associated with a fouling-cleaning cycle of wall cell pores. Finally the role of alternative signal molecules, such as ROS, and corresponding signaling pathways are also discussed and modeled in the context of the above-mentioned framework.
Autores: Garcia, A. C.; Olaetxea, Maite; Santos, L. A.; et al.
ISSN 2314-6133  Vol. 2016  2016  págs. 3747501
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.
Autores: Abros'kin, D. P., (Autor de correspondencia); Fuentes, M; García-Mina, José María; et al.
ISSN 1064-2293  Vol. 49  Nº 10  2016  págs. 1099 - 1108
The effect of humic acids (HAs) and their iron complexes (Fe¿HAs) on the input of the main mineral elements into wheat seedlings, as well as on the efficiency of photosynthesis and the lipid profile of plants, under iron deficiency has been studied. The input of iron from Fe¿HA complexes and its predominant accumulation in roots are demonstrated. It is found that HAs increase the efficiency of photosynthesis due to enhanced electron transport in photosystem II. It is shown that the application of HAs and Fe¿HAs is accompanied by an enhanced input of Zn into plants, which could increase the antioxidant status of plants under iron deficiency conditions. In addition, a pronounced increase in the content of lipids in plants is revealed, which is indicative of the effect of HAs on plant metabolism. The obtained results suggest that the positive effect of Fe¿HAs and HAs on plants under iron deficiency conditions is due to a combination of factors, among which the effect of HAs on the antioxidant status of plants and the plant lipid metabolism predominates.
Autores: Olaetxea, Maite; Mora, V.; Bacaicoa, E.; et al.
ISSN 0032-0889  Vol. 169  Nº 4  2015  págs. 2587 - 2596
The physiological and metabolic mechanisms behind the humic acid-mediated plant growth enhancement are discussed in detail. Experiments using cucumber (Cucumis sativus) plants show that the shoot growth enhancement caused by a structurally well-characterized humic acid with sedimentary origin is functionally associated with significant increases in abscisic acid (ABA) root concentration and root hydraulic conductivity. Complementary experiments involving a blocking agent of cell wall pores and water root transport (polyethylenglycol) show that increases in root hydraulic conductivity are essential in the shoot growth-promoting action of the model humic acid. Further experiments involving an inhibitor of ABA biosynthesis in root and shoot (fluridone) show that the humic acid-mediated enhancement of both root hydraulic conductivity and shoot growth depended on ABA signaling pathways. These experiments also show that a significant increase in the gene expression of the main root plasma membrane aquaporins is associated with the increase of root hydraulic conductivity caused by the model humic acid. Finally, experimental data suggest that all of these actions of model humic acid on root functionality, which are linked to its beneficial action on plant shoot growth, are likely related to the conformational structure of humic acid in solution and its interaction with the cell wall at the root surface.
Autores: Kolodziej, A.; Fuentes, M; et al.
ISSN 0929-5607  Vol. 20  Nº 5 - 6  2014  págs. 667 - 675
The effects of the humic acid (HA) nature and the activated carbon (AC) surface chemistry on the effectiveness of HA removal were investigated. Brown (BHA) and gray (GHA) humic acid fractions of different structure and physicochemical properties were tested in the adsorption process using mesoporous ACs. The modification of chemical structure and surface properties of AC was achieved by ammonization (AC/N) and hydrogen treatment (AC/H). Both approaches led to a decrease in the oxygen content followed by an increase in the carbon basicity, maintaining the porous texture of AC nearly unaltered. Over twice higher removal degree of BHA and GHA was observed for the modified ACs. The kinetics of adsorption of HA fractions have been discussed using the pseudo-second-order model and the intraparticle diffusion model. All ACs showed a higher adsorption capacity toward BHA compared to GHA, which is mainly attributed to the lower molecular weight of BHA. The shape of the equilibrium isotherms indicates a strong competition between water and HA molecules for adsorption sites of the carbon surface.
Autores: Jannin, L.; Arkoun, M.; Etienne, P.; et al.
ISSN 0721-7595  Vol. 32  Nº 1  2013  págs. 31 - 52
Despite its high capacity to take up nitrate from soil, winter rapeseed (Brassica napus) is characterized by a low N recovery in seeds. Thus, to maintain yield, rapeseed requires a high fertilization rate. Increasing nutrient use efficiency in rapeseed by addition of a biostimulant could help improve its agroenvironmental balance. The effects of marine brown seaweed Ascophyllum nodosum on plant growth have been well described physiologically. However, to our knowledge, no study has focused on transcriptomic analyses to determine metabolic targets of these extracts. A preliminary screening of different extracts revealed a significant effect of one of them (AZAL5) on rapeseed root (+102 %) and shoot (+23 %) growth. Microarray analysis was then used on AZAL5-treated or nontreated plants to characterize changes in gene expression that were further supported by physiological evidence. Stimulation of nitrogen uptake (+21 and +115 % in shoots and roots, respectively) and assimilation was increased in a similar manner to growth, whereas sulfate content (+63 and +133 % in shoots and roots, respectively) was more strongly stimulated leading to sulfate accumulation. Among the identified genes whose expression was affected by AZAL5, MinE, a plastid division regulator, was the most strongly affected. Its effect was supported by microscopic analysis showing an enhancement of chloroplast number per cell and starch content but without a significant difference in net photosynthetic rate.
Autores: Vetvicka, V., (Autor de correspondencia); Vashishta, A.; Fuentes, M; et al.
ISSN 1096-620X  Vol. 16  Nº 7  2013  págs. 625 - 632
Despite the rather common presence of humic acid (HA), our full knowledge of its biological effect is still lacking. In this article, we first performed a physicochemical characterization of several HAs, and next, we evaluated their ability to affect interleukin-2 secretion, antibody secretion, wound healing (an in vitro model using HaCaT cells), cancer growth (the Lewis lung carcinoma model), and protection against hepatotoxicity. In all tested reactions, HA showed significant stimulation on immune reactions, including suppression of cancer growth and inhibition of lipopolysaccharide-induced hepatotoxicity. These effects were dependent on its chemical properties. The pleiotropic effects of HA observed in this article suggest the possible role of these compounds in human nutrition.
Autores: Fuentes, M; Olaetxea, Maite; et al.
ISSN 0375-6742  Vol. 129  2013  págs. 14 - 17
The main objective of this study is to investigate the more relevant binding sites (functional groups) involved in the complexation of Fe(III) and Cu(II) by humic-based structures. To this aim we have generated a set of seven humic-based samples (MHA) by the application of a hemi-synthetic process consisting in the oxidative polymerization of different combinations of three sources of natural organic molecules: two humic acids obtained from peat and leonardite, and natural tannin extracted from the quebracho tree (Schinopsis sp.) bark. These MHA were extensively characterized by using complementary analytical techniques (13C NMR, size-exclusion chromatography, electron paramagnetic resonance, and total phenol-reductant content), and their ability to complex Fe(III) and Cu(II) was also calculated by fluorescence quenching method. The data were studied by using general correlation matrix and principal component analysis. The results obtained, taken together, indicated that in a set of humic-based structures presenting carboxylic, phenol and O-alkyl groups, and diverse aliphatic/aromatic character, the complexation of Fe(III) mainly involved specific structural arrangements including carboxylic groups distributed in aliphatic domains. However, Cu(II) complexation involved singular structural arrangements including phenols (and probably substituted phenols) and O-alkyl groups in side chains of aromatic domains.
Autores: García-Mina, José María, (Autor de correspondencia); Bacaicoa, E.; Fuentes, M; et al.
ISSN 0168-9452  Vol. 198  2013  págs. 39 - 45
Numerous studies have investigated the molecular and physiological-morphological mechanisms induced in plant roots in response to specific nutrient deficiencies. Both transcriptional and post-transcriptional mechanisms are involved that increase root uptake under nutrient deficiency. Root nutrient deficiency-stress root responses are mainly regulated by the nutrient status in the shoot. The signals involved in shoot to root cross-talk regulation processes for the activation of nutrient-deficiency induced root responses are not clearly elucidated. The physiological-molecular events in the leaf linked to the nutrient availability for metabolic use, are also poorly known. In this context, we focus our attention on iron plant nutrition. Some experimental evidence suggests the existence of a regulatory system concerned with the optimization of the metabolic use of iron, mainly under conditions of iron starvation. This system seems to be activated by the deficiency in iron-availability for metabolic processes in the leaf and regulates the activation of some iron-stress root responses. This regulation seems to be probably expressed by affecting the production and/or translocation of the activating signal sent from the shoot to the root under conditions of iron deficiency in the shoot.
Autores: Fuentes, M; Fortuno, M.; Perez-Sarmiento, F.; et al.
ISSN 0022-5142  Vol. 92  Nº 15  2012  págs. 3065 - 3071
BACKGROUND: Iron (Fe) chlorosis is a serious problem affecting the yield and quality of numerous crops and fruit trees cultivated in alkaline/calcareous soils. This paper describes the efficiency of a new class of natural hetero-ligand Fe(III) chelates (Fe-NHL) to provide available Fe for chlorotic lemon trees grown in alkaline/calcareous soils. These chelates involve the participation in the reaction system of a partially humified lignin-based natural polymer and citric acid. RESULTS: First results showed that Fe-NHL was adsorbed on the soil matrix while maintaining available Fe for plants in alkaline/calcareous solution. The effects of using three different sources as Fe fertilisers were also compared: two Fe-NHL formulations (NHL1, containing 100% of Fe as Fe-NHL, and NHL2, containing 80% of Fe as Fe-NHL and 20% of Fe as Fe-ethylenediamine-N,N'-bis-(o-hydroxyphenylacetic) acid (Fe-EDDHA)) and Fe-EDDHA. Both Fe-NHL formulations increased fruit yield without negative effects on fruit quality in comparison with Fe-EDDHA. In the absence of the Fe-starter fraction (NHL1), trees seemed to optimise Fe assimilation and translocation from Fe-NHL, directing it to those parts of the plant more involved in development. CONCLUSION: The field assays confirmed that Fe-NHL-based fertilisers are able to provide Fe to chlorotic trees, with results comparable to Fe-EDDHA. Besides, this would imply a more sustainable and less expensive remediation than synthetic chelates. Copyright (c) 2012 Society of Chemical Industry
Autores: Jannin, L., (Autor de correspondencia); Arkoun, M.; Ourry, A.; et al.
ISSN 0032-079X  Vol. 359  Nº 1 - 2  2012  págs. 297 - 319
Background & aims: Winter rapeseed (Brassica napus) is characterized by a low N recovery in seeds and requires high rates of fertilization to maintain yield. Its nutrient use efficiency could be improved by addition of a biostimulant such as humic acids whose physiological effects have been described previously in some plant species. However, to our knowledge, no study has focused on transcriptomic analyses to determine metabolic targets of this extract. Methods: A preliminary screening of ten humic acids revealed a significant effect of one of them (HA7) on rapeseed root growth. Microarray analysis was then used on HA7-treated or non-treated plants to characterize changes in gene expression that were further supported by physiological evidence. Results: Stimulation of nitrogen uptake (+15% in shoots and +108% in roots) and assimilation was found to be increased in a similar manner to growth while sulfate content (+76% in shoots and +137% in roots) was more strongly stimulated leading to higher sulfate accumulation. In parallel, microscopic analysis showed an enhancement of chloroplast number per cell. Conclusion: It is therefore suggested that HA7, which promotes plant growth and nutrient uptake, could be used as a supplementary tool to improve rapeseed nitrogen use efficiency.
Autores: Azcona, Iñaki; Pascual, I; Aguirreolea, Jone Miren; et al.
ISSN 1436-8730  Vol. 174  Nº 6  2011  págs. 916 - 924
A greenhouse experiment was conducted to evaluate the effects of humic substances extracted from composted sewage sludge on growth, phenological development, and photosynthetic activity of pepper (Capsicum annuum L. cv. Piquillo) plants. Humic substances derived from composted sludge (HSS) were compared with those derived from leonardite (HSL). Two doses of both humic substances were assayed (200 and 500 mg C [L substrate](-1)) and compared with a control (C). HSS showed higher nitrogen content and a higher percentage of aliphatic carbon, as well as a lower content of aromatic and phenolic carbon than HSL. HSS significantly increased plant dry-matter production (up to 560%), plant height (86%151%), and leaf area (436%-1397%) during the early stages of pepper development. Net photosynthesis and stomatal conductance increased in the treatments with HSS (up to 48% and 63%, respectively) at the vegetative stage. In addition, HSS accelerated the phenological development of pepper plants, reducing significantly the number of days to flowering and ripening, which occurred 12 and 14 d earlier than in control plants, respectively. In general, the treatments with HSS and HSL did not markedly affect chlorophyll and nutrient concentrations in the leaves. At maturity, only small differences in total fruit yield, number of fruits per plant, and fruit size were observed between amended and control plants. The results suggest that the mechanisms through which HSS affected plant growth and development were not associated with an improved nutrient uptake. Although the identity of the growth-promoting factors remains to be found, the results suggest that they may be linked to the chemical structure of the humic substances.
Autores: Bacaicoa, E.; V.; Zamarreño, Ángel; et al.
ISSN 0981-9428  Vol. 49  Nº 5  2011  págs. 545 - 556
The aim of this study was to investigate the effects of IAA and ABA in the shoot-to-root regulation of the expression of the main Fe-stress physiological root responses in cucumber plants subjected to shoot Fe functional deficiency. Changes in the expression of the genes CsFRO1, CsIRT1, CsHA1 and CsHA2 (coding for Fe(III)-chelate reductase (FCR), the Fe(II) transporter and H+-ATPase, respectively) and in the enzyme activity of FCR and the acidification capacity were measured. We studied first the ability of exogenous applications of IAA and ABA to induce these Fe-stress root responses in plants grown in Fe-sufficient conditions. The results showed that IAA was able to activate these responses at the transcriptional and functional levels, whereas the results with ABA were less conclusive. Thereafter, we explored the role of IAA in plants with or without shoot Fe functional deficiency in the presence of two types of IAA inhibitors, affecting either IAA polar transport (TIBA) or IAA functionality (PCIB). The results showed that IAA is involved in the regulation at the transcriptional and functional levels of both Fe root acquisition (FCR, Fe(II) transport) and rhizosphere acidification (H+-ATPase), although through different, and probably complementary, mechanisms. These results suggest that IAA is involved in the shoot-to-root regulation of the expression of Fe-stress physiological root responses.
Autores: Mora, V.; Bacaicoa, E.; Zamarreño, Ángel; et al.
ISSN 0176-1617  Vol. 167  Nº 8  2010  págs. 633 - 642
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).
Autores: Fuentes, M; Francisco J. ; et al.
ISSN 0361-5995  Vol. 74  Nº 1  2010  págs. 74 - 86
An adequate knowledge of the chemical and structural features that characterize the main fractions of humic substances in solution is of great interest to better understand a number of processes occurring in nature. Qualitative analysis of the spectra derived from diverse analytical techniques is frequently complicated, however, partially due to the quantity and complexity of the data. In this context, multivariate statistical analysis has proven to be a useful tool to integrate and interpret all this information. In this study, we applied Pareto analysis to the spectrum data derived from the application of diverse analytical techniques to several samples of humic substances. The humic substances considered in the study belong to the following groups: gray humic acid (GHA), brown humic acid (BHA), and fulvic acid (FA). The analytical techniques applied were ultraviolet¿visible light, synchronous fluorescence, and Fourier transform infrared spectroscopies, 13C nuclear magnetic resonance spectrometry, and pyrolysis gas chromatography¿mass spectrometry. The results show the efficiency of Pareto analysis at discriminating between the different groups of humic substances. Th is discrimination corresponded to specific spectral regions for each group, which corresponded to singular structural features. Thus, GHA presented a marked aliphatic character and low functionality. The BHA group presented high structural homogeneity characterized by a high aromatic character,
Autores: Fuentes, M; González-Vila, F.J.; et al.
ISSN 0047-2425  Vol. 39  Nº 4  2010  págs. 1486 - 1497
Autores: V.; Olaetxea, Maite; E.; et al.
Libro:  Nitric oxide in plants: metabolism and role in stress physiology
2014  págs. 243 - 264
A number of studies have demonstrated the key role of nitric oxide in the regulation of many fundamental physiological processes that includes plant responses to abiotic and biotic stresses. On the other hand, beneficial action of humic substances on plant growth has been well corroborated, particularly when plants are subjected to abiotic stresses. Furthermore, several recent works have reported the functional links between the plant growth promoting action of humic substances and nitric oxide production and function in plants. In this article, we try to briefly review and discuss the main results showing the relationships between nitric oxide function and humic substances action on plants, also stressing the nitric oxide-dependent involvement of other plant growth regulators, such as auxin, ethylene, abscisic acid, and cytokinins.