Nuestros investigadores

Ángel Zamarreño Arregui

Publicaciones científicas más recientes (desde 2010)

Autores: Fuentes, Marta; 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: Sanchez-Romera, B.; Calvo-Polanco, M.; Ruiz-Lozano, J. M.; et al.
ISSN 0032-0781  Vol. 59  Nº 2  2018  págs. 248 - 261
Jasmonic acid (JA) and arbuscular mycorrhizal (AM) symbioses are known to protect plants against abiotic and biotic stresses, but are also involved in the regulation of root hydraulic conductance (L). The objective of this experiment was to elucidate the role of JA in the water relations and hormonal regulation of AM plants under drought by using tomato plants defective in the synthesis of JA (def-1). Our results showed that JA is involved in the uptake and transport of water through its effect on both physiological parameters (stomatal conductance and L) and molecular parameters, mainly by controlling the expression and abundance of aquaporins. We observed that def-1 plants increased the expression of seven plant aquaporin genes under well-watered conditions in the absence of AM fungus, which partly explain the increment of L by this mutation under well-watered conditions. In addition, the effects of the AM symbiosis on plants were modified by the def-1 mutation, with the expression of some aquaporins and plant hormone concentration being disturbed. On the other hand, methyl salicylate (MeSA) content was increased in non-mycorrhizal def-1 plants, suggesting that MeSA and JA can act together in the regulation of L. In a complementary experiment, it was found that exogenous MeSA increased L, confirming our hypothesis. Likewise, we confirmed that JA, ABA and SA are hormones involved in plant mechanisms to cope with stressful situations, their concentrations being controlled by the AM symbiosis. In conclusion, under well-watered conditions, the def-1 mutation mimics the effects of AM symbiosis, but under drought conditions the def-1 mutation changed the effects of the AM symbiosis on plants.
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: Chini, A.; Monte, I.; Zamarreño, Ángel; et al.
ISSN 1552-4450  Vol. 14  Nº 2  2018  págs. 171 - 178
Biosynthesis of the phytohormone jasmonoyl-isoleucine (JA-Ile) requires reduction of the JA precursor 12-oxo-phytodienoic acid (OPDA) by OPDA reductase 3 (OPR3). Previous analyses of the opr3-1 Arabidopsis mutant suggested an OPDA signaling role independent of JA-Ile and its receptor COI1; however, this hypothesis has been challenged because opr3-1 is a conditional allele not completely impaired in JA-Ile biosynthesis. To clarify the role of OPR3 and OPDA in JA-independent defenses, we isolated and characterized a loss-of-function opr3-3 allele. Strikingly, opr3-3 plants remained resistant to necrotrophic pathogens and insect feeding, and activated COI1-dependent JA-mediated gene expression. Analysis of OPDA derivatives identified 4,5-didehydro-JA in wounded wild-type and opr3-3 plants. OPR2 was found to reduce 4,5-didehydro-JA to JA, explaining the accumulation of JA-Ile and activation of JA-Ile-responses in opr3-3 mutants. Our results demonstrate that in the absence of OPR3, OPDA enters the beta-oxidation pathway to produce 4,5-ddh-JA as a direct precursor of JA and JA-Ile, thus identifying an OPR3-independent pathway for JA biosynthesis.
Autores: Sánchez-Rodríguez, A. R.; S.; Zamarreño, Ángel; et al.
ISSN 1049-9644  Vol. 116   2018  págs. 90 - 102
Entomopathogenic fungi have traditionally been assumed to help regulate insect populations. However, some hypocrealean ascomycetes, such as Beauveria bassiana, play other, poorly understood ecological roles that might be useful in developing novel strategies for both increased crop production and crop protection. The primary aims of this work were (a) to assess endophytic colonization of bread wheat and durum wheat plants by the applied fungus B. bassiana strain EABb 04/01-Tip; (b) to examine the impact of various B. bassiana inoculation methods on growth, yield, phytohormone levels and nutrient uptake in the plants, and (c) to quantify mortality of cotton leafworm (Spodoptera littoralis) larvae fed with leaves from inoculated plants. Three experiments involving different inoculation methods (viz., 'soil treatment', 'seed dressing' and 'leaf spraying'), and a fourth experiment to assess mortality in S. littoralis larvae fed with leaves from endophytically-colonized plants, and were conducted according to a completely randomized design. Beauveria bassiana successfully established within, and colonized, bread wheat and durum wheat plants. The fungus was, for the first time, re-isolated from grains produced by plants inoculated using the 'seed dressing' and 'soil treatment' methods. The fungus boosted spike production in bread wheat inoculated using the 'seed dressing' and 'soil treatment' methods, and also in durum wheat but only using the 'soil treatment' method. 'Seed dressing' increased grain yield by about 40%, and also root length, in bread wheat compared with control plants. Mortality in S. littoralis larvae fed with leaves from inoculated plants ranged from 30% using the 'seed dressing' method to 57% using the 'leaf spraying' method compared with 0% when fed the control leaves. However, no fungal outgrowth was detected in larval cadavers. The sustainability of crop production and crop protection strategies based on B. bassiana therefore depends on the effectiveness of the inoculation method and on the particular host plant.
Autores: Quiroga, G.; Erice, G.; Aroca, R.; et al.
ISSN 0378-3774  Vol. 202  2018  págs. 271 - 284
Climate change is leading to the intensification of drought effects worldwide, which considerably reduce crop production. A better understanding of the drought-tolerance mechanisms would lead into a more productive agriculture. The arbuscular mycorrhizal (AM) symbiosis has been shown to improve plant tolerance to drought. Salicylic acid (SA) is a phenolic compound involved in many aspects of plant growth and development. Apart from its role in biotic interactions, it is also involved in the regulation of important plant physiological processes, including plant water relations under stressful conditions. However, despite the importance of SA in plant physiology and in AM colonization, little is known about its effect on regulation of root water transport. Thus, the aim of this work was to study the combined effect of AM symbiosis and SA on root hydraulic properties under drought stress, with special focus on how these factors can alter radial root water transport pathways through aquaporin regulation. Also, the crosstalk between SA and other phytohormones was taken into account. Results showed that the AM symbiosis modifies root hydraulic responses to drought episodes. Under these conditions, AM plants showed increased Lpr and Lo. Exogenous SA application decreased Lpr and Lo under drought. SA modulation of water conductivity could be due to a fine-regulation of root aquaporins (as ZmPIP2:4 or ZmTIP1;1). Furthermore, SA application differently modulated the percentage of water flowing by the apoplastic pathway, decreasing its contribution to total root water flow in AM plants and increasing it in non-AM plants. An intricate relationship between Lpr, aquaporins and endogenous levels of SA, ABA and jasmonic acid was observed. Future studies should explore more in detail the crosstalk mechanism between these hormones in the regulation of water transport in AM roots, in order to better understand the mechanism through which the AM symbiosis copes with drought stress. (C) 2017 Elsevier B.V. All rights reserved.
Autores: Monte, I.; Ishida, S.; Zamarreño, Ángel; et al.
ISSN 1552-4450  Vol. 14  Nº 5  2018  págs. 480 - 488
The phytohormone jasmonoyl-isoleucine (JA-Ile) regulates defense, growth and developmental responses in vascular plants. Bryophytes have conserved sequences for all JA-Ile signaling pathway components but lack JA-Ile. We show that, in spite of 450 million years of independent evolution, the JA-Ile receptor COI1 is functionally conserved between the bryophyte Marchantia polymorpha and the eudicot Arabidopsis thaliana but COI1 responds to different ligands in each species. We identified the ligand of Marchantia MpCOI1 as two isomeric forms of the JA-Ile precursor dinor-OPDA (dinor-cis-OPDA and dinor-iso-OPDA). We demonstrate that AtCOI1 functionally complements Mpcoi1 mutation and confers JA-Ile responsiveness and that a single-residue substitution in MpCOI1 is responsible for the evolutionary switch in ligand specificity. Our results identify the ancestral bioactive jasmonate and clarify its biosynthetic pathway, demonstrate the functional conservation of its signaling pathway, and show that JA-Ile and COI1 emergence in vascular plants required co-evolution of hormone biosynthetic complexity and receptor specificity.
Autores: Calvo-Polanco, M.; Ibort, P.; Molina, S.; et al.
Revista: PLANTA
ISSN 0032-0935  Vol. 246  Nº 5  2017  págs. 987 - 997
The effect of ethylene and its precursor ACC on root hydraulic properties, including aquaporin expression and abundance, is modulated by relative air humidity and plant sensitivity to ethylene. Relative air humidity (RH) is a main factor contributing to water balance in plants. Ethylene (ET) is known to be involved in the regulation of root water uptake and stomatal opening although its role on plant water balance under different RH is not very well understood. We studied, at the physiological, hormonal and molecular levels (aquaporins expression, abundance and phosphorylation state), the plant responses to exogenous 1-aminocyclopropane-1-carboxylic acid (ACC; precursor of ET) and 2-aminoisobutyric acid (AIB; inhibitor of ET biosynthesis), after 24 h of application to the roots of tomato wild type (WT) plants and its ET-insensitive never ripe (nr) mutant, at two RH levels: regular (50%) and close to saturation RH. Highest RH induced an increase of root hydraulic conductivity (Lp(o)) of non-treated WT plants, and the opposite effect in nr mutants. The treatment with ACC reduced Lp(o) in WT plants at low RH and in nr plants at high RH. The application of AIB increased Lp(o) only in nr plants at high RH. In untreated plants, the RH treatment changed the abundance and phosphorylation of aquaporins that affected differently both genotypes according to their ET sensitivity. We show that RH is critical in regulating root hydraulic properties, and that Lp(o) is affected by the plant sensitivity to ET, and possibly to ACC, by regulating aquaporins expression and their phosphorylation status. These results incorporate the relationship between RH and ET in the response of Lp(o) to environmental changes.
Autores: J.M.; Zamarreño, Ángel; et al.
ISSN 0098-8472  Vol. 143  2017  págs. 10 - 19
The use of plant growth promoting rhizobacteria (PGPR) is a proven management strategy to improve plant growth. The aim was to reveal the genomic and proteomic basis of the plant tolerance to saline soil conditions. Combination of whole transcriptome analysis and proteomic profiling helped further the understanding of the complexity of salt tolerance responses. Arabidopsis plants were grown inoculated or not with Bacillus megaterium and irrigated or not with salt. Physiological, genomic and proteomic approaches were combined to reveal plant salt tolerance mechanisms. Microarray analyses revealed the up-regulation of the jasmonic acid metabolism (CYP94B3, lipooxigenase 4 and allene-oxide cyclase) under saline conditions. Knock-out mutants of the gene of interest CYP94B3, responsible of JA-Ile catabolism, were used to confirm the obtained results. Salinity resulted in leaf Na accumulation with decreased chlorophyll content, but PGPR inoculation helped to overcome the stress. Proteomic analysis showed enhanced monodehydroascorbate reductase (MDHAR) content together with ATP synthase. CYP94B3 knock-out plants confirmed the key role of JA-Ile turnover to overcome moderate saline stress. Subsequent experimentation showed that CYP94B3 was important for salt tolerance under moderate and severe salt stress. Inoculation with B. megaterium was a valuable tool to reveal the importance of JA-Ile turnover and to recover Arabidopsis plants from saline stress.
Autores: Ibort, P.; Molina, S.; Nunez, R.; et al.
ISSN 0305-7364  Vol. 120  Nº 1  2017  págs. 101 - 122
Background and Aims Plant growth-promoting bacteria (PGPB) are soil micro-organisms able to interact with plants and stimulate their growth, positively affecting plant physiology and development. Although ethylene plays a key role in plant growth, little is known about the involvement of ethylene sensitivity in bacterial inoculation effects on plant physiology. Thus, the present study was pursued to establish whether ethylene perception is critical for plant-bacteria interaction and growth induction by two different PGPB strains, and to assess the physiological effects of these strains in juvenile and mature tomato (Solanum lycopersicum) plants. Methods An experiment was performed with the ethylene-insensitive tomato never ripe and its isogenic wildtype line in which these two strains were inoculated with either Bacillus megaterium or Enterobacter sp. C7. Plants were grown until juvenile and mature stages, when biomass, stomatal conductance, photosynthesis as well as nutritional, hormonal and metabolic statuses were analysed. Key Results Bacillus megaterium promoted growth only in mature wild type plants. However, Enterobacter C7 PGPB activity affected both wild-type and never ripe plants. Furthermore, PGPB inoculation affected physiological parameters and root metabolite levels in juvenile plants; meanwhile plant nutrition was highly dependent on ethylene sensitivity and was altered at the mature stage. Bacillus megaterium inoculation improved carbon assimilation in wild-type plants. However, insensitivity to ethylene compromised B. megaterium PGPB activity, affecting photosynthetic efficiency, plant nutrition and the root sugar content. Nevertheless, Enterobacter C7 inoculation modified the root amino acid content in addition to stomatal conductance and plant nutrition. Conclusions Insensitivity to ethylene severely impaired B. megaterium interaction with tomato plants, resulting in physiological modifications and loss of PGPB activity. In contrast, Enterobacter C7 inoculation stimulated growth independently of ethylene perception and improved nitrogen assimilation in ethylene-insensitive plants. Thus, ethylene sensitivity is a determinant for B. megaterium, but is not involved in Enterobacter C7 PGPB activity.
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: B.; JM; Zamarreño, Ángel; et al.
ISSN 0940-6360  Vol. 26  Nº 2  2016  págs. 111 - 122
Hormonal regulation and symbiotic relationships provide benefits for plants to overcome stress conditions. The aim of this study was to elucidate the effects of exogenous methyl jasmonate (MeJA) application on root hydraulic conductivity (L) of Phaseolus vulgaris plants which established arbuscular mycorrhizal (AM) symbiosis under two water regimes (well-watered and drought conditions). The variation in endogenous contents of several hormones (MeJA, JA, abscisic acid (ABA), indol-3-acetic acid (IAA), salicylic acid (SA)) and the changes in aquaporin gene expression, protein abundance and phosphorylation state were analyzed. AM symbiosis decreased L under well-watered conditions, which was partially reverted by the MeJA treatment, apparently by a drop in root IAA contents. Also, AM symbiosis and MeJA prevented inhibition of L under drought conditions, most probably by a reduction in root SA contents. Additionally, the gene expression of two fungal aquaporins was upregulated under drought conditions, independently of the MeJA treatment. Plant aquaporin gene expression could not explain the behaviour of L. Conversely, evidence was found for the control of L by phosphorylation of aquaporins. Hence, MeJA addition modified the response of L to both AM symbiosis and drought, presumably by regulating the root contents of IAA and SA and the phosphorylation state of aquaporins.
Autores: JM; R; Zamarreño, Ángel; et al.
ISSN 0140-7791  Vol. 39  Nº 2  2016  págs. 441 - 522
Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However, the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated with the host plant-AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non-AM and AM plants. Three different water regimes were applied, and their effects were analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non-AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non-AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions, plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.
Autores: I.; Aroca, R.; M.; et al.
ISSN 0031-9317  Vol. 155  Nº 3  2015  págs. 338 - 354
Although climate scenarios have predicted an increase in [CO2] and temperature conditions, to date few experiments have focused on the interaction of [CO2] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO2. The main goal of this study was to analyze the effect of interacting [CO2] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO2] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO2] (400 vs 700 mu molmol(-1)) and temperature (ambient vs ambient+4 degrees C) in CO2 gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO2] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO2] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO2] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity.
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: Ricardo ; Juan Manuel ; Zamarreño, Ángel; et al.
ISSN 0176-1617  Vol. 170  Nº 1  2013  págs. 47 - 55
Arbuscular mycorrhizal (AM) symbiosis can alleviate salt stress in plants. However the intimate mechanisms involved, as well as the effect of salinity on the production of signalling molecules associated to the host plant-AM fungus interaction remains largely unknown. In the present work, we have investigated the effects of salinity on lettuce plant performance and production of strigolactones, and assessed its influence on mycorrhizal root colonization. Three different salt concentrations were applied to mycorrhizal and non-mycorrhizal plants, and their effects, overtime, analyzed. Plant biomass, stomatal conductance, efficiency of photosystem II, as well as ABA content and strigolactone production were assessed. The expression of ABA biosynthesis genes was also analyzed. AM plants showed improved growth rates and a better performance of physiological parameters such as stomatal conductance and efficiency of photosystem II than non-mycorrhizal plants under salt stress since very early stages - 3 weeks - of plant colonization. Moreover, ABA levels were lower in those plants, suggesting that they were less stressed than non-colonized plants. On the other hand, we show that both AM symbiosis and salinity influence strigolactone production, although in a different way in AM and non-AM plants. The results suggest that AM symbiosis alleviates salt stress by altering the hormonal. profiles and affecting plant physiology in the host plant.
Autores: Ariz, Idoia; Asensio, A. C.; Zamarreño, Ángel; et al.
ISSN 0031-9317  Vol. 148  Nº 4  2013  págs. 522 - 537
An understanding of the mechanisms underlying ammonium (NH4+) toxicity in plants requires prior knowledge of the metabolic uses for nitrogen (N) and carbon (C). We have recently shown that pea plants grown at high NH4+ concentrations suffer an energy deficiency associated with a disruption of ionic homeostasis. Furthermore, these plants are unable to adequately regulate internal NH4+ levels and the cell-charge balance associated with cation uptake. Herein we show a role for an extra-C application in the regulation of C¿N metabolism in NH4+-fed plants. Thus, pea plants (Pisum sativum) were grown at a range of NH4+ concentrations as sole N source, and two light intensities were applied to vary the C supply to the plants. Control plants grown at high NH4+ concentration triggered a toxicity response with the characteristic pattern of C-starvation conditions. This toxicity response resulted in the redistribution of N from amino acids, mostly asparagine, and lower C/N ratios. The C/N imbalance at high NH4+ concentration under control conditions induced a strong activation of root C metabolism and the upregulation of anaplerotic enzymes to provide C intermediates for the tricarboxylic acid cycle. A high light intensity partially reverted these C-starvation symptoms by providing higher C availability to the plants. The extra-C contributed to a lower C4/C5 amino acid ratio while maintaining the relative contents of some minor amino acids involved in key pathways regulating the C/N sta
Autores: Fuentes, Marta; 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.