Nuestros investigadores

María Garnica Ochoa

Publicaciones científicas más recientes (desde 2010)

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: Garnica, María; Bacaicoa, E.; Mora, V.; et al.
ISSN 1471-2229  Vol. 18  Nº 105  2018  págs. 14
Background: The release of phytosiderephores (PS) to the rhizosphere is the main root response to iron (Fe) deficiency in graminaceous plants. We have investigated the role of the Fe status in the shoot as well as of the signaling pathways controlled by three relevant phytoregulators-indolacetic acid (IAA), ethylene and nitric oxide (NO) - in the regulation of this root response in Fe-starved wheat plants. To this end, the PS accumulation in the nutrient solution and the root expression of the genes encoding the nicotianamine aminotransferase (TaNAAT) and ferritin (TaFER) have been evaluated in plants subjected to different treatments. Results: The application of Fe to leaves of Fe-deficient plants prevented the increase in both PS root release and TaNAAT gene expression thus showing the relevant role of the shoot to root communication in the regulation of PS root release and some steps of PS biosynthesis. Experiments with specific hormone inhibitors showed that while ethylene and NO did not positively regulate Fe deficiency induced PS root release, auxin plays an essential role in the regulation of this process. Moreover, the application of IM to Fe-sufficient plants promoted both PS root release and TaNAAT gene expression thus indicating that auxin might be involved in the shoot to root signaling network regulating Fe-deficiency root responses in wheat Conclusions: These results therefore indicate that PS root release in Fe-deficient wheat plants is directly modulated by the shoot Fe status through signaling pathways involving, among other possible effectors, auxin.
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: A.; S.; V; et al.
ISSN 1664-462X  Vol. 6  Nº 317  2015 
Higher plants have to cope with fluctuating mineral resource availability. However, strategies such as stimulation of root growth, increased transporter activities, and nutrient storage and remobilization have been mostly studied for only a few macronutrients. Leaves of cultivated crops (Zea mays, Brassica napus, Pisum sativum, Triticum aestivum, Hordeum vulgare) and tree species (Quercus robur, Populus nigra, Alnus glutinosa) grown under field conditions were harvested regularly during their life span and analyzed to evaluate the net mobilization of 13 nutrients during leaf senescence. While N was remobilized in all plant species with different efficiencies ranging from 40% (maize) to 90% (wheat), other macronutrients (K-P-S-Mg) were mobilized in most species. Ca and Mn, usually considered as having low phloem mobility were remobilized from leaves in wheat and barley. Leaf content of Cu-Mo-Ni-B-Fe-Zn decreased in some species, as a result of remobilization. Overall, wheat, barley and oak appeared to be the most efficient at remobilization while poplar and maize were the least efficient. Further experiments were performed with rapeseed plants subjected to individual nutrient deficiencies. Compared to field conditions, remobilization from leaves was similar (N-S-Cu) or increased by nutrient deficiency (K-P-Mg) while nutrient deficiency had no effect on Mo-Zn-B-Ca-Mn, which seemed to be non-mobile during leaf senescence under field conditions.
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: V.; A.; Garnica, María; et al.
ISSN 0981-9428  Vol. 86  2015  págs. 66 - 71
The importance of zinc (Zn) has been of little concern in human nutrition despite a strong decrease of this element in crops since the rise of high yielding varieties. For better food quality, Zn biofortification can be used, but will be optimal only if mechanisms governing Zn management are better known. Using Zn deficiency, we are able to demonstrate that Zn is not remobilized in Brassica napus (B. napus). Thus, remobilization processes should not be targeted by biofortification strategies. This study also complemented previous work by investigating leaf responses to Zn deficiency, especially from proteomic and ionomic points of view, showing for example, an increase in Manganese (Mn) content and of the Mn-dependent protein, Oxygen Evolving Enhancer.
Autores: V.; P.; L.; et al.
ISSN 0721-7595  Vol. 33  Nº 2  2014  págs. 305 - 316
Different strategies, known as crop biofortification, can be used to increase micronutrient concentrations in harvested parts to reduce nutrient deficiencies in the human diet. Apart from fertilization and genetic selection, a more environmentally friendly, less expensive, and more immediate solution could rely on the use of biostimulants derived from natural materials. Two biostimulants, AZAL5 and HA7, which are derived from seaweed and black peat, respectively, have been previously described as promoting growth of Brassica napus and having a substantial effect on gene expression. They were further studied to evaluate their effects on N and S and a wide range of other nutrients (that is, K, Ca, P, Mg, Fe, Na, Mn, B, Si, Cu, and Zn). Providing these two biostimulants in the nutrient solution did not change the mineral supply significantly, but they mostly stimulated root growth and macronutrient uptake (N, S, K, and P) at a level similar to growth. Both biostimulants also stimulate chloroplast division. More surprisingly, they also increased Mg, Mn, Na, and Cu plant concentrations and root-to-shoot translocation of Fe and Zn. These observations were associated with an increased expression of a Cu transporter (COPT2) and NRAMP3, a gene putatively involved in Fe and Zn translocation. Overall, this study showed that specific nutrient balance and transport were stimulated by both biostimulants more significantly than growth, offering new perspectives for biofortification strateg.
Autores: V.; A.; A.; et al.
Revista: PLOS ONE
ISSN 1932-6203  Vol. 9  Nº 10  2014 
During the last 40 years, crop breeding has strongly increased yields but has had adverse effects on the content of micronutrients, such as Fe, Mg, Zn and Cu, in edible products despite their sufficient supply in most soils. This suggests that micronutrient remobilization to edible tissues has been negatively selected. As a consequence, the aim of this work was to quantify the remobilization of Cu in leaves of Brassica napus L. during Cu deficiency and to identify the main metabolic processes that were affected so that improvements can be achieved in the future. While Cu deficiency reduced oilseed rape growth by less than 19% compared to control plants, Cu content in old leaves decreased by 61.4%, thus demonstrating a remobilization process between leaves. Cu deficiency also triggered an increase in Cu transporter expression in roots (COPT2) and leaves (HMA1), and more surprisingly, the induction of the MOT1 gene encoding a molybdenum transporter associated with a strong increase in molybdenum (Mo) uptake. Proteomic analysis of leaves revealed 33 proteins differentially regulated by Cu deficiency, among which more than half were located in chloroplasts. Eleven differentially expressed proteins are known to require Cu for their synthesis and/or activity. Enzymes that were located directly upstream or downstream of Cu-dependent enzymes were also differentially expressed.
Autores: MC; F.; García-Mina, José María; et al.
ISSN 0031-9317  Vol. 151  Nº 4  2014  págs. 375 - 389
This study examines the extent to which the predicted CO2 -protective effects on the inhibition of growth, impairment of photosynthesis and nutrient imbalance caused by saline stress are mediated by an effective adaptation of the endogenous plant hormonal balance. Therefore, sweet pepper plants (Capsicum annuum, cv. Ciclón) were grown at ambient or elevated [CO2] (400 or 800 µmol mol(-1)) with a nutrient solution containing 0 or 80 mM NaCl. The results show that, under saline conditions, elevated [CO2] increased plant dry weight, leaf area, leaf relative water content and net photosynthesis compared with ambient [CO2], whilst the maximum potential quantum efficiency of photosystem II was not modified. In salt-stressed plants, elevated [CO2 ] increased leaf NO3(-) concentration and reduced Cl(-) concentration. Salinity stress induced ABA accumulation in the leaves but it was reduced in the roots at high [CO2], being correlated with the stomatal response. Under non-stressed conditions, IAA was dramatically reduced in the roots when high [CO2] was applied, which resulted in greater root DW and root respiration. Additionally, the observed high CK concentration in the roots (especially tZR) could prevent downregulation of photosynthesis at high [CO2], as the N level in the leaves was increased compared with the ambient [CO2], under salt-stress conditions. These results demonstrate that the hormonal balance was altered by the [CO2], which resulted in significant changes at the grow
Autores: Arkoun, M.; Jannin, L.; Laîné, P.; et al.
ISSN 0032-079X  Vol. 362  Nº 1 - 2  2013  págs. 79 - 92
Background and aims: Urea is the major nitrogen (N) form supplied as fertilizer in agriculture. However, urease, a nickel-dependent enzyme, allows plants to use external or internally generated urea as a nitrogen source. Since a urease inhibitor is frequently applied in conjunction with urea fertilizer, the N-metabolism of plants may be affected. The aim of this study was to determine physiological and molecular effects of nickel deficiency and a urease inhibitor on urea uptake and assimilation in oilseed rape. Methods: Plants were grown on hydroponic solution with urea as the sole N source under three treatments: plants treated with nickel (+Ni) as a control, without nickel (¿Ni) and with nickel and phenylphosphorodiamidate (+Ni+PPD). Urea transport and assimilation were investigated. Results: The results show that Ni-deficiency or PPD supply led to reduced growth and reduced 15N-uptake from urea. This effect was more pronounced in PPD-treated plants, which accumulated high amounts of urea and ammonium. Thus, Ni-deficiency or addition of PPD, limit the availability of N and decreased shoot and root amino acid content. The up-regulation of BnDUR3 in roots indicated that this gene is a component of the stress response to nitrogen-deficiency. A general decline of glutamine synthetase (GS) activity and activation of glutamate dehydrogenase (GDH) and increases in its expression level were observed in control plants.
Autores: Artola, E.; Cruchaga, S.; Ariz, Idoia; et al.
ISSN 0167-6903  Vol. 63  Nº 1  2011  págs. 73 - 79
The use of urea as an N fertilizer has increased to such an extent that it is now the most widely used fertilizer in the world. However, N losses as a result of ammonia volatilization lead to a decrease in its efficiency, therefore different methods have been developed over the years to reduce these losses. One of the most recent involves the use of urea combined with urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT), in an attempt to delay the hydrolysis of urea in the soil. The aim of this study was to perform an in-depth analysis of the effect that NBPT use has on plant growth and N metabolism. Wheat plants were cultivated in a greenhouse experiment lasting 4 weeks and fertilized with urea and NBPT at different concentrations (0, 0.012, 0.062, 0.125%). Each treatment was replicated six times. A non-fertilized control was also cultivated. Several parameters related with N metabolism were analysed at the end of growth period. NBPT use was found to have visible effects, such as a transitory yellowing of the leaf tips, at the end of the first week of treatment. At a metabolic level, plants treated with the inhibitor were found to have more urea in their tissues and a lower amino acid content, lower glutamine synthetase activity, and lower urease and glutamine synthetase content at the end of the study period, whereas their urease activity seemed to have recovered by this stage.
Autores: Garnica, María; Houdusse, F.; Zamarreño, A.M.; et al.
ISSN 0176-1617  Vol. 167  Nº 15  2010  págs. 1264 - 1272
Ammonium can result in toxicity symptoms in many plants when supplied as a sole nitrogen source. Nitrate reduces the negative effects caused by ammonium and promotes plant growth. In order to explore the mechanism responsible of this beneficial effect, we investigated whether nitrate application causes significant changes in the indoleacetic acid (IAA)- and cytokinin-plant distribution and abscisic acid (ABA) accumulation in wheat (Triticum aestivum L.) plants grown with ammonium. Two differentdoses of nitrate were supplied to ammonium-fed plants (100 mu M and 5 mM), to determine whether the effects of nitrate require significant doses (nutritional character), or can be promoted by very low doses (signal effect). The results showed that the presence of NO(3)(-) was associated with clear increases in the active forms of cytokinins (zeatine (Z), trans-zeatine riboside (tZR), isopentenyl adenosine (IPR)) and reduction of the levels of the lower active forms (cis-zeatine riboside (cZR)), independently of the dose applied. Likewise. the presence of nitrate also enhanced IAA shoot content, which correlated with higher cytokinin levels and a tendency toward lower ABA concentration. This study presents further evidence that the possible signal effect of NO(3)(-) involved in its beneficial effect on the growth of wheat plants fed with NH(4)(+) could be mediated by a coordinated action of the levels of cytokinins, IAA and ABA in the shoot.
Autores: Mora, V.; Bacaicoa, E.; Zamarreño, A.M.; 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: Garnica, María; Houdusse, F.; Zamarreño, Ángel; et al.
ISSN 0022-5142  Vol. 90  Nº 3  2010  págs. 357 - 369
BACKGROUND: In certain plant species, ammonium or urea nutrition can cause negative effects on plant development which can result in toxic symptoms. Some authors suggest that the presence of nitrate can alleviate these symptoms by increasing ammonium and urea assimilation, avoiding its accumulation. In order to study this hypothesis, wheat (Triticum aestivum L.) seedlings were grown with various nitrogen supplies containing the main nitrogen forms (ammonium, nitrate and urea). Amino acids content and the activity of the three main enzymes involved in nitrogen assimilation (nitrate reductase, glutamine synthetase and urease) were studied. RESULTS: The application of nitrate along with urea and/or ammonium was not associated with a time¿sustained increase in the activity of glutamine synthetase and urease. Amino acid analysis revealed that nitrate induced changes in amino acid metabolism enhancing its concentration. Likewise the content of protein was also higher in nitrate¿treated plants. CONCLUSION: These results suggest that the effect of nitrate is compatible with a rapid and transient increase in the activity of glutamine synthetase and urease during the first hour after the onset of treatments. Nevertheless, a possible effect of nitrate reducing ammonium accumulation through the activation of alternative metabolic pathways different from that involving glutamine synthetase cannot be ruled out.
Autores: Garnica, María; F.; S.; et al.
Libro:  Nitrate: occurrence, characteristics and health considerations
2012  págs. 67 - 82
The aims of this chapter are: (i) First, to present new experimental evidenceshowingthe signal-role of nitrate in the correction and improvement of the deleterious effects of ammonium-and/or urea-based nutritionin different plant species, either dicotyledonous or monocotyledonous. Likewise, we discuss the different and complementary mechanisms, which are expressed at diverse but interconnected molecular and physiological levels, responsible for this specific role of nitrate. This discussion is accompanied by the propositionof different hypothesisthat could explain these experimental results and orientate future research in this important field as well. (ii) Second, we also discuss the different methodologies that might be developed in order to apply this basic researchin the development of new nitrogenfertilizerswith higher metabolic efficiency and lower potential environmental risks. (iii) Finally, we propose a framework for future research oriented to do a synthesis-involving and inter-connecting this basic and applied research -related to both the future development of nitrogen-related fertilizersand cropyield ¿quality improvement.