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La densidad, o concentración de materia, es un concepto muy relevante pero que genera muchas dificultades de comprensión. Para medir la competencia en la estimación de la densidad del alumnado de la ESO, se pasó un cuestionario acompañado de un juego de materiales a 196 alumnos de los cuatro cursos de la ESO en dos colegios. La estimación de la densidad depende del peso percibido, el tamaño o la viscosidad, lo que a veces lleva a estimaciones erróneas. En todos los cursos, más del 40 % de los alumnos consideran la densidad como una propiedad extensiva; en torno a un 50 % usan modelos –no siempre coherentes– más cercanos a una propiedad intensiva y específica. Existen además dificultades para predecir los cambios en densidad con el estado de agregación o la temperatura, lo que sugiere que deben introducirse cambios en su enseñanza., Density, or concentration of matter, is a central concept in science, and yet creates many learning and comprehension difficulties. To estimate how competent Secondary School students at estimating density are, we administered a 4-item questionnaire to 196 students at the 4 courses in two schools. Our results suggest that the estimation of density is dependent on the quantity and quality of sensorial information available - perceived weight, size or viscosity-, which sometimes lead to wrong estimations. In all levels, more than 40 % of the students treated density as an extensive property; around 50 % used intermediate models –sometimes inconsistent– closer to the idea of density as an intensive and specific property. The students had difficulties to predict changes in density with the state of aggregation or temperature, which calls for changes in the way density is taught.

This is the peer reviewed version of the following article: Armendáriz, O., Gil-Monreal, M., Zulet, A., Zabalza, A. and Royuela, M. (2016), Both foliar and residual applications of herbicides that inhibit amino acid biosynthesis induce alternative respiration and aerobic fermentation in pea roots. Plant Biol J, 18: 382–390. doi:10.1111/plb.12412, which has been published in final form at http://dx.doi.org/10.1111/plb.12412. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. The objective of this work was to ascertain whether there is a general pattern of carbon allocation and utilisation in plants following herbicide supply, independent of the site of application: sprayed on leaves or supplied to nutrient solution. The herbicides studied were the amino acid biosynthesis-inhibiting herbicides (ABIH): glyphosate, an inhibitor of aromatic amino acid biosynthesis, and imazamox, an inhibitor of branched-chain amino acid biosynthesis. All treated plants showed impaired carbon metabolism; carbohydrate accumulation was detected in both leaves and roots of the treated plants. The accumulation in roots was due to lack of use of available sugars as growth was arrested, which elicited soluble carbohydrate accumulation in the leaves due to a decrease in sink strength. Under aerobic conditions, ethanol fermentative metabolism was enhanced in roots of the treated plants. This fermentative response was not related to a change in total respiration rates or cytochrome respiratory capacity, but an increase in alternative oxidase capacity was detected. Pyruvate accumulation was detected after most of the herbicide treatments. These results demonstrate that both ABIH induce the less-efficient, ATP-producing pathways, namely fermentation and alternative respiration, by increasing the key metabolite, pyruvate. The plant response was similar not only for the two ABIH but also after foliar or residual application. A. Zulet and M. Gil-Monreal received funding from fellowships through the Ministerio de Educación and Universidad Pública de Navarra, respectively. This work was financially supported by a grant from the Ministerio Español de Economía y Competitividad (AGL-2013-4067R).

Incluye 1 fichero de datos Acetolactate synthase inhibitors (ALS-inhibitors) and glyphosate (GLP) are two classes of herbicide that act by the specific inhibition of an enzyme in the biosynthetic pathway of branched-chain or aromatic amino acids, respectively. The physiological effects that are detected after application of these two classes of herbicides are not fully understood in relation to the primary biochemical target inhibition, although they have been well documented. Interestingly, the two herbicides’ toxicity includes some common physiological effects suggesting that they kill the treated plants by a similar pattern despite targeting different enzymes. The induction of aerobic ethanol fermentation and alternative oxidase (AOX) are two examples of these common effects. The objective of this work was to gain further insight into the role of fermentation and AOX induction in the toxic consequences of ALS-inhibitors and GLP. For this, Arabidopsis T-DNA knockout mutants of alcohol dehydrogenase (ADH) 1 and AOX1a were used. The results found in wild-type indicate that both GLP and ALS-inhibitors reduce ATP production by inducing fermentation and alternative respiration. The main physiological effects in the process of herbicide activity upon treated plants were accumulation of carbohydrates and total free amino acids. The effects of the herbicides on these parameters were less pronounced in mutants compared to wild-type plants. The role of fermentation and AOX regarding pyruvate availability is also discussed. This work was financially supported through a grant from the Ministerio Espanol de Ciencia y Tecnología (AGL-2010-18621 and AGL-2013-40567-R). A. Zulet and M. Gil-Monreal received funding from fellowships through the Ministerio de Educación and the Universidad Pública de Navarra, respectively.

Background: The herbicides glyphosate (Gly) and imazamox (Imx) inhibit the biosynthesis of aromatic and branched-chain amino acids, respectively. Although these herbicides inhibit different pathways, they have been reported to show several common physiological effects in their modes of action, such as increasing free amino acid contents and decreasing soluble protein contents. To investigate proteolytic activities upon treatment with Gly and Imx, pea plants grown in hydroponic culture were treated with Imx or Gly, and the proteolytic profile of the roots was evaluated through fluorogenic kinetic assays and activity-based protein profiling. Results: Several common changes in proteolytic activity were detected following Gly and Imx treatment. Both herbicides induced the ubiquitin-26 S proteasome system and papain-like cysteine proteases. In contrast, the activities of vacuolar processing enzymes, cysteine proteases and metacaspase 9 were reduced following treatment with both herbicides.Moreover, the activities of several putative serine protease were similarly increased or decreased following treatment with both herbicides. In contrast, an increase in YVADase activity was observed under Imx treatment versus a decrease under Gly treatment. Conclusion: These results suggest that several proteolytic pathways are responsible for protein degradation upon herbicide treatment, although the specific role of each proteolytic activity remains to be determined A. Zulet and M. Gil-Monreal received funding from Spanish fellowships through the Ministerio de Educación and the Universidad Pública de Navarra, respectively. This work was financially supported through grants from the Spanish Ministry of Education and Science (AGL-2010-18621) and Max Planck Society and the COST Action CM1004 for funding.

The final publication is available at Springer via http://dx.doi.org/10.1007/s00344-013-9345-5 Quinate (1,3,4,5-tetrahydroxycyclohexanecarboxylate) is a compound synthesized in plants through a side branch of the shikimate biosynthesis pathway. Plants treated with herbicides that inhibit amino acid biosynthesis (branched-chain and aromatic) accumulate quinate in their leaves. The objective of this study was to evaluate whether quinate mimics the effects of herbicides in plants. In pea plants, exogenous application of quinate through the nutrient solution was compared with leaf spraying at a concentration of 4 and 400 mM, respectively, and evaluated in parallel to the effects of herbicides. The analysis facilitated an assessment of the phytotoxicity and potential use of quinate as a natural herbicide. The application of quinate through the nutrient solution, but not the spray, was lethal, although both treatments affected plant growth. Quinate was absorbed and translocated to other plant organs remote from the application site, and an increase in the levels of aromatic amino acids and caffeic acid (that is, compounds located after quinate in the shikimate biosynthesis pathway) was detected, which indicates that quinate was metabolized and incorporated into the shikimate pathway. Exogenous application of quinate affected the carbohydrate content in the leaves and roots in a way similar to the toxic effects of herbicides. The phytotoxic effects of quinate reported in this study suggest that this compound deregulates the shikimate pathway and mimics some physiological effects described in the mode of action of herbicides inhibiting amino acid biosynthesis. A. Zulet received a grant from the Spanish Ministry of Education and Science. This work was supported through funding from the Spanish Ministry of Science and Innovation (AGL- 2010-18621/AGR).

Acetolactate synthase (ALS; EC 4.1.3.18) and ketol-acid reductoisomerase (KARI; EC 1.1.1.86) are two consecutive enzymes in the biosynthesis of branched-chain amino acids. Several commercial herbicides inhibit ALS as their primary site of action. KARI has also attracted attention as a potential target for herbicides. Although potent and selective inhibitors of KARI have been discovered, these inhibitors display less herbicidal activity than ALS-inhibiting herbicides. To obtain a better understanding of these findings, we have compared the physiological effects induced in pea plants after KARI or ALS inhibition. Although, both types of inhibitors induce growth arrest and photosynthesis inhibition, plant death occurs more rapidly under ALS inhibition than KARI inhibition. Carbohydrates accumulated in the leaves and roots following treatments with both inhibitors. The carbohydrate accumulation in the leaves occurred as a consequence of a decrease in sink strength. In contrast, the free amino acid content was only affected through ALS inhibition. These results indicate that although KARI and ALS inhibition block the same biosynthetic pathway and exert common effects on carbon metabolism, nitrogen metabolism is more affected via ALS than KARI inhibition. Thus, metabolic alterations in nitrogen metabolism induced through ALS inhibitors might contribute to the increased efficacy of these chemicals as herbicides. M. Igal received a grant from the Public University of Navarre. A. Zulet and M. Gil-Monreal receive funding through fellowships from the Spanish Ministry of Education and the Public University of Navarre, respectively. This work was financially supported through grants from the Spanish Ministry of Education and Science (AGL-2010-18621).

The herbicide glyphosate reduces plant growth and causes plant death by inhibiting the biosynthesis of aromatic amino acids. The objective of this work was to determine whether glyphosate-treated plants show a carbon metabolism pattern comparable to that of plants treated with herbicides that inhibit branched-chain amino acid biosynthesis. Glyphosate-treated plants showed impaired carbon metabolism with an accumulation of carbohydrates in the leaves and roots. The growth inhibition detected after glyphosate treatment suggested impaired metabolism that impedes the utilization of available carbohydrates or energy at the expected rate. These effects were common to both types of amino acid biosynthesis inhibitors. Under aerobic conditions, ethanolic fermentative metabolism was enhanced in the roots of glyphosate-treated plants. This fermentative response was not related to changes in the respiratory rate or to a limitation of the energy charge. This response, which was similar for both types of herbicides, might be considered a general response to stress conditions. L. Orcaray and A. Zulet were the recipients of grants from the Spanish Ministry of Education. This work was supported by the Spanish Ministry of Education and Science (AGL-2007-61134/AGR and AGL-2010- 18621).