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[EN] Enzymatic activity and soluble protein content in relation to salt stress tolerance were investigated in Calendula officinalis seedlings after 24 days of treatment with different salt treatments, including NaCl, CaCl2, MgCl2 and mixtures of them. The marigold seedlings were used in order to investigate the possible salt-inducible responses and the possible alleviative role of calcium and magnesium salts in respect with adverse salinity conditions. Activity of superoxide dismutase (SOD; EC 1.15.1.1) and peroxidase (POD; EC 1.11.1.7) generally slightly decreased under salt treatments, with minor variations from the value recorded for control series and within applied treatments. Catalase (CAT; EC 1.11.1.6) activity was stimulated by NaCl salinity and MgCl2 addition; its activity was found to be lowest under calcium and magnesium chloride treatments solely

Soil salinisation is an increasing problem for agriculture, affecting the most productive crop areas in the world those cultivated under irrigation in arid and semi-arid regions. In addition, a significant fraction of the world's land surface is naturally saline and is not available for agriculture. Cultivation of these salinised areas, if possible, would contribute to the increase in food production needed in the next few decades to feed a growing world population. Unfortunately, our present crops are all salt-sensitive, to a greater or lesser degree, and classical breeding has not succeeded in improving their resistance to salinity. Similarly, genetic engineering approaches have not yet delivered commercial salt-tolerant 'biotech' (GM) crops. Yet a small percentage (ca. 0.25%) of wild angiosperm species halophytes are adapted to saline soils in their natural habitats, and many are able to complete their life cycle at salinity levels similar to, or even higher than sea water. Halophytes could be cultivated in salinised land already lost for agriculture, and also in naturally saline, marginal soils, using brackish water, reclaimed industrial/urban waste water, or even sea water for irrigation. Most important, this 'saline agriculture' will not compete with conventional crops for increasingly scarce resources, such as fertile land and good-quality irrigation water. Several salt-tolerant taxa are being investigated as potential 'new' halophytic crops and others can be developed in the near future, to be used, for example: i) as human food or for animal feed; ii) for production of biofuels: biomass generation for bioethanol, and biodiesel obtained from oleaginous seeds; iii) for the production of secondary metabolites with medical, nutraceutical, cosmetic or other industrial applications; iv) as new ornamental plants, for gardening and landscape architecture. As the crop potential of many of these species is unknown and some may have undesirable agronomic characteristics, we propose that more effort should be invested in the domestication of promising halophytic taxa, establishing breeding programmes to transform these amazing wild plants into useful crops.

The patterns of ion uptake were analysed in three dicotyledonous (Arthrocnemum macrostachyum, Sarcocornia fruticosa and Inula crithmoides) and two monocotyledonous (Juncus acutus and J. maritimus) halophytes, collected from a salt marsh in SE Spain. The experimental design included four plots in different positions within the marsh, and three sampling periods corresponding to spring, summer and autumn 2011. Electric conductivity, pH, and Na+, K+, Ca2+, Mg2+ and Cl- contents were determined in saturated soil extracts. In plants, the same ions were extracted in boiling water. In soil samples, spatial variation in the measured parameters among plots was higher than the seasonal variation within plots, whereas in plants significant differences in ion contents were detected only between species, but not between plots or sampling seasons for a given species. The dicot species under study are Na+ and Cl- accumulators, showing significant higher levels of these ions than the monocot taxa, but a direct correlation between ion content in soil and plants could be not established

[EN] We have studied whether two common osmolytes proline (Pro) and glycine betaine (GB) accumulate in plants of different Plantago species in response to salt and water stress, which would suggest that these compatible solutes and osmoprotectants fulfil a functional role of in the plants stress tolerance mechanisms. Plants of P. coronopus, P. major, P. crassifolia and P. lagopus were treated with increasing NaCl concentrations or subjected to water stress, under controlled conditions in the greenhouse. GB and Pro contents in control, non-stressed plants were relatively low and, in most cases, did not change, or increased only moderately when the plants were maintained without water or were grown in the presence of up to 400 mM NaCl, for four weeks. However, higher salt concentrations (450 600 mM NaCl), which these taxa never encounter in their natural habitats, induced a significant accumulation of Pro in all species but P. major, the most salt-sensitive one. These data indicate that GB and Pro do not act as functional osmolytes in Plantago species, and do not contribute to osmotic adjustment under natural conditions; however, these plants have the potential to activate Pro-mediated mechanisms of salt tolerance at very high, artificial salinity levels

Accumulation of compatible solutes or osmolytes is a general response of plants to abiotic stress conditions, but we still have very limited knowledge on the relevance of this response for stress tolerance mechanisms of a given tolerant species. We have determined the levels of common osmolytes (proline, glycine betaine and total soluble sugars) in three Juncus species, two salt tolerant (J. acutus and J. maritimus) and one salt-sensitive (J. articulatus), subjected to salt or water stress treatments. Correlation of the patterns of osmolyte accumulation with salt tolerance of the three taxa, indicated that biosynthesis of Pro (but not the increase of glycine betaine or sugar contents) plays a relevant role in the stress tolerance of the analysed Juncus species

[EN] The study of the mechanisms of response to salt stress is one of the most active research topics in plant biology, not only due to its unquestionable academic interest but also because of its economic implications, since high soil salinity is together with drought one of the major causes of reduction of crop yields worldwide. These studies have shown a series of basic mechanisms of response to abiotic stress, which include, among others, the synthesis and accumulation in the cytoplasm of `compatible solutes or osmolytes', used for osmotic balance and as `osmoprotectants'. Today, there is overwhelming evidence that osmolyte, and especially proline accumulation, represents a general and reliable biochemical marker for salt stress. However, and despite the large amount of data available regarding this response mechanism, our knowledge of the importance of osmolyte biosynthesis for salt tolerance of any given species under natural conditions, is still very limited. This is partly due, in our opinion, to the approaches commonly used in these studies, which rely on experiments performed with salt-sensitive plants (glycophytes) instead of halophytes, plants naturally adapted to high soil salinities under artificial laboratory or greenhouse conditions. In this review, we describe and comment on data supporting these ideas, and point out that extreme caution should be taken when assessing the biological relevance of laboratory results., Work in the UPV laboratories is being funded by the Spanish Ministry of Science and Innovation (project CGL2008-00438/BOS), with contribution from the European Regional Development Fund. M.N.G. acknowledges the support provided by the Romanian POSDRU project "Develoing the innovation capacity and improving the impact of research through post-doctoral programmes", and by COST Action FA0901: "Putting Halophytes to work-From Genes to Ecosystems" for his stay in Valencia in the frame of a Short Term Scientific Mission.

Supported by the Spanish Ministry of Science and Innovation (project CGL2008-00438/BOS), with contribution from the European Regional Development Fund.

[EN] AbstractIntroductionSalinity and drought are the most important environmental stress conditions reducing crop yields worldwide and limiting the distribution of wild plants in nature. Soil salinity, especially secondary salinity caused by anthropogenic practices, such as prolonged irrigation, lead to substantial agricultural yield losses, especially in arid and semiarid regions. Drought, caused by reduced water content in the soil, occurs due to disorders in nature's water cycle, chiefly when evapotranspiration exceeds precipitation in a certain area, to the point where soil water reserves can no longer support plant growth. Drought and salt stress trigger the activation of a series of basic stress mechanisms that includes among others, the control of ion transport, exclusion and compartmentalization, as well as the accumulation of compatible solutes ('osmolytes'), and the activation of antioxidant systems. These mechanisms are conserved in all plants, stress tolerant and sensitive alike, and don't necessarily confer tolerance. To decipher those mechanisms and have a better understanding on the contribution of different stress responses to the stress tolerance of a given species, we have carried out comparative studies on the responses to drought and salinity in a number of genetically related taxa with different tolerance potentials.MethodologyThe experimental approach was mostly based on i) establishing the relative tolerance to water and salt stress in the studied species from their distribution in nature (in the case of wild species) and through the relative inhibition of growth in the presence of stress, and ii) correlating changes in the levels of biochemical 'stress markers' associated to specific response pathways (ion transport, osmolyte accumulation¿) upon stress treatments, with the already established relative tolerance to stress. This strategy proved to be appropriate to distinguish mere general responses to stress from those mechanisms relevant for stress tolerance of the investigated species and cultivars. The work also sheds light on other aspects affected by salt stress, specifically regarding germination and reproductive success or anatomical changes in salt-stressed plants. The expression patterns of the gene NHX1, encoding a vacuolar Na+/H+ antiporter were also studied in the Plantago taxa, as a first step in the full characterisation of this ion transporter, that appears to play an important role in the mechanisms of salt tolerance in this genus.ConclusionThe results obtained in this work contribute to a better understanding of general stress tolerance mechanisms in plants, and provides clear insights into the mechanisms conferring tolerance, specifically, to drought and salt stress in some wild species and crops. This work also shed more light on the highly efficient responses to stress in halophytes, plants that could be viewed as nature's answer to the aforementioned adverse environmental conditions via evolution and adaptation. Halophytes can therefore be considered as a suitable source - underutilized at present, in our opinion - of knowledge, genetic resources and biotechnological tools for the needed improvement of stress tolerance in crops., [ES] ResumenIntroducción La salinidad y la sequía son las condiciones de estrés ambiental más importantes, que reducen los rendimientos de los cultivos en todo el mundo y que limitan la distribución de las plantas silvestres en la naturaleza. La salinidad del suelo, especialmente la salinización secundaria causada por prácticas antropogénicas, como la irrigación prolongada, conducen a pérdidas importantes de rendimiento agrícola, especialmente en las regiones áridas y semiáridas. La sequía, provocada por la reducción de contenido de agua en el suelo, se produce debido a alteraciones en el ciclo del agua en la naturaleza, principalmente cuando la evapotranspiración excede la precipitación en un área determinada, hasta el punto que las reservas de agua del suelo ya no pueden soportar el crecimiento de la planta. La sequía y el estrés salino desencadenan la activación de una serie de mecanismos básicos de respuesta, que incluyen entre otros el control del transporte, la exclusión y la compartimentación de iones, así como la acumulación de solutos compatibles ('osmolitos'), y la activación de sistemas antioxidantes. Estos mecanismos están conservados en todas las plantas, tolerantes y sensibles a estrés por igual, y no confieren necesariamente tolerancia. Para descifrar estos mecanismos y conseguir una mejor comprensión de la contribución de diferentes respuestas a estrés a la tolerancia al estrés en una especie dada, hemos llevado a cabo estudios comparativos sobre las respuestas a la sequía y la salinidad, en un número de taxones relacionados genéticamente con diferentes potenciales de tolerancia. MetodologíaEl enfoque experimental se basó principalmente en i) establecer la tolerancia relativa al estrés hídrico y al estrés salino en las especies estudiadas, a partir de su distribución en la naturaleza (en el caso de especies silvestres) y atendiendo a la inhibición relativa de su crecimiento en presencia de estrés, y ii) correlacionar cambios en los niveles de 'marcadores bioquímicos de estrés' asociados a vías específicas de respuesta (transporte de iones, acumulación de osmolitos ...) inducidos por los tratamientos de estrés, con la tolerancia relativa a estrés de las plantas, previamente establecido. Esta estrategia ha resultado ser apropiada para distinguir meras respuestas generales a estrés de los mecanismos relevantes para la tolerancia a estrés de las especies y cultivares investigados. El trabajo también arroja luz sobre otros aspectos afectados por el estrés salino, específicamente en relación con la germinación y el éxito reproductivo, o cambios anatómicos en las plantas tratadas con sal. También se estudiaron los patrones de expresión del gen NHX1, que codifica un antiportador vacuolar Na+/H+, en las especies de Plantago, como un primer paso en la caracterización completa de este transportador de iones, que parece desempeñar un papel importante en los mecanismos de tolerancia a sal en este género.Conclusión Los resultados obtenidos en este trabajo contribuyen a una mejor comprensión de los mecanismos generales de tolerancia al estrés en plantas, y proporcionan ideas claras sobre los mecanismos que confieren tolerancia, en concreto, a la sequía y al estrés salino, en algunas especies silvestres y cultivadas. Este trabajo también arroja más luz sobre las respuestas a estrés altamente eficientes en halófitas, plantas que podrían ser vistas como la respuesta de la naturaleza a las condiciones ambientales adversas antes mencionadas, a través de la evolución y la adaptación. Por lo tanto, las halófitas pueden ser consideradas como una fuente adecuada - infrautilizada en la actualidad, en nuestra opinión - de conocimiento, recursos genéticos y herramientas biotecnológicas para la necesaria mejora de la tolerancia al estrés en plantas cultivadas., [CAT] ResumIntroducció La salinitat i la sequera són les condicions d'estrès ambiental més importants, que redueixen els rendiments dels cultius a tot el món i que limiten la distribució de les plantes silvestres en la naturalesa. La salinitat del sòl, especialment la salinització secundària causada per pràctiques antropogèniques, com la irrigació perllongada, condueixen a pèrdues importants de rendiment agrícola, especialment en les regions àrides i semiàrides. La sequera, provocada per la reducció de contingut d'aigua en el sòl, es produeix a causa d'alteracions en el cicle de l'aigua en la naturalesa, principalment quan la evapotranspiració excedeix la precipitació en un àrea determinada, fins al punt que les reserves d'aigua del sòl ja no poden suportar el creixement de la planta. La sequera i l'estrès salí desencadenen l'activació d'una sèrie de mecanismes bàsics de resposta, que inclouen entre uns altres el control del transport, l'exclusió i la compartimentació d'ions, així com l'acumulació de soluts compatibles ('osmolits'), i l'activació de sistemes antioxidants. Aquests mecanismes estan conservats en totes les plantes, tolerants i sensibles a estrès per igual, i no confereixen necessàriament tolerància. Per a desxifrar aquests mecanismes i aconseguir una millor comprensió de la contribució de diferents respostes a estrès a la tolerància a l'estrès en una espècie donada, hem dut a terme estudis comparatius sobre les respostes a la sequera i la salinitat, en un nombre de taxons relacionats genèticament amb diferents potencials de tolerància. MetodologiaL'enfocament experimental es va basar principalment en i) establir la tolerància relativa a l'estrès hídric i a l'estrès salí en les espècies estudiades, a partir de la seua distribució en la naturalesa (en el cas d'espècies silvestres) i atenent a la inhibició relativa de el seu creixement en presència d'estrès, i ii) correlacionar canvis en els nivells de 'marcadors bioquímics d'estrès' associats a vies específiques de resposta (transport d'ions, acumulació d'osmolits ...) induïts pels tractaments d'estrès, amb la tolerància relativa a estrès de les plantes, prèviament establert. Aquesta estratègia ha resultat ser apropiada per a distingir meres respostes generals a estrès dels mecanismes rellevants per a la tolerància a estrès de les espècies i conreus investigats. El treball també llança llum sobre altres aspectes afectats per l'estrès salí, específicament en relació amb la germinació i l'èxit reproductiu, o canvis anatòmics en les plantes tractades amb sal. També es van estudiar els patrons d'expressió del gen NHX1, que codifica un anti-portador vacuolar Na+/H+, en les espècies de Plantago, com un primer pas en la caracterització completa d'aquest transportador d'ions, que sembla exercir un paper important en els mecanismes de tolerància a sal en aquest gènere.Conclusió Els resultats obtinguts en aquest treball contribueixen a una millor comprensió dels mecanismes generals de tolerància a l'estrès en plantes, i proporcionen idees clares sobre els mecanismes que confereixen tolerància, en concret, a la sequera i a l'estrès salí, en algunes espècies silvestres i conreades. Aquest treball també llança més llum sobre les respostes a estrès altament eficients en halòfites, plantes que podrien ser vistes com la resposta de la naturalesa a les condicions ambientals adverses abans esmentades, a través de l'evolució i l'adaptació. Per tant, les halòfites poden ser considerades com una font adequada - infrautilitzada en l'actualitat, en la nostra opinió - de coneixement, recursos genètics i eines biotecnològiques per a la necessària millora de la tolerància a l'estrès en plantes conreades., Al Hassan, M. (2016). Comparative analyses of plant responses to drought and salt stress in related taxa: A useful approach to study stress tolerance mechanisms [Tesis doctoral no publicada]. Universitat Politècnica de València. doi:10.4995/Thesis/10251/61985., TESIS