Is the sensitivity to ammonium nutrition related to nitrogen accumulation?

Nitrate and ammonium can be used as nitrogen sources by most plant species although plant response to continuous ammonium nutrition is species dependent. In the present study, the effect of the nitrogen source (nitrate and ammonium) on growth, photosynthetic parameters, nitrogen content and nitrogen assimilating-enzymes (nitrate reductase, glutamine synthetase and glutamate dehydrogenase) was investigated in wheat (Triticum aestivum L.), tomato (Solanum lycopersicum L.) and lucerne (Medicago truncatula L.). Obtained results showed that these plant species vary in their sensitivity to NH4+ nutrition, with wheat to be highly sensitive, tomato moderately sensitive and lucerne tolerant to ammonium nutrition. For the three plant species, the growth reduction was correlated closely to ammonium accumulation in leaves. Moreover, contrary to that was observed for wheat plants, glutamine synthetase and glutamate dehydrogenase activities were higher in roots than in leaves, for tomato and lucerne plants. Taken together, these data suggest that the site of ammonium assimilation is a key factor controlling tolerance to ammonium nutrition in the different plant species, with plants being more tolerant when ammonium is assimilated in roots

Does the Source of Nitrogen Affect the Response of Tomato Plants to Saline Stress?

The aim of the present study was to investigate the effects of the source of nitrogen (N) nutrition on the response of tomato (Solanum lycopersicum L. cv. Rio Grande) plants to saline stress (100 mM NaCl). To this end, plant growth, chlorophyll and carbohydrate levels, ion contents as well as N compounds and main N-metabolizing enzymes (nitrate reductase and glutamine synthetase) were analyzed in salt-treated and control plants grown in the presence of either NO3-, NH4+, or the mixture of NO3- and NH4+. Our results showed that plant growth declined under saline stress but NO3--fed plants were less sensitive to salinity than NH4+-fed plants. This different sensitivity was due mainly to a better maintenance of root growth and root nitrate reductase activity in NO3--fed plants. Concomitantly, leaf chlorophyll content was significantly decreased, regardless of the N source. Salinity affects the uptake of several nutrients in a different way, depending on the N source. Thus, sodium was accumulated mainly in NH4+-fed plants, especially in roots, displacing other cations such as NH4+and potassium. It is concluded that the N source is a major factor affecting tomato responses to saline stress, plants being more sensitive when NH4+ is the source used. The different sensitivity is discussed in terms of a competition for energy between N assimilation and sodium exclusion processes

Arbuscular mycorrhizal symbiosis elicits shoot proteome changes that are modified during cadmium stress alleviation in Medicago truncatula

Background : Arbuscular mycorrhizal (AM) fungi, which engage a mutualistic symbiosis with the roots of most plant species, have received much attention for their ability to alleviate heavy metal stress in plants, including cadmium (Cd). While the molecular bases of Cd tolerance displayed by mycorrhizal plants have been extensively analysed in roots, very little is known regarding the mechanisms by which legume aboveground organs can escape metal toxicity upon AM symbiosis. As a model system to address this question, we used Glomus irregulare-colonised Medicago truncatula plants, which were previously shown to accumulate and tolerate heavy metal in their shoots when grown in a substrate spiked with 2 mg Cd kg-1.[br/] Results : The measurement of three indicators for metal phytoextraction showed that shoots of mycorrhizal M. truncatula plants have a capacity for extracting Cd that is not related to an increase in root-to-shoot translocation rate, but to a high level of allocation plasticity. When analysing the photosynthetic performance in metal-treated mycorrhizal plants relative to those only Cd-supplied, it turned out that the presence of G. irregulare partially alleviated the negative effects of Cd on photosynthesis. To test the mechanisms by which shoots of Cd-treated mycorrhizal plants avoid metal toxicity, we performed a 2-DE/MALDI/TOF-based comparative proteomic analysis of the M. truncatula shoot responses upon mycorrhization and Cd exposure. Whereas the metalresponsive shoot proteins currently identified in non-mycorrhizal M. truncatula indicated that Cd impaired CO2 assimilation, the mycorrhiza-responsive shoot proteome was characterised by an increase in photosynthesisrelated proteins coupled to a reduction in glugoneogenesis/glycolysis and antioxidant processes. By contrast, Cd was found to trigger the opposite response coupled the up-accumulation of molecular chaperones in shoot of mycorrhizal plants relative to those metal-free.[br/] Conclusion : Besides drawing a first picture of shoot proteome modifications upon AM symbiosis and/or heavy metal stress in legume plants, the current work argues for allocation plasticity as the main driving force for Cd extraction in aboveground tissues of M. truncatula upon mycorrhization. Additionally, according to the retrieved proteomic data, we propose that shoots of mycorrhizal legume plants escape Cd toxicity through a metabolic shift implying the glycolysis-mediated mobilization of defence mechanisms at the expense of the photosynthesis-dependent symbiotic sucrose sink

Effet de l'hydromorphie sur la croissance de quatre variétés de trèfle (Trifolium subterraneum L.)

Effect of waterlogging on growth of four varieties of clover (Trifolium subterraneum L.). Waterlogged soils are characterized by a prolonged oxygen deficit. Their improvement, by adapted cultural techniques, will be of interest. In this context, we observed the effect of flooding on the growth of four varieties of clover (Trifolium subterraneum L.) (in order to make these soils more profitable for agriculture). Applying hypoxic stress, at the second compound leaf stage, for 5, 10 and 20 days, revealed differences in tolerance. Indeed, the biomass production of the Park variety was stimulated in hypoxia (26% and 5%, respectively, after 10 and 20 d of treatment). At final harvest (20 d of hypoxia), the total biomass production of Larisa, Montbaker and Clare decreased to 7%, 10% and 36%, respectively. This result is probably due to the ability of each variety to produce adventitious roots, which is generally thought to be an adaptation to waterlogging.Les sols hydromorphes sont caractérisés par un déficit prolongé en oxygène. Leur valorisation, par des techniques culturales adaptées, serait intéressante à considérer. Dans ce contexte, l'étude de l'effet de l'hydromorphie sur la croissance de quatre variétés de trèfle (Trifolium subterraneum L.), permet d'envisager de mieux rentabiliser de tels milieux pour l'agriculture. L'application du stress hypoxique, au stade deuxième feuille trifoliée, pendant 5, 10 et 20 jours, a révélé différents degrés de tolérance d'une variété à l'autre. En effet, la variété Park voit la production de sa biomasse stimulée en hypoxie de 26 % et 5 % respectivement après 10 et 20 jours de traitement. A la récolte finale (20 jours d'hypoxie), Larisa, Montbaker et Clare accusent une baisse de production de biomasse totale respectivement de 7 %, 10 % et 36 %. Ce résultat serait probablement dû à l'aptitude de chacune des quatre variétés à produire ou non des racines adventives reconnues comme caractère adaptatif à l'hydromorphie

Compréhension des mécanismes impliqués dans la réponse au cadmium de Medicago truncatula en interaction symbiotique avec Glomus intraradices (analyses physiologiques et moléculaires)

L étude de l interaction tripartite M. truncatula G. intraradices-cadmium nous a permis par la combinaison des approches physiologiques et moléculaires de décrypter les mécanismes impliqués directement ou indirectement dans cette interaction. Les études morphologiques et physiologiques ont révélé la sensibilité de M. truncatula Jemalong 5 vis-à-vis du Cd2+ (2 ppm). En plus de l amélioration de la croissance de la plante, nous avons démontré que la symbiose mycorhizienne à arbuscule (SMA) confère à la plante une certaine tolérance vis-à-vis du Cd2+et oriente la plante vers une stratégie de phytoextraction. L approche protéomique effectuée a révélée 30 protéines au niveau des racines et 23 protéines des organes aériens dont le niveau d accumulation vari significativement en réponse à l un ou l autre des traitements. Suite à l analyse de la distribution fonctionnelle des protéines identifiées, nous avons démontré l implication de la SMA dans la sur-accumulation de protéines potentiellement responsables de l atténuation de la toxicité du Cd2+ via des propriétés anti-oxydantes. L étude ciblée de l expression des gènes impliqués dans la défense, a permis d exclure la mise en place d un mécanisme de régulation globale de ces gènes en réponse à la SMA. L identification et la quantification des isoflavonoïdes dans les racines de M. truncatula suite aux différents traitements ont par ailleurs mis en évidence l implication potentielle de ces molécules dans la réponse au stress cadmique.In this work, we have combined physiological and molecular approaches to decipher the mechanisms involved directly or indirectly in the triple interaction Medicago truncatula-Glomus intraradices-cadmium . The morphological and physiological studies have revealed the sensitivity of M. truncatula Jemalong 5 towards Cd2 + (2 ppm). In addition to the improvement of development of plant by colonization , AMS confers to plant a certain tolerance towards cadmium stress, attenuating phytotoxic effects of Cd2 + by the dilution of its content in plant tissues, directing the plant to a phytoextraction strategy. The non-targeted proteomic approach revealed proteins whose accumulation showed significant change following the various treatments, including 30 proteins in roots and 23 proteins in aerial organs that were identified by LC-MS / MS and MALDI-TOF. Following the analysis of the functional distribution of these proteins, we have demonstrated the involvement of AMS in the up-accumulation of proteins potentially responsible for the alleviation of the toxicity of Cd2 + by decreasing the oxidative stress. The targeted study of the expression of genes involved in defence, has ruled out a global regulation of these genes in response to AMS. The identification and quantification of isoflavonoids in roots of M. truncatula following the various treatments also have highlighted the potential involvement of these molecules in response to cadmium stress.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Effects of some seed-coat dormancy breaking treatments on germination of three Calligonum species occurring in Southern desert of Tunisia

The germination response of three Calligonum species (C. azel Maire, C. arich Le Houérou et C. comosum L’Hérit.) to mechanical, physical and chemical scarifications, applied for overcoming dormancy, has been studied under controlled conditions. The above-mentionned speceis are three dominant and economically important species widely distributed in active sand dunes in the Eastern Great Erg of Tunisia. In all three Calligonum species, the germination of the untreated (control) seeds was relatively low, indicating the presence of coat-imposed dormancy in a fraction of the studied seeds. Chemical scarification with sulphuric acid (96%) was effective in breaking seed dormancy and consequently in increasing the rate and the final percentage of germination. However, treatments with sulphuric acid above 20 min significantly decreased the amount of dead seeds. Compared to other pretreatments, the 20-30 min acid treatments for C. azel and C. arich and boiling water or 30 min acid treatment for C. comosum decreased the number of days to first germination by 2-6 days. Overall, this study demonstrated that physical dormancy caused by impermeable seed-coat appeared to be the main reason of the low germination level of the untreated seeds. The 30-min sulphuric acid (96%) treatment was the most suitable in breaking the seed dormancy and enhancing the germination of Calligonum species.Les effets de scarifications physique et chimique sur la germination de semences de trois espèces du genre Calligonum (C. azel Maire, C. arich Le Houérou et C. comosum L’Hérit.) pour lever leur dormance ont été étudiés en conditions contrôlées. Ces trois espèces arbustives pérennes présentent une importance économique et sont largement distribuées sur les dunes du sable mobiles du Grand Erg oriental de la Tunisie. Chez ces trois espèces, la germination des semences témoins (non traitées) était relativement faible et indique la présence d’une dormance tégumentaire pour une fraction des graines étudiées. La scarification chimique par l’acide sulfurique (96%) s’est avérée très efficace pour lever l’état de dormance des semences et par conséquent augmenter le pourcentage de germination. Cependant, le traitement par l’acide sulfurique pendant au minimum 20 minutes a diminué significativement le taux de mortalité des graines. Comparés aux autres prétraitements, les traitements par l’acide sulfurique pendant 20 et 30 minutes pour C. azel et C. arich et par l’eau bouillante et le traitement acide pendant 30 minutes pour C. comosum ont diminué le délai de germination de leurs semences par 2 à 6 jours. Enfin, cette étude démontre que la dormance physique des semences des trois espèces de Calligonum causée par l’imperméabilité du tégument paraît être la raison principale du faible taux de germination des graines non traitées et le trempage dans l’acide sulfurique (96%) pendant 30 minutes était le plus efficace pour lever la dormance des graines et augmenter par conséquent le pourcentage de germination des trois espèces de Calligonum.Dhief Adel, Gorai Mustapha, Aschi-Smiti Samira, Neffati Mohamed. Effects of some seed-coat dormancy breaking treatments on germination of three Calligonum species occurring in Southern desert of Tunisia. In: Ecologia mediterranea, tome 38 n°1, 2012. pp. 19-27

Response of seed germination of Tunisian Allium ampeloprasum to temperature and salt stresses

High salinity and temperature are major problems inhibiting seeds germination and threatening plant cover in arid environment such as the conditions in some regions in Tunisia. Thus, the use of adapted species to rehabilitate these regions could be an alternative to overcome these environmental constraints. In the present study, we intended to evaluate the effect of salt and temperature on seed germination of the wild leek (A. ampeloprasum L.) from two different Tunisian islands (Kneiss & Djerba). Three temperatures (15° C, 23° C & 30° C) and four salinity levels (0, 75, 150 & 225 mM NaCl) were tested in a 14 h dark : 10 h light photoperiod. The two studied populations showed a similar behaviour. The optimum temperature for seed germination was 15° C. Germination was inhibited by an increase in both temperature and salinity. Salt stress decreased both the final germination rate and the final germination percentage (PG%). Delay of germination (T0) and the time to half of germination (T50) significantly (p < 0.05) increased in response to salt and temperature increasing. An interaction between salinity and temperature completely inhibited germination in 225 mM NaCl at 30° C. Seeds transferred from salt solution to distilled water showed a recovery percentage (R%) varying from 0 to 40.6 %. Viability test showed that all non-germinated seeds were alive proving that A. ampeloprasum adopted a strategy of temporal inhibition of germination to survive under salt and temperatures increasing. As such it could be classified as a moderately salt tolerant species.Réponse à la température et à la salinité de la germination des semences d’Allium ampeloprasum en Tunisie. La salinité et les températures élevées sont les principaux problèmes inhibant la germination des semences et menaçant le couvert végétal dans les environnements arides comme c’est le cas dans certaines régions de Tunisie. Ainsi, pour réhabiliter ces régions, des espèces adaptées peuvent être utilisées pour contourner ces contraintes environnementales. Dans la présente étude, on a évalué l’effet du sel et de la température sur la germination des semences d’Allium ampeloprasum de deux îles tunisiennes (Kneiss & Djerba). Trois températures (15° C, 23° C & 30° C) et quatre niveaux de salinité (0, 75, 150 & 225 mM NaCl) ont été testés à une photopériode de 10 h. Les deux populations étudiées ont montré des comportements similaires. L’optimum thermique pour la germination a été de 15° C. La germination a été inhibée par une augmentation de température et de salinité. Le sel a diminué le taux de germination finale et le pourcentage de germination (PG%). Le délai de germination (T0) et le temps pour 50 % de germination (T50) ont augmenté significativement en réponse à une augmentation de la température et de la salinité. Une interaction entre la salinité et la température a complètement inhibé la germination à 30° C avec 225 mM NaCl. Les semences transférées à l’eau distillée ont montré un pourcentage de recouvrement variant de 0 à 40,6 %. Le test de viabilité a montré que toutes les semences non germées étaient viables, prouvant ainsi que A. ampeloprasum adopte une stratégie d’inhibition temporaire de germination pour survivre à des hautes températures et salinités. A. ampeloprasum peut être classifié comme une espèce modérément tolérante.Guenaoui Chedia, Ksiksi Taoufik Saleh, Aschi-Smiti Samira, Neffati Mohamed. Response of seed germination of Tunisian Allium ampeloprasum to temperature and salt stresses. In: Revue d'Écologie (La Terre et La Vie), tome 67, n°4, 2012. pp. 399-408