Réponse à un stress salin croissant de la germination des graines et de la croissance des pousses d’une poacée menacée, Cenchrus ciliaris L.

Cenchrus ciliaris L. (Buffel Grass), a perennial Poaceae, is a threatened species in arid regions of Tunisia. In the present work, involvement of soil salinization on its scarcity is evaluated through studying seeds germination and shoot growth ability under NaCl stress (0, 50, 100, 200 and 300 mM). Our results showed that at moderate stress including 50 and 100 mM NaCl, C. ciliaris sustained sufficient germination capacity (GC ), adequate germination mean time (GMT ) and recovery aptitude (13 %) after transferring seeds to distilled water. Shoot growth was reduced to 50 % by 50 and 100 mM NaCl treatments relative to control, inducing neither lipid oxidation nor tissues dehydration. Salt-induced stimulation of gaïacol peroxidase (GPX, EC. 1.11.1.7) activity seemed to be efficient against oxidative stress. Severe stress, including 200 and 300 mM NaCl, lengthened seeds dormancy, decreased GC and germination rate (increasing GMT) with low germination recovery. While plant growth was not severely affected, increasing malonydialdehyde (MDA) production indicated that 200 and 300 mM NaCl provoked lipid oxidation and that GP X could no longer overcome oxidative stress. It seems that soil salinization with doses greater than 100 mM NaCl may contribute to C. ciliaris scarcity by lowering germination capacity and seedlings growth and establishmentCenchrus ciliaris L. (Cenchrus cilié) est une poacée pérenne cataloguée parmi les espèces menacées dans les régions arides de la Tunisie. Dans le présent travail, l'implication de la salinisation des sols dans la rareté de cette espèce est évaluée par l'étude de la germination des graines et la croissance de la partie aérienne sous stress NaCl (0, 50, 100, 200 et 300 mM). Nos résultats montrent qu'au cours d'un stress salin modéré (50 et 100 mM NaCl), C. ciliaris manifeste une bonne capacité germinative (CG), un temps moyen de germination adéquat (TMG) et une reprise de la germination (13 %) après le transfert de semences à l'eau distillée. La production de biomasse de la partie aérienne est réduite de 50 % pour les traitements 50 et 100 mM NaCl par rapport au témoin, sans toutefois induire l'oxydation des lipides, ni la déshydratation des tissus. L'induction de l'activité gaïacol peroxydase (GPX, EC. 1.11.1.7) semble être efficace dans la lutte contre le stress oxydatif éventuellement provoqué par les doses 50 et 100 mM NaCl. Pour un stress salin sévère (200 et 300 mM NaCl), on constate une augmentation de la dormance des graines, une diminution de la CG, une augmentation du TMG et une faible reprise de la germination après transfert à l'eau distillée. Bien que la production de biomasse aérienne se maintienne à 50 % par rapport au témoin, on a mesuré une augmentation des teneurs en malonydialdehyde (MDA), suggérant que la GPX n'est plus efficace pour lutter contre l'oxydation des lipides membranaires. Il semble qu'une salinisation du sol supérieure à 100 mM NaCl peut contribuer à la raréfaction de C. ciliaris par une diminution de la capacité germinative et de la croissance et de l'implantation des jeunes plants

Effect of iron deficiency on the localization of phosphoenolpyruvate carboxylase in common bean nodules

Phosphoenolpyruvate carboxylase (PEPC) plays an important role in nodules, when there is an increase in the demand for energy. This enzyme provides carbon skeletons to sustain amino acid synthesis and malate to support energy required to fix nitrogen. Since PEPC is important for nodules, and there is lack of information about the effect of some nutrient deficiency in the expression and localization of this enzyme in legume nodules, this work focused on the localization of PEPC in nodules under iron deficiency of two common bean cultivars: Flamingo tolerant and Coco blanc sensitive to iron (Fe) deficiency. The results of immunolocalization using polyclonal antibody showed that this enzyme was detected in all regions of nodule sections; but the signal intensity was increased in Fe-deficient nodules as compared to Fe-sufficient ones in the tolerant cultivar, whereas the intensity was less pronounced in nodules of Fe-deficient plants than in those of Fe-sufficient plants for the sensitive cultivar Coco blanc. This work showed that the symbiotic tolerance of Flamingo to iron deficiency was linked to the increase of PEPC enzymes expression. However, the activity of these enzymes supported the energy required in bacteroids to maintain the nitrogenase activity.Keywords: Common bean, immunolocalization, iron deficiency, nodules, phosphoenol pyruvate carboxylas

Régulation de l'assimilation de l'azote minéral chez Arabidopsis en conditions de stress salin

L activité de croissance des plantes se trouve souvent limitée par les conditions contraignantes de l environnement. La salinité du sol est l une des majeures contraintes abiotiques qui ne cesse d envahir les surfaces cultivés chaque année. Elle entraine chez les espèces glycophytes des perturbations d ordre osmotique, nutritionnel et métaboliques. La nutrition et le métabolisme de l azote minéral constituent des étapes primordiales dans la synthèse des acides aminés et des composés azotés indispensables chez les plantes. Par conséquent, l étude de l expression des enzymes impliquées dans l assimilation d azote telle que l asparagine synthétase (AS, EC 6.3.5.4) chez l arabette des dames (Arabidopsis thaliana) permet d avancer nos connaissances sur la régulation transcriptionnelle du métabolisme azoté sous stress salin. Au cours des travaux de recherche entamés dans le cadre de cette thèse, un intérêt particulier est accordé au gène ASN2 chez Arabidopsis. Les résultats obtenus ont montré que la mutation ASN2 a accentué les effets du NaCl sur l assimilation de l ammonium. Le mutant asn2-1 se montre plus sensible au stress salin que le sauvage malgré que l absence des transcrits du gène ASN2 est associé à une expression importante du gène ASN1. L inhibition de l activité glutamine synthétase (GS, EC 6.3.1.2), la faible activité aminatrice de la GDH (NADH-GDH, EC 1.4.1.2) sous stress salin ainsi que l absence des transcrits ASN2 seraient à l origine de l accumulation de l ammonium chez le mutant asn2-1. Toutefois, l application exogène de l ammonium nous a montré que l action du NaCl sur l expression de l asparagine synthétase n est pas directement liée à l accumulation endogène d ammonium. L accumulation d autres métabolites tels que l asparagine, la glutamine et la glutamate pourrait être à l origine des effets du sel sur l expression des gènes ASN.Plant growth activity is often limited by constraint environment conditions. Soil salinity is one of major abiotic stress which is becoming more problematic every year. In glycophytes species, it induced osmotic, nutritional and metabolic disturbances. The nitrogen nutrition and metabolism constitute an essential step in amino acid and nitrogen compounds synthesis in plants. Therefore, studying the expression of enzymes involved in nitrogen assimilation such as asparagine synthetase (AS, EC 6.3.5.4) in Arabidopsis thaliana will improve our knowledge on the transcriptional regulation of nitrogen metabolism under salt stress. In the present work of this thesis, a special attention was taken on AS gene (ASN2) wild type and mutants. Obtained results showed that ASN2 mutation accentuated the salt-induced effects on ammonium assimilation. The asn2-1 mutant was more sensitive to salt stress than the wild type, while the ASN2 transcript absence was associated with an important ASN1expression. The observed inhibition of glutamine synthetase (GS, EC 6.3.1.2) activity, the low aminatrice GDH (NADH-GDH, EC 1.4.1.2) activity under salt stress as well as the ASN2 transcript loss brought to an ammonium accumulation in asn2-1mutant. However, exogenous ammonium application showed that NaCl effect on asparagine synthetase expression was not directly related to the endogenous ammonium accumulation. Other metabolites accumulation such as asparagine, glutamine and glutamate could be involved in the obtained salt-effects on ASN expression in Arabidopsis.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Biochemical and Physiological Changes in Response to Salinity in Leaves and Roots of Two Durum Wheat (Triticum Durum Desf.) Genotypes

Salt stress is a major abiotic stress that limits agricultural productivity in many regions of the world. To understand the molecular basis of the salt stress response, two wheat (Triticum durum Desf.) cultivars, Karim and Azizi, which are of agronomic significance in Tunisia, were grown under non-saline and saline conditions (100 mM). Leaves and roots of control and salt-stressed plants were harvested after 11 days of salt treatment. Karim cultivar may behave as a typical Na+ include, which compartmentalizes Na+ within the leaf cell vacuoles where it could be used as an osmoticum to lower the osmotic potential necessary for the maintenance of the plant hydric status. While, accumulation of K+ was greater in Karim cultivar compared to Azizi, in both organs, presenting an important manifestation of salinity tolerance. Significant changes in metabolism of antioxidative system were observed, with an increase in protein tyrosine nitration, which indicates that salinity stress induces a nitro-oxidative stress

Variations in α-, β-amylase and α-glycosidase activities in two genotypes of wheat under NaCl salinity stress

Two wheat differing in salt sensitivity, was examined for osmolyte contents and activities of α-amylase, β-amylase and α-glucosidase enzymes involved in seeds germination, in absence as well as in presence of  100, 150, 200 and 300 mM NaCl. The inhibitory effects of NaCl differed, depending on the species tested. In wild wheat specie (Triticum monococcum), with reduced germination percentage and lower relative water  content, the   increase in NaCl concentration resulted in the decrease in endogenous level of proline, total soluble sugars and activities of the main enzymes involved in the germination process. In contrast, cultivated  wheat specie (Triticum aestivum) seed in response to salt stress accumulated higher proline and total soluble  carbohydrate concentrations  which improved  their  water  status and the enzyme  activities  involved  in the germination  process. Differential response of the different species of wheat to salt stress is governed by the accumulation of osmolytes in seeds