Adel Amar AMOURI

Legumes are very important plants both ecologically and agriculturally because they are able to interact symbiotically with rhizobia for biological nitrogen fixation and soil fertilization. Medicago truncatula Gaertn. is an important model legume rich in protein. Salinity represents, today, the major cause of land degradation and crop productivity limitation around the world and affects physiology and metabolism in legumes. In this study, we analyzed the physiological and biochemical responses of rootlets in two contrasting ecotypes of Medicago truncatula (Tru 131, tolerant and Jemalong, sensitive) to different level of NaCl, (68, 102 and 137 mM). Results showed that the tolerant ecotype has a lower water potential than Jemalong. Root protein content of Tru 131 was decreased than Jemalong, this can be explained by accumulation of protein oxidation in the sensitive genotype. Moreover, NaCl increased guaiacol peroxidase activity GPX in rootlets of Tru 131, this enzyme has a protective role against the molecules ROS accumulated during oxidative stress. On the other hand, under salt stress the total content of ascorbate (ASC + DHA) and Glutathione (GSH + GSSG) was increased in the tolerant genotype Tru 131 compared to Jemalong. These results show how the tolerant genotype activate the antioxidative defense system at root level against damages caused by oxidative stress under salinity.

En Algérie, les sols sont soumis à une forte érosion hydrique due aux conditions climatiques drastiques qui diminuent le couvert végétal. Cette érosion affecte plus de 28 % des terres de l’Algérie du Nord. Ce sont les terres à fortes pentes des massifs telliens qui sont les plus touchées (Hadjiat, 1997 ; Nedjraoui, 2003). Sur ces sols nus en pente, l’utilisation des espèces annuelles à resemis naturel et des légumineuses herbacées pérennes doit être fortement encouragée (Abdelguerfi et al., 2008). A cet effet, la culture des légumineuses comme la luzerne, s’avère une bonne alternative pour contrer les aléas fréquents de l’environnement tels que les stress abiotiques afin de contribuer efficacement à la lutte contre les changements climatiques.

Le présent livre décrit est une synthèse bibliographique relative à la biologie de l’adaptation au stress salin et hydrique des plantes légumineuses. En particulier, la plante modèle Medicago truncatula Gaertner (la Luzerne). Ce modeste livre discute sur les légumineuses et leur intérêt environnementale ( adaptation au stress hydrique et salin), la variabilité génétique de ces plantes et aussi l'aspect génomique de la plante modèle Medicago truncatula Gaertn. Je tiens à remercier Pr HADJADJ AOUL Seghir de l’université d’Oran 1 pour ces précieux conseils afin d’élaborer ce petit livre.

Abstract
The study on the assessment of the variability of salt stress tolerance, focused on two contrasting genotypes of the plant M. truncatula under four levels of salt stress (distilled water as control 0; 68; 102 and 137 mM) of sodium chloride (NaCl) solution, one is tolerant (Tru 131) and the (Jemalong) the sensitive one. The data analysis of germination aptitude showed that the (Tru 131) genotype had the best germinatif ability, compared to (Jemalong). The soluble protein analysis, showed a high protein synthesis during salt stress application in the tolerant genotype compared to the sensitive one (Jemalong). The introduction of the most tolerant genotype (Tru 131) in arid and semi-arid areas in Algeria and Mediterranean regions, can improve significantly the vegetal productivity in order to ensure a good animal food and contribute to the fertilization of agricultural land.

Abstract

Four expressed sequence tag-simple sequence repeat (EST-SSRs) primers were used to show genetic variability in nine accessions of M. truncatula comparing with two contrasting Medicago truncatula genotypes (Tru 131, tolerant and Jemalong, sensitive). The amplification of the DNA isolated from individual seedlings for each genotype with four primers (MTIC 044, MTIC 124, MTIC 077 and MTIC 335) produced a total of 24 alleles. The sizes of the alleles detected ranged from 100 to 300 bp. These EST-SSRs markers were more polymorphic than the MTIC 044 (low polymorphism). The average of 6 alleles per primers was detected and gave moderate values of polymorphic information content (PIC) ranged from 0.12 to 0.49 and genetic diversity (Hi) from 0,13 to 0,48. The clustering analysis showed that the Algerian ecotypes (Tru 1, Tru 2, Tru 3 and Tru 4) are associated with (Tru 5 and Tru 9) Syrian and Jordanian ecotypes respectively and Tunisian ecotypes, some of these genotypes are associated with the tolerant ecotype (Tru 131 DZA).

Abstract
In order to have more information on early seedling development under salinity stress (one of the important factors limiting plant productivity and also crop growth), it will be interesting to examine radicle growth in comparison to plumule elongation under different salinity stress conditions. In this study, we assessed the variability of four genotypes of the plant model Medicago truncatula under four levels of salt stress (distilled water as control 0, 68, 102 and 137 mM) of sodium chloride (NaCl) solution. Several studies are focalised in root or radical development because is the most sensitive part of the plant and controls rapid transmission information to other plant parts. In order to evaluate the degree of radicle sensitivity, we measured the plumule length to radicle length ratio (PL: RL ratio). Also, we investigated the relationship between storage protein content, seed weight and salinity tolerance degree. The results show that Tru 131 and Tru 673 genotypes, with a low ratio (radicle more resistant (longer) than plumule) and high storage protein content, are more tolerant to salinity stress than the sensitive genotypes Tru 26 and Jemalong that had a high ratio (radicle more sensitive (shorter) than plumule) and low storage protein content. We concluded that the most tolerant genotype (Tru 131) with rich protein and high seed weight can be cultivated in saline and semi-arid areas in Algeria and Mediterranean regions to improve the legumes productivity. Although, the genotype (Tru 673) that had a low seed vigour, appear tolerant (high PL:RL ratio) despite coming from 'aged seeds'. This additional data shows the influence of 'aged seeds' on seed vigour and root growth because seeds contain all of the genetic resources of the plant.