Plateforme Télé-Enseignement de l'Université Oran 1 Ahmed Ben Bella

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.

RÉSUMÉ. Analyse comparative de la tolérance à la salinité du gamétophyte mâle et du sporophyte chez Medicago au stade germination. De nombreuses études ont montré une corrélation positive entre les réponses du pollen et de celles du sporophyte à un ensemble de stress. Une étude comparative de la tolérance à la salinité du gamétophyte mâle et du sporophyte au stade germination, a été effectuée sur six écotypes d'espèces annuelles du genre Medicago. A été mesuré, au stade sporophytique, le taux de germination des graines, au stade gamétophytique, le taux de germination du pollen après application d'un stress salin à différentes concentrations de NaCl (0 ; 68 ; 102 et 137 mM). L'analyse des données relatives au sporophyte et au gamétophyte montre que les six écotypes diffèrent significativement entre eux en absence et en présence de stress pour le taux de germination. Le génotype Tru 42 de l'espèce M. truncatula a montré une meilleure capacité germinative, apparaît comme le plus tolérant et le génotype Pol 248 de M. polymorpha le moins tolérant. Ces résultats montrent qu'une correspondance entre l'aptitude du sporophyte et celui du gamétophyte pour la tolérance à la salinité, existe chez Medicago, ce qui permet d'envisager la possibilité d'appliquer la sélection au stade gamétophytique, une technique rapide et économique.

ABSTRACT. Comparative analysis of salinity tolerance of the male gametophyte and the sporophyte in Medicago at the germination stage. Many studies have shown a positive correlation between the responses of pollen and those of the sporophyte to a set of stress. A comparative study of the salinity tolerance of the male gametophyte and the sporophyte has been undertaken on six ecotypes of annual species of Medicago. The seed germination rate at sporophytic stage and the pollen germination rate at gametophytic stage have been assessed after stress exposition under different salt concentration of NaCl (0; 68; 102 and 137 mM). The sporophyte and the gametophyte data analysis showed that the six ecotypes differed significantly between themselves with or without stress application for the germination rate. The Tru 42 genotype of M. truncatula showed the best germinatif ability, appeared as the most tolerant and the genotype Pol 248 of M. polymorpha the least tolerant. This result showed the existence of a correspondence between sporophytic and gametophytic aptitude for salt tolerance in Medicago, this allows the possibility to apply gametophytic selection, fast and economical technique.