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In continuation of the search of eco-friendly and safe alternatives for chemical pesticide for weeds management, essential oils (EOs) of forestry tree may be a good candidate. Here, the EOs of Eucalyptus maculata were extracted by hydrodistillation and the study of their chemical composition was carried out by GC and GC/MS analysis. The allelopathic effects of E. maculata EOs was tested against two common weeds in Tunisia: Sinapis arvensis (dicot) and Phalaris canariensis (monocot) and Triticum durum as cereal monocot cultivated crop. The application of EOs has been carried out in two stages of growth: pre-emergence and post emergence. Analysis of the EOs resulted in the identification of 46 components representing 97.7% of the total oil. 1.8-Cineole was detected as the principal compound accounted for 42% of the oil totality and oxygenated monoterpenes (61.5%) was the major subclass that characterize E. maculata growing in Tunisia. On pre-emergence stage, Eucalyptus EOs significantly reduced germination and seedling growth of all tested species in a dose dependent manner and the phytotoxic effect of the EOs was differently effective depending on doses and tested species. On post-emergence stage, volatile oil induces a phytotoxic effect against all tested plants, a decrease in relative water content, an increase of relative electrolyte leakage percentage and levels of proline and malondialdehyde contents which explain their significant phytotoxic potential. Thus, E. maculata EOs inhibits germination and seedling growth of tested herbs in pre-emergence stage and post emergence stage, therefore E. maculata EOs shows potential towards weed management.

Salinity and Phoma medicaginis infection represent significant challenges for alfalfa cultivation in South Africa, Europe, Australia, and, particularly, Tunisia. These constraints have a severe impact on both yield and quality. The primary aim of this study was to establish the genetic basis of traits associated with biomass and growth of 129 Medicago sativa genotypes through genome-wide association studies (GWAS) under combined salt and P. medicaginis infection stresses. The results of the analysis of variance (ANOVA) indicated that the variation in these traits could be primarily attributed to genotype effects. Among the test genotypes, the length of the main stem, the number of ramifications, the number of chlorotic leaves, and the aerial fresh weight exhibited the most significant variation. The broad-sense heritability (H²) was relatively high for most of the assessed traits, primarily due to genetic factors. Cluster analysis, applied to morpho-physiological traits under the combined stresses, revealed three major groups of accessions. Subsequently, a GWAS analysis was conducted to validate significant associations between 54,866 SNP-filtered single-nucleotide polymorphisms (SNPs) and seven traits. The study identified 27 SNPs that were significantly associated with the following traits: number of healthy leaves (two SNPs), number of chlorotic leaves (five SNPs), number of infected necrotic leaves (three SNPs), aerial fresh weight (six SNPs), aerial dry weight (nine SNPs), number of ramifications (one SNP), and length of the main stem (one SNP). Some of these markers are related to the ionic transporters, cell membrane rigidity (related to salinity tolerance), and the NBS_LRR gene family (associated with disease resistance). These findings underscore the potential for selecting alfalfa genotypes with tolerance to the combined constraints of salinity and P. medicaginis infection. [ABSTRACT FROM AUTHOR]

The problem of salinity is multiple. In addition to salt stress, ion toxicity ([Na.sup.+] and [Cl.sup.-] dissolved in irrigation water or in soil solution), and mineral nutrition perturbation, plants have difficulty absorbing water from soil because of its elevated osmotic pressure, which leads to water stress and thus complicates and impairs their physiological state in an exponential way. Consequently, cells try to adjust their water potential by ion homeostasis regulation via vacuolar compartmentation and (or) extrusion out of the cell of the toxic ions ([Na.sup.+] and [Cl.sup.-]). Nevertheless, if this is not sufficient, the plant has to use another way to face salt stress, which consists in the synthesis and accumulation of a class of osmoprotective compounds known as compatible solutes, mainly amino compounds and sugars. Energetically, this osmotic strategy is more expensive than ion homeostasis regulation. A secondary aspect of salinity stress in plants is the stress-induced production of reactive oxygen species leading to an oxidative stress whose damage reduction could be realized via the production of antioxidants. Perception and signal mechanisms represent the first events of plant stress adaptation, and the main pathways followed are calcium, abscissic acid (ABA), mitogen-activated protein kinases (MAPKinases), salt overly sensitive (SOS) proteins, and ethylene. Mots-cles : compartimentation vacuolaire, exclusion du sodium, homeostasie ionique, osmoregulation, signalisation cellulaire du stress, tolerance a la salinite. Le probleme de la salinite est multiple, car en plus de la toxicite des ions [Na.sup.+] et [Cl.sup.-] (dissous dans l'eau d'irrigation ou presents dans la solution du sol) et de la perturbation de la nutrition minerale (suite aux interactions entre les ions), les plantes ont du mal a absorber l' eau du sol du fait de sa pression osmotique elevee, et cela se traduit par un stress hydrique en plus du stress salin, compliquant et alterant ainsi de facon exponentielle leur etat physiologique. Les cellules tendent par consequent a ajuster leur propre potentiel hydrique en retablissant l'homeostasie ionique cellulaire, que ce soit par la compartimentation vacuolaire des ions toxiques ([Na.sup.+] et [Cl.sup.-]) absorbes et (ou) leur exclusion hors de la cellule. En revanche, si cela n' est pas suffisant, la plante devra utiliser un autre moyen pour faire face au stress salin, qui consiste a synthetiser et accumuler des solutes organiques osmoprotecteurs, principalement des composes amines et des sucres. Sur le plan energetique, cette strategie osmotique est beaucoup plus couteuse que la regulation de l'homeostasie ionique. D'autre part, une forte concentration saline dans le sol induit chez la plante la production de formes actives d'oxygene qui provoquent un stress oxydatif dont la reduction des dommages pourrait se faire par le biais de la production d' antioxydants. Ces principales reactions cellulaires elaborees par la plante afin de faire face et de s' adapter au stress salin sont inevitablement precedees par une cascade d'elements de signalisation et de regulation qui peuvent emprunter differentes voies impliquant notamment celle du calcium, de l' acide abscissique (ABA), des << mitogen-activated protein kinases >> (MAPKinases), des proteines << salt overly sensitive >> (SOS) et de l'ethylene. Key words: ion homeostasis, osmoregulation, salinity tolerance, sodium exclusion, stress cellular signalization, vacuolar compartmentation., Introduction Les effets nefastes de la salinite sur la croissance des plantes sont generalement associes au faible potentiel osmotique de la solution du sol et au niveau eleve de toxicite [...]

After identifying and isolating a grapevine (Vins vinifera L.) NHX vacuolar antiporter and before initializing functional genomic studies, we juged necessary to acquire a minimum of knowledge about the VvNHXl protein. Thus, we realized a bioinformatic analysis to determine its basic characteristics and to get structural informations that could guide us through the functional characterization. We have determined important physico-chemical parameters (molecular mass, isoelectric point, hydrophobic regions, etc.) and obtained interesting structural data (primary, secondary, and tertiary strnctures; conserved domains and interaction motives; etc.). The VvNHXl gene, which encodes this 541 amino-acid protein with a predicted molecular mass of 60 kDa, is made of 14 exons and measures 6.5 kb. The amino-acidic composition of this protein is very important, in particular, for the establishment of the a-helix structure, which represents more than 50% of the protein, but also for charge distribution, which generates critical electrostatic interactions for the ionic flux. The secondary structure of VvNHXl contains multiple transmembrane a-helix segments that are made of hydrophobic amino-acid residues, thus facilitating its insertion in the membrane. Globally, VvNHXl has one hydrophobic N-terminal region, made of 10 transmembrane segments with 440 amino-acid residues, and one hydrophilic C-terminal region, made of 100 residues. The region located between the fourth and fifth transmembrane segments represents, with its structure mainly heliRecu coidal and the presence of a favourable electrostatic environment, the pore where cation flux is performed across the membrane. VvNHXl contains various interaction domains as well as several putative posttranslational modification sites, mainly at the C-terminus but also at the N-terminus, that play an important part in regulating protein activities, influence protein structural stability, or interact with other proteins or signalling molecules. Key words: NHE antiporter, bioinformatics, topological structure, posttranslational modification, Vitis vinifera. Apres avoir identifie et isole un antiport vacuolaire de type NHX chez la vigne cultivee (Vins vinifera L.) et avant d'initier des travaux de genomique fonctionnelle, nous avons juge necessaire d'acquerir un minimum de connaissances en ce qui concerne la proteine VvNHXl. A cet egard, nous avons effectue une analyse bioinformatique afm d'en determiner les caracteristiques generales et de disposer d'informations structurales pouvant orienter les travaux de caracterisation fonctionnelle. Nous avons ainsi determine d'importants parametres physico-chimiques (masse moleculaire, point isoelectrique, regions hydrophobes, etc.) et obtenu des donnees structurales interessantes (structures primaire, secondaire et tertiaire; domaines conserves et motifs d'interaction; etc.). Le gene VvNHXl codant cette proteine de 541 acides amines, dont la masse moleculaire est estimee a 60 kDa, est compose de 14 exons et mesure 6,5 kb. La composition en acides amines de cette proteine est tres importante, notamment, pour l'etablissement de la structure en helice α, laquelle represente plus de la moitie de la proteine, ainsi que pour la distribution des charges qui genere des interactions electrostatiques capitales pour l'echange d'ions. La structure secondaire de VvNHXl comporte plusieurs helices α transmembranaires formees par des residus d'acides amines hydrophobes qui facilitent son insertion au niveau membranaire. Globalement, VvNHXl possede une partie N-terminale hydrophobe, constituee de 10 regions transmembranaires denombrant 440 residus d'acides amines, et une partie C-terminale hydrophile, composee de 100 residus. La region comprise entre les quatrieme et cinquieme segments transmembranaires represente, de par sa structure en majorite helicoidale ainsi que (existence d'un environnement electrostatique favorable aux cations, le pore par lequel vont s'engouffrer les cations lors de leur traversee membranaire. Par ailleurs, la presence de differents domaines d'interaction ainsi que de multiples sites putatifs de modification post-traductionnelle, principalement localises au niveau de la partie C-terminale mais egalement au niveau N-terminal, est d'une grande importance pour la regulation de l'activite de la proteine, sa stabilite structurale ainsi que ses interactions avec d'autres proteines mais egalement avec des molecules de signalisation cellulaire. Mots-cles : antiport NHE, bioinformatique, structure topologique, modification post-traductionnelle, Vitis vinifera., Introduction En utilisant une approche genes candidats, nos recents travaux sur la vigne cultivee (Vins vinifera L.) ont abouti a (identification et (isolement d'un antiport vacuolaire de type NHX, la [...]

This review provides a comprehensive overview of the effects of drought on the growth of medic plants; then, it explores some drought tolerance traits including the morpho-physiological and biochemical parameters. In addition, medic plants were compared to other legumes and to cereals. At the molecular level, the response of Medicago plants to drought was also highlighted. Results of several independent experiments showed that the reduction of plant biomass production of medic plants ranged between 12 and 73% under water deficit stress. Cereals are more tolerant to drought than legumes. Yield reduction in cereals ranged between 25 and 40% versus 20 and 80% in legumes. For cereal species, wheat exhibited the lowest (25%) yield reduction as compared to barley and maize (34 and 40%), respectively. In legumes, reductions were about 20, 40, and 60% in lentils, chickpea, and common bean. Medic drought tolerance was found to be associated with traits like the ability to maintain the photosynthetic activity, the optimization of root development, the water use efficiency, the osmoregulation capacity via the decrease of osmotic potential, accumulation of mineral (K+) or organic solutes (proline), and the modification of carbohydrate metabolism toward the accumulation of soluble sugars. Water deficit stress induces a lipid and protein metabolism adaptation via the accumulation of some amino acids and the decrease in malondialdehyde concentrations. The target traits suggested in medic for breeding and for genetic engineering are related to water relations, such as relative water content, water use efficiency as well as root development. [ABSTRACT FROM AUTHOR]