Molecular characterisation of a mycorrhizal inoculant that enhances Trifolium alexandrium resistance under water stress conditions

The occurrence of drought is an economically important problem in Morocco. The use of mycorrhizal technology offers a possibility to overcome this problem. A mycorrhizal fungal inoculum “AoufousComplex” isolated in Morocco was shown to enhance Trifolium alexandrium resistance in water deficit situation. The efficiency of this inoculum was confirmed in this study. In order to identify this inoculum, specific primers were used to amplify the 18S subunit. The AluI RFLP typing of the PCR products revealed a single pattern showing no diversity. Phylogenetic analyses of seven sequences including other glomeromycetes allowed an unambiguous identification of the “Aoufous Complex” as Glomus mosseae strains

Water stress induces overexpression of superoxide dismutases that contribute to the protection of cowpea plants against oxidative stress

Water stress is known to induce active oxygen species in plants. The accumulation of these harmful species must be prevented by plants as rapidly as possible to maintain growth and productivity. The aim of this study was to determine the effect of water stress on superoxide dismutase isozymes (SOD, EC 1.15.1.1.) in two cowpea cultivars [Vigna unguiculata L. Walp., cv. Bambey 21 (B21) and cv. TN88-63]. Plants were submitted to water stress by withholding water supply and the expression of SOD was characterized during stress induction. In the same time, photosynthesis characteristics were determinedthrough the measurement of the quantum yield of PS II photochemistry and the energy absorption rate per reaction centre. Results show how water stress regulates the synthesis and the activity of superoxide dismutase isoforms and how these enzymes contribute to protect photosynthesis against the damageable effects of superoxide radicals in cowpea. Increased MnSOD and FeSOD activity and concentration were shown to be induced by water stress and associated with protection of photosystem II photochemistry and whole plant growth against oxidative stress in these plants. On the contrary, plants unable to express high MnSOD and/or FeSOD isoforms showed more sensitivity to water stress

Statut Hydrique Et Capacites Photosynthetiques De Deux Varietes De Niebe (Vigna unguiculata (L.) Walpers) Soumises Au Stress Hydrique

Le statut hydrique et les variations des échanges de CO2 photosynthétique ont été étudiées chez deux variétés de niébé (Vigna unguiculata L. Walp.). Les processus biochimiques susceptibles d\'être à l\'origine de ces variations ont été interprétés en relation avec les conditions hydriques de ces plantes. Les paramètres photosynthétiques associés aux échanges de CO2 entre la plante et l\'atmosphère ont été déterminés à l\'aide de l\'analyseur de gaz à capteurs infrarouges. L\'intensité du stress hydrique a été évaluée par la mesure du potentiel hydrique et du contenu relatif en eau des plantes. La courbe de libération de l\'eau obtenue en représentant le contenu relatif en eau en fonction du potentiel hydrique confirme la plus grande résistance de la variété Bambey 21 par rapport à TN88-63 au stress hydrique. Le stress hydrique induit la diminution de la conductance stomatique et du taux de photosynthèse nette tandis qu\'il provoque une augmentation de la concentration intercellulaire de CO2 dans la chambre sous-stomatique, lesquelles observations sont plus marquées chez TN88-63 que chez Bambey 21. L\'interprétation intégrée des variations de ces paramètres permet de mieux montrer leur caractère discriminant pour la comparaison de variétés vis-à-vis du stress hydrique.Water status and variations of photosynthetic CO2 exchange parameters were studied in two cowpea varieties (Vigna unguiculata (L.) Walp.) with contrasted responses to water stress. The biochemical processes supposed to sustain these variations were analysed mostly in relation to the water status of the plants, with particular emphasis on the relationships between these processes. Photosynthetic parameters were determined using an infrared gas analyser and water stress intensity was assessed through water potential and relative water content measurements. The water release curve obtained by plotting the relative water content as a function of water potential confirms the higher resistance to water stress of the Bambey 21 variety, as compared to the TN88-63. Water stress induced a decrease in stomatal conductance and in net photosynthesis rate, while it caused an increase in the intercellular CO2 concentration in the sub-stomatal chamber. The changes were more pronounced in TN88-63 than in Bambey 21. The integrated interpretation of variations in these parameters allows to better explain the discriminating characters for the comparison of varieties with regard to water stress. Keywords: Photosynthèse, stress hydrique, échanges gazeux, niébé, Côte d\'Ivoire.Agronomie Africaine Vol. 19 (1) 2007: pp. 29-4