21-J Agro Crop Sci-Mhadhbi et al

21-J Agro Crop Sci-Mhadhbi et al - J. Agronomy & Crop...

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MISCELLANEOUS Behaviours of Medicago truncatula–Sinorhizobium meliloti Symbioses Under Osmotic Stress in Relation with the Symbiotic Partner Input: Effects on Nodule Functioning and Protection H. Mhadhbi 1 , V. Fotopoulos 2 , N. Djebali 1 , A. N. Polidoros 2 & M. E. Aouani 1,3 1 Laboratoire Interactions Le ´gumineuses Microorganismes (LILM), Centre de Biotechnologie, Technopo ˆ le Borj Cedria (CBBC), Hammam lif, Tunisia 2 Institute of Agrobiotechnology, CERTH, Thermi, Greece 3 NEPAD/North Africa Biosciences Network, National Research Center, El Buhouth St, Cairo, Egypt Introduction Legumes in symbiosis with rhizobia have the ability to support production of protein-rich seeds and fodder by Fxing atmospheric nitrogen, in addition to their beneFcial effect on productivity of cereals and other crops in agricul- tural rotations (Graham and Vance 2003). However, this association is often compromised by severe environmental stresses, mainly salinity and drought (Zahran 1999). As much as 60 % of legume production in the developing world occurs under conditions of signiFcant drought stress (Graham and Vance 2003, Zhang et al. 2007). It is there- fore important to elucidate the drought tolerance mecha- nisms of these species in order to improve their agronomic performance. Nevertheless, the variability of legume responses to osmotic stress and the complexity of their genetic control make it difFcult to Fnd ways to alleviate water deFcit-induced stress. Moreover, the interaction of plant with the micro-symbiont further convolutes the understanding of symbiosis tolerance mechanisms. The symbiosis is an associative mode-life between two partners where each one contributes to the energy charge and bene- Fts from the produced nutrients. Plant behaviour is a determinant factor for the success of symbiosis under stressful conditions (Sadiki and Rabih 2001, Djilianov et al. 2003). The infection process is highly sensitive to stress, although rhizobia are tolerant even to stress condi- tions that inhibit plant growth (Zahran 1999), and have a Keywords antioxidant enzymes; nitrogen-Fxing capacity; osmotic stress; symbiotic interactions; tolerance Correspondence H. Mhadhbi Laboratoire Interactions Le ´gumineuses Microorganismes (LILM), Centre de Biotechnologie, Technopo ˆ le Borj Cedria (CBBC), BP 901, 2050 Hammam lif, Tunisia Tel/±ax: +216 79 412 828 Email: mhadhbihay@yahoo.fr Accepted January 7, 2009 doi:10.1111/j.1439-037X.2009.00361.x Abstract Three genotypes of the model legume Medicago truncatula were assessed for symbiotic effectiveness in cross inoculation with two strains of Sinorhizobium meliloti under mannitol-mediated osmotic stress. Symbioses showed different tolerance levels revealed on plant growth, nitrogen-Fxing capacity and indices of nodule functioning and protection. The variability of stress response was essentially correlated with performance at non-stressful conditions. Symbiosis attitude depended on bacterial partner, host-plant genotype and their interac- tion. Plant genotype manifested the highest contribution to symbiotic efFciency
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21-J Agro Crop Sci-Mhadhbi et al - J. Agronomy & Crop...

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