Physiological studies of tolerance to saline stress in Lotus glaber and their correlation with Mesorhizobium loti

FABRICIO CASSÁN; VIRGINIA LUNA Y OSCAR A RUIZ

IIB-INTECh. Chascomús. Buenos Aires

Taller; TALLER INTERDISCIPLINARIO SOBRE ASPECTOS GENETICOS, MOLECULARES Y FISIOECOLOGICOS DEL LOTUS SPP. Y SUS SIMBIONTES.; 2005

CONICET-CIC-ANPCYT-CYTED

Soil salinity represents the biggest cause of abiotic stress in cultivable plants around the world. In Argentina at least 34.000.000 has had they are subjected to the excess of water and mineral salts and a drastic reduction in their productivity. Soil salinity determines two types of stress in plant: HIDRIC and IONIC stresses. Plants strategy to tolerate this condition is directed to the activation of multiple metabolic ways in order to maintain the general homeostasis. These biochemical and physiological mechanisms include: (a) modifications in the phytohormones balance; (b) osmo-protectors synthesis; (c) synthesis of scavengers for active species of oxygen (EAO); (d) toxic ions mobilization and compartmentalization. The “Pampa Deprimida del Salado” concentrates near 70% of the Argentinean livestock activity and their productive efficiency is intimately binding to its edaphically characteristic: nutritionally poor soils with high concentrations of salts, high pH and high fluctuations of the useful water, determined by seasonal cycles of drought and flood. In this way, the search of tolerant plant populations, as well the understanding of the physiological basis of the genotypes tolerance to this ecosystem can be considered as a high-priority topic of study. Preliminary observations of the IIB-INTECh indicate the existence of highly tolerant genotypes to salinity in different populations of Lotus glaber (Bona et al. 2002) turning this legume an excellent experimental model. Since the perspective of the symbiosis, previous works of the IIB-INTECh indicate the necessity to use several Mesorhizobium loti strains for significantly nodulate an established population of Lotus glaber (Ruiz et al. 2003). At level of the symbiosis Lotus-mesorhizobium rehearsals have not been developed to verify if the physiologic state of the tolerant plant affects the infection processes, colonization and effective biological fixation of bacterial N or if the fixation efficiency is due to a minimum number of nodulating strains in the soil. Our hypothesis suggests that at least in part, tolerance to salinity in Lotus glaber, it would depend on the association capacity with different strains of native Mesorhizobium loti and in compensation the physiologic state of the plant could be decisive for the effective colonization bacterial and N2 biological fixation. To corroborate this hypothesis we have thought about the following general objectives: (a) to elucidate the physiologic and biochemical mechanisms of tolerance to the saline stress in Lotus glaber populations and the modulation of the environmental answer for their association with Mesorhizobium loti. (b) to identify efficient symbiotic associations among tolerant populations of Lotus glaber and Mesorhizobium loti strains that allow to optimize their installation under adverse edaphic conditions. Bona G. et al. (2002). Resúmenes Taller de Lotus. IIB-INTECh. Ruiz O. et al. (2003). CYTED-BIOFAG. IIB-INTECh.