Resumo

FARELEIRA, P.; MATOS, N.; FERREIRA, E.  e  MARQUES, J. F.. Salt and temperature tolerance of Sinorhizobium strains isolated from dry environments in Alentejo. Rev. de Ciências Agrárias [online]. 2007, vol.30, n.2, pp.187-198. ISSN 0871-018X.

The main objective of this work was to obtain rhizobial strains able to nodulate annual medics and highly adapted to the environmental conditions present in degraded soils. Since populations of rhizobia vary in their tolerance to environmental factors, screening for resistant strains was pursued. Soil samples were collected in different regions in Southern Portugal, severely affected by drought, high temperatures, and, in some places, salinity; rhizobial strains were isolated using Medicago polymorpha as trap-host. The effects of environmental stressful conditions, such as salinity or high temperatures, in the growth of the isolated strains were studied. Among the 41 isolates that were ana-lysed here, 11 showed good growth capacity in the presence of 1.4 M sodium chloride and 10% soil extract, and 22 could grow upon incubation at 45 ºC. Three strains were able to grow under the simultaneous effects of salinity and high temperature. NMR analysis of ethanolic cell-free extracts of salt tolerant strains showed that, in most cases, cell growth in medium containing high salt concentrations resulted in the accumulation of the compatible solutes described for Sinorhizobium: the dipeptide N-acetylglutaminylglutamine amide, betaines, trehalose, glutamate, and proline. Analysis by in vivo ³¹P-NMR of a salt tolerant strain originated from a schistous soil with low-phosphorus content, revealed the presence of high levels of intracellular inorganic phosphate reserves (polyphosphates). This suggests a high potential for the utilization of the strain in soils affected by both salinity and phosphorus deficiency.

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