Functional characterisation of three Italian Populus alba L. genotypes under salinity stress

The functional response to salt stress was studied in three Populus alba L. genotypes, from three localities of Italy: genotype 6K3 from northern Italy, genotype 2AS11 from middle-southern Italy, and genotype 14P11 from a coastal zone in southern Italy. Plants of the three genotypes were submitted to a progressive salt stress by NaCl irrigation during 4 weeks. The severity of symptoms was linked to the sodium accumulated in leaves of salt-stressed plants. Genotype 2AS11 accumulated significantly less sodium in leaves than the other genotypes, arising the hypothesis that mechanisms for sodium exclusion at root level could exist in this genotype. Its height growth was significantly reduced by salt stress but diameter growth and leaf abscission were not affected. 14P11 and 6K3 accumulated significantly more sodium in leaves and they were significantly affected by leaf abscission and reduction of height and diameter growth. Genotype 6K3 was the most salt-sensitive and its leaves had more extensive necrosis than 14P11 and 2AS11. The transcription profile of plasma membrane H+-ATPase and tonoplast H+-ATPase genes revealed a different regulation in response to salt stress in 2AS11 and 14P11, but it was unchanged in 6K3. The different response to salinity could be related to different ability to exclude sodium in roots and to different regulation of ion transport across membranes of leaf cells. The differences observed could be the expression of evolutive adaptation to the ecological conditions of original provenances. Likely a different genetic basis underlies the different degree of salt tolerance observed.