Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 5.18

MOLECULAR RESPONSE TO SALT STRESS OF THREE ITALIAN POPULUS ALBA GENOTYPES FROM DIFFERENT LATITUDES

I. BERITOGNOLO*, M. PIAZZAI*, R. MULEO**, I. PAOLUCCI*, E. KUZMINSKY*, M. SABATTI*, G. SCARASCIA-MUGNOZZA*

*) Dipartimento di Scienze dell’Ambiente Forestale e delle sue Risorse, Università degli Studi della Tuscia, via S. Camillo de Lellis snc, 01100 Viterbo

**) Dipartimento di Produzione Vegetale, Università degli Studi della Tuscia, via S. Camillo de Lellis snc, 01100 Viterbo

Populus alba, salt stress, H+ATPase, gene expression, Real-Time PCR

Soil salinity is one of the most significant abiotic stresses for cultivated as well as for forest plants. Because of their high genetic variability in salt tolerance, forest trees could serve to recover and cultivate lands affected by secondary salinisation. Populus spp is considered a model plant for research on forest trees. It is also promising as biomass producing crop, for CO₂ sequestration and bio-remediation of degraded soils. Populus alba is present as natural species in Italian riparian habitats and shows a relatively high salt tolerance when compared to other cultivated and natural species, such P. nigra, P. deltoides, P. x euramericana and P. trichocarpa. Salinity imposes two stresses on plant tissues: a water deficit and ion specific stresses resulting from altered K⁺/Na⁺ ratio and Na⁺ and Cl^- concentration that are toxic to plants. Plants respond to elevated Na⁺ concentrations by maintaining low cytosolic Na⁺ concentrations and a high cytosolic K⁺/Na⁺ ratio. The strategies to achieve that include Na+ extrusion and/or the intracellular compartmentalization of Na⁺ in the vacuole. This active transport depends on the proton gradients established by proton pumps. Plasma membrane H⁺ATPase (proton pumps) plays an important role in the establishment and maintenance of ion homeostasis during salt stress. In experiments on herbaceous plants it was observed that salt stress can induce the differential expression of H⁺ATPase genes in tolerant genotypes when compared to less tolerant ones. H+ATPase genes are considered as good physiological markers of salt stress.

The objective of the present work is to investigate the molecular basis of salt tolerance in P. alba by using H⁺ATPase as candidate genes. In our study we compared three P. alba genotypes selected from natural populations and adapted to a range of ecological conditions: genotype 6K3 from Bormida valley in Piemonte region (Lat 44°30’ N), genotype 2AS11 from Sele valley (Lat 40°38’ N) in Campania region and genotype 14P11 from Sinni valley (Lat 40°09’ N) in Basilicata region. The three genotypes studied were selected on the basis of their origin and for the divergence of morphological and phenological adaptive traits. Salt stress experiments with potted cuttings were set-up in green house conditions. The degree of salt tolerance was assessed as difference in relative growth rate and ecophysiological parameters (transpiration, water potential, photosynthesis) between stressed and control plants. The three genotypes were submitted to irrigation with NaCl solution and showed a different tolerance to salt stress, being 14P11 the more tolerant to high salinity levels. These genotypes could represent valuable genetic resources and an interesting experimental model to study the physiological mechanisms leading to salt tolerance. Leaf samples were collected during the salt stress experiment at different levels of salinity and used for molecular analyses. Some fragments belonging to P. alba H⁺ATPase genes were cloned by PCR and the obtained H⁺ATPase sequences were used to design specific primers for RT-PCR. First analyses of gene expression by RT-PCR showed a differential expression of H⁺ATPase genes in salt stressed plants when compared to control plants. We are carrying out quantitative analyses of gene expression by Real Time RT-PCR (Light Cycler, Roche) in order to quantify the transcript level of H⁺ATPase genes relatively to housekeeping genes (Elongation Factor, 18S). Results of quantitative RT-PCR will be presented in correlation to plant growth and salinity level and the possible role of H⁺ATPase genes in salt tolerance will be discussed.