It has been shown that abscisic acid (ABA) and salicylic acid (SA) act as endogenous signal molecules responsible for inducing abiotic stress tolerance in plants. However, our knowledge on the role of both phytohormones in response to environmental conditions in halophytic plants is still limited. In this study endogenous ABA and SA levels, growth parameters and chlorophylls content were determined in leaves and roots of the halophyte Prosopis strombulifera cultivated under increasing NaCl and Na 2 SO 4 concentrations, at 30 and 70 % relative humidity (RH) conditions. Endogenous ABA and SA content differed depending on the salt type and concentration, RH, plant age and the organ analyzed. Under low RH conditions P. strombulifera growth was strongly inhibited and chlorophyll a and b content were decreased. In leaves of Na 2 SO 4 -treated plants at 30 % RH, high ABA levels were correlated with protection against dehydration and ion toxicity. Instead, high SA levels were correlated with the damaging effect of sulfate anion and low RH on plant growth. NaCl-treated plants growth was also inhibited at 30 % RH although levels of both hormones were not significantly increased. Taken together, the salt toxic effects on growth parameters and photosynthetic pigments were accentuated by low RH conditions and these responses were reflected on ABA and SA content.

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Prosopis genus is an important member of semiarid, arid and saline environments around the world. This genus includes shrubs and trees that exhibit a high economic and ecological potential in different American regions. These plants are considered to be unique terrestrial species due to their combined ability to fi x nitrogen and grow under high-salinity conditions. The South American halophyte, Prosopis strombulifera (Lam) Benth, is distributed from the Arizona desert (U.S.A.) to Patagonia (Argentina) and is especially abundant in the salinized areas of central Argentina. The soil of these areas is characterized by similar proportions of NaCl and Na 2 SO 4 . P. strombulifera species showed a halophytic response to NaCl surviving up to 1 M NaCl in in-vitro experiments, but in contrast, a strong growth inhibition at lower Na 2 SO 4 concentrations was observed . These differential responses to the most abundant salts present in salinized soils of Argentina make this species an excellent model to study salt-tolerance mechanisms in halophytic plants. This chapter provides an overview of different salt tolerance mechanisms in the American halophyte Prosopis strombulifera , especially phytohormone pattern, oxidative responses and production of biomolecules. This halophyte may be considered as a new useful genetic source to improve crop salt tolerance and a promising plant as source of natural products for pharmaceutical industry.

Salinity is one of the major abiotic stresses that adversely affect the crop productivity and growth of the whole plant. The halophytic Prosopis strombulifera (Fabaceae) shrub is a useful plant model to study the molecular and physiological mechanisms involved in salinity tolerance. In this work, the isolation and characterization of the mRNA for a new atypical LEA protein (PsLEA3) is reported. PsLEA3 has alanine as the most abundant amino acid followed by serine. This characteristic is different from typical LEA proteins which have high glycine content. PsLEA3 shows a negative average of hydropathy and remains localized in the chloroplast. The phylogenetic relationship between related LEA proteins and PsLEA3 showed that this protein belongs to the same group as a LEA protein of Arabidopsis. Northern analysis revealed a differential expression of this atypical LEA mRNA in P. strombulifera plants under NaCl and Na 2 SO 4 treatments. Over-expression in roots of Na 2 SO 4 -treated plants from W o -1.9 MPa was associated with abscisic acid (ABA) and its conjugate (ABA-glucose ester) accumulation as well as with the root length of these plants, showing an inhibition and toxicity induced by sulphate anion present in the medium.