Production of the faba bean in semi-arid and coastal areas may be limited by the salt sensitivity of faba bean symbiosis. Accordingly, this study was done to analyse the effects of salt on the effective symbiosis of faba bean (Vicia faba L. var. minor cultivar Alborea) and salt-tolerant Rhizobium leguminosarum biovar. viciae strain GRA19. After 4 weeks of growth, the nutrient solutions were supplemented with 50, 75 and 100 mM NaCl for 21 d. Plants were harvested four times at weekly intervals, beginning at 4 weeks. Vicia faba tolerated low (50 mM NaCl) but not higher levels (75 and 100 mM NaCl) of salt stress. Salinity affected shoot growth more than root growth. At the end of the culture, the total nitrogen content in the shoot was affected more than plant growth; conversely, in the root, growth was influenced more than total nitrogen content. In nodules, nitrogen fixation (acetylene reduction activity) was more sensitive to salinity than ammonium assimilation (glutamine synthetase and glutamate synthase).

Polyamines (PAs) are related to many aspects of the plant’s life cycle, including responses to biotic and abiotic stress. On the other hand, halophytic plants are useful models for studying salt tolerance mechanisms related to the adaptive strategies that these plants present in adverse environments. Furthermore, some halophytes have high economic value, being recommended instead of glycophytes as alternative agricultural crops in salt-affected coastal zones or saline farmlands. In recent years, the understanding of the role of PAs in salt-tolerant plants has greatly advanced. This mini review reports on the advances in the knowledge of PAs and their participation in achieving better salt tolerance in 10 halophytes. PAs are associated with responses to heavy metals in phytoremediation processes using certain salt-tolerant species (Atriplex atacamensis, A. halimus, Inula chrithmoides, and Kosteletzkya pentacarpos). In crops with exceptional nutritional properties such as Chenopodium quinoa, PAs may be useful markers of salt-tolerant genotypes. The signaling and protection mechanisms of PAs have been investigated in depth in the extreme halophyte Mesembryanthemum crystallinum and Thellungiella spp., enabling genetic manipulation of PA biosynthesis. In Prosopis strombulifera, different biochemical and physiological responses have been reported, depending on the type of salt (NaCl, Na₂SO₄). Increases in spermidine and spermine have been positively associated with stress tolerance as these compounds provide protection in Cymodocea nodosa, and Solanum chilense, respectively. In addition, abscisic acid and salicylic acid can improve the beneficial effect of PAs in these plants. Therefore, these results indicate the great potential of PAs and their contribution to stress tolerance.