Salt-tolerance of Phaseolus vulgaris L. is a function of the potentiation extent of antioxidant enzymes and the expression profiles of polyamine encoding genes

•Two bean genotypes (Phaseolus vulgaris) were selected to investigate which physiological and molecular mechanisms are more determinant for salt tolerance.•Salinity resulted in a marked decrease in growth, water status, stomatal conductance and photosynthesis for both genotypes.•Potassium, glucose and fructose contents were differentially higher in the salt-tolerant genotype.•Putrescine and spermidine contents decreased while spermine concentration significantly increased along with antioxidant enzymes activities under salinity mainly in the salt-tolerant genotype. Selection and improvement of crop salt tolerance constitutes an urgent need for increasing agricultural and food production to feed the growing human population. Two bean (Phaseolus vulgaris L.) genotypes, namely Tema and Djadida varying in their tolerance to NaCl, were selected to investigate the determinant physiological and molecular mechanisms underlying salt tolerance. At the physiological level, salinity resulted in a significant decrease in growth, water status, stomatal conductance and photosynthesis for both genotypes. The potassium content was higher in the salt-tolerant genotype Tema under normal and saline conditions. Both genotypes had a significant increase in proline, glucose, fructose and sucrose concentrations, but glucose and fructose were differentially higher in the salt-tolerant genotype. While putrescine and spermidine concentrations decreased, spermine concentration significantly enhanced under salt stress along with antioxidant enzymes activities namely catalase, glutathione reductase and ascorbate peroxidase. The increase was higher in the salt-tolerant genotype. The expression levels of genes encoding enzymes involved in spermine biosynthesis revealed an upregulation of spermine synthase (SPMS) and a downregulation of polyamine oxidase (PAO4). Overall, the difference between genotypes is more quantitative than qualitative; the salt-tolerant genotype Tema displayed a better physiological and molecular response under salinity. By measuring these molecules in salt-stressed plants, several genotypes could be screened for breeding programmes leading to improve salt tolerance in beans.