Effect of salt stress on growth, chlorophyll content, lipid peroxidation and antioxidant defence systems in Phaseolus vulgaris L.

• Antioxidant defence systems between two bean genotypes are analysed under salinity.
• Differences are quantitative rather than qualitative except for phenolic metabolism.
• Oxidative stress in bean is counteracted mainly by the enzymatic defence system.
• Phenolic compounds decrease in the low-yielding genotype under high salinity.
• Phenolic compounds are induced in high-yielding genotype under extreme conditions.

Salinity is one of the major abiotic stresses which affects plant cell metabolism and reduces plant productivity. Variations in the antioxidant defence systems under salinity among two bean genotypes were investigated. Our results indicate that the difference between the genotypes in response to salinity is a quantitative trait rather than qualitative since they develop the same strategies with a significant variation in the rate of synthesis and accumulation, with the exemption of the antioxidant defence based on the synthesis of phenolic compounds. For both genotypes, salinity induced a marked reduction in dry matter gain in roots and shoots along with oxidative stress as indicated by the significant increase in malondialdehyde content. In addition, the photosynthetic pigments decreased with the increase of salinity. The only qualitative difference that we found among both genotypes was the decrease of total production of phenolic compounds in leaves that was only detectable in the low-yielding genotype under high salinity. The high-yielding genotype may have a better protection against oxidative damages by increasing the activity of antioxidant enzymes and the amounts of total flavonoids and ascorbic acid under high salinity, which allows maintaining higher yield even upon stress conditions. These results indicate that salt induced oxidative stress in bean is mainly counteracted by enzymatic defence systems, and that the metabolism of phenolic compounds is induced under very extreme conditions. The selection of genotypes for this trait will increase yield under stress conditions.