Exogenous application of salicylic acid alleviates cadmium toxicity and reduces hydrogen peroxide accumulation in root apoplasts of Phaseolus aureus and Vicia sativa

We examined ameliorative effects of salicylic acid (SA) on two cadmium (Cd)-stressed legume crops with different Cd tolerances, viz. Phaseolus aureus (Cd sensitive) and Vicia sativa (Cd tolerant). Cd at 50 μM significantly increased the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^·−) in root apoplasts of P. aureus and V. sativa. When comparing the two species, we determined that Cd-induced production of H₂O₂ and O₂^·− was more pronounced in P. aureus root apoplasts than in V. sativa root apoplasts. V. sativa had higher activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) than P. aureus in root symplasts and apoplasts. Seed-soaking pretreatment with 100 μM SA decreased Cd-induced production of H₂O₂ and O₂^·− in apoplasts of both species, and increased activities of symplastic and apoplastic SOD, symplastic APX, and apoplastic CAT under Cd stress. Hence, SA-induced Cd tolerances in P. aureus and V. sativa are likely associated with increases in symplastic and apoplastic antioxidant enzyme activities.