Canola (Brassica napus) enhances sodium chloride and sodium ion tolerance by maintaining ion homeostasis, higher antioxidant enzyme activity and photosynthetic capacity fluorescence parameters

Under salt stress, plants are forced to take up and accumulate large amounts of sodium (Na+) and chloride (Cl−). Although most studies have focused on the toxic effects of Na+ on plants, Cl− stress is also very important. This study aimed to clarify physiological mechanisms underpinning growth contrasts in canola varieties with different salt tolerance. In hydroponic experiments, 150 mM Na+, Cl− and NaCl were applied to salt-tolerant and sensitive canola varieties. Both NaCl and Na+ treatments inhibited seedling growth. NaCl caused the strongest damage to both canola varieties, and stress damage was more severe at high concentrations of Na+ than Cl−. High Cl− promoted the uptake of ions (potassium K+, calcium Ca2+) and induced antioxidant defence. Salt-tolerant varieties were able to mitigate ion toxicity by maintaining lower Na+ content in the root system for a short period of time, and elevating magnesium Mg2+ content, Mg2+/Na+ ratio, and antioxidant enzyme activity to improve photosynthetic capacity. They subsequently re-established new K+/Na+ and Ca2+/Na+ balances to improve their salt tolerance. High concentrations of Cl salts caused less damage to seedlings than NaCl and Na salts, and Cl− also had a positive role in inducing oxidative stress and responsive antioxidant defence in the short term.