Reactive oxygen species production and antioxidative defense in pea (Pisum sativum L.) root nodules after short-term aluminum treatment

Pea plants (Pisum sativum L.) were treated with 50 μM aluminum chloride at pH 4.5 for 2 or 24 h at room temperature. Following treatment, root nodule Al uptake, the generation of reactive oxygen species (ROS, O2−· and H2O2), and the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) were investigated. Aluminum accumulation was found chiefly in the apoplast of the nodule cortex, endodermis and meristem, while the formation of peroxide was detected in the nodule cortex, infection threads and bacteroidal tissue. Further, there were increased levels of superoxide in the meristem and bacteroidal tissue. The activity of SOD (EC 1.15.1.1) and POX (EC 1.11.1.7) increased in the Al-treated nodules and the roots of pea plants, whereas CAT (EC 1.11.1.6) activity decreased. The Al absorbed by the nodules induced ROS production. The POX and SOD are important ROS-scavengers in Al-stressed nodules.