Accumulation Capability for Cs⁺ and Effects of Cs⁺ on Antioxidant Parameters in Maize

The threat of radiocesium pollution has led to an increased interest in elucidating the mechanisms of this mental toxicity in organism. In this study, three-leaf stage maize (Zea mays L. cv. Chuandan No.15) seedlings raised in hydroponic culture system, were provided with a nutrient solution containing 0, 0.5, 1, 5, 10 or 20 mmol/L Cs⁺ supplied by cesium chloride (CsCl) solution. Uptake and distribution of Cs⁺ in maize seedlings leaves, stems and roots, and the effects on antioxidant characteristics were investigated after 0, 7, 14, 21 and 28 d of the Cs⁺ treatment. The results demonstrate that various organs of maize seedlings show different abilities of accumulation on Cs⁺. Cs⁺ contents are up to 1.6-fold and 5.1-fold higher in roots as compared to leaves and stems (following 28 days’ exposure to 20 mmol/L Cs⁺), and Cs⁺ contents of roots, stems and leaves are up to 16.3fold, 18.0fold and 24.7fold higher than exposure to 0.5 mmol/L Cs⁺, respectively. The root is a primary Cs⁺ accumulation organ, which is higher than that of stem and leaf. Both transfer factor and bioconcentration factor show significantly positive relationship with treatment time. For antioxidant parameters analysis, the activities of peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) increase at first, and then decline with increasing concentration of applied Cs⁺ and also with the duration of exposure time. Contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), however, obviously increase with the increasing of the Cs⁺ concentration and exposure time. The capacity of clearing up the harmful peroxide for POD and CAT is limited, and then POD and CAT activities are inhibited under higher Cs⁺ concentration, and antioxidant system is likely impaired in some way.