Antioxidant responses of edible and model plant species subjected to subtoxic zinc concentrations

Zinc (Zn) is a common heavy metal in polluted soils, as it is a widespread pollutant deriving both from natural sources and anthropogenic activities. The antioxidant tolerance/defence mechanisms against oxidative stress induced by subtoxic concentrations of Zn (50 and 150 μM ZnSO₄) were studied in a widespread edible plant (lettuce; Lactuca sativa L.) and in an important model plant (Arabidopsis thaliana (L.) Heynh.). After 10 days (Arabidopsis) and 20 days (lettuce) of Zn exposure, Zn uptake/translocation was evaluated in both roots and shoots, while indicators of oxidative stress and stress intensity, total antioxidant capacity, and enzymatic and non-enzymatic antioxidative defence were measured in leaves. From an overall comparison of the two species, Zn root uptake in Arabidopsis subjected to 50 and 150 μM ZnSO₄ was approximately 3- and 5-fold lower than in lettuce, while Zn translocation from roots to apical leaves was more efficient in Arabidopsis (23.7 vs 21.3% at 50 μM ZnSO₄ and 19.3 vs 12.9% at 150 μM ZnSO₄). Generally, a higher degree of Zn-induced oxidative stress (863.8 vs 21.3 μg g^-1 FW H₂O₂ and 1.33 vs 0.75 μM g^-1 FW MDA_eq at 150 μM ZnSO₄) and antioxidant response (441.2 vs 258.5 mM g^-1 FW TEAC and 91.0 vs 54.9% RSA at 150 μM ZnSO₄) were found in lettuce. The aim of this study is understanding (a) if subtoxic Zn levels can affect Zn uptake and translocation in the studied species and (b) if this eventual Zn absorption can influence plant oxidative status/antioxidant response. Considering that soil contamination by Zn can affect crop production and quality, the results of this research could be important for environmental, nutritional and human health issues.