Physiological Responses of Beet and Cabbage Plants Exposed to Copper and their Potential Insertion in Human Food Chain

Copper (Cu) can be toxic to vegetables when it is absorbed and accumulated at large concentrations, a fact that increases the risk of excessive addition of this metal to the human food chain. The aims of the current study are (1) to determine the Cu concentrations that have critical toxic effects on beet and cabbage plants, and the potential of these plants to enter the human food chain; as well as (2) to assess the physiological and biochemical responses of representatives of these vegetables grown in nutrient solution presenting increasing Cu concentrations. Beet and cabbage plants were grown for 75 days in pots filled with sand added with nutrient solution presenting six Cu concentrations: 0.00, 0.52, 1.02, 1.52, 2.02 and 2.52 mg Cu L -1 . Dry matter yield and Cu accumulation in different plant organs were evaluated. Photosynthetic pigment contents, lipid peroxidation levels (TBARs), superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POD, EC 1.11.1.7) activity, and hydrogen peroxide (H2O2 ) concentrations in leaves were evaluated. Critical Cu concentrations that led to toxicity in plant organs such as beetroot and cabbage head, which are often found in human diets, corresponded to 1.43 mg Cu L -1 and 1.59 mg Cu L -1 , respectively. High Cu concentrations in the nutrient solution have increased Cu concentrations and accumulation in plant tissues. This outcome justified the increased POD and SOD enzyme activity in the leaves of beet and cabbage plants, respectively, as well as was the cause of reduced plant growth in both crops. Cabbage plants presented higher tolerance to increased Cu levels in the growing environment than beet plants. However, it is necessary being careful at the time to consume both vegetables, when they are grown in Cu-enriched environments.