Nitric Oxide Attenuates Oxidative Stress Induced by Arsenic in Lettuce (Lactuca sativa) Leaves

Lettuce plants were exposed to different toxic levels of arsenic (As) to induce an oxidative stress response, and the role of nitric oxide (NO) (provided as sodium nitroprusside (SNP)) as an attenuating agent of this stress condition was evaluated. Plants were treated with 50 mu M of As with or without 100 mu M SNP added to the nutrient solution. The hydrogen peroxide, superoxide anion, and malondialdehyde concentrations and enzymatic activities were measured. The increase in As concentration detected in the leaves was followed by a significant increase in H2O2 and malondialdehyde (MDA) concentrations. However, the presence of SPN promoted a reduction in the concentration of these oxidative agents and also reduced the translocation of As to the shoots. The enzymatic activities in the plants exposed to As were increased, which indicates the active participation of these enzymes in the reduction of oxidative stress induced by the metalloid. In the plants exposed to As and SNP, the enzymatic activities were not so high; this result was possibly related to the direct action of NO in scavenging the generated toxic metabolites and with the reduction in the translocation of the pollutant to the shoots. Lettuce and leaves of other vegetables are usually ingested, and this study shows an alternative to avoid human contamination with As.