Alleviation of Cr(VI)-induced oxidative stress in maize (Zea mays L.) seedlings by NO and H2S donors through differential organ-dependent regulation of ROS and NADPH-recycling metabolisms

Chromium (Cr) contamination in soil is a growing concern in relation to sustainable agricultural production and food safety. Nitric oxide (NO) and, more recently, hydrogen sulfide (H2S) are considered to be new signalling molecules with biotechnological applications in the agronomical sector. Using 9-day-old maize (Zea mays) seedlings exposed to 200 mu M Cr(VI), the potential mitigating effects of exogenous NO and H2S on chromium-induced stress in maize seedlings were investigated in roots, cotyledons and coleoptiles. Analysis of Cr content, lipid peroxidation, antioxidant enzymes (catalase and superoxide dismutase isozymes), peroxisomal H2O2-producing glycolate oxidase and the main NADPH-regenerating system revealed that chromium causes oxidative stress, leading to a general increase in these activities in coleptiles and roots, with the latter organ being the most affected. However, cotyledons behaved in an opposite manner. Moreover, exogenous applications of NO and H2S to Cr-stressed maize seedlings triggered a significant response, involving the virtual restoration of the values for all these activities to those observed in unstressed seedlings, although their specific impact on ROS and NADPH-recycling metabolisms depends on the seedling organ involved. Taken together, the data indicate that gas transmitters, NO and H2S, which act as a defence against the negative effects of hexavalent chromium contamination, are alternative compounds with potential biotechnological applications.