Salt-induced antioxidant metabolism defenses in maize (Zea mays L.) seedlings.

Salinity alters general metabolic processes and enzymatic activities, causing increased production of reactive oxygen species (ROS). Expression of antioxidant defense genes would, in turn, be triggered to defend the cell against oxidative damage. We report that salt disturbed antioxidant metabolism in maize seedlings, causing detrimental effects on the growth and development of maize plantlets, increased hydrogen peroxide production and altered antioxidant activities and transcripts profiles. Excessive ROS levels were accompanied by increased catalase (CAT) activity in photosynthesizing shoots, along with induction of mRNA accumulation. Increased accumulation of superoxide dismutase (SOD) transcripts was also observed although no significant changes in total SOD enzymatic activity and isozyme profiles were detected. Higher salt concentrations (above 0.25 M NaCl) were highly detrimental to the plants, causing arrested growth and severe wilting, among other effects. Histochemical detection of H(2)O(2) by 3,3-diaminobenzidine (DAB) staining indicated a collapse of the leaf veins, with hydrogen peroxide leaking to neighboring cells. In agreement to these observations, Sod1, Sod2, Sod4, Sod4A, as well as all Cat transcripts were severely inhibited in plants exposed to high salt concentrations.