Increased antioxidative capacity in maize calli during and after oxidative stress induced by a long lead treatment.

Maize (Zea mays L., cv. Samodek) callus cultures were exposed for long period (22 months) to lead (0.5 mM lead chloride) and leadcontent, oxidative damage and antioxidative response were evaluated at different steps. Inductively coupled plasma (ICP) emissionspectroscopy analysis showed that lead entered the cells and it accumulated, but its internal concentration wasmaintained 10-fold less than theexternal one. Increase of both polyamine and lipid peroxide content indicated that cells underwent a stress condition due to an oxidative attack,counteracted by an increase of antioxidative defence enzyme activities, ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase(GR, EC 1.6.4.2). After 10 months, from the start of the lead treatment, a stock of calli was transferred for 6months in a lead-deprivedmediumand then re-exposed to lead for a further 6months. Analysis indicated that lead-deprived calli maintained high levels ofAPX and GR activities,suggesting that, over the experimental time-course, cells with high APX and GR activity were selected and allowed to enrich the cultures.These cultures, after a new lead treatment, showed a lower oxidative damage compared to continuously lead-treated calli.