Prooxidative and antioxidative properties of cucumber (Cucumis sativus L.) callus in vitro and young in vivo plantlets in response to copper ions

The effects of different concentrations of copper ions (Cu²⁺ in the form of CuSO₄ × 5H₂O) on in vivo cucumber (Cucumis sativus L. ‘Edinstvo’) seedlings as well as on in vitro hypocotyl-derived callus were considered. Callus induction from hypocotyls was more prolific than from roots or cotyledons. Thus, callus obtained from hypocotyls of 7-day-old cucumber plants was cultured for 5 weeks on Murashige and Skoog medium containing 4 mg dm-3 2,4-D + 1 mg dm-3 BA supplemented with 0.01 mM, 0.1 mM or 1.0 mM of Cu²⁺. Biochemical indices related to oxidative stress were assessed. Cu²⁺ at 0.01 mM stimulated callus induction but 1.0 mM Cu²⁺ negatively affected callus formation and growth. LPO intensity was significantly lower than the control at all concentrations of Cu²⁺ but significantly higher than the control in plants exposed to 0.01 or 0.1 mM Cu²⁺. A similar trend was observed for the generation of the superoxide radical in both callus and plantlets. Superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APOX) activity increased in both callus and plantlets, but the level of increase in these antioxidant enzyme systems depended on the Cu²⁺ concentration. Cu²⁺ ions had a stronger (i.e., more negative) influence on oxidative stress in cucumber seedlings than on cucumber callus.