Effects of extended exposure to cadmium and subsequent recovery period on growth, antioxidant status and polyamine pattern in in vitro cultured carnation

The effect of different doses of Cd (0.05, 0.1 and 0.2 mM) and subsequent period in a Cd-free medium on growth, the antioxidant status and the polyamine (PA) pattern was studied using in vitro cultured nodal segments of carnation. The Cd within the tissues increased in parallel with its concentration in the culture medium, inhibited growth, altered the concentration of some minerals and decreased the levels of pigments and the total antioxidants. However, the concentration of ascorbate (Asc) + dehydroascorbate (DHA) and the Asc redox status remained unaffected, and malondialdehyde (MDA) increased only with 0.2 mM Cd. Cd also affected PA metabolism, decreasing the total PA concentration and disturbing the relative predominance of each PA fraction. Cd exposure increased the total putrescine (Put)/(spermidine (Spd) + spermine (Spm)) ratio, and an opposite pattern was recorded during the phase in Cd-free medium. Regarding individual amines, Cd induced significant changes mainly in the free Put levels. Our results suggest that Cd produces oxidative stress and that PA (especially free Put and the total Put/(Spd+Spm) ratio), are good indicators of the stress caused by Cd.