This study aimed to investigate the effects of possible zinc (Zn) and molybdenum (Mo) contaminations on the critically endangered
European Bluestar (Amsonia orientalis). The effects of Zn and Mo were tested in a dose-dependent manner on in vitro
cultures. Zn at 0.1 mM in the medium inhibited root development whereas Mo showed the same effect only at ≥2.5 mM concentration.
Gradual inhibition of shoot development was observed after treatment with both metals. Protein contents were also
negatively affected by increasing metal concentrations, while proline levels increased gradually. Successive increases in metal
concentrations resulted in higher hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations. The activity of the
antioxidant enzymes, peroxidase (POD) and catalase (CAT), were found to be enhanced in response to increasing metal concentrations.
Superoxide dismutase (SOD) activity decreased after Zn treatment but increased after Mo treatment. A marked
increase in POD and CAT in response to metal stress suggests that these enzymes might have a significant cooperative role in
regulating H2O2 production, although CAT, in response to drought and salt stress, has been reported to only play a supplementary
role in A. orientalis. These results indicated that A. orientalis is susceptible to long-term Zn stress but can tolerate up to 2.5
mM Mo in the long-term. Deficiency of Mo is more common than high toxic concentrations in the environment. Therefore Zn
contamination should be considered as one of the major threats for A. orientalis in its native habitat.