This study aimed to investigate the effects of drought stress on Amsonia orientalis, an endangered ornamental plant with a limited natural distribution in Europe. Effects of polyethylene glycol (PEG)-mediated drought stress (-0.15, -0.49, -1.03 and -1.76 MPa osmotic potentials) were tested on in vitro cultures. In general, root lengths and numbers, total protein, chlorophyll a and carotenoid contents were negatively influenced at elevated levels of the stress factor. The successive decrease in the tested osmotic potentials resulted in gradually higher H2O2, malondialdehyde (MDA) and proline contents. Activities of the antioxidant enzymes, peroxidase (POD) and catalase (CAT), were found to be enhanced in response to the decreasing osmotic potential tested, whereas increased superoxide dismutase (SOD) activity was observed at the -0.15 MPa osmotic potential. Strong activation of POD enzymes under drought stress suggests that POD enzymes might have a major role in regulating the H2O2 content, while CAT has only a supplementary role in A. orientalis. These results indicated that although A. orientalis is susceptible to long-term drought, the species may survive during mild drought stress because the development of the plant was not totally inhibited but only limited. Nevertheless, the species should be introduced to well-irrigated lands, after evaluation of the soil’s water status, in order to ensure the continuation of its generations.
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.