Influence of NaCl and mannitol on peroxidase activity and lipid peroxidation in Centaurea ragusina L. roots and shoots

Centaurea ragusina L. is a Croatian endemic plant species growing on cliffs above the Adriatic Sea, but there is no information about its physiological behavior or stress tolerance. To investigate the response of C. ragusina plants to salinity and drought, we have analysed soluble peroxidase (POD; EC 1.11.1.7) activity, anionic isoperoxidase pattern, levels of malondialdehyde (MDA) and hydrogen peroxide in C. ragusina plants exposed to these stresses. Rooted plantlets grown on MS image nutrient medium supplemented with mannitol (300 mM) and different concentrations of NaCl (150, 300, 450 or 600 mM) were harvested after 5, 10 and 15 days. Both osmotic treatments significantly increased MDA and hydrogen peroxide contents in C. ragusina shoots after 10 days of stress, while in roots these parameters showed no significant difference compared to control in overall. POD activity of salt-stressed plants changed with respect to different saline treatments and plant organs – in shoots enzymatic activity markedly increased in response to lower saline treatments, especially 300 mM NaCl; otherwise it was similar as in control plants while in roots of plants grown under 450 and 600 mM NaCl it significantly decreased. Drought increased POD activity of both shoots and roots especially after 10 days of experiment. Generally, change in the POD isoenzyme pattern of treated plants was in accordance with the activity change in time. Several POD isoforms (P3, P4 and P9) were specifically induced by salinity and drought.