Exogenous proline alleviates the effects of H2O2-induced oxidative stress in wild almond species (Prunus spp.)

The effect of proline (PRO) on antioxidant system in leaves of eight species of wild almond (Prunus spp.) exposed to H2O2-mediated oxidative stress was studied. The levels of endogenous PRO and hydrogen peroxide (H2O2), and the activities of total superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (POD) were measured. The degradation of chlorophyll but not of carotenoids occurred in leaves in a solution of 5 mM H2O2. An increase in membrane lipid peroxidation were observed in H2O2 treatment, as assessed by malondialdehyde (MDA) level and percentage of membrane electrolyte leakage (EL). Significant increases in total SOD activity and CAT activity, as well as decreases in APX and POD, were detected in H2O2-treated leaves. The three SOD isoforms showed different behaviors, as Mn-SOD activity was enhanced by H2O2, whereas Fe-SOD and Cu/Zn-SOD activities were inhibited. In addition, proline (PRO) accumulation up to 0.1 µmol/g fresh weight, accompanied by significant decreases in ascorbate and glutathione levels, was observed in H2O2-treated leaves. After two different treatments with 10 mM PRO + 5 mM H2O2, total SOD activity and CAT activity were similar to the levels of control plants, while POD and APX activities were higher if compared to the leaves exposed only to H2O2. PRO+H2O2 treatments also caused a strong reduction in cellular H2O2 content, MDA, and EL. The results showed that PRO could have a key role in protecting against oxidative stress injury of wild almond species, so decreasing membrane oxidative damage.