Salinity tolerance of purslane (Portulaca oleracea L.) is achieved by enhanced antioxidative system, lower level of lipid peroxidation and proline accumulation

Purslane is a drought- and salt-tolerant annual plant, which contains high amounts of beneficial omega-3 fatty acids and antioxidant vitamins. That purslane is adaptable to both dry and saline conditions make it a prime candidate to form edible landscape in areas with dry conditions and salty soils, which are often present together where land is irrigated. In this study, 2-month-old purslane seedlings were subjected to 0, 70, 140 mM NaCl concentrations, and their growth, leaf relative water content (RWC), proline content, lipid peroxidation level and the activities of some antioxidant enzymes were determined after 18 and 30 days of salt stress exposure. Growth of purslane plants was more suppressed under 140 mM NaCl than 70 mM NaCl. Leaf RWC increased after 18 days but decreased after 30 days under both 70 and 140 mM NaCl treatments. Peroxidation of lipid membranes, as measured by malondialdehyde (MDA) level, did not change after 70 and 140 mM NaCl exposures for 18 days while increased under 140 mM NaCl treatment after 30 days. The 140 mM NaCl treatment of purslane seedlings for 18 days caused a decrease in superoxide dismutase (SOD; EC 1.15.1.1) activity. 70 and 140 mM NaCl treatments for 18 days caused 13% and 33% decreases in peroxidase (POX; EC 1.11.1.7) activity, respectively. Catalase (CAT; 1.11.1.6) showed 2.5 times higher activity after 140 mM salinity treatments on day 18 while showing 9% decrease in its activity after 140 mM NaCl on day 30. Although ascorbate peroxidase (APX; EC 1.11.1.11) activity decreased under 140 mM NaCl on day 18, it increased by 95% and 81% under 70 and 140 mM salinity treatments, respectively. The 18-day treatment of purslane seedlings with 140 mM NaCl caused a 3.5 times higher activity of glutathione reductase (GR; EC 1.6.4.2) than in control group. After 30 days of 70 and 140 mM salinity treatments, GR activity was 49% and 97% higher than in control plants. Increasing concentrations of salinity caused an increase in free proline content. These results suggest that salinity tolerance of purslane plants might be closely related with the increased capacity of antioxidative system to scavenge reactive oxygen species and thus suppressed level of lipid peroxidation and with the accumulation of osmoprotectant proline under salinity conditions.