Copper Effects on Growth, Lipid Peroxidation, and Total Phenolic Content of Rosemary Leaves under Salinity Stress

Plant growth is often limited by low levels of soil micronutrients such as copper (Cu), especially in calcareous salt-affected soils of arid and semiarid regions. The aim of this work was to investigate individual and combined effects of salinity and Cu on growth, leaf relative water content (LRWC), cell membrane permeability, lipid peroxidation, and total phenolic content (TPC) of rosemary (Rosmarinus officinalis L.) in a hydroponic experiment. A factorial arranged experiment with three salinity levels (i.e., 0, 50, and 100 mM NaCl), and three levels of copper (i.e., 0, 0.5, and 1.0 μM Cu2+, as CuSO4) was performed. The salt stress led to a significant decrease in leaf relative water content especially at 0 μM Cu2+. Salt treatments (50 and 100 mM) were found to increase electrolyte leakage and malonyldialdehyde content of rosemary; however, this increase was greater at 0 μM than 1.0 μM Cu2+. Regardless of Cu treatments, salinity (50 and 100 mM) induced significant increases in TPC by 13 and 29%, respectively. The application of 1.0 μM Cu at the 50 mM NaCl treatments increased total phenolic content by 19% compared to 0μM Cu. Copper nutrition resulted in greater accumulation of phenolic compounds in plant roots and thereby decreasing lipid peroxidation under salt stress conditions.