Effects of calcium, stress on contents of chlorophyll and carotenoid, LPO levels, and antioxidant enzyme activities in Mentha

The distribution of chlorophyll and carotenoid contents and antioxidant enzyme activities such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate-dependent peroxidase (AsA-dep POD, EC 1.11.1.11), guaiacol-dependent peroxidase (Gua-dep POD, EC 1.11.1.7), and lipid peroxidation levels (LPO) were investigated according to the leaf positions of Mentha pulegium grown in the presence of 4000 muM Ca2+ and in the absence of Ca2+ on the 14th day after the start of treatments. After reaching the highest values at leaf 6, chlorophyll-carotenoid content, SOD, CAT activities decreased as the leaves aged. The variations in chlorophyll-carotenoid contents and antioxidant enzyme activities were investigated with decreasing Ca2+ concentrations ranging from 2000 to 0 muM with respect to time. The chlorophyll-carotenoid values increased in the absence of Ca2+ approximately 4.5-fold compared to the control plant over the 19 days of the stress period. SOD activity also increased approximately 2-fold with decreasing Ca2+ concentrations on the loth day and decreased afterward. Whereas CAT, AsA-dep, and Gua-dep POD activities were observed under the control levels up to 14th day and then increased over them. The LPO levels in the stress conditions increased with decreasing Ca2+ concentrations during the most of the treatment period. The peroxidation of polyunsaturated fatty acids in M. pulegium membranes was highly suppressed by at least 100 muM Ca2+ concentration in the growth medium