Relationship among chlorophyll-carotenoid content, antioxidant enzyme activities and lipid peroxidation levels by Mg-2 deficiency in the Mentha pulegium leaves

The variations in the antioxidant defence mechanism and lipid peroxidation (LPO) level were investigated according to the leaf positions of Mentha pulegium L. in the absence and excess of Mg2+ on the 14th day. The maximum activities of 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) and guaiacol-dependent peroxidase (Gua-dep POD, EC 1.11. 1.7) in both stress and control conditions were observed in leaf position 6, and the activities decreased with age (P < 0.05). The LPO level variations in the leaves have an opposite trend compared to the antioxidant enzyme activities along the stems (P < 0.05). The LPO levels were highest in the absence of Mg2+ (P < 0.01). Variations in the antioxidant enzyme activities, the chlorophyll-carotenoid content and the LPO levels were also investigated under Mg2+ deficient conditions (from 2000 to 0 PM Mg2+) with respect to time. SOD and AsA-dep POD activities showed a co-operative function to protect the membrane of M. pulegilan against damage. Mg2+ deficiency caused significantly lower levels in the chlorophyll and carotenoid content (r = - 0.558 and r = - 0.419, P < 0.01) in leaf 6 between the 3rd and 17th days. In Mg2+ deficient plants, after the 17th day, there was a significant increase in LPO level (r = 0.589, P < 0.01) while the antioxidant enzyme activities and the chlorophyll-carotenoid content decreased more than the corresponding values for the control. This indicated that the senescence process of M. pulegium was accelerated by the Mg deficiency. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.