Alterations of the antioxidative enzyme activities, lipid peroxidation levels, chlorophyll and carotenoid contents along the peppermint (<em>Mentha piperita</em> L.) leaves exposed to copper deficiency and excess stress conditions

Abstract

Several physiological responses of Mentha piperita L. leaves at different positions along the stern were investigated under Cu²⁺ deficiency conditions and compared with excess and control. Chlorophyll and carotenoid contents and the ratio of chlorophylls to carotenoids in all leaf positions were significantly lower than those of control under Cu²⁺ deficiency. The highest decreases were determined under excess condition. 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) activities in all leaf positions in the absence of Cu²⁺ were higher than control and showed a positive correlation with each other. SOD activities under excess conditions were higher than deficiency, while all of the other enzyme activities were significantly lower than control. Co-operative functions of all these enzymes in the absence of Cu²⁺ resulted in lower lipid peroxidation levels (LPO) than control and excess conditions. Except for Gua-dep POD, all other antioxidant enzyme activities reached their maximum, while LPO level their minimum at leaf position 6. The antioxidant enzyme activities and LPO level variations were investigated with decreasing Cu²⁺ concentration ranging from 3.2 x 10^-2 to 0 µM depend on the incubation time, and the results were showed an increase of 2.4-fold for SOD, 4-fold for CAT, 2-fold for AsA-dep POD and 3-fold for Gua-dep POD activities in the absence of Cu²⁺ compared to the control on the 12^th day. Although enhancing antioxidant enzyme activities, LPO levels also increased approximately 2-fold compared to control in the absence of Cu²⁺ on the 12^th day and its levels significantly increased with decreasing of Cu²⁺ afterwards.
Abbreviations: AsA-dep POD = ascorbate-dependent peroxidase.; CAT = catalase.; Gua-dep POD = guaiacol-dependent peroxidase.; MOA = malondialdehyde.; LPO = lipid peroxidation.; ROS = reactive oxygen species.; 6-0HDA = 6-hydroxydopamine.; SOD = superoxide dismutase.; TBA = thiobarbituric acid.