Copper affects the enzymes of the ascorbate‐glutathione cycle and its related metabolites in the roots of Phaseolus vulgaris

Abstract

The involvement of the ascorbate‐glutathione cycle in the defence against Cu‐induced oxidative stress was studied in the roots of Phaseolus vulgaris L. cv. Limburgse vroege. All the enzymes of this cycle [ascorbate peroxidase (APOD), EC 1.11.1.11; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; dehydroascorbate reductase (DHAR), EC 1.8.5.1; glutathione reductase (GR), EC 1.6.4.2] were increased, and the total ascorbate and glutathione pools rose after a 15 μM root Cu treatment. In the first hours after the start of the experiment, the accumulation of dehydroascorbate (DHA), formed as a result of a Cu‐mediated direct oxidation of ascorbate (AA), was limited by a non‐enzymatic reduction using glutathione (GSH) as the reductant. At 24 h, the enzyme capacities of both DHAR and GR were increased to maintain the redox status of the AA and GSH pools. After 72 h of Cu application, the DHAR capacity was inhibited and MDHAR was responsible for maintaining the AA pool in its reduced form. Although the GR capacity was enhanced after 72 h in the treated plants, the GSSG/GSH ratio was increased. This could be due to direct participation of GSH in the detoxification of Cu through reduction and complexation.

Responses of Antioxidative Enzymes to Accumulation of Copper in a Copper Hyperaccumulator of Commoelina communis

“…There is some evidence that modification of membrane structure could activate production of oxygen free radicals and induce lipid peroxidation (Gupta et al 1999;Elstner et al 1988). Lipid peroxidation mediated by activated oxygen species should be accompanied by changes in activities of antioxidative enzymes involved in oxygen metabolism.…”

“…Hence, the presence of excess copper can cause oxidative stress in plants (Halliwell and Gutteridge 1984;Gupta et al 1999). In plant cells, several mechanisms are available to cope with free radicals in which antioxidative enzymes play a prominent role.…”

Copper-stress induced alterations in protein profile and antioxidant enzymes activities in the in vitro grown Withania somnifera L.

“…Higher concentration of Cu can induce the formation of harmful ROS, leading to lipid peroxidation. This indicates that the oxidative stress is created in plant cells due to the overloading of metals (Gupta et al 1999;Weckx and Clijsters 1996). SOD, CAT and POX Fig.…”

Localization and activity of lipoxygenase in Cd-treated seedlings of Phaseolus coccineus

“…However, it cannot be excluded that the LOX activity may be modulated also in an indirect way via changes in the redox state of plants. Heavy metal stress resulted in changes of the level of cellular compounds like ascorbate, GSH, H 2 O 2 (Gupta et al 1999;Cuypers at al. 2000;.…”