Response of the ascorbate-glutathione cycle to excess copper in Arabidopsis thaliana (L.)

An operation of the ascorbate-glutathione cycle was investigated in leaves of Arabidopsis thaliana treated with excess Cu (0, 5, 25 50 and 100 muM) for 1, 3 and 7 days. After one-day-treatment significant increase of dehydroascorbate reductase (DHAR) activity and decrease of GSH level was found independently on Cu concentration. Activity of monodehydroascorbate reductase (MDHAR) increased but ascorbate peroxidase (APX) decreased at 5 muM Cu. In plants grown at 25 muM Cu decrease of APX and glutathione reductase (GR) activities was observed. After 3 days of the treatment metabolite level (AA, DHA, GSH and GSSG) increased considerably, particularly at higher Cu concentrations. Plants exposed to 50 and 100 muM Cu showed elevated GR and MDHAR activity, while those grown at 25 muM Cu elevated GR activity but diminished APX activity. Prolongation of exposition time to Cu for 7 days resulted in decrease of APX activity at 5 and 50 muM Cu and DHAR activity at 100 muM Cu. MDHAR activity in plants exposed to 25 and 100 muM Cu and DHAR at 5 muM Cu were greater than control. GSH level decreased significantly at all Cu concentrations and DHA content was elevated at 50 and 100 muM Cu. Changes in activities of the enzymes and metabolite levels of the cycle were first of all a time-dependent, but also Cu-concentration-dependent. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.