Acclimation of beans to oxidative stress by treatment with sublethal iron levels

The relationship between Fe2+-overloading enhanced antioxidative mechanism and protection from successive oxidative stress in plant cells was studied. The involvement of Fe2+ in the reduction of superoxide (O-2(-)) and peroxi de (H2O2) to hydroxyl radical (OH) suggests that excess Fe leads to oxidati ve stress. An excess of free Fe was induced in Phaseolus vulgaris (cv. Pint o) plants by soaking the roots in a 900 mu mol/L Fe(III)-EDTA solution for 24 h. As a result, Fe content in bean leaves increased from 160 mg Fe kg(-1 ) dry weight to 530 mg Fe kg(-1) dry weight. Oxidative stress responses wer e detected by monitoring changes in the activities and contents of a few co mponents of the antioxidative mechanism. The Fe treatment resulted in incre ased activity of ascorbate peroxidase (APX, EC 1.11.1.11) from 5.3 to 18.2 mu mol ascorbate g(-1) fresh weight min, increased ascorbate content from 6 .6 to 10 mg g(-1) fresh weight, and increased catalase (EC 1.11.1.6) and gl utathione reductase (GR, EC 1.6.4.2) activities by 380 % and 55 %, respecti vely Fe treatment induced the activity of Fe-SOD (SOD, EC 1.15.11) isozyme, which was not detected in the control bean leaves. The increase in the ant ioxidative mechanism resulted in acclimation of the Fe treated beans to sub sequent methyl viologen treatment relative to control bean plants.