Alterations in the antioxidative system of suspension-cultured soybean cells (Glycine max) induced by oxidative stress. -Physiol. Plant. 97: 388-396.The objectives of this study were the changes of antioxidative key enzyme activities under stress conditions induced by a peroxidizing herbicide using photoheterotrophically grown, suspension-cultured soybean celts (Glycine max L.). Within two days, 50 to 500 ruW oxyfluorfen, a p-nitrodiphenyl ether herbicide, caused up to 100% inhibition of growth, while simultaneously, the chlorophyll was 25% to completely bleached. The major cellular antioxidants aseorbate and glutathione showed different responses. Under stress conditions with more than 250 nM oxyfluorfen, the eellular ascorbale concentration was halved, whereas dehydroascorbate remained roughly constant. The glutathione content (approximately one-fifth of that of aseorbate in untreated control cells) increased nearly 3-fold in the presence of 250 TM oxyfluorfen. Under this condition, oxidized glutathione was 5 times above the control level. The specific activities of selected enzymes participating in cellular defence, namely aseorbate peroxidase, glutathione reduetase, monodehydroascorbate reduetase. peroxidase and catalase increased by 40 to 70% with oxyfluorfen concentrations between 50 and 500 nM, while dehydroascorbate reduetase showed a significant decrease. Glutathione transferase activity even increased 6-fold under oxyfluorfen stress.