Effect of cercosporin on antioxidant enzymes and ion leakage in toxin-sensitive and -resistant cultivars of rice (Oryza sativa)

Treatment with cercosporin, a red toxin responsible for "narrow brown leaf spot" disease on leaves of rice (Oryza sativa L.), caused oxidative damage and changes in the activity of oxygen scavenging enzymes - peroxidase and c atalase. Punctured leaves of potted plants of the toxin-sensitive cultivar Labelle and the toxin-resistant cultivar Red rice were treated with 20 mu l of 100 mu M Cercosporin in 10% acetone for 3, 15, 30 and 45 hours (stresse d plants), and with 10% acetone alone, respectively. Punctured untreated le aves were controls. Changes in peroxidase and catalase activity were measur ed quantitatively. Enzyme activities changed specifically in the stressed l eaves as a result of tissue damage. A higher level of peroxidase activity i n the resistant plant could mean a greater potential for plant response to the action of toxin. ion leakage was used as an indicator of cell membrane damage in response to the presence of cercosporin and depended on plant cul tivar. Labelle showed a significant increase in ion leakage in the presence of the toxin - about 0.7 mS per 6 h. Red rice leaves showed no significant ion leakage. The results correlated with toxin-sensitivity/resistance of t he studied rice cultivars.