Systemic acquired disease resistance (SAR) of plants may result from an oxidative burst in their tissues caused by both increased production of ROS and decreased antioxidant activity, in particular, enzymatic. Here we tested whether the exogenous inhibitors of superoxide dismutase (SOD) and catalase (CAT), respectively, diethyldithiocarbamate (DDC) and aminotriazole (AT), can systemically protect rice (Oryza sativa L.) from blast disease caused by fungus Magnaporthe oryzae Conouch et Kohn. The possible involvement of ROS in the protection was also examined. It was found that DDC did not affect fungal spore germination, and AT partially retarded it. Both compounds were non-toxic to plants and, when applied to the 4th leaf, greatly reduced the disease symptoms on the challenged 5th leaf. The protective action of AT apparently depended on the presence of hydrogen peroxide since the protection was diminished by a scavenger of H2O2 (dimethylthiourea) applied to the same leaf after AT, while exogenous H2O2, applied in place of AT, controlled the disease. Endogenous peroxide might accumulate due to inhibition of CAT that was actually observed in AT-treated leaves. Treatments of the 4th leaf with DDC or AT stimulated superoxide formation in the diffusate of the infected 5th leaf (as against treatment with water) pointing to the possible involvement of ROS in systemic defense responses. The same diffusates had enhanced fungitoxicities, which were reduced when antioxidants were added to the diffusate. Therefore, inhibitors of antioxidant enzymes systemically reduced rice blast, possibly via SAR. Both mechanisms of SAR induction (in the treated leaf) and expression (in the systemically protected leaf) might be mediated by ROS.
Russian Journal of Plant Physiology – Springer Journals
Published: Aug 14, 2015
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