Evidence from electron-spin resonance for the formation of free radicals during infection of Avena sativa by Drechslera spp.

When the spin trap 1,2-dihydroxybenzene-3,5-disulphonate (tiron) is present in intercellular washing fluids of oat leaves inoculated with the highly virulent Drechslera avenae and Drechslera siccans an electron spin resonance (ESR) spectrum of four lines is obtained. The development of chlorosis and necrotic lesions coincided with the detection of the ESR signal indicative of oxygen radicals 62 h post inoculation. With the weakly virulent Drechslera graminea and Drechslera nobleae no ESR signal was detectable. Non-specific elicitors from mycelium of compatible and incompatible Drechslera spp. did not mediate an oxygen reduction in the intercellular space of oat leaflets. Consequently, these data suggest that oxygen radicals may trigger plant cellular necrosis.