Electron spin resonance evidence for the formation of free radicals in plants exposed to ozone.

Electron spin resonance (ESR) spectroscopy was used to demonstrate that free radicals are formed in O3-fumigated plant leaves prior to the formation of visible leaf injury. ESR signals with a g-value of 2.0037 to 2.0043, were observed in pea (Pisum sativum L. cv. Feltham first) and bean (Phaseolus vulgaris L. cv. Pinto) plants that had been fumigated for 4 h with 70–300 nl l-1 of ozone after they had been treated with the spin-trap N-t-butyl-α-phenylnitrone (PBN). The size of the ESR signals increased with the concentration of ozone used but the nature of the trapped radicals could not be identified. However, further experiments using an inhibitor of ethylene biosynthesis, aminoethoxyvinyl glycine (AVG), showed that the reaction between ozone and ethylene is the cause for ozone toxicity. These results indicate that formation of (stress) ethylene in plants is involved in ozone-mediated leaf injury, that AVG did not act as an antioxidant and that lipid peroxidation rather than ozonolysis is the mechanism by which ozone exerts its toxicity in plants. [ABSTRACT FROM AUTHOR]