Effects of ethrel on peroxidase of iceberg lettuce leaf tissue

The effect of ethrel (0.1-1.0 mM) on the development of both peroxidase activity and brown spots in 56-day old lettuce leaves was studied. The results showed that ethrel reduces both soluble and cell wall-bound peroxidase activity in lettuce leaves, the effect being independent of the incubation medium pH, the ethylene-releasing ability of ethrel therefore being not limiting. At the same time, brown spots appeared in lettuce leaves only after incubation at high concentration (1.0 mM). These results suggest that the ethrel treatments that led to the development of brown spots were not related with the effect of ethrel in inducing peroxidase, thus ruling out any key control of peroxidase in the development of ethylene-induced brown spots.