Effects of CO2 on Total Phenolics, Phenylalanine Ammonia Lyase, and Polyphenol Oxidase in Lettuce Tissue

Abstract An atmosphere of air + 15% CO 2 caused CO 2 injury in lettuce ( Lactuca sativa L.) in about 10 days at 0°C. However, subsequent removal of CO 2 was necessary for the brown stain symptoms to develop. Under CO 2 treatment, phenylalanine ammonia lyase (PAL) was induced and its activity correlated well with the development of the injury. Nevertheless, PAL activity did not seem responsible for the differences in susceptibility to CO 2 injury among the 3 lettuce cultivars included in this study. Prevention of the development of brown stain symptoms by CO 2 probably was due to its inhibition of phenolics production and the inhibition of polyphenol oxidase activity.