Singlet oxygen generation from the reaction of ozone with plant leaves

Aqueous extracts of the intercellular fluid from Sedum album L. leaves generated singlet oxygen chemiluminescence at 1270 nm when exposed to a nitrogen gas stream containing ozone at 21 +/- 2 ppm. The concentration of ascorbic acid in the intercellular fluid extracts was 310 +/- 40 microM. The intensity of the singlet oxygen chemiluminescence from the intercellular fluid extracts was comparable with the chemiluminescence from a control solution containing 300 microM ascorbic acid. The intensity of the singlet oxygen emission from intercellular fluid treated with ascorbate oxidase was 0.19 +/- 0.07 of the intensity of the singlet oxygen chemiluminescence from untreated samples of intercellular fluid extract. The simplest explanation for the effect of ascorbate oxidase is that ascorbic acid is the major ozone target generating singlet oxygen. Much weaker singlet oxygen chemiluminescence was detected at 1270 nm when intact S. album L. plant tips were exposed to a nitrogen gas stream containing ozone at 22 +/- 5 ppm. Various explanations for the relatively low intensity of the singlet oxygen chemiluminescence from intact S. album L. plant tips are discussed.