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UV-induced synthesis of hydrogen peroxide

Suspension-cultured rose cells irradiated with UV (254 mm, 558 J m{sup {minus}2}) showed a transient efflux of K{sup +}, and a production of H{sub 2}O{sub 2} measured by chemiluminescence of luminol in the presence of peroxidase. The peak concentration of H{sub 2}O{sub 2}, attained at about 60-90 min after irradiation, was 2-5 uM. The addition of superoxide dismutase to irradiated cells stimulated luminscence, suggesting that the H{sub 2}O{sub 2} came at least in part from superoxide that was present in the extracellular medium. Treatments that inhibited the UV-induced efflux of K{sup +} also inhibited the appearance of H{sub 2}O{sub 2}, though the converse was not always true, suggesting that K{sup +} efflux was necessary for H{sub 2}O{sub 2} synthesis, but not vice-versa. H{sub 2}O{sub 2} in the extracellular space is required for lignin synthesis in many plant tissues. Phenolic compounds, the other substrates for lignin, are induced by UV. We suggest that the UV-stimulated production of H{sub 2}O{sub 2} is part of a coordinated induction of lignin synthesis.