Detoxification of SO sub 2 by apoplastic enzymes

When taken up by leaves, SO{sub 2} can affect various sites like biomembranes or enzymes, and may cause intracellular acidification. It is known that plants are capable of detoxifying SO{sub 2} in different cell organelles by oxidation or reductive metabolization and thereby decrease of even avoid damage. Detoxification via oxidation also takes place in the aqueous phase of the cell wall. Fumigation of leaves with SO{sub 2} resulted in an increase in the amount of extractable soluble cell wall peroxidase. We have isolated soluble and cell wall bound peroxidases from barley leaves and spruce needles, both of which are capable of oxidizing sulfite to sulfate in vitro and in situ (ca. 2 {mu}mol SO{sub 3}{sup 2{minus}} oxidized mg{sup {minus}1} Chl and h). To what extent this process contributes to the overall detoxification of leaves to SO{sub 2} is not known at present.