Damage by Ozone and Protection by Ascorbic Acid in Barley Leaves

Summary Barley seedlings were fumigated with acute ozone concentrations at different light intensities for 4 h. Effects on leaf conductance of H 2 O vapour, plasma membrane permeability and Rubisco activity were analyzed. Some of the plants were supplied with ascorbic acid by the roots, and the protective effect against damage by ozone was determined. Ozone fumigation impaired light regulation of leaf conductance and light regulation of Rubisco activity and increased the permeability of plasma membranes. High light intensity during ozone fumigation increased these effects. This was mostly due to a higher amount of ozone in the leaves at increased leaf conductance. Ascorbic acid supply protected plasma membrane permeability and light regulation of Rubisco against damage by ozone. Effects of ozone on plasma membrane permeability and Rubisco regulation were closely related, suggesting that effects on Rubisco were mediated by effects on membrane permeability.