DAMAGE BY OZONE AND PROTECTION BY ASCORBIC-ACID IN BARLEY LEAVES

Barley seedlings were fumigated with acute ozone concentrations at dif ferent light intensities for 4 h. Effects on leaf conductance of H2O v apour, plasma membrane permeability and Rubisco activity were analyzed . Some of the plants were supplied with ascorbic acid by the roots, an d the protective effect against damage by ozone was determined. Ozone fumigation impaired light regulation of leaf conductance and light reg ulation of Rubisco activity and increased the permeability of plasma m embranes. High light intensity during ozone fumigation increased these effects. This was mostly due to a higher amount of ozone in the leave s 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 w ere mediated by effects on membrane permeability.