BIOCHEMICAL-PLANT RESPONSES TO OZONE .3. ACTIVATION OF THE DEFENSE-RELATED PROTEINS BETA-1,3-GLUCANASE AND CHITINASE IN TOBACCO-LEAVES

A single pulse of O3 (0.15 microliter per liter, 5 hours) induced beta-1,3-glucanase and chitinase activities in O3-sensitive and -tolerant tobacco (Nicotiana tabacum L.) cultivars. In the O3-sensitive cultivar Bel W3, the response was rapid (maximum after 5 to 10 hours) and was far more pronounced for beta-1,3-glucanase (40- to 75-fold) than for chitinase (4-fold). In the O3-tolerant cultivar Bel B,beta-1,3-glucanase was induced up to 30-fold and chitinase up to 3-fold under O3 concentrations that did not lead to visible damage. Northern blot hybridization showed a marked increase in beta-1,3-glucanase mRNA in cultivar Bel W3 between 3 and 24 hours following O3 treatment, a transient induction in cultivar Bel B, and no change in control plants. The induction of beta-1,3-glucanase and chitinase activities following O3 treatment occurred within the leaf cells and was not found in the intercellular wash fluids. In addition, O3 treatment increased the amount of the beta-1,3-glucan callose, which accumulated predominantly around the necrotic spots in cultivar Bel W3. The results demonstrate that near-ambient O3 levels can induce pathogenesis-related proteins and may thereby alter the disposition of plants toward pathogen attack.