SynopsisTypical phytopathological defence reactions of tobacco have been studied in response to ozone. After a single standard ozone pulse (5 h, 150 nl 1−1) β-l,3-glucanase was induced up to 40-fold in the sensitive tobacco cv. Bel W3, which developed necrotic lesions following the treatment. The activity was elevated 10-fold in the tolerant Bel B without concomitant injury. A decrease within 24 h occurred only in Bel B. Tyramine hydroxycinnamoyl-CoA transferase activity was induced 6- to 7-fold in both cultivars with a maximum after 5–8 h. Tyramine conjugates as the product of this reaction could not be isolated and were apparently rapidly integrated into the cell wall. Precultivation of Bel B plants in a greenhouse containing up to 70% of the outdoor ozone concentration resulted in a 4-fold induction of β-l,3-glucanase and a further increase after an administered ozone pulse. Pretreatment (30 nl 1−1 ozone, 7 h per day, 23 days) of sensitive Bel W3 caused increased injury and ethylene formation upon a subsequent ozone pulse. β-l,3-glucanase was induced to the same level as in non-pretreated control plants. In a comparison with other major air pollutants (SO2, NO2), only ozone induced the above reactions. However, a combined treatment of ozone and NO2 led to synergistic effects. These data indicate that ambient ozone is able to change the phytopathological disposition of plants. This finding may have practical significance for the usual plant experiments carried out in greenhouses with non-filtered air.
Modes of action of non-pathogenic strains of Fusarium oxysporum in controlling Fusarium wilts