OZONE AFFECTS BIRCH (BETULA-PENDULA ROTH) PHENYLPROPANOID, POLYAMINE AND ACTIVE OXYGEN DETOXIFYING PATHWAYS AT BIOCHEMICAL AND GENE-EXPRESSION LEVEL

We have studied ozone-induced reactions at biochemical and mRNA level in two birch clones that differ in their ozone-sensitivity. When expos ed to a single 8 hour ozone pulse (150 ppb), first visible injuries ap peared in 24 hours in the sensitive clone and lead eventually to parti al tissue chlorosis and necrosis, while the insensitive clone was unaf fected. Cell plasma membrane damage was measured by vital stain Evan's Blue permeability. After ozone-exposure, the relative number of vital stain permeable cells increased equally in both clones reaching maxim um at 24 hours and decreasing thereafter The damaged cells were random ly distributed, but in some leaves of the sensitive clone cell death s pread forming necrotic lesions. The total cellular activities of super oxide dismutase, peroxidase and glutathione reductase increased follow ing the change in the relative Evan's Blue permeability. The enzyme ac tivity increase was considerably higher in the sensitive clone suggest ing that it is somehow related to the cell damage. PAL, that controls the phenylpropanoid biosynthesis, is a good indicator of the coordinat ed plant defense responses. Gene encoding PAL was induced rapidly but transiently in both clones during the ozone exposure. This indicates t hat defense responses were induced in both clones, when only the sensi tive clone showed widespread cell death. This suggests that the ozone- induced defense reactions and cell death in these birch clones are two separately controlled processes. Increased putrescine levels have oft en been suggested to be involved in plant ozone tolerance. On the cont rary to the induction of putrescine accumulation usually detected in o zone tolerant plants, the accumulation of free putrescine occurred in the ozone sensitive birch done.