Ozone affects shikimate pathway transcripts and monomeric lignin composition in European beech (Fagus sylvatica L.)

The shikimate pathway plays a pivotal role in the formation of aromatic secondary compounds in plants. It finally leads to the formation of, for example, stilbenes, flavonoids, and lignins. Ozone effects on transcript levels of the shikimate pathway were studied in leaves of European beech saplings in the greenhouse (300 nl l−1, 8 h/day, 30 days), and in leaves of adult beech trees at the Kranzberg Forest free-air ozone fumigation site (ambient and twice ambient ozone levels) between June and October 2004. Quantitative real-time RT-PCR (qRT-PCR) with RNA isolated from beech saplings showed a strong induction of 3-deoxy-d-arabino-heptulosonate-7-phosphate synthase3 (DAHPS3), 3-dehydroquinate dehydratase/shikimate dehydrogenase (DHQD/SD), 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS), and chorismate mutase (CM) starting at day seven from the onset of ozone treatment. In contrast, sun leaves of adult European beech showed only a weak elevation of shikimate pathway transcripts throughout the vegetation period studied. In addition, we examined lignin content and monomeric structure in leaves of European beech saplings from the greenhouse experiment. Leaves exhibiting highest amount of ozone-dependent lesions had the highest lignin content as determined according to Klason. Moreover, with increasing leaf damage, the syringyl (S) monomer content decreased, whereas the content of guaiacyl (G) and p-hydroxyphenyl (H) units increased. These results overall suggest that the composition of lignin is affected by ozone and is already regulated at early steps of the shikimate pathway.