Jyrki LOPONEN-a, Vladimir OSSIPOV-a,b, Julia KORICHEVA-b,
Erkki HAUKIOJA-b and Kalevi PIHLAJA-a
a- Laboratory of Physical Chemistry, Department of Chemistry, University of Turku
FIN-20014 Turku, Finland
b- Laboratory of Ecological Zoology, Department of Biology, University of Turku,
FIN-20014 Turku, Finland
Many of the changes caused by pollutants appear initially at the biochemical level and only later at ultrastructural and cell level, and finally as visible symptoms. This makes biochemical compounds potential as the indicator of the adverse effects of pollutants.
In this study the leaves of birch trees (Betula pubescens Ehrh.) growing in a gradient of air pollution (the Harjavalta copper-nickel smelter, SW Finland) were collected for detection of the air pollution effects on the concentration and composition of low molecular mass phenolic (LMMP) compounds. These compounds are not biochemically active and they are not transported from the leaves to stem as products of primary metabolism. Moreover, they are not subject to catabolism but can accumulate the information about the impact of pollution on the plant organism. Low molecular mass phenolics are represented in the birch leaves by flavonoid glycosides and derivatives of hydroxybenzoic and hydroxycinnamic acids with quinic acid or glucose.
The initial reactant for the synthesis of the main plant phenolics is phenylalanine, one of the end products of the shikimate pathway. Only gallic acid is formed from an intermediate compound of the shikimate pathway. Gallic acid is encountered in a wide range of esterified fomms ranging from simple monoesters to the complex polyesters with glucose. It is supposed that acetylated form of ß-D glucogallin can be a special reserve for the regulation of gallotannin synthesis in the birch leaves. The synthesis of gallic acid derivatives might depend on the biosynthetic activity of the shikimate pathway.
The main LMMP:s were isolated by preparative HPLC and identified by chromatographic (analytical HPLC), chemical (hydrolysis) and spectroscopic (UV, NMR, MS) techiniques. It was found, that in the young leaves for 1-O-galloyl-ß-D-(2-O-acetyl)-glucopyranose, trans-5-caffeoylquinic acid, trans-5-p-coumaroylquinic acid and quercetin-3-O-ß-D-galactopyranoside, these correlation coefficients and differences in the concentration between the control plot and the plot closest to the pollution source were significant. In the mature leaves, differences between the control and polluted areas were significant only for two compounds: 1-O-galloyl-ß-D-(2-O-acetyl)-glucopyranose and trans-5-caffecylquinic acid. It can also be a consequence of the balanced gathering of flavonoids and phenolics of more simple structure: gallic and p-coumaric acid derivatives. It can be concluded that air pollution is a stress factor that causes accumulation of some LMMP:s in the birch leaves by activation of the biosynthetic productivity of the shikimate pathway under an anthropogenic stress.