The influence of cinnamic acid, 1-tryptophane, 3,4-dihydroxyphenylalanine, 2,4-dichlorophenol modifying IAA-oxidase activity and indoleacetic acid on the development and reproduction of cereal aphids in laboratory conditions was tested. We observed that IAA and Try stimulated the reproduction of cereal aphids whereas CA, DOPA and DCP decreased it.

Content of total phenols in not treated plants of Chenopodium album biotype susceptible to atrazine was 40% higher compared to resistant one. Atrazine applied at 1 kg per hectare increased the amount of these compounds in both biotypes, especially as regards on the level of monophenols in susceptible biotype, which was 3 times higher than in untreated plants. Amount of monophenols in atrazine-resistant biotype increased slightly due to atrazine application. After application of atrazine the polyphenols/monophenols ratio decreased from 4.2 to 1.1 in susceptible biotype, while it was not much changed in resistant biotype. Atrazine increased the content of flavanols in S biotype eight-times compared with untreated plants, while in resistant one this phenomenon was not observed. IAA-oxidase activity measured in vitro was modified by leaf extracts from C. album and Echinochloa crus-galli. Than the extracts from triazine-treated resistant biotype were more capable of protecting the indoloacetic acid (IAA) against enzyme activity. It may suggest that the mechanism susceptibility or resistance to herbicide is not only involved with PS II complex, but consists also in formation in plant the systems which favour or protect the auxin degradation, respectively.