Electronic Journal of Polish Agricultural Universities is the very first Polish scientific journal published exclusively on the Internet, founded on January 1, 1998 by the following agricultural universities and higher schools of agriculture: University of Technology and Agriculture of Bydgoszcz, Agricultural University of Cracow, Agricultural University of Lublin, Agricultural University of Poznan, Higher School of Agriculture and Teacher Training Siedlce, Agricultural University of Szczecin, and Agricultural University of Wroclaw. ELECTRONIC JOURNAL OF POLISH AGRICULTURAL UNIVERSITIES 2003 Volume 6 Issue 2 Series BIOLOGY Copyright © Wydawnictwo Akademii Rolniczej we Wroclawiu, ISSN 1505-0297 CHRZANOWSKI G., CIEPIELA A. P., SPRAWKA I., SEMPRUCH C., SYTYKIEWICZ H., CZERNIEWICZ P. 2003. ACTIVITY OF POLYPHENOLOXIDASE IN THE EARS OF SPRING WHEAT AND TRITICALE INFESTED BY GRAIN APHID (Sitobion avenae /F./) Electronic Journal of Polish Agricultural Universities, Biology, Volume 6, Issue 2. Available Online http://www.ejpau.media.pl ACTIVITY OF POLYPHENOLOXIDASE IN THE EARS OF SPRING WHEAT AND TRITICALE INFESTED BY GRAIN APHID (Sitobion avenae /F./) Grzegorz Chrzanowski, Antoni P. Ciepiela, Iwona Sprawka, Cezary Sempruch, Hubert Sytykiewicz, Paweł Czerniewicz Department of Molecular Biology and Biophysics, University of Podlasie, Siedlce, Poland ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES ABSTRACT Polyphenoloxidase (PPO) plays an important role in plant resistance to insects, and in the detoxication of phenolic compounds taken in the nutrient components. Activity of PPO was examined in the ears of spring wheat and triticale. Extraction of enzymatic protein was carried out from acetone powder with the use of 0.05M phosphoric buffer of pH 7.4. The cultivars of spring wheat have possessed higher activity of PPO than cultivars of triticale. Feeding of the grain aphid has reduced this enzyme activity in the all analysed species and cultivars. Key words: polyphenoloxidase, spring wheat, spring triticale, Sitobion avenae. INTRODUCTION Polyphenoloxidase [EC 1.10.3.1] is a widespread enzyme found in plant cells, located in the chloroplast thylakoid membranes [3]. This enzyme is capable of dehydrogenating of o-diphenols to produce o-quinones. However, it indicates the highest activity toward hydroxylation of monophenols to diphenols [13]. In case of oxygen shortage in the PPO reaction environment it may act like peroxidase by utilizing hydrogen peroxide or ethyl as an acceptor of electrons [1].