EN
The objective of the research was to determine biochemical changes in the aboveground parts of plants resistant and susceptible to photosystem II inhibitors and ALS inhibitors. Differences in fluorescence measurement, free amino acids content, ALS activity and rate of heat energy production enabled adaptation and development of biochemical methods for determination of resistant biotypes. Resistant biotypes were characterized by variable fluorescence curves, the increase in valine, leucine and isoleucine concentration and increase of heat energy production. Results obtained on the basis of described methods were compared with biological test (determination of resistance index) as reference method. Measurements of plant leaf fluorescence, heat energy production and amino acid content were useful methods for identification of herbicide resistant weeds.