Abstract For establishing metribuzin-resistant, photoautotrophic Chenopodium rubrum cell cultures plated cells, callus cultures or suspension cultures were subjected to selection proce dures. The most effective procedure was the stepwise increase in the concentration of the herbicide from 0.01 μᴍ to 10 μᴍ in suspension cultures, which resulted in the isolation of eight different metribuzin-resistant photoautotrophic cell lines. Conjugation metabolism or a decrease in the uptake and translocation of the selective agent were not responsible for resist ance, which was stable in the absence of the inhibitor over numerous growth cycles. Meas urements of the photosynthetic electron transport, analyses of fluorescence induction kinetics and determination of the binding properties of 14C-labelled metribuzin to isolated thylakoids indicated that resistance of the cell lines is based on an alteration in the photosystem II her bicide-binding protein (D 1 protein). RFLP analysis of the psbA gene of the eight resistant cell lines demonstrated that none of them possess an amino acid exchange in position 264 of the D1 protein leading to altered herbicide-binding properties.
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