Triazine Resistance in Phalaris Paradoxa: Physiological and Molecular Analyses

Triazine resistance in a mutant biotype of Phalaris paradoxa is accompanied by changes in the chlorophyll fluorescence induction curve, and by reduced quantum yield for electron transport, indicating altered photosystem II activity. H owever, light-saturated rates of electron transport in isolated chloroplasts, rates ofCO₂; uptake in leaves and dry weight production of the triazine resistant biotype, are equal or superior to those of the wild type. A single mutation in the psbA gene, leading to a serine to glycine shift at position 264 of the thylakoid membrane 32 kD_a Q_B protein, was found in the herbicide resistant mutant. The results indicate that triazine resistance is not necessarily linked to inferior photosynthetic and growth performance.