Altered photosynthetic performance of a natural Arabidopsis accession is associated with atrazine resistance.

Natural variation for photosynthetic traits was studied by determining chlorophyll fluorescence parameters in a collection of Arabidopsis accessions. This screen revealed only one single accession (Ely), exhibiting photosynthetic characteristics markedly different from all others, while a few lines showed small but significant variation. Detailed genetic and physiological analyses showed reduced fitness for Ely compared with the standard laboratory strain Ler for various growth parameters. At low temperature (15 degrees C), Ely had a higher electron transport rate than Ler, indicating increased photosystem II efficiency under this condition, while at high temperature (30 degrees C) the opposite was observed. Ely had a high sensitivity to UV-B radiation compared with Ler and was atrazine resistant. This atrazine-resistance and related chlorophyll fluorescence traits were maternally inherited, pointing towards chloroplast-located gene(s). Definite proof that Ely is atrazine-resistant was obtained by sequencing the psbA gene, encoding the D1 protein of photosystem II, revealing a point mutation causing the same amino acid change as found in other atrazine-resistant species. Additional nuclear encoded genetic variation was also present, as was concluded from the small but significant differences in phenotype between Ely and its reciprocal crosses with Ler. It was concluded that the photosynthetic yield is highly conserved and that only severe selection pressure results in marked variations in photosynthetic performance.