Günter F. Wildner1, Ursula Heisterkamp1, Achim Trebst1
1Biochemie der Pflanzen, Ruhr-Universität Bochum, Postfach 102148, D-4630 Bochum 1, Bundesrepublik Deutschland
Tóm tắt
The resistance against herbicides (inhibitors of the electron accepting side) of photosystem II originates from mutations of the psb A gene, coding for the D 1 or QB binding protein. Each of the five mutants used in the present study had single base changes in the psbA gene that resulted in a unique amino acid substitution at a different residue of the D1 protein (Val-219, Ala-251, Phe-255, Ser-264, Leu-275). The differences of the I50-values in the electron transfer reaction of H2O to dichlorophenolindophenol were used to analyze the correlation of these amino acid residue changes to their impact on the binding of diverse chemical classes of inhibitors. The binding domains on the D1 protein of the inhibitors overlap, but are nevertheless distinct. Even minor changes in the chemical structure of the inhibitors resulted in changes of the resistance toward a specific amino acid residue.
A pattern of response of the inhibitors to the amino acid substitutions evolves that allows easy differentiation between the groups of PS II inhibitors. Two principally different response curves emerge for two different families of PS II inhibitors, that had been proposed earlier already on functional studies with wild types. But the response pattern of newly described inhibitors, like ketonitrile and quinolone derivatives, in the mutants allows to group them with confidence and in turn generalize the phenol type family. In none of the five mutants, studied here, is there a marked cross-resistance to the new phenol type inhibitors. Just the opposite, in several cases, there is negative cross-resistance (or supersensitivity). Because of this response pattern this group of inhibitors cannot be oriented with certainty in the three dimensional folding model of the D1 protein.
