Inhibition of Photosynthesis by 4-Nitro-6-alkylphenols: Structure-Activity Studies in Wild Type and Five Mutants of Chlamydomonas reinhardtii Thylakoids

Photosynthesis inhibition data were determined with thylakoids o f the green alga Chlamy­ domonas reinhardtii on twenty-two 2-bromo-4-nitro-6-alkyland 2,4-dinitro-6-alkyl-phenols. Wild type and five different mutants o f the algae were employed with defined changes in the psbA gene and a single amino acid substitution in the herbicide binding protein D 1 o f photo­ system II. Their response to the various inhibitors was quite different from that o f the wild type. Tolerance as well as enhanced inhibitory activity was found in the mutants, with toler­ ance in all phenols in the val219ile and o f some in the phe255tyr mutant and supersensitivity o f most phenols in the ala251val, ser264ala and leu275phe mutant. This implies that the phenols are bound specifically to the D 1 protein. Structure-activity studies revealed parabolic relationships with all descriptors increasing with the alkyl chain length for wild type and most mutant inhibition values. Molecular modelling chains in different phenols in the QB binding niche same direction.