Interference by nickel(II) salts and their 5-methylimidazole-4-carboxylatecoordination compounds on the chloroplast redox chain

Nickel(II) salts and their coordination compounds with ethyl 5-methylimidaz ole-4-carboxylate (emizco), [Ni(emizco)(2)Cl-2], [Ni(emizco)(2)Br-2], [Ni(e mizco)(2)(H2O)(2)](NO3)(2). H2O Ni(NO3)(2), inhibit photosynthetic electron flow (basal, phosphorylating and uncoupled) and ATP-synthesis, therefore b ehave as Hill reaction inhibitors. Coordination compounds are more potent i nhibitors than the salts. It was found that the target for NiCl2; NiBr2 and Ni(NO3)(2) is at the b(6)f level. On the other hand, the complexes [Ni(Emi zco)(2)Cl-2], [Ni(Emizco)(2)Br-2] and [Ni(emizco)(2)(H2O)(2)](NO3)(2). H2O binding sites are located at Q(B)(D1)-protein and b(6)f level. Therefore, t hey have a common inhibition site located at b(6)f avoiding the PQH(2) oxid ation. The Q(B) inhibition site was corroborated by variable chlorophyll a fluorescence yield [v(j)]. The emizco ligand has no activity on photosynthe tic electron flow.