Carotenoid and cytochrome b 559 reactions in photosystem II in the presence of tetraphenylboron

The effect of herbicides on components of the PS II reaction centre measured by EPR

“…The presence of ADRY on the split Ph-signal are of interest because they reagents is known to result in the transient photocould lead to a better understanding of the strucoxidation of carotenoid in PS II [41,42]. This tural relationship between these two acceptors and effect was used as a test of the putative ADRY the iron atom.…”

The Metal Centers of the Photosynthetic Oxygen‐evolving Complex *

“…The specific function of this cytochrome remains elusive, although these data have been interpreted as evidence supporting an earlier hypothesis as a redox-coupled proton pump (Butler, 1978). Evidence that this cytochrome is capable of being oxidized as well as reduced with equal probability by PS-I1 has been taken as evidence that there exists two hemes within this cytochrome which function independently and in parallel as electron carriers (Velthuys, 1981).…”

Activity of Photosystem II Herbicides Is Related with Their Residence Times at the D 1 Protein

“…They interrupt electron transport between Qa and Q b. Interaction o f diuron-type herbicides with plastoquinone was first proposed by van Rensen [4], It is now widely accepted that the mechanism of action is a displacement of Q B from its binding site at the D 1 protein. This was in dependently and simultaneously proposed by Velthuys [5] for the PS II complex, and by W raight [6] for the reaction center of purple photosynthetic bacteria. It is thought that the inhibitors reside at the D 1 protein for a relatively long time instead of Q b; they cannot be reduced, and thus inhibit elec tron flow.…”

“…They are supposed to be much higher than the corre sponding param eters for a reduced complex, E2 and E4. This is caused by the fact that the second ary acceptor Q B binds very strongly to its binding niche when it is in the semiquinone form, whereas both the fully reduced and the oxidized forms are easily exchanged [5,6]. In the semireduced state it is then difficult to replace the quinone by a herbi cide molecule.…”