PLANT PHYSIOLOGY , Vol 107, Issue 1 187-197, Copyright © 1995 by American Society of Plant Biologists
A Mutation in the D-de Loop of D1 Modifies the Stability of the S2QA- and S2QB- States in Photosystem II
P. Maenpaa, T. Miranda, E. Tyystjarvi, T. Tyystjarvi, Govindjee, J. M. Ducruet, A. L. Etienne and D. Kirilovsky
Department of Biology, University of Turku, SF-20500 Turku, Finland (P.M., E.T., T.T.)
Photosystem II electron transfer, charge stabilization, and photoinhibition
were studied in three site-specific mutants of the D1 polypeptide of
Synechocystis PCC 6803: E243K, E229D, and CA1 (deletion of three glutamates
242-244 and a substitution, glutamine-241 to histidine). The phenotypes of
the E229D and E243K mutants were similar to that of the control strain (AR)
in all of the studied aspects. The characteristics of CA1 were very
different. Formate, which inhibits the QA- to QB- reaction, was severalfold
less effective in CA1 than in AR. The S2QA- and S2QB- states were
stabilized in CA1. It was previously shown that the electron transfer
between QA- and QB was modified in CA1 (P Maenpaa, T. Kallio, P. Mulo, G.
Salih, E.-M. Aro, E. Tyystjarvi, C. Jansson [1993] Plant Mol Biol 22:
1-12). A change in the redox potential of the QA/QA- couple, which renders
the reoxidation of QA- by back or forward reactions more difficult, could
explain the phenotype of CA1. Although the rates of photoinhibition
measured as inhibition of oxygen evolution, Chl fluorescence quenching, and
decrease of thermoluminescence B and Q bands were similar in AR and CA1,
the CA1 strain more quickly reached a state from which the cells were
unable to recover their activity. The results described in this paper
suggest that a modification in the structure of the D-de loop of D1 could
influence the properties of the couple QA/QA- in D2 and the mechanism of
recovery from photoinhibition.
