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Impairment of photosystem 2 activity at the level of secondary quinone electron acceptor in chloroplasts treated with cobalt, nickel and zinc ions
Author(s) -
Mohanty Narendranath,
Vass Imre,
Demeter Sándor
Publication year - 1989
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1989.tb06208.x
Subject(s) - photochemistry , chemistry , electron acceptor , photosystem ii , hydroxylamine , photosystem i , metal ions in aqueous solution , p700 , photosynthetic reaction centre , acceptor , tris , metal , photosynthesis , electron transfer , organic chemistry , biochemistry , physics , condensed matter physics
The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea ( Pisum sativum L. cv. Bombay) chloroplasts. In Co 2+ ‐, Ni 2+ ‐ or Zn 2+ ‐treated chloroplasts 2,6‐dichlorophenolindophenol‐Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co 2+ ‐, Ni 2+ or Zn 2+ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)‐inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash‐induced thermoluminescence studies revealed that the S 2 Q − A charge recombination was insensitive to metal ion addition. The S 2 Q − B charge recombination, however, was inhibited with increase in the level of Co 2+ , Ni 2+ or Zn 2+ . The observed sensitivity of S 2 − B charge recombination in comparison to the stability of S 2 Q − A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. Q B . We suggest that Co 2+ , Ni 2+ or Zn 2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify Q B site, leading to the loss of PS 2 activity.