ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
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 Co2+-, Ni2+- or Zn2+-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. Co2+-, Ni2+ or Zn2+ 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 S2Q−A charge recombination was insensitive to metal ion addition. The S2Q−B charge recombination, however, was inhibited with increase in the level of Co2+, Ni2+ or Zn2+. The observed sensitivity of S2−B charge recombination in comparison to the stability of S2Q−A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. QB. We suggest that Co2+, Ni2+ or Zn2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify QB site, leading to the loss of PS 2 activity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1989.tb06208.x
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