Influence of sulfate on polarized spectra of thylakoids
1990
Morin, L. | Popovic, R. (Quebec Univ., Montreal (Canada). Dept. of Chemistry) | Cegielski, R. | Dudkowiak, A. | Skibinski, A. | Frackowiak, D.
The light reactions of photosynthesis are sensitive targets of sulfate inhibitory effects. Various spectral methods can be used in diagnosis of the effects of pollutants. Beauregard et al. found that incubation with sulfate induced two effects related to the water-splitting complex: (I) Inhibition of the oxygen evolution activity dependent on chloride and calcium ions. (2) Partial depletion of the 18 000 and 23 000 polypeptides from the photosystem (PS) 2 complex. These two effects can explain the observation of Shimazaki that chloroplasts isolated from sulfate treated plants show low activity of the water-splitting system. The presence of Cl- ions diminishes the loss of the oxygen evolution ability caused by sulfate what can be explained as some stabilizing effects of these ions on 18 000 and 23 000 polypeptides. Both Cl- and Ca+ ions exhibit specific interactions with PS2 complexes involved in oxygen evolution process, but the enhancement of this reaction due to each of these ions is different. In the present paper, the polarized spectra of sulfate treated and control thylakoids, both embedded in polymer films, are compared to check how the treatment influences the thylakoid membrane structure and manual interactions between antenna pigments. To check the influence of immobilization and film deformation on the PS2 spectra, the isotropic and stretched films containing isolated PS2 particles were also measured.
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