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Abstract
Previous analysis of photosynthetic electron transport of isolated thylakoid membranes in iron‐deficient sunflower plants showed a decrease in the whole chain and photosystem I (PSI) activities, whereas photosystem II (PSII) activity resulted to be unaffected (Tognini et al., 1996). On the basis of these results, the analysis of the molecular composition of thylakoid membranes was carried out. By using immuno‐blotting methods, a decrease in the protein content of PSI in iron‐deficient plants was detected, while light‐harvesting complex II (LHCII) increased and PSII core complex (CC) did not change compared to the controls. In iron‐deficient plants, the tetramethylbenzidine staining of thylakoid protein gels showed a decrease in the content of cytochrome f and cytochrome b6, while cytochrome bS59 remained unchanged in control and stressed plants.
Green gels of thylakoid membranes seemed to confirm the above results; the green band corresponding to PSI holocomplex resulted less intense in chlorotic samples and the green bands of the lowest molecular weight, corresponding to LHCII, were increased in iron‐deficient thylakoid membranes in comparison to the controls.
The HPLC analysis of the pigments associated with the green bands separated by Deriphat PAGE showed that the xanthophylls associated with both photosystems shifted toward the de‐epoxidated form following iron starvation, indicating the onset of a protective mechanism against photoinhibition at the levels of both photosystems.