Heavy metal as Cd can antagonise uptake and transport of other metal elements such as Mn, Zn, and Fe in leaves of Vicia faba L. concentrations of Cd or Zn up to 100 µM remarkably decreased chlorophyll content compared to control. The degradation in Chl. b under such stress was slower than that of Chl. a. and Cd had more inhibitory effect on both pigments than Zn even under low concentration (50 µM). The results cleared that Zn can strongly antagonise this toxic effect of Cd especially with high Zn concentrations and where full protection and restoration of chlorophyll levels was recorded. Measurements of Na, Mg, P, K, Ca, Cu, Al, Mn, and Zn bounded to the cell membrane, revealed a significant decrease of Ca, K and Mg in the presence of Cd or Zn, also the disappearance of Fe peak was observed at 100 µM Cd. This could be due to Cd ions interaction with the manganese cluster which is present in the evolving complex on the donor side of PSΠ. The effect of metal toxicity for Zn and or Cd, in this study, could be observed in many damages to the cell organelle ultrastructure. Changes in chloroplast ultrastructure and lipid composition of the thylakoid membranes alter the operability of the photosynthetic electron transport chain. The chloroplast treated with 100 µM Cd has a reduced number of intact grana, as well as reduced chloroplast size. Combined treatment of cadmium and zinc led to more changes in the shape of cellular components, such as, the shape of chloroplasts was almost spherical, the grana were completely damaged and a large part of chloroplast appeared with disturbed envelopes. Increasing Zn over Cd concentration treatment acquired beneficial effect as it can successfully antagonize the harmful effect of Cd.
Key words: Cadmium, Zinc, ultrastructure, photosynthetic apparatus, Vicia faba L.
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