The importance of the intracellular glutathione pool of rape cells exposed to heavy metal stress

Uranium is a widespread radioactive toxic heavy metal, released into the biosphere mostly by military purposes and nuclear industry. It is taken up by plant root systems and its chemical toxicity is much more dangerous than the radiological. Thus cell suspensions of rape (Brassica napus) revealed similar intracellular defence reactions after uranium exposure like it is described for other heavy metals (1).
Glutathion is one of the key players in this network, because of its ability to complex xenobiotics via the action of glutathione-S-transferase, its redox-capacity, and/or as precursor in the biosynthesis of heavy metal-binding peptides, e.g. phytochelatines.
Rape cells react with a decrease of the cytoplasmic glutathione pool, revealed by HPLC and TLC, respectively. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements gave an insight in interactions between glutathione and uranium. The possible reduction of the soluble uranium(VI) to an insoluble oxidation state of (IV) by glutathione can be excluded, because of lacking uranium(IV) in the cytoplasm, detected by photoacustic measurements. These findings and the time course of dropping the glutathione pool suggest an involvement in the biosynthesis of pytochelatines, which is proven by HPLC. Experiments addressing the physiological relevance of these parts of cellular defence mechanisms are under way, especially to elucidate whose impact on intracellular heavy metal sequestration.

(1) Clemens, S. (2001). "Molecular mechanisms of plant metal tolerance and homeostasis." Planta V212 (4): 475-486.