Effects of buthionine sulfoximine on cd-binding Peptide levels in suspension-cultured tobacco cells treated with cd, zn, or cu.

Inhibition of cell growth and accumulation of Cd-binding peptide were measured in cultured tobacco cells exposed to buthionine sulfoximine. This inhibitor of glutathione metabolism caused little or no reduction of growth (at 0.1 millimolar) in the absence of Cd, but growth was greatly reduced in cultures exposed to buthionine sulfoximine and >/=22 micromolar Cd. Decreased cell growth was directly correlated with decreased levels of Cd-binding peptide and increased levels of what is thought to be free Cd. Zinc inhibited growth of tobacco cells only at the highest levels examined (900-1800 micromolar Zn), but buthionine sulfoximine had no additional significant effect. Similar results were observed for Cu (45-90 micromolar). Results suggest that synthesis of plant Cd-peptide involves gamma-glutamylcysteine synthetase or a related enzyme and that Zn accumulation in tobacco cells does not cause formation of significant Cd-peptide ligand.