Accumulation of non-protein metal-binding polypeptides (gamma-glutamyl-cysteinyl)n-glycine in selected cadmium-resistant tomato cells.

Tomato cell suspensions have been selected for sustained growth on normally lethal concentrations of CdCl2. In cadmium-resistant (CdR) cells, Cd2+ is found complexed with non-protein, cysteine-rich polypeptides which accumulate in high amounts when cells are grown in the presence of Cd2+. Sequence and linkage analysis of these peptides by triple quadrupole mass spectrometry establishes structures of (gamma-Glu-Cys)3-Gly and (gamma-Glu-Cys)4-Gly. Necessity of these peptides for the CdR phenotype is demonstrated by inhibition of their accumulation by buthionine sulfoximine, a specific inhibitor of gamma-glutamylcysteine synthetase. Treatment of CdR cells with a concentration of buthionine sulfoximine below that inhibiting growth in the absence of Cd2+ renders CdR cells sensitive to Cd2+ ion.