CONTRIBUTIONS OF CELL-WALL AND METAL-BINDING PEPTIDE TO CD-TOLERANCE AND CU-TOLERANCE IN SUSPENSION-CULTURED CELLS OF TOMATO

Possible roles of cell wall and cytoplasmic peptides in the tolerance of cells to Cu2+ and Cd2+ ions were studied in suspension-cultured cells of tomato (Lycopersicon esculentum L. cv. Palace). Cu2+ and Cd2+ ions inhibited-growth of wild type cells at concentrations more than 100 and 200-mu-M, respectively. Tomato cells readily developed tolerance to Cd2+ ions up to 1 mM but not to Cu2+ ions, after repeated subculturings in the presence of the respective ions. Such a metal-specific adaptation of cells was not due to the difference in the total uptakes between Cd2+ and Cu2+ ions by cells. Wild-type cells accumulated Cd2+ preferentially into the cytoplasmic peptide fraction and Cu2+ into the cell-wall fraction, when grown under the subtoxic metal conditions, Under excess metal conditions, Cd-tolerant cells produced greater amounts of Cd-binding peptides in the cytoplasm and retained lesser amounts of Cd2+ ions in the cell wall than did wild-type cells. In contrast, tomato cells grown in the presence of Cu2+ ions synthesized no detectable amounts of Cu-binding peptides in the cytoplasm and retained most of the Cu2+ in the cell-wall fraction, irrespective of cell lines. These results suggested that the cytoplasmic peptides rather than cell wall properties have a primary role in the response of tomato cells to excess metal environments.