The inhibition of tomato fruit ripening by silver

Mature green tomato fruit, infiltrated with STS (up to 10 μmol) while still attached to the plant, ripened unevenly to give extensive green areas on an otherwise red background. Pericarp wall tissue from the two contrasting areas was analysed for various organic constituents. Both the green and, to a certain extent, the red tissue from treated fruit showed differences from normal in AIS, acidity, and PE activity. PG activity, which usually increases rapidly as tomatoes ripen, was low in the green but not significantly different from normal in the red tissue from STS-treated fruit. TEM examination revealed that electron-dense particles were present in the cell walls of phloem elements in vascular bundles of the green tissue, but these deposits were not found in the red tissue from the same fruit. X-ray microanalysis of the particles suggested that they contained concentrations of silver and sulphur. The results are interpreted as suggesting that silver is affecting those sites in the cell that would subsequently be involved in promoting the synthesis of PG.