Changes in Proline Content Accompanying the Uptake of Zinc and Copper by Lemna minor

Abstract

Lemna minor L. grown in Hoagland solution containing zinc (10 ppm) or copper (5 ppm) for 4 d accumulated high levels of these metals. Zinc and Cu accumulation in the test plants was accompanied by a specific pattern of change in proline content. The latter showed a steep rise during early stages (peak at 12-24 h) followed by a gradual decline until 96 h of treatment. In a dose-response study, lower metal concentrations induced a sharp rise in proline level with a maximum value at 5 ppm, which declined when the concentration was further enhanced. There was a correspondence between the level of proline and total free amino acids in metal treated plants. The possibility of proline involvement in tolerance mechanisms to heavy metals has been discussed.