CHANGES IN PROLINE CONTENT ACCOMPANYING THE UPTAKE OF ZINC AND COPPER BY LEMNA-MINOR

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. © 1993 Annals of Botany Company.