SYNTHESIS AND DEGRADATION OF PHYTOCHELATINS IN CADMIUM-SENSITIVE AND CADMIUM-TOLERANT SILENE VULGARIS

In response to external Cd supply Cd-tolerant Silene vulgaris plants p roduce three times less phytochelatins than Cd-sensitive ones. Phytoch elatin synthase activity in roots of both ecotypes was measured in ord er to determine whether a lower enzyme activity could be responsible f or the lower phytochelatin production, The phytochelatin synthase acti vity in tolerant plants, grown in the absence or in the presence of Cd , tended to be slightly lower than that in sensitive ones. However, th e difference was too small to account for the differential phytochelat in contents observed. Observations on phytochelatin synthesis in excis ed roots and on the recovery of the level of glutathione, the precurso r of phytochelatins, after arresting the Cd exposure, suggested that t olerant plants did not exhibit a decreased capacity to synthesize glut athione. Furthermore, the relative decrease in the phytochelatin conce ntration after arresting the Cd-exposure was identical for both popula tions, indicating that the difference in phytochelatin concentrations was not the result of a differential rate of phytochelatin degradation .