These authors contributed equally to this work.
Function of phytochelatin synthase in catabolism of glutathione-conjugates
Article first published online: 24 JAN 2007
The Plant Journal
Volume 49, Issue 4, pages 740–749, February 2007
How to Cite
Blum, R., Beck, A., Korte, A., Stengel, A., Letzel, T., Lendzian, K. and Grill, E. (2007), Function of phytochelatin synthase in catabolism of glutathione-conjugates. The Plant Journal, 49: 740–749. doi: 10.1111/j.1365-313X.2006.02993.x
- Issue published online: 24 JAN 2007
- Article first published online: 24 JAN 2007
- Received 1 September 2006; revised 18 October 2006; accepted 19 October 2006.
- abiotic stress;
- heavy metal;
Detoxification of xenobiotic compounds and heavy metals is a pivotal capacity of organisms, in which glutathione (GSH) plays an important role. In plants, electrophilic herbicides are conjugated to the thiol group of GSH, and heavy metal ions form complexes as thiolates with GSH-derived phytochelatins (PCs). In both detoxification processes of plants, phytochelatin synthase (PCS) emerges as a key player. The enzyme is activated by heavy metal ions and catalyzes PC formation from GSH by transferring glutamylcysteinyl residues (γ-EC) onto GSH. In this study with Arabidopsis, we show that PCS plays a role in the plant-specific catabolism of glutathione conjugates (GS-conjugates). In contrast to animals, breakdown of GS-conjugates in plants can be initiated by cleavage of the carboxyterminal glycine residue that leads to the generation of the corresponding γ-EC-conjugate. We used the xenobiotic bimane in order to follow GS-conjugate turnover. Functional knockout of the two PCS of Arabidopsis, AtPCS1 and AtPCS2, revealed that AtPCS1 provides a major activity responsible for conversion of the fluorescent bimane-GS-conjugate (GS-bimane) into γ-EC-bimane. AtPCS1 deficiency resulted in a γ-EC-bimane deficiency. Transfection of PCS-deficient cells with AtPCS1 recovered γ-EC-bimane levels. The level of the γ-EC-bimane conjugate was enhanced several-fold in the presence of Cd2+ ions in the wild type, but not in the PCS-deficient double mutant, consistent with a PCS-catalyzed GS-conjugate turnover. Thus AtPCS1 has two cellular functions: mediating both heavy metal tolerance and GS-conjugate degradation.