Populus alba (white poplar) thiol-peptide compounds allow intracellular and extracellular cadmium detoxification

Cadmium (Cd) is a toxic heavy metal introduced into the environment through natural and human activities. Populus alba is a promising species for phytoremediation due to its ability to synthesize thiol-peptides like glutathione (GSH) and phytochelatins (PCn), which play a crucial role in heavy metal detoxification. In this study, we developed an HPLC-ESI-MS/MS method to quantify intracellular and extracellular thiol-peptides in P. alba ‘Villafranca’ clone exposed to different Cd concentrations over short- and long-term periods. We also evaluated functional responses, including biometric traits and photosynthetic efficiency. Despite prolonged Cd exposure, plants showed high resistance, with no effects on growth or PSII performance. Cd treatment significantly increased PCn levels, particularly in roots, with PC2, PC3, and PC4 contributing to detoxification. Notably, GSH and PCn were detected extracellularly, suggesting a plasma membrane efflux mechanism. Sodium orthovanadate, an inhibitor of plasma membrane transporters, strongly reduced extracellular GSH and only partially affected PCn efflux. These results suggest that GSH and PCn may not share the same transport pathways. This study underscores the dual role of thiol-peptides in Cd detoxification, through intracellular sequestration and extracellular extrusion, and highlights P. alba as a model for studying Cd toxicity mitigation in plants.