New insights into the regulation of phytochelatin biosynthesis in A. thaliana cells from metabolite profiling analyses.

Céline Ducruix (1) , Christophe Junot (1) , Julie Fievet (2) , Florent Villiers (2) , Eric Ezan (1) , Jacques Bourguignon (2)

1 LEMM - Laboratoire d'Etude du Métabolisme des Médicaments
2 LPCV - Laboratoire de physiologie cellulaire végétale

In higher plants and some fungi, heavy metals induce the synthesis of chelating peptides known as phytochelatins (PCs). They are characterized by the general structure (gamma-Glu-Cys)(n)-Gly, but in some plant species, the C-terminal glycine can be replaced by serine, glutamine, glutamate or alanine, leading to iso-phytochelatins (iso-PCs). Although the distribution of iso-PCs is considered to differ from one species to another, we previously showed that Arabidopsis thaliana (A. thaliana) cells are able to synthesize most PC-related peptides (PCs and iso-PCs) described in the literature. We also observed an accumulation of the dipeptide gamma-glutamylcysteine (gamma-EC) when cadmium (Cd) (200 muM) was added to the culture medium, suggesting that either glutathione synthetase or glycine availability could be a limiting factor for the biosynthesis of PC-related peptides. In this context, the aim of the present work was to seek new insights into the regulation of PC synthesis by performing metabolic profiling using liquid chromatography-mass spectrometry. The levels of PC-related peptides and their precursors were measured in A. thaliana cells following Cd exposure. A range of doses (0, 50, 200 and 400 muM CdNO(3)) and kinetic studies (from 1 to 48 h) showed a dose threshold (50 muM CdNO(3)) and a lag time between the appearance of PCs and iso-PCs concomitant with the gamma-EC accumulation induced by Cd, occurring at cadmium concentrations above 50 muM. This accumulation was suppressed by supplementation of the culture medium with 25 mM glycine. Glycine supplementation had a limited impact on the concentrations of glutathione and PCs whereas the levels of most iso-PCs were significantly increased. Taken together, these results indicate that GSH is involved in the biosynthesis of the iso-PCs in vivo, and that the biosynthesis of PC-related peptides is limited by the availability of glycine in the presence of high cadmium concentrations.

Mots clés: plant; Arabidopsis thaliana; heavy metal; cadmium; phytochelatin; biosynthesis; glutathione; metabolite profiling; mass spectrometry

Domaines: Biochimie, Biologie Moléculaire

Céline Ducruix, Christophe Junot, Julie Fievet, Florent Villiers, Eric Ezan, et al.. New insights into the regulation of phytochelatin biosynthesis in A. thaliana cells from metabolite profiling analyses.. Biochimie, 2006, 88 (11), pp.1733-1742. ⟨10.1016/j.biochi.2006.08.005⟩. ⟨hal-00121168⟩