title: New insights into the regulation of phytochelatin biosynthesis in A. thaliana cells from metabolite profiling analyses.
abstract: 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 microM) 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 microM CdNO3) and kinetic studies (from 1 to 48 h) showed a dose threshold (50 microM CdNO3) 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 microM. 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.
authors.affiliation: Service de pharmacologie et d'immunologie, DSV/DRM, CEA, 91191 Gif-sur-Yvette cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Ducruix
authors.forename: C
authors.initials: C
authors.lastname: Junot
authors.forename: J-B
authors.initials: JB
authors.lastname: Fiévet
authors.forename: F
authors.initials: F
authors.lastname: Villiers
authors.forename: E
authors.initials: E
authors.lastname: Ezan
authors.forename: J
authors.initials: J
authors.lastname: Bourguignon
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis*; D003470:Culture Media; D005978:Glutathione / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D019216:Metals, Heavy / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D054811:Phytochelatins; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D029681:Arabidopsis Proteins; D003470:Culture Media; D019216:Metals, Heavy; D054811:Phytochelatins; D005978:Glutathione; D009584:Nitrogen