Three families of thiol peptides are induced by cadmium in maize.
Phytochelatins ((gamma GluCys)nGly) are synthesized from glutathione by plants exposed to metals like Cd2+, Cu2+ and Zn2+. An intracellular complex formed by phytochelatins with Cd2+ and sulfide is thought to detoxify the metal possibly by sequestration in the vacuole. It was found that maize seedlings exposed to Cd2+ produced phytochelatins and two additional families of cysteine-containing peptides, (gamma GluCys)n and (gamma GluCys)nGlu. All thiol peptides with n = 2 and 3 were purified and their structure characterized by tandem mass spectrometry. For maize plants exposed to Cd2+ for 7 days, phytochelatins were synthesized preferentially in the first 24 h whereas the amounts of (gamma GluCys)n and (gamma GluCys)nGlu were the highest thereafter. This was probably due to an initial large pool of glutathione available in control plants compared with a dearth of gamma GluCys and no detectable gamma GluCysGlu. The (gamma GluCys)nGlu peptides were induced exclusively by Cd2+ as they were below the detection limit in control seedlings that contained low amounts of phytochelatins and (gamma GluCys)n. Since the Cys moiety of the peptides is essential for binding Cd2+, a role for accumulated (gamma GluCys)n and (gamma GluCys)nGlu in detoxifying Cd2+ in plants must be considered.
Meuwly
P
P
Department of Botany, University of Guelph, Ont., Canada.
Thibault
P
P
Schwan
A L
AL
Rauser
W E
WE
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002104:Cadmium / Q000493:pharmacokinetics / Q000633:toxicity*; D005978:Glutathione / Q000378:metabolism; D008658:Inactivation, Metabolic; D008667:Metalloproteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010452:Peptide Biosynthesis; D010455:Peptides / Q000737:chemistry / Q000235:genetics; D054811:Phytochelatins; D010940:Plant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D003313:Zea mays / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*
D000596:Amino Acids; D008667:Metalloproteins; D010455:Peptides; D010940:Plant Proteins; D002104:Cadmium; D054811:Phytochelatins; D005978:Glutathione