Changes in cysteine, glutathione and phytochelatins in roots of maize seedlings exposed to cadmium

The effects of Cd on the contents of free cysteine, total glutathione and phytochelatin (PC) were measured in roots of intact maize seedlings. Crude extracts in 100 mM HCl were separated by reverse-phase HPLC and thiols quantitated by continuous addition of Ellman's reagent. Exposure to 3 {mu}M Cd for 15 min caused PCs to appear. The kinetics indicated that shorter PCs were substrates for longer PCs. Total glutathione levels declined with PC synthesis, free cysteine contents changed little. In the 1 cm apical region a high production of PCs occurred with a moderate loss of total glutathione. In the nature region (1-10 cm), PC content was 2.5 fold less than in species and total glutathione levels declined drastically. Exposure to 0.05 {mu}M Cd for 24 h induced PCs, more PCs appeared with greater Cd supplies. The roots produced PCs in excess of that required to chelate the Cd present, as if some PCs were compartmentalized or had not yet formed Cd-PC complexes.