Impact of root Cd concentration on production of cysteine, non-protein thiols (NP-SH), glutathione (GSH), reduced glutathione (GSSG), and phytochelatins (PCs) in Eichhornia crassipes exposed to different dilutions of brass and electroplating industry effluent (25%, 50%, and 75%), and synthetic metal solutions of Cd alone (1, 2.5, and 3.5 ppm) and with Cr (1 ppm Cd + 1 ppm Cr, 2.5 ppm Cd + 3 ppm Cr, and 3.5 ppm Cd + 4 ppm Cr) was assessed in a 45 days study. Different treatments were used to understand and compare differential antioxidant defense response of plant under practical drainage (effluent) and experimental synthetic solutions. The production of NP-SH and cysteine was maximum under 2.5 ppm Cd + 3 ppm Cr treatments i.e., 1.78 µmol/g fw and 288 nmol/g fw, respectively. The content of GSH declined whereas that of GSSG increased progressively with exposure duration in all treatments. HPLC chromatograms revealed that the concentrations of PC2, PC3, and PC4 (248, 250, and 288 nmol-SH equiv.g-1 fw, respectively) were maximum under 1 ppm Cd, 1 ppm Cd + 1 ppm Cr, and 2.5 ppm Cd + 3 ppm Cr treatments, respectively. PC2, PC3, and PC4 concentrations increased with Cd accumulation in the range 812-1354 µg/g dry wt, 1354-2032 µg/g dry wt and 2032-3200 µg/g dry wt, respectively. Thus, the study establishes a direct proportionality relationship between concentration/length of phytochelatins and root Cd concentrations, upto threshold limits, in E. crassipes.
Keywords: Cadmium (Cd); cysteine; gluathione (GSH); heavy metals; non-protein thiols (NP-SH); phytochelatins (PCs).