Effect of Heavy Metals on Nitrate Reductase Activity of Eichhornia crassipes and Pistia stratiotes
Department of Botany and Microbiology, University of Lagos, Akoka, Yaba, Lagos, Nigeria.
Accepted on February 15, 2005
Effects of eight heavy metals (Ag, Cd, Cr, Cu, Hg, Ni, Pb and Zn) on nitrate reductase activity of Echhornia crassipes and Pistia stratiotes were investigated. Plantlets were grown hydroponically in quarter-strength Hoagland’s solution and supplemented with 0, 0.1, 0.3, 0.5, 1.0, 3.0 and 5.0 mM of each of the metals for 3 weeks. The results showed that heavy metals, depending on the nature, concentration and duration of exposure inhibit the activity of the enzyme. Low concentration (0.1mM) of zinc activated the enzyme activity in E. crassipes while 0.1 and 0.3mM of the same metal boosted the enzyme activity in P. stratiotes. Moreover, the inhibitory effect of mercury was most severe.