EFFECT OF CATIONS, INCLUDING HEAVY-METALS, ON CADMIUM UPTAKE BY LEMNA-POLYRHIZA L

Cations, including calcium, magnesium, potassium, sodium, copper, iron , nickel and zinc, inhibited (up to 40%) extracellular binding and int racellular uptake of cadmium by Lemna polyrhiza in solution culture, T est plants showed a high capacity of extracellular cadmium binding whi ch was competitively inhibited by copper, nickel and zinc; however, ca lcium, magnesium and potassium caused non-competitive inhibition, Tron and sodium increased K-m and decreased V-max, thereby causing mixed i nhibition of extracellular binding, Intracellular cadmium uptake displ ayed Michaelis-Menten kinetics, It was competitively inhibited by calc ium, magnesium, iron, nickel and zinc. Monovalent cations (sodium and potassium) caused non-competitive and copper caused mixed inhibition o f intracellular cadmium uptake, Thus, high levels of cations and metal s in the external environment should be expected to lower the cadmium accumulation efficiency of L. polyrhiza.