Cadmium transport in submerged macrophyte Ceratophyllum demersum L. in presence of various metabolic inhibitors and calcium channel blockers

Transport of Cd2+ in Ceratophyilum demersum was light dependent process requiring metabolic energy. The extent of Cd influx was linear upto 10 μM external Cd2+, however, beyond that plants showed metal uptake plateau after 120 min. Cadmium influx was more in the light than in the dark. Various uncouplers: 2,4-dinitrophenol (DNP), carbonyl cyanide m-chlorophenylhydrazone (CCCP), and ATPase inhibitor N-N′-dicycloherxylcarbomidide (DCCD) limited this process. Cadmium ion and Ca2+ were antagonistically decreasing uptake of each other. Cd2+ influx followed Michaelis-Menten (Cd2+) saturation kinetics with a low value of Km 40.0 μM which increased in the presence of Ca2+ (66.66 μM). Verapamil and nifedipine, blockers of voltage dependent calcium channels reduced Ca2+ uptake in the plant, however, provoked Cd2+ augmentation in both continuous and short Cd2+ exposure experiments. Highly significant Cd2+ influx provoked by verapamil and nifedipine was possibly due to enhanced diffusion of Cd2+ in the dark.