Effects of Increasing Concentrations of Cu on Metal Uptake Kinetics and Biomass Yields

ABSTRACT Rice (Oryza sativa L.) plants were grown for 1 month in nutrient solutions containing Cu concentrations ranging from 0.002 to 6.25 mg/L-and then subjected to kinetic studies of metal absorption and to biomass yield measurements. A biphasic kinetic pattern was found for Cu uptake rates, with a transition phase occurring at metal concentrations between 0.05 and 0.25 mg/L. From the apparent Vmax and Km values, it is proposed that Cu is absorbed by an active mechanism up to concentrations of 0.05 mg/L in the nutrient solution, with a passive absorption mechanism progressively taking over for increasing concentrations of the metal. The Cu uptake pattern is discussed in relation to biomass yields, which reach a maximum value in the 0.25 mg/L Cu treatment at the end of the 30-day experimental period. Data on translocation rates of Cu to the shoot are also presented.