title: On the uptake and release of zinc (65Zn) in the growing alga Selenastrum capricornutum Printz.
abstract: A Zn- and pH-buffered medium was used to study the accumulation of Zn in batch-cultured algae (Selenastrum capricornutum Printz.). All experiments were carried out using (65)Zn radiotracers, which were measured by gamma-ray spectrometry. Zinc was applied in the presence of nitrilotriacetic acid (NTA), leading to free Zn(2+) concentrations ranging from 4.2 x 10(-11) to 1.6 x 10(-7) mol litre(-1). During the 75-h experiments, the rates of Zn influx and efflux were determined, the latter with full consideration for algal growth rates. Algal growth stopped completely at a free Zn(2+) concentration of 1.6 x 10(-8) mol litre(-1). Initial Zn binding was determined and, based on free Zn(2+) concentrations, presented by the apparent dissociation constant K(diss) and capacity C as 4.6 x 10(-9) mol litre(-1) and 19.8 x 10(6) mol gDW(-1), respectively. The rate constant of Zn efflux could be calculated as a constant 0.021 +/- 0.003 h(-1), irrespective of the Zn concentrations applied. The rates of Zn influx were expressed by the V(max) and K(M) values as 3.3 x 10(-10) mol gDW(-1) s(-1) and 6.3 x 10(-9) mol litre(-1), respectively. These values, which are based on applied free Zn(2+) concentrations, are compatible with the operation of a high-affinity low-concentration carrier mechanism. The results suggest that, under the conditions applied, free Zn(2+) may be the most relevant Zn species for Zn uptake; furthermore, relative growth rate may be regarded as a relatively sensitive signal for Zn stress circumstances.
authors.affiliation: Delft University of Technology, Interfaculty Reactor Institute, Department of Radiochemistry, Mekelweg 15, 2629 JB Delft, The Netherlands.
authors.forename: H T
authors.initials: HT
authors.lastname: Wolterbeek
authors.forename: A
authors.initials: A
authors.lastname: Viragh
authors.forename: J E
authors.initials: JE
authors.lastname: Sloof
authors.forename: G
authors.initials: G
authors.lastname: Bolier
authors.forename: B
authors.initials: B
authors.lastname: van der Veer
authors.forename: J
authors.initials: J
authors.lastname: de Kok