Abstract
Tobacco has previously been used in investigations of metals and radionuclide uptake. This study presents determination of bioaccumulation and translocation of 60Co2+ ions in tobacco plants (Nicotiana tabacum L.) grown in Hoagland’s nutrient solution. Cobalt concentration in tobacco plants increased with increasing concentration in nutrient solution. Bioaccumulation from the initial concentration C0 = 0.96 μM Co reached 90% after 7 day cultivation. Only small amounts of Co accumulated in roots, up to 2 - 4 % were removable from roots by washing with 0.1 M CoCl2, indicating that this portion of Co is bound to the root surface in ion-exchangeable form. Tobacco roots retained approximately 2/3 of accumulated cobalt and 1/3 was transported to shoots. Autoradiography revealed that 60Co was preferentially localized in younger leaves. Prolongation of cultivation time did not change the [Co]roots : [Co]shoots ratio significantly. Relationships between growth rate, transpiration rate, uptake and distribution of cobalt in plant tissue are discussed.
Highlights
Many papers explaining mechanism of uptake, translocation and detoxication of cobalt have been published (BAKKAUS et al, 2005; PEREZ-ESPINOZA et al, 2005; WOODARD et al, 2003; MORENO-CASELLES et al, 1997)
Transpiration rate at 22 ± 1°C and 50 % humidity was linear within 7 days (Fig. 1)
Small amount of cobalt, up to 2-4 % was removable from roots at the end of the experiment by washing with 0.1 M CoCl2, indicating that this portion of cobalt was bound to the surface of the roots in ion-exchangeable form
Summary
Many papers explaining mechanism of uptake, translocation and detoxication of cobalt have been published (BAKKAUS et al, 2005; PEREZ-ESPINOZA et al, 2005; WOODARD et al, 2003; MORENO-CASELLES et al, 1997). A number of mechanisms have been proposed on how cobalt is taken up and transported through the plant (WOODARD et al, 2003). It was suggested that cobalt cannot be detoxified via the phytochelatin system in plant cell (OVEN et al, 2002). This is in contrast with results obtained for other metals such as Cd and Zn. On the other hand, OVEN et al (2002) identified cysteine as a compound involved in Co complexation in cobalt hyperaccumulator Crotalaria cobalticola suspension cells. Cobalt induced cysteine increase in non-hyperaccumulator species, suggesting that there are other cellular mechanisms that enable cobalt tolerance and hyperaccumulation
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