Influence of nutrient medium composition on uranium toxicity and choice of the most sensitive growth related endpoint in Lemna minor
Faculty of Sciences. Biology
Journal of environmental radioactivity. - London
, p. 427-437
University of Antwerp
Uranium (U) toxicity is known to be highly dependent on U speciation and bioavailability, To assess the impact of uranium on plants, a growth inhibition test was set up in the freshwater macrophyte Lemna minor. First growth media with different compositions were tested in order to find a medium fit for testing U toxicity in L. minor. Following arguments were used for medium selection: the ability to sustain L. minor growth, a high solubility of U in the medium and a high percentage of the more toxic U-species namely UO22+. Based on these selection criteria a with a low phosphate concentration of 0.5 mg L-1 and supplemented with 5 mM MES (2-(N-morpholino)ethanesulfonic acid) to ensure pH stability was chosen. This medium also showed highest U toxicity compared to the other tested media. Subsequently a full dose response curve for U was established by exposing L. minor plants to U concentrations ranging from 0.05 mu M up to 150 mu M for 7 days. Uranium was shown to adversely affect growth of L. minor in a dose dependent manner with EC10, EC30 and EC50 values ranging between 1.6 and 4.8 mu M, 7.7-16.4 mu M and 19.4-37.2 mu M U, respectively, depending on the growth endpoint. Four different growth related endpoints were tested: frond area, frond number, fresh weight and dry weight. Although differences in relative growth rates and associated ECx-values calculated on different endpoints are small (maximal twofold difference), frond area is recommended to be used to measure U-induced growth effects as it is a sensitive growth endpoint and easy to measure in vivo allowing for measurements over time. (C) 2015 Elsevier Ltd. All rights reserved.