PARENT SESSION
PS19 - Bioavailability
Sunday, 17 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P178) Determination of a conditional binding constant for copper to wheat roots for biotic ligand modelling.

Hale, Beverly¹, Boyle, David^*,1, ¹ University of Guelph, Guelph, ON, Canada

ABSTRACT- An experiment was performed to determine the time needed to saturate the surface of wheat roots with copper. These data were then modelled with the Langmuir equation and a copper-root binding constant was calculated. Durum wheat cultivar Arcola was grown hydroponically to the age of 21 days. These plants were then exposed to one of three copper buffered exposure solutions and sampled over 48 hours. Free copper (Cu²⁺) concentrations were 9.8 x 10^-7, 5.7 x 10^-6 and 4.6 x 10^-5 M respectively. Before exposure, plant shoots were cropped and cauterized in an attempt to limit metal translocation to the shoot but still maintain root membrane integrity. After the exposure period the root Cu content was determined using atomic absorption spectrometry (AAS). Curves were fitted to the data using SigmaPlot. Root saturation times for the 9.8 x 10^-7, 5.7 x 10^-6 and 4.6 x 10^-5 M Cu²⁺ solutions were determined to be 71, 34 and 23 hours respectively. Maximum root Cu contents were predicted to be 151, 170 and 496 g Cu / g dry root tissue. Fresh, cauterized, 21 day old seedlings were then exposed to one of 8 different solutions with Cu²⁺ concentrations ranging between 1.88 x 10^-9 and 5.02 x 10^-4 M for 96 hours. Root Cu content was again measured using AAS and Cu levels significantly exceeded maximum levels previously predicted. These data were modelled using the Langmuir equation, y = ax/1+bx, with an R square value of 0.974. From the evaluation of the equation parameters a value for the conditional root binding constant was determined.

Key words: BLM, copper, bioavailability, wheat