Root cadmium desorption methods and their evaluation with compartmental modeling

P>Desorption of plant roots is often employed in studies of plant physiology and nutrition; however, there have been few studies on the validity of desorption procedures. Branched and in-line kinetic models with five compartments - cadmium (Cd)-chelate, Cd2+, root apoplast, root symplast and vacuole - were developed to evaluate the efficacy of diethylenetriaminepentaacetic acid (DTPA) and CaCl(2) methods for the desorption of Cd from roots of durum wheat seedlings. Solution Cd2+ could exchange with apoplast and symplast Cd simultaneously in the branched model and sequentially in the in-line model. A 10-min desorption with 1 x 10-6 M DTPA at room temperature or cold (0 degrees C) 5 x 10-3 M CaCl(2) was required to achieve 99% recovery of apoplast-bound 109Cd when experimental results were interpreted with the branched model. However, when the same data sets were analysed with the in-line model, only partial desorption was achieved. Arguments are presented that suggest that the branched model is correct. It is suggested that compartmental modeling is a suitable tool for the study of plant root uptake and desorption kinetics, and that there are advantages over more commonly used calculation procedures.