Absorption and translocation of Cd in bush beans (Phaseolus vulgaris)

Abstract

A series of experiments was conducted to examine some factors affecting the absorption and translocation of Cd in young bean plants (Phaseolus vulgaris L. cv. Bulgarian). Absorption of Cd by roots was reduced in the presence of other cations of increasing valency or ionic radii. Reduced absorption was also found in the presence of EDTA. Concentration of Cd in exudates from excised stems increased with increased passage of Cd solutions and approached the concentration in the external medium (4.5 μM Cd). This was apparently associated with saturation of adsorption sites in the stems. The stem behaved as a cation exchange column resulting in a chromatographic distribution of Cd towards the top of the plant. These experiments indicate that Cd existed in the xylem fluid as a free or weakly complexed cation. Additional experiments showed that the total amount of Cd absorbed by bean plants was elevated by inducing higher transpiration rates. The effect of water flux on Cd transport indicated apoplastic flow to the stele.