PHYTOCHELATIN CONCENTRATIONS AND BINDING STATE OF CD IN ROOTS OF MAIZE GENOTYPES DIFFERING IN SHOOT ROOT CD PARTITIONING

To investigate Cd binding in the root system as a possible cause of di fferential Cd distribution in maize inbred lines, Cd present in solubl e> and <insoluble pools> in roots of a <shoot Cd excluder> (B73) and a <non-shoot Cd excluder> (H98) was determined after extraction of the roots in HEPES buffer solution (pH 6.5). At a similar root Cd concentr ation (approximately 70 mug Cd g-1 dry wt.), about 49 % of the Cd conc entration in roots of H98 but 25% of that in roots of B73 was removed during extraction (<soluble pool>). The acid-soluble thiol concentrati ons in roots of the <shoot Cd excluder> B73 were much lower compared w ith those of the <non-shoot Cd excluder> H98. Exposure of B73 and H98 plants to the same Cd concentration in solution resulted in nearly equ al acid-soluble thiol concentrations in the root extracts. Binding cha racteristics of Cd to structural components of the roots (<insoluble p ool>) were similar for both maize inbreds. The relationship between tr ansport of Cd from roots to shoots and amounts of Cd complexed to acid -soluble thiol compounds in the soluble pool> of non-shoot Cd excluder s> compared with shoot Cd excluders> is discussed.