Uptake and retranslocation of leaf-applied radiolabelled cadmium (Cd-109) was studied in three diploid (Triticum monococcum, AA), four tetraploid (Triticum turgidum, BBAA) and two hexaploid (Triticum aestivum, BBAADD) wheat genotypes grown for 9 d under controlled environmental conditions in nutrient solution. Among the tetraploid wheats, two genotypes were primitive (ssp. dicoccum) and two genotypes modern wheats (ssp. durum), Radiolabelled Cd was applied by immersing the tips (3 cm) of mature leaf into a Cd-109 radiolabelled solution. There was a substantial variation in the uptake and export of Cd-109 among and within wheat species. On average, diploid wheats (AA) absorbed and translocated more Cd-109 than other wheats. The largest variation in Cd-109 uptake was found within tetraploid wheats (BBAA), Primitive tetraploid wheats (ssp, dicoccum) had a greater uptake capacity for Cd-109 than modern tetraploid wheats (ssp, durum), In all wheats studied, the amount of the Cd-109 exported from the treated leaf into the roots and the remainder of the shoots was poorly related to the total absorption, For example, bread wheat cultivars were more or less similar in total absorption, but differed greatly in the amount of Cd-109 retranslocated. The diploid wheat genotype 'FAL-43' absorbed the lowest amount of Cd-109, but retranslocated the greatest amount of Cd-109 in roots and remainder of shoots, The results indicate the existence of substantial genotypic variation in the uptake and retranslocation of leaf-applied Cd-109. This variation is discussed in terms of potential genotypic differences in binding of Cd to cell walls and the composition of phloem sap ligands possibly affecting Cd transport into sink organs.
