Uptake and retranslocation of leaf-applied cadmium (Cd-109) in diploid, tetraploid and hexaploid wheats

Uptake and retranslocation of leaf-applied radiolabelled cadmium (Cd-109) w as studied in three diploid (Triticum monococcum, AA), four tetraploid (Tri ticum turgidum, BBAA) and two hexaploid (Triticum aestivum, BBAADD) wheat g enotypes grown for 9 d under controlled environmental conditions in nutrien t solution. Among the tetraploid wheats, two genotypes were primitive (ssp. dicoccum) and two genotypes modern wheats (ssp. durum), Radiolabelled Cd w as applied by immersing the tips (3 cm) of mature leaf into a Cd-109 radiol abelled solution. There was a substantial variation in the uptake and expor t of Cd-109 among and within wheat species. On average, diploid wheats (AA) absorbed and translocated more Cd-109 than other wheats. The largest varia tion 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 amou nt of the Cd-109 exported from the treated leaf into the roots and the rema inder 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 an d retranslocation of leaf-applied Cd-109. This variation is discussed in te rms of potential genotypic differences in binding of Cd to cell walls and t he composition of phloem sap ligands possibly affecting Cd transport into s ink organs.