Submitted to: Journal of Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/1/2000
Publication Date: 2/1/2000
Citation: CAKMAK, I., WELCH, R.M., HART, J.J., NORVELL, W.A., OZTURK, L., KOCHIAN, L.V. UPTAKE AND RE-TRANSLOCATION OF LEAF-APPLIED CADMIUM (109 CD) IN DIPLOID, TETRAPLOID AND HEXAPLOID WHEATS. JOURNAL OF EXPERIMENTAL BOTANY. 2000. v. 51. p. 221-226. Interpretive Summary: Cadmium can be toxic to humans if consumed in excessive amounts. Wheat grain can accumulate relatively high levels of Cd if the mother plant is propagated on high-Cd soils; naturally occurring high-Cd soils are found in certain regions USA including some western states and in some northern western states. The UN's Codex alimentarius committee is currently reviewing limits to Cd in wheat grain for international trade. Some of th durum wheat currently produced in the USA may not meet the new limits being suggested. Therefore, significantly decreasing high-Cd levels in wheat grain harvested from these areas would allow the continued shipment of durum wheat products to international markets that in the future may put in place Cd limits on wheat grain trade. We studied the uptake and re-translocation of Cd in different wheat genotypes (including several diploid, tetraploid, and hexaploid genotypes). There was substantial variation in the uptake and export of Cd among and within wheat species. Total Cd absorption was poorly correlated to Cd re-translocation from older leaves to newer leaves and roots. The diploid wheat genotype 'FAL-43' absorbed the lowest amount of Cd, but re-translocated the most Cd to roots and young leaves. These results show that there is substantial genotypic variation in the uptake and re-translocation of Cd in wheat species and these differences can be exploited to decrease the amount of Cd accumulated in wheat grain.
Technical Abstract: Uptake and re-translocation of leaf-applied radio-Cd was studied in three diploid (Triticum monococcum, AA) four tetraploid (Triticum turgid, 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 were modern wheats (ssp. durum). Radio-labeled Cd was applied via immersing the tips (3 cm) of mature leaf into a radio-Cd labeled solution. There was a substantial variation in the uptake and export of radio-Cd among and within wheat species. On average, diploid wheats (AA) absorbed and translocated more radio-Cd than other wheats. The largest variation in radio-Cd; uptake was found within tetraploid wheats (BBAA). Primitive tetraploid wheats (ssp. dicoccum) had a greater uptake capacity for radio-Cd than modern tetraploid wheats (ssp. durum). In all wheats studied, the amount of radio-Cd exported from the treated leaf into the roots and the remainder of 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 radio-Cd re-translocated. The diploid wheat genotype 'FAL-43' absorbed the lowest amount of radio-Cd, but re-translocated the greatest amount of radio-Cd to roots and remainder of shoots. The results indicate the existence of substantial genotypic variation in the uptake and re-translocation of leaf-applied radio-Cd. 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 phloem sink organs.