Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2000
Publication Date: 6/14/2000
Citation: CAKMAK, I., WELCH, R.M., ERENOGLU, B., ROMHELD, V., NORVELL, W.A., KOCHIAN, L.V. INFLUENCE OF VARIED ZINC SUPPLY ON RE-TRANSLOCATION OF CADMIUM (109 CD) ANDRUBIDIUM (86 RB) APPLIED ON MATURE LEAF OF DURUM WHEAT SEEDLINGS. PLANT AND SOIL JOURNAL. 2000. v. 219. p. 279-284. Interpretive Summary: Cadmium can be toxic to humans if consumed in excessive amounts; several international organizations are currently developing Cd-limits for certain food crops to limit importation of high-Cd crops in international markets. Wheat grain can accumulate relatively high levels of Cd if the mother plant is propagated on high-Cd soils, especially durum wheats grown in certain regions of the northern USA which have naturally occurring high-Cd soils. Therefore, significantly decreasing high-Cd levels in durum 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 durum grain trade. We studied the effect of increasing Zn supply on the movement of Cd within wheat seedlings in order to understand the physiology of Cd movement within durum wheats. Our results demonstrate that increasing Zn supply can significantly reduce the amount of Cd translocated from shoots to roots. These results imply that the inhibitor action of increased Zn supply on Cd re-translocation in durum wheat seedlings is mediated by ZnxCd interactions during phloem sap loading. Strategies to reduce phloem loading of Cd are being sought.
Technical Abstract: Effect of varied Zn supply (0, 0.1. 1. 5 uM) on re-translocation of radio-labeled Cd and Rb from mature leaf to root and other parts of shoot was studied in 11-d-old durum wheat (Triticum durum cv. C-1252) seedlings grown in nutrient solution. Applications of radio-Cd & radio-Rb was via immersing tips (3 cm) of mature leaf in radio-labeled solutions for 10 s at tthree different times over a 42 h period. Differences in Zn supply for 11 did not affect plant growth nor cause visual leaf symptoms at either the lowest or the highest Zn supply. Only at the nil Zn supply (0 uM), shoot & root mass tended to decrease & increase, respectively, causing a lower shoot/root mass ratio. Partitioning of more mass to roots than shoots, indicated existence of a mild Zn deficiency stress at the nil-Zn treatment. Irrespective of Zn supply, plants could re-translocate 3.8% & 38% of the total absorbed radio-Cd & radio-Rb from the treated leaf to roots & other parts of shoots within 42 h, respectively. At nil-Zn, 2.8% of the total absorbed radio-Cd was re-translocated from the treated leaf, particularly into roots. The highest re-translocation of radio-Cd (6.5%) was found in plants supplied with 0.1 uM Zn. Increases in Zn supply reduced radio-Cd re-translocation from 6.5% to 4.3% at 1 uM Zn & 1.3% at 5 uM Zn. With the exception of the nil-Zn treatment, the proportion of re-translocated radio-Cd was greater in remainder of shoot than roots. Contrary to the radio-Cd results, re-translocation of radio-Rb was not (at 0, 0.1, & 1 uM Zn) or only slightly (at 5 uM) affected by changing Zn supply. Thus, increased Zn supply may inhibit Cd re-translocation by inhibiting Cd phloem sap loading.