Location: Adaptive Cropping Systems LaboratoryTitle: Lack of Zn inhibition of Cd accumulation by rice (Oryza sativa L.) supports non-Zn transporter uptake of Cd Author
|Bouwkamp, Jon - University Of Maryland|
Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2015
Publication Date: 12/28/2016
Citation: Green, C.E., Chaney, R.L., Bouwkamp, J. 2016. Lack of Zn inhibition of Cd accumulation by rice (Oryza sativa L.) supports non-Zn transporter uptake of Cd. Journal of Plant Nutrition. 40:869-877.
Interpretive Summary: Excessive cadmium (Cd) accumulation in rice on contaminated fields in Asia has caused human Cd disease, so understanding the mechanism used by rice in accumulating Cd compared to other plant species may help identify management or breeding approaches to lower risk from Cd thru rice. Our previous work showed that even when soils had 100-times more Zn than Cd and were highly contaminated by Zn mine wastes, rice grain Zn was not increased while grain Cd was greatly increased. Recently it has been reported that rice absorbs Cd on its Mn2+ transporter in roots while other plant species (wheat, lettuce, spinach, sunflower) have been shown to absorb Cd on their Zn2+ transporters. In this study we tested the ability of increased soluble Zn2+ up to phytotoxic levels on absorption of Cd by rice. We used chelator-buffered nutrient solutions to provide highly controlled chemical activity of Cd2+ ion, and controlled and varied levels of Zn2+. These results confirm that Zn does not inhibit Cd accumulation in rice at levels of Cd which cause excessive Cd absorption by rice in the field, explaining why high soil Zn did not protect subsistence rice farm families from Cd disease when their rice crops were grown on mine waste contaminated rice soils, while persons consuming other crops and garden foods have not been harmed by soil Cd.
Technical Abstract: Rice (Oryza sativa L.) grown on Cd contaminated soils has been linked to health problems in subsistence rice farmers in Japan and China. For other crops, normal geogenic Zn inhibits the increased uptake of Cd on contaminated soils. A study was conducted using a multi-chelator buffered nutrient solution (EGTA for all the cationic micronutrients except Fe; Ferrozine for Fe2+) to characterize the interaction of Zn and Cd in uptake and translocation of Cd in 'Lemont' rice. The activity of free Zn2+ was varied from 10-7.6 to 10-5.2 M, while activity of free Cd2+ was held constant at 10-10.7 M. Zinc free activity 10-5.6 M and higher were phytotoxic to rice, resulting in severe chlorosis, reduced growth of roots and shoots, and an increase in Cd concentration in the shoots. In contrast to previous studies with wheat, lettuce and spinach, free Zn2+ maintained at adequate to sub-phytotoxic levels (10-7.6 to 10-6.1) did not inhibit Cd uptake by the rice plants. Increased Cd slightly reduced shoot Mn levels, in agreement with recent evidence that Cd is accumulated on the NRAMP5 of rice, a Mn transporter rather than the ZIP1 high affinity Zn transporter previously believed to transport Cd2+ in rice and other species.