Effects of zinc fertilization on grain cadmium accumulation, gene expression, and essential mineral partitioning in rice

Authors: TAVAREZ, MICHAEL - Lehman College; Grusak, Michael; SANKARAN, RENUKA - Lehman College

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2022
Publication Date: 9/14/2022
Citation: Tavarez, M., Grusak, M.A., Sankaran, R.P. 2022. Effects of zinc fertilization on grain cadmium accumulation, gene expression, and essential mineral partitioning in rice. Agronomy. 12. Article 2182. https://doi.org/10.3390/agronomy12092182.
DOI: https://doi.org/10.3390/agronomy12092182

Interpretive Summary: Cadmium is a toxic heavy metal that can cause health issues in humans if ingested in foods. Because rice is an important staple food crop and it’s known that some rice varieties can accumulate high levels of cadmium in grains, strategies are needed to reduce cadmium levels in rice. Thus, experiments were conducted to increase our understanding of how the transport of cadmium is regulated throughout the rice plant, especially in relation to other absorbed metals, such as the essential micronutrient, zinc. Rice plants were grown with or without cadmium and were fertilized with two levels of zinc. Results showed that external cadmium had no effect on zinc accumulation in grains, but higher external zinc increased grain cadmium levels in two of three varieties. This research demonstrates that zinc fertilization of rice, to enhance yield or grain zinc levels, may have negative consequences if cadmium is present in the soil and if the rice variety being grown has a capacity to accumulate cadmium.

Technical Abstract: Cadmium (Cd) is a toxic heavy metal that can cause severe health issues if ingested. Certain varieties of rice can accumulate high levels of the metal in edible tissues thereby transferring the toxin into the food chain. As chemical analogs, interactions between the essential mineral zinc and the toxic heavy metal cadmium play an important role in regulating the transport of both minerals to rice grains. Understanding these interactions is crucial for limiting cadmium and increasing zinc transfer to the food chain. Previous studies have reported conflicting results suggesting synergistic and antagonistic relationships between the minerals. The goal of this work was to identify the effect of external cadmium and zinc on the uptake and translocation of both minerals from roots to grains of rice that differ in grain cadmium concentrations. The results showed that a higher input of external zinc increased cadmium translocation and accumulation to the grain in two of three varieties, while external cadmium does not influence zinc accumulation. Cadmium synergy and antagonism with other essential minerals were also examined and the effects differed between rice lines. Our results showed that the differential expression of the transport proteins OsNramp5, OsHMA2, and OsHMA3 as well as genes involved in the synthesis of glutathione and phytochelatin could have contributed to differences in grain Cd accumulation. These results add to the knowledge of cadmium and zinc partitioning in one of the most consumed plant foods in the world and can assist fortification efforts to establish rice lines that are both safe and nutritious.