Silicon alleviates long-term copper toxicity and influences gene expression in Nicotiana tabacum

Authors: FLORA, CHRISTOPHER - University Of Toledo; KHANDEKAR, SUSHANT - University Of Toledo; Boldt, Jennifer; LEISNER, SCOTT - University Of Toledo

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2018
Publication Date: 3/27/2019
Publication URL: https://handle.nal.usda.gov/10113/6368293
Citation: Flora, C.S., Khandekar, S., Boldt, J.K., Leisner, S. 2019. Silicon alleviates long-term copper toxicity and influences gene expression in Nicotiana tabacum. Journal of Plant Nutrition. 42(8):864-878. https://doi.org/10.1080/01904167.2019.1589508.
DOI: https://doi.org/10.1080/01904167.2019.1589508

Interpretive Summary: Environmental stress such as heavy metal toxicity can significantly decrease crop yields. Toxic metals accumulate in soils due to fertilizer and pesticide application, along with industrial pollution, and excess levels of essential micronutrients such as copper (Cu) can be phytotoxic. Silicon (Si) supplementation is beneficial for plant growth, and aids in abiotic and biotic stress tolerance. In this study, we evaluated the ability of Si to alleviate long-term Cu toxicity in the low Si accumulator Nicotiana tabacum (tobacco). The addition of Si to the hydroponic nutrient solution alleviated growth inhibition in roots and shoots of tobacco plants exposed to Cu toxicity. In addition, it correlated with increased Si accumulation in both roots and foliar tissue. However, Cu levels declined in roots but remained elevated in leaves. The expression of Cu transporter genes was reduced, and ethylene synthesis is favored when tobacco roots under extended Cu stress are supplemented with Si. Taken together, we hypothesize Si may regulate components of Cu homeostasis, ethylene production, and polyamine production to aid in stress alleviation. Furthermore, our findings may serve as the foundation for extensive genomic, proteomic, and metabolomic investigation of Si involvement in these pathways.

Technical Abstract: Silicon (Si) is beneficial for plant growth, and aids in abiotic and biotic stress tolerance. In this study, we evaluated the ability of Si to alleviate long-term heavy metal (Copper; Cu) toxicity in the low Si accumulator Nicotiana tabacum. Si addition alleviated growth inhibition in roots and shoots of tobacco plants exposed to Cu toxicity. In addition, Si-mediated Cu toxicity alleviation correlated with increased Si accumulation in both roots and foliar tissue. Furthermore, Cu levels remained elevated in leaves, but declined in roots. Therefore, we examined root mRNA levels of several genes involved in Cu homeostasis. Cu Transporter 1 (COPT1) and Metallothionein 2 (MT2) expression was reduced in plants supplemented with Si while under Cu toxic conditions. Recently, ethylene (ET) and polyamine synthesis were implicated in Si-mediated drought resistance. To determine if Si could affect ET and polyamine biosynthesis, we investigated mRNA levels of several biosynthetic genes within each metabolic pathway. Our findings suggest ET synthesis is favored when tobacco roots under extended Cu stress are supplemented with Si.