Submitted to: Silicon in Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2008
Publication Date: 10/26/2008
Citation: Li, J., Frantz, J., Leisner, S. 2008. Alleviation of Copper Toxicity in Arabidopsis Thaliana and Zinnia Elegans by Silicon Addition. Silicon in Agriculture Proceedings. 1:46.
Interpretive Summary: Copper is an essential plant nutrient and is also an active ingredient in some pesticides. Elevated doses of copper can kill plants, however. Silicon, on the other hand, is not an essential plant nutrient, but many beneficial effects on plants grown with silicon have been reported. One of these beneficial effects is reducing the toxicity of metals, but its role in reducing copper toxicity has not been reported widely. We studied the role of silicon in plant response to copper stress in the model genetic plant Arabidopsis thaliana and the floriculture crop Zinnia. Based on visible plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of a stress-induced enzyme, silicon was found to greatly reduce copper stress. Monitoring the expression of some copper-related genes indicated that, while the genes had more expression in toxic copper conditions, the expression of the genes were greatly reduced when silicon and copper were present at the same time. Taken together, our findings indicate that silicon addition can improve the resistance of some plants to Cu stress, and this improvement operates on multiple levels ranging from whole plant symptoms to changes in gene expression. If this improved tolerance to elevated copper levels is similar in additional crop plants, the use of silicon may allow copper-containing pesticides to be used more effectively in crop production.
Technical Abstract: While the role of silicon in plants has been studied for over 150 years, and this element can mitigate the effects of certain heavy metals, its role in Cu metabolism is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in Arabidopsis thaliana L. (Heyn) and Zinnia elegans L. Si was found to mitigate Cu toxicity stress based on plant symptoms and reduced PAL (phenylalanine ammonia lyase, EC 126.96.36.199) activity, a stress-induced enzyme, in both arabidopsis and zinnia. However, the effects of silicon on Cu stress in zinnia were not as dramatic as those on arabidopsis. Real-time reverse transcriptase-PCR indicated that the RNA levels of two arabidopsis copper transporter genes, COPT1 (copper transporter 1) and HMA5 (heavy metal ATPase subunit 5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of plants to Cu stress, and this improvement operates on multiple levels ranging from physiological changes to alterations of gene expression.