Global DNA Methylation in Canadian Red Maple (Acer rubrum) in Northern Ontario (Canada): Association with Soil Cation Exchange Capacity (CEC) and Metal Contamination.

The Greater Sudbury Region (GSR) is known for an abundance of nickel (Ni), copper (Cu) and various other metal deposits. Recent studies revealed high enrichment factors for these metals between metal-contaminated and reference sites. Red maple (Acer rubrum) copes with soil metal contamination by not storing Ni, Cu, and Zn in its tissues.  Analysis of the effects of metals at molecular level is lacking. The main objective of the present study was to assess molecular changes in red maple populations growing in metal contaminated areas. The exchangeable cations were quantified by ICP-MS analysis of ammonium acetate (pH 7) extracts of soil samples with the total exchange capacity being estimated as the sum of the exchangeable cations. Cytosine and adenine methylations were measured using tandem mass spectrometry (MS/MS) coupled with LC (LC-MS/MS) in A. rubrum populations from metal- contaminated and uncontaminated sites. There were significantly lower levels of cation exchange capacities in metal-contaminated sites compared to reference uncontaminated areas. In general, global modified cytosine ratios in genomic DNA revealed a decrease in cytosine methylation in metal-contaminated sites compared to uncontaminated populations. But  A. rubrum genotypes from one site were recalcitrant to metal-induced DNA alterations even after  more than 30 years of exposure to nickel and copper. Comparative analysis of DNA methylation with other trembling aspen (Populus tremuloides) and red oak (Quercus rubra) populations will be discussed.