Nickel and Copper Toxicity in Deschampsia Cespitosa: Analysis of Morphological Changes and Gene Expression.

The Greater Sudbury Region (GSR) in Northern Ontario is recognized for its nickel, copper and other metal deposits. Deschampsia cespitosa can colonize and flourish in metal-contaminated areas due to its stress adaptations. Recent analyses have demonstrated that D. cespitosa is a metal-excluder, as it stores high levels of elements in its roots with limited translocation to aerial tissues. Detailed analysis of the D. cespitosa response to soil metal contamination is lacking. The main objectives of the present study are to assess metal toxicity levels and the extent of global DNA methylation in D. cespitosa growing in metal-contaminated soil. For the field study, root and leaf samples were collected from metal-contaminated and reference sites. Cytosine methylation was measured using tandem mass spectrometry (MS/MS) coupled with liquid chromatography (LC-MS/MS). Nickel toxicity was also analyzed under controlled conditions. Seeds were collected from individuals on two contaminated sites and grown until an average height of 20 cm. Plants were split into four groups and treated respectively with a control (0 mg/kg) and three nickel nitrate doses (5.6 mg/kg, 1600 mg/kg and 4800 mg/kg) for seven days. Damage rating and root and leaf biomass were recorded to determine nickel effect on plant aspect and growth. Significant variation in global methylation within and among populations was found. No association between global DNA methylation and metal contamination was established. Significant differences for damage rating, root and leaf biomass were observed between the 1600 mg/kg (total Ni) and the 5.6 mg/kg (bioavailable Ni) treatment. The latter dose did not cause any observable damage. The 4800 mg/kg treatment was extremely toxic; all plants were dying within 48 hours after treatment. The regulation of tolerance genes associated with Ni is being assessed using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Future studies will include transcriptome analysis and novel gene identification.