High Level of Nicotianamine Synthase (NAS3) and Natural Resistance Associated Macrophage Protein (NRAMP4) Gene Transcription Induced by Potassium Nitrate in Trembling Aspen (Populus tremuloides)

Changes in gene transcription in response to excess metal concentrations have been reported in many organisms, including yeast, microorganisms and plants. Most investigations on the effects of nickel toxicity in plants use commercial salts whose effects have not been analyzed in detail. The main objective of the present study was to determine the effects of different doses of nickel nitrate and potassium nitrates on gene transcription in Populus tremuloides. Four month-old P. tremuloides seedlings were treated with different doses of nitrate salts including 150 mg/kg, 500 mg/kg, 800 mg/kg and 1, 600 mg/kg. A significant increase of Nicotianamine Synthase (NAS3) gene transcription was induced by the 400 mg/kg and 800 mg/kg of nickel nitrate doses compared to water. This upregulation was driven by nitrate rather than nickel. Likewise, the 800 mg/kg and 1,600 mg/kg doses of potassium nitrate resulted in significant increase in the transcription of Natural Resistance Associated Macrophage Protein (NRAMP4) gene compared to water control and the 150 mg/kg dose. This differential transcription of this gene was caused by potassium. Our results also confirmed that the low level of bioavailable nickel in metal–contaminated soils (<150 mg/kg) cannot induce differential transcription of NAS3 and NRAMP4. The use of nitrate without nickel should be required as additional controls in any study assessing effects of Ni using nickel nitrate salts.