Attenuation of Mercury Phytotoxicity with a High Nutritional Level of Nitrate in Alfalfa Plants Grown Hydroponically

Abstract Background and aims Mercury (Hg) is one of the most dangerous pollutant heavy metals to the environment, which causes several toxic effects in plants upon accumulation, such as induction of oxidative stress. Nitrogen (N) is one of the most limiting macronutrient for plants, being mostly assimilated as NO3─ which is reduced to NO2─ by the enzyme nitrate reductase (NR), prior its reduction to NH4+.Methods We studied the physiological alterations caused by Hg (0, 6 and 30 µM) in alfalfa plants grown at two different levels of NO3─: low, (2 mM; LN), and high (12 mM; HN) for one week using a semi-hydroponic culture system.Results Several parameters of oxidative stress such as lipid peroxidation, chlorophyll content, biothiol concentration and, ascorbate peroxidase (APX) and glutathione reductase (GR) activity showed that HN plants were less affected by Hg. Nitrate reductase activity and NO3─ concentration was altered under Hg stress, with lower impact in plants nourished with high NO3─. Conclusions Our results highlight the importance of the nitrogen nutritional status to improve tolerance to toxic metals like Hg.