Attenuation of mercury phytotoxicity with a high nutritional level of nitrate in alfalfa plants grown hydroponically

Abstract

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. Nitrate (NO3

–

) is the prevalent form to

incorporate nitrogen (N) in higher plants, through its reduction to nitrite (NO2

–

) by the enzyme nitrate reductase

(NR). 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. Several parameters of oxidative stress such as lipid peroxidation, chlorophyll content, biothiol concen tration, and ascorbate peroxidase (APX) and glutathione reductase (GR) activities showed that HN plants were

less affected by Hg. Nitrate reductase activity and NO3

– concentration were also altered under Hg stress, with

lower impact in plants nourished with high NO3

–

. Our results highlight the importance of the NO3

– nutritional

status to improve tolerance to toxic metals like Hg