Lead- and Nickel-Induced Heavy-Metal Toxicity in Vigna mungo L. Seedlings and Detoxification through Exogenous Nitrogen Application

Heavy-metal stress is one of the major stresses affecting plant growth and productivity globally. In order to improve the yields of plants, growing under heavy-metal stress became remarkably important for sustainable agriculture. Plants experience oxidative stress upon exposure to heavy metals that lead to cellular damage. In addition, plants accumulate metal ions that disturb cellular ionic homeostasis. This experiment was undertaken with an objective to determine how the rate of seed germination, seedling growth and leaf area is influenced by various concentrations of heavy metals, lead and nickel at 10, 50 and 100 µM/L concentration in black gram (Vignamungo L.) seedlings. These concentrations significantly affect all these parameters. Lower concentration, that is, 10 µM/L of lead and nickel showed less affect than high concentration, that is, 50 and 100 µM/L. Shoot length was more affected than the root length in Vignamungo seedlings. Nickel showed more toxic effect than lead at all the aforementioned concentrations as compared to control. However, the addition of 5 mM/L nitrogen (ammonium nitrate) to the plants somehow minimised the effect and was beneficial to the plants. This study suggests that cultivation of Vignamungo in toxic soils having heavy metals should be avoided or appropriate control measures be adopted to maintain the heavy metal content of the soil below the damaged (threshold) level, for this nitrogen may be used as a good detoxifier.