Alteration of macronutrients, metal translocation and bioaccumulation as potential indicators of nickel tolerance in three Vigna species

Macronutrients (Na⁺, K⁺, Ca²⁺, Mg²⁺), yield and yield components, bioaccumulation and translocation of metal in plant parts of three <i>Vigna</i> species (<i>V. cylindrica</i>, <i>V. mungo</i>, <i>V. radiata</i>) were evaluated at 0, 50, 100 and 150 mg kg^-1 soil of Nickel (Ni). A marked inhibition (<i>p</i> < 0.001) in the distribution of various macronutrients was noticed in these <i>Vigna</i> species except for Mg²⁺ content of the shoot and leaves. Similarly, all species retained more Ca²⁺ in their roots (<i>p</i> < 0.05) as compared to the aerial tissues. Ni induced a drastic decline (<i>p</i> < 0.001) for various yield and yield attributes except for 100 seed weight. Toxicity and accumulation of Ni in plant tissues considerably increased in a concentration dependent manner. <i>Vigna</i> species signify an exclusion approach for Ni tolerance as both bioaccumulation factor (BF) and translocation factor (TF) were less than 1.0. The Ni content of plants being root > shoot > leaves > seeds. Scoring for percentage stimulation and inhibition (respective to control) at varying levels of Ni revealed tolerance of the species in an order of <i>V. radiata</i> > <i>V. cylindrica</i> > <i>V. mungo</i>. The acquisition of Ni tolerance in <i>V. radiata</i> seems to occur through an integrated mechanism of metal tolerance that includes sustainable macronutrients uptake, stronger roots due to greater deposition of Ca²⁺in the roots, restricted transfer of Ni to above ground tissues and seeds as well as exclusion capacity of the roots to bind appreciable amount of metal to them. Thus, metal tolerant potential of <i>V. radiata</i> could be of great significance to remediate metal contaminated soil owing lesser impact of Ni on macro-nutrients, hence the yield.