Plant growth regulators and fertilizer increase phytoextraction efficiency of <i>Tagetes minuta</i> under lead-contaminated soil

Soil contamination with heavy metals severely threatens food security and human health worldwide. Heavy metal contamination must be controlled through sustainable and economical technologies. To enhance the phytoextraction of lead (Pb), the plants with resistance against Pb stress and maximum production of biomass could serve as a potential candidate for the phytoremediation of Pb-contaminated soils. The current study was conducted to illuminate the effect of gibberellic acid (GA3), indole acetic acid (IAA), and fertilizers (NPK) on plant growth and Pb phytoextraction capabilities of Tagetes minuta. A pot experiment was conducted with various combinations of PGRs (GA3 and IAA) and fertilizer (NPK). Our results showed that, under Pb stress, plant growth, several physiological and biochemical parameters were significantly reduced. The exogenous foliar spray of PGRs (GA3 and IAA) and NPK alleviated this stress, leading to significant improvements in all recorded parameters. The T7 treatment (Pb + EDTA + GA3 + IAA + NPK) significantly increased the fresh and dry biomass of root (7.20 and 4.45 g pot−1) and shoot (15.93 and 9.74 g pot−1) respectively as compare to control C (without treatment) and C1 (only Pb). The photosynthetic pigment (chlorophyll) and relative water content were significantly enhanced by the combined treatment (T7 Treatment) under Pb stress. The highest chlorophyll a, b and total chlorophyll were noted in T7 treatment and these were 3.22, 2.35, and 3.02 times greater than those of C1 (Only Pb). The highest content of free proline and total phenolic contents were biosynthesized in T7 treatment as compared to control C and C1. In the case of antioxidant enzymatic activities, the maximum increase in catalase (2.38 times), superoxide (2.4 times), and peroxidase (2.21 times) were noted in T7 treatment as compared to Control C and C1. The T7 Treatment, significantly increased the phytoextraction potential of Tagetes minuta as compared to control C and C1. The maximum values of BCF (8.96), BAC (2.85) and RF (6.29%) were noted under T7 treatment (Pb + EDTA + GA3 + IAA + NPK). Tagetes minuta showed hyperaccumulation potential for Pb, based on bioconcentration factor (BCF) > 1. It is concluded from our results that exogenous application of GA3, IAA and NPK reduces Pb stress while EDTA application enhances Pb phytoextraction and ultimately the phytoremediation potential of Tagetes minuta. Further study is recommended, to investigate the role of these treatment on stress related genes expression.