Morpho-physiological attributes, antioxidant activities, proximate seed analysis, and phytoremediative prospective of two castor bean genotypes in lead spiked soil

Abstract

Anthropogenic activities like mining, smelting, and the use of batteries and paints discharge heavy metals, particularly lead (Pb), into the soil. Castor bean (Ricinus communis L.), a non-edible oil seed crop, demonstrated a considerable aptitude for phytoremediation of heavy metal contaminated soils. Furthermore, environmentally sustainable attributes and economic benefits of castor bean are attracting the attention of researchers. Hence, the current study evaluated the phytoremediation capabilities of two castor bean genotypes (NIAB-2020 and DS-30) on Pb-contaminated soil (400 and 800 mg/kg) until physiological maturity in a pot study under greenhouse conditions. Results indicated that plant agronomic traits, including plant height, biomass, root length, leaf number, and leaf area, declined under Pb stress. Physiological parameters, such as relative water content, stomatal conductance, transpiration rate, and photosynthetic activity, also decreased, while electrolyte leakage increased. Total activity of antioxidants like superoxide dismutase (SOD) and peroxidase (POD) were declined; however, catalase (CAT) and ascorbate peroxidase (APX) increased in both castor genotypes. Additionally, osmolytes content like total soluble proteins (TSP) and total free amino acids (TFA) were decreased, while total soluble sugars (TSS) and total phenolic content (TPC) increased under Pb stress. Metal uptake response in the roots and shoots exhibited a significant capacity for Pb accumulation, demonstrating effectiveness of castor bean in reducing Pb concentration. Proximate seed analyses showed a slight reduction in seed quality at 400 and 800 mg/kg, while Pb concentration remained undetected. Consequently, this study underscores the capability of castor bean as a viable entrant for restoring the soils contaminated with Pb.