An investigation on reduction capability of lead and its influence on withanolides in in vitro shoots of Withania somnifera (L.) Dunal.

• The present study exerted heavy metal (Lead) accumulation and translocation capability of Withania somnifera shoots under lethal and non-lethal doses of Lead • In planta synthesis of Lead nanoparticles indicates that the presence specialized detoxification, sequestration and reduction mechanism in in vitro shoot cultures of Withania somnifera • Adsorption and translocation of Lead to aerial parts (stems and leaves) of the cultures was facilitated by liquid culture medium, and the addition of plant growth regulator (BAP), chelating agent (EDTA) and other mineral ions (Mg2+, K2+, Ca2+ and others) in the growth medium • Shoots exposed to non-lethal doses of Pb (800 µM) over prolonged period (12 days), significantly increased biomass and secondary metabolite (withanolides) production. Green synthesis of nanoparticles using biological extracts/live organisms has been the best substitute for chemical/physical synthesizing methods. Live plants can convert simple metal ions into metal nanoparticles using their intrinsic metabolic processes. In addition, medicinal plants with a hyperaccumulation potential also have high reduction potential which can be utilized for in planta synthesis of metal nanoparticles. Lead (Pb), a non-essential heavy metal, is known to stimulate various biological processes in plants at higher concentrations. Therefore, a medicinal plant with a hyperaccumulation potential was selected to investigate its potential for in planta reduction of Pb. In the present study, in vitro grown 45 days old Withania somnifera (L.) Dunal shoots were exposed to lead acetate (PbAC 2) at varying concentrations (acute: 300–4800 µM; chronic: 50–800 µM) for 12–48 h and 4–12 days, respectively. It revealed that cultures grown in 800 µM PbAC 2 for 12 days of exposure (C5) recorded significantly higher biomass (17.28 g) and increase in the divalent metal ions such as calcium from 1412 (control) to 1787 mg kg-1 (C5), potassium 21,109 (control) to 24,779 mg kg-1 (C5), and iron from 11 (control) to 82 mg kg-1 (C5), with lead (Pb) accumulation reaching up to 405 mg kg-1 (C5). Compared to the control shoots (0.783, 0.805 & 1.3 mg g-1), C5 shoots positively correlated with secondary metabolites namely withaferin A (3.14 mg g-1) and withanolide A (0.960 mg g-1) production and negatively with withanone (1.027 mg g-1). Also, C5 shoots had spherical shaped nanoparticles with a mean particle size of 25±10 nm which was then identified as lead nanoparticles (PbNPs). To our knowledge, the present study is the first of its kind where the in planta synthesis of PbNPs/PbONPs by in vitro shoot cultures of W. somnifera is reported along with accumulation of higher biomass and selective withanolides under Pb stress. [ABSTRACT FROM AUTHOR]