Nanomaterial-induced modulation of morpho-physio-biochemical attributes and enhancement of anticancer compounds in Tagetes erecta L. callus cultures

Seeds of Tagetes erecta L. (Asteraceae) variety sweet orange were inoculated on half-strength Murashige and Skoog (MS) basal medium. Seedling-derived hypocotyl and leaf explants were cultured on MS media supplemented with different concentrations (0.5-3 mg L-1) of plant growth regulators to induce callus. Among both the explants, leaf exhibited superior callus induction compared to hypocotyl explants on the optimized medium containing BAP (1.5 mg L-1) and NAA (1 mg L-1). The optimized medium was subsequently supplemented with nanomaterials (NMs) like zinc oxide nanoparticles (ZnONPs), silicon dioxide nanoparticles (SiO2NPs), and multi-walled carbon nanotubes (MWCNTs) along with their respective bulk materials at different concentrations (2-16 mg L-1). The results indicated that NM treatments evoked notable changes in morpho-physio-biochemical parameters compared to bulk materials, with MWCNTs showing the highest efficacy. The maximum biomass (5216±25.88 mg FW and 268±15.78 mg DW) was recorded at 8 mg L-1 MWCNTs. At this concentration, biochemical parameters were also highest, including chl a (15.61±0.10 µg g-1 FW), chl b (7.91±0.20 µg g-1 FW), total chl (23.53±0.23 µg g-1 FW), and carotenoids (27.53±0.63 µg g-1 FW) in dimethyl sulfoxide (DMSO) extract, total soluble sugar (6.30±0.12 mg g-1 FW), proline (0.38±0.009 µM g-1 FW), free radical scavenging activity (70.49±0.12%), total phenolics (6.61±0.02 µg GAE g-1 FW), and total flavonoids (13.16±0.25 µg QE g-1 FW). Moreover, this treatment also significantly increased antioxidant enzyme activities, including superoxide dismutase (SOD; 726.71±0.08 U g-1 FW), guaiacol peroxidase (GPX; 4.82±0.03 µM min-1 g-1 FW), catalase (CAT; 457.56±0.56 µM min-1 g-1 FW) and polyphenol oxidase (PPO; 10.06±0.09 nM min-1 g-1 FW). Concurrently, MWCNTs significantly reduced malondialdehyde (MDA; 13.48±0.11 nM g-1 FW) and hydrogen peroxide (H2O2; 12.98±0.16 nM g-1 FW) levels. Furthermore, NM treatments markedly enhanced lupeol yield to 186.835±1.58 µg g-1 DW (53.14-fold higher as compared to control) at 2 mg L-1 MWCNTs, and β-sitosterol yield to 22.093±0.08 µg g-1 DW (2.23-fold higher as compared to control) at 4 mg L-1 SiO2NPs. Correlation analysis revealed distinct variations among the measured parameters depending on the NM treatments. Overall, the present study provides a basis for large-scale production of these anticancer compounds and paves the way for elucidating metabolic pathways and nanomaterial-mediated metabolic engineering in this valuable plant.