A comprehensive study of the hormetic influence of biosynthesized AgNPs on regenerating rice calli of indica cv. IR64.

Rice is one of the most widely cultivated crops worldwide; however, it is not amenable to genetic manipulations, owing to its poor response to tissue culture and regeneration in vitro. To improve its response to tissue culture, we evaluated the influence of biosynthesized silver nanoparticles on callus induction, regeneration and rhizogenesis in Indica rice cv. IR64. Silver nanoparticles were biosynthesized by using silver nitrate and Parthenium hysterophorus plant extract, and were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy, Transmission electron microscopy and X-ray diffraction. The biosynthesized silver nanoparticles (PHAgNPs), when supplemented in tissue culture medium, promoted callus induction frequency, callus regeneration and rhizogenesis at concentrations of 10 mg l ^-1, 5 mg l^-1 and 10 mg l^-1, respectively. Further examination of the endogenous hormonal levels in regenerating calli revealed that AgNPs enhanced regeneration by alleviating abscisic acid and ethylene levels in the plant tissue. The stimulatory influence eliciting the regeneration response was found to be optimal with the supplementation of 5 mg l^-1 PHAgNPs in the regeneration medium; the malondialdehyde, proline and hydrogen peroxide levels were also lower than those in the control, thus suggesting improved antioxidant status. Our results indicated that biosynthesized PHAgNPs may have the potential to positively influence tissue culture of recalcitrant varieties.