Metallic nanoparticles are very useful, effective, and usually synthesized by toxic and expensive chemicals. Silver nanoparticles (AgNPs), measuring less than 100 nm, have shown promising impact in several biomedical investigations. These can inhibit microbial growth and aid in medicine administration. Six substrates of Carica papaya were used to synthesize silver nanoparticles that can limit the growth of bacteria and fungi. In this article, we report the synthesis of AgNPs from the leaf, seed, callus, peel, fruit juice, and bark of Carica papaya. AgNPs synthesized from callus showed the most promising results when tested against the growth of bacteria like Xanthomonas campestris, Erwinia carotovera, Bacillus subtilis, and fungi (Aspergillus niger and Fusarium oxysporum) when compared with other extracts’ efficacy, and the callus was regenerated from petiole and midrib explants of Carica papaya in MS basal media supplemented with NAA and Kinetin (1 + 0.5 mg/L). A ratio of 1:20 of substrate extract to 1 mM AgNO₃ produced the most effective nanoparticles in terms of capping, quality, and stability when tested through surface plasmon resonance (SPR) within the 400–435 nm range. The nanoparticle sizes of all six types were measured using Image J software on micrographs of SEM at 200 nm resolution. The average diameters were analyzed through Origin software, and the finest AgNPs were observed to be synthesized from callus extract, i.e., 18.91 nm with rod-like morphology. Energy dispersive X-ray (EDX) at 2.6 keV revealed 43.38, 75.39, 70.611, 36.54, 58.57, and 45.94 percent elemental silver in AgNPs formed from the leaf, callus, juice, seed, bark, and peel extract, respectively. Silver nanoparticles synthesized from callus extract were smaller and exhibited the most effective antimicrobial potential, with the highest inhibitory zone of 19 mm against Xanthomonas campestris bacterium and up to 14 mm against Aspergillus niger fungus. Furthermore, the percentage of elemental Ag (measured through EDX) was found to be highest in the nanoparticles synthesized from callus compared to those synthesized from the leaf, seed, peel, fruit juice, and bark of Carica papaya. Hence, the callus extract is the most suitable substrate for the reduction of silver nitrate solution in 1:20 to form the finest silver nanoparticles in an effective biogenic way.

In this study, the callus of Carica papaya was treated with silver nitrate solution to form silver nanoparticles which were later used as anti-contaminant substances in micropropagation media on C. nocturnum (cestrum, night queen) and Rosa indica (rose) in tissue culture medium. For this purpose, the rose and cestrum explants were cultured using murashige and skoog (MS) media containing 2 mg/l benzylaminopurine (BAP). After micropropagation of the shoots, different concentrations of biogenically synthesized silver nanoparticles (AgNPs) i.e., 2, 3, and 5 ppm were added into the MS media, for dose optimization. The morphology of tissue-cultured plants in control and experimental has been studied and compared through fluorescent microscopy and Scanning Electron Microscopy (SEM). The cells, tissues, and vascular bundles of C. nocturnum and rose tissue culture plants were studied in both control and treated plants. AgNPs added at a concentration of 5 ppm to the tissue culture medium of both test plants were safe and effective in controlling the contamination and the bacterial and fungal attack in the tissue culture medium was reduced; it gave the highest percentage of survived plants in both the rose and the cestrum plant. No significant difference was observed in the chlorophyll content of the plants maintained on treatment medium having AgNPs concentration of 5 ppm and the control plants maintained on medium without nanoparticles. The molecular assessment of the stress impact of AgNPs treatment was analyzed through expression of the SAND and PP2A housekeeping genes in treated plants and control plants by comparing their mRNA profile on real-time PCR, and the results showed equal expression of SAND and PP2A in both the control and treated plants. This study proves that low amounts of bio-synthesized silver nanoparticles when supplied in tissue culture media can act as an anti-contaminant in rose and cestrum in vitro cultures without affecting its morphology, physiology, and genetics.