Aim: The aim of this study was to investigate different concentrations of iron oxide nanoparticles in and benzylaminopurine (BAP) bell pepper anther culture on the traits of callus formation, embryogenesis, regeneration and rooting.

Material and methods: The experiment was conducted as a factorial experiment in a completely randomized design under in vitro culture conditions. Flower buds of appropriate size (equal sepal to petal ratio or slightly longer petal) were collected from the greenhouse and acetocarmine solution was used to determine the growth and development stage of microspores. The results showed that the most suitable stage for embryogenesis induction was the late mononuclear stage and the early binuclear stage. In order to sterilize the flower buds, 70% ethanol for 30 seconds and 5% sodium hypochlorite for 20 minutes were used and after each stage they were washed three times with sterile distilled water. Then, the anthers were separated from the flower bud and placed in C medium containing 2 mg/L naphthalene acetic acid (NAA), different concentrations of BAP (0, 0.1, 0.5, and 1 mg/L) and different concentrations of iron oxide nanoparticles (0, 1, 10, and 20 mg/L). After that, the explant cultured in C medium were kept at 35°C in the dark for 8 days in order to apply heat treatment. Then, they were transferred to 25°C in the light for 4 days. After this period, in order to induce embryogenesis, the explants were transferred from C medium to R medium and were subcultured every three weeks until embryos emerged. For further growth and root development, the embryos were transferred to V medium. Results: The results of the analysis of variance of the data showed that using different concentrations of iron oxide nanoparticles had a significant effect on the percentage of embryogenesis, regeneration and rooting of the plant, but did not have a significant effect on the percentage of callus formation. The results of comparing the average data showed that among the different concentrations of iron oxide nanoparticles, the 1 mg/L treatment had the highest percentage of embryogenesis (11.11). Also, the results of comparing the average effect of the nanoparticles on the percentage of regeneration showed that the 1 mg/L treatment had the highest percentage of regeneration (16.66). The results of the interaction effects showed that among the different concentrations of iron oxide nanoparticles and BAP, the highest percentage of embryogenesis was observed in the treatment of 20 mg/L iron oxide nanoparticles and 0 mg/L BAP. Also, the treatment of 20 mg/L iron oxide nanoparticles and 0 mg/L BAP had the highest percentage of regeneration (33.33%). After sufficient growth and root formation, the obtained plants were removed from the glass culture containers and transferred to pots containing sterilized culture medium and watered for adaptation. The tops of the pots were covered with plastic cups, and after three days, the cups were pierced and the plastic was gradually removed from the plant for further adaptation. Ploidy levels were determined by chromosome counting by staining the root tip cells. The results showed that out of the 23 obtained plants, 21 were diploid and had 2n=2x=24 chromosomes and 2 were haploid and had n=x=12 chromosomes. Conclusion: In bell pepper anther culture, different concentrations of iron oxide nanoparticles along with plant growth regulators at different concentrations showed a great effect on embryogenesis, regeneration, and rooting.