## 4 Discussion
The application of 200 mg\(\cdot\)dm\({}^{-3}\) of the solution decreased the total number of contaminations (11.1%), especially fungi ones (0%), which are the most common contaminants during tissue culture initiation. [PERSON] et al. [39] obtained the highest percentage of disinfected and regenerating explants of _Heeva brasiliensis_ when AgNPs were used at a concentration of 10 mg\(\cdot\)dm\({}^{-3}\) for 20 min, in comparison to mercuric chloride or sodium hypochlorite. The effect of AgNPs application was studied by [PERSON] et al. [40] in _Arabidopsis thaliana_ seeds, potato leaves, and tomato cotyledons. The authors noted that the use of 100 mg\(\cdot\)dm\({}^{-3}\) for 1 or 5 min was ideal for disinfection, and the treatment had no negative effect on explants. AgNPs are also applied in media supplementation. [PERSON] et al. [26] observed that disinfection of _Arancaria excelsa_, combined with the immersion of explants in 200 mg\(\cdot\)dm\({}^{-3}\) AgNPs for 180 min, reduced the contamination rate from 61.5% to 11.3%, while the addition of 400 mg\(\cdot\)dm\({}^{-3}\) in the media decreased the contamination rate from 81.25% to 18.75%. Both methods were also used by [PERSON] et al. [41], and the authors noted that both methods--explants immersion and media supplementation--reduced contamination rate in almond \(\times\)peach rootstock. [PERSON] et al. [42] used AgNPs both as immersion and media supplementation in _Penniset aloperoxidase_ tissue culture initiation. They obtained the highest number of contamination-free explants when the explants were soaked in 100-250 mg\(\cdot\)dm\({}^{-3}\) AgNPs solution, or when the AgNPs were added to the media at a concentration of 4 mg\(\cdot\)dm\({}^{-3}\) for nodes and 16 mg\(\cdot\)dm\({}^{-3}\) for fillers. [PERSON] et al. [43] proved that the addition of 50 to 200 mg\(\cdot\)dm\({}^{-3}\) AgNPs to the medium completely decontaminated cultures of _Vanilla planifolia_. Supplementation of media with AgNPs was also used in the presented experiment, and it was observed that the treatment reduced the contamination rate, which confirms the results of other researchers. The addition of AgNPs to the media, apart from reducing the contamination rate, may influence the growth and development of explants. [PERSON] et al. [44] noted that bacterial contamination was significantly reduced in the case of _Rosa_ hybrid explants when they had been soaked in a solution of 200 mg\(\cdot\)dm\({}^{-3}\) of AgNPs for 20 min. However, supplementation of the medium with 100 mg\(\cdot\)dm\({}^{-3}\) AgNPs not only reduced the contamination rate but inhibited the phenolic compounds' exudation as well. The positive effect of the AgNPs media supplementation was observed in many plant species cultivated in vitro. In the case of _Tecomella undulata_, the number of regenerating shoots and their number increased when the MS medium contained 10 mg\(\cdot\)dm\({}^{-3}\) AgNPs [45], while the use of a higher concentration, 60 mg\(\cdot\)dm\({}^{-3}\), enhanced the number of shoots and their length [46]. The positive effect of the AgNPs use was also noted in the case of cowpea and Brassica [47]. However, the use of nanomaterials gives rise to many doubts and questions, and they might be deposited in tissues [48]. The phytotoxicity of AgNPs is assessed with such features as growth potential, seed germination rate, biomass, or leaf surface area [49; 50; 51]. In the presented experiment, the use of AgNPs reduced the contamination rate of explants but noticeably inhibited the regeneration capacity and growth of shoots. A similar effect was proved by many researchers. [PERSON] et al. [43] studied the influence of AgNPs on _Vanilla planifolia_ shoot regeneration and they obtained the highest shoot number of shoots, over 14, when the media contained 25 or 50 mg\(\cdot\)dm\({}^{-3}\) AgNPs, but the use of nano-silver at a higher concentration of 200 mg\(\cdot\)dm\({}^{-3}\) decreased the number of shoots to 4.55.