## 4 Discussion
However, the increase in the POX activity under fluoride-induced stress is observed more often. In our study, POX activity has been different in the cases of embryos and roots and between cultivars. In embryos, POX activity in the Delaware and Tobak cultivars increased with 5.0 mmol-dm\({}^{-3}\) of NaF, and for 8.0 mmol-dm\({}^{-3}\) of NaF it started to decrease the most in the Tobak cultivar (58%). Only the Arkadia cultivar saw increases in POX activity in all of the NaF concentrations. POX activity may increase during germination phase due to plant response to wounding stress induced by radicle penetration through the micropylar endosperm which is accompanied by the rupture, or wounding of this tissue. [43]. However, it is largely unknown how F is deposited in seeds and the levels at which it is toxic to embryos [44]. Contrary to the embryos, the POX activity in roots escalated with the increase in the NaF concentration, while the decrease was only observed in the Tobak cultivar in 2.5 mmol-dm\({}^{-3}\) of NaF. We have also remarked that the activities for roots differed among cultivars. Roots have usually shown a greater tendency to accumulate fluoride than other parts of plants [35]. In the study by [PERSON] and [PERSON] [38], greater POX root activity was characteristic for HD 3086 wheat cultivar resistance to F in normal conditions and under F-induced stress, and it demonstrated superior tolerance mechanisms in terms of H\({}_{2}\)O\({}_{2}\) production and utilization. Hence, those differences may indicate the existence of more tolerant cultivars which have a better ability to scavenge H\({}_{2}\)O\({}_{2}\)[44]. However, we have reported that the NaF concentration has a higher impact on CAT and POX activities than the cultivar of wheat. In our previous study on winter wheat seedlings, we also observed that the fluoride concentration in the soil had the greatest influence on the activity of antioxidant enzymes [40]. The evaluation of the germination of seeds is important for the provision of successful, high-yield crop production. Many authors also report that increased levels of F negatively affect wheat germination [16; 31; 45; 46; 47]. In our study, sodium fluoride also reduced a number of germinated seeds (GI%) in all of the wheat cultivars, but at different levels. The lowest GI% was observed in 10 mmol-dm\({}^{-3}\) of NaF, and it was 14% for the Arkadia cultivar and 17% for the Delaware cultivar. However, in the same concentration, the GI% for the Tobak cultivar was 50%. [PERSON] et al. [45] suggested that this might be caused by the inhibition of phytase enzymes by fluoride. This enzyme is very important during germination and contributes to the degradation of phytate (also known as phytic acid). Phytate is widely recognized as a main source of stored energy for germinating seeds and a compound of phosphorus (up to 80% of total P in seeds). [PERSON] et al. [48] also suggested that fluoride inhibits the carbohydrate metabolism during germination; hence, seeds are unable to grow. [PERSON] et al. [49] considered that it may be due to a reduction of amylase activity. Plant root systems play a vital role in water and nutrient uptakes, and thus in the growth, physiology, and metabolism of all plants [50]. Root length measurement is considered a rapid phytotoxicity test method for chemicals such as fluoride [51]. Study of this indicator is also used to identify plant cultivars tolerant to many abiotic stresses [13; 52; 53]. The reduction of root length due to F toxicity has been reported in many crops such as wheat, rice, barley, rye, and various plant species (e.g., peas, cucumbers, radishes, tomatoes, and sunflowers) [25; 31; 38; 40; 41; 46; 54]. In the study by [PERSON] and [PERSON] [55] on the root and shoot growth of chickpeas, an inhibitory effect of even 1.0 mmol-dm\({}^{-3}\) of a NaF concentration was revealed. In our study, we also reported a decrease in root length, which was dependent on the cultivar.