## 4 Discussion  
The importance of the process of breaking seed dormancy, which leads to the initiation of germination, is widely known, and this study has been used by many authors as a model for assessing crop resistance to biotic and abiotic stresses [29; 30; 31]. From physiological and biochemical points of  
Figure 3: Germination index in wheat seeds after incubation in NaF solutions. Figure 2: Root length in wheat after 72 h of incubation in NaF solutions. Data are given as means \(\pm\) SD (n = 100). Values marked with the same letters do not differ statistically at \(p\) = 0.05 (post hoc Tukey HSD test). view, germination occurs after restored metabolic activity. Then, a large number of specific metabolic events, such as antioxidants enzymes activity, take place. When the seeds initiate growth, they need appropriate internal and environmental conditions. However, changes in these conditions caused by toxic substances such as NaF result in changes in the seed's metabolism [32; 33; 34]. The high levels of fluoride lead to the production and accumulation of ROS, as well as changes in the enzymatic antioxidant system. This system comprises of antioxidant enzymes, such as CAT and POX. Many authors suggest that oxidative damage is a major effect of F toxicity to plants. Due to the effects on these antioxidant enzymatic systems, many researchers have also studied the adverse effect of F on the metabolic processes of plants [1; 35; 36]. In the current study, the analysis of CAT and POX activities has been used for the first time in wheat embryos under fluoride-induced stress. In addition, the activities of those enzymes in wheat roots have been presented, which are not examined very often. The results have shown the inhibiting effects of sodium fluoride on CAT activity in both embryos and roots. The activity decreased with the increase in the sodium fluoride concentration in all of the cultivars, and the highest inhibition of CAT activity in embryos and roots has been observed for the Tobak cultivar at 87% and 97%, respectively. The reduced activity of enzyme antioxidants such as CAT can lead to lipid peroxidation and membrane damage [37]. CAT activity during the seed imbibition phase is usually low and initially increases during the seedling stage [21]. However, in our study, because of the NaF solutions, CAT activity in the embryos and roots was lower than in the control samples, while the level of inhibition was dependent on the cultivar. Differences in CAT activity among the cultivars under fluoride-induced stress were also observed by [PERSON] and [PERSON] [38]. In their study, CAT activity decreased drastically in the roots of the F-tolerant wheat cultivar HD 3086, compared with the less tolerant WH1105. Fluoride combines easily with many heme enzymes such as CAT, which has iron in its structure. Moreover, fluoride anion coordinated with the heme iron is proven to be hydrogen bonded to the distal histidine (His64) and to a water molecule in this enzyme. Hence, iron which allows CAT to react with the hydrogen peroxide is blocked [39]. However, wheat under fluoride-induced stress may also cause both an increase and a decrease in CAT activity. Such changes are noted by [PERSON] et al. [40] in leaves of the winter wheat cultivar Skagen. After the application of NaF and KF into the soil, CAT activity boosts with the increases of fluoride concentrations in the soil. The differences in CAT activity are observed among different plant cultivars as well. Many similar changes are recognized in different crops. [PERSON] [41] discovered that CAT activity steadily escalates with the increase of NaF in four rice cultivars. In the studies by [PERSON] et al. [42], CAT also showed its increased activity in tea leaves under fluoride-induced stress. As has been mentioned earlier, POX, similar to CAT, also reacts with H\({}_{2}\)O\({}_{2}\). The distal histidine contributes to the stability of the fluoride complex in POX in a similar way to CAT, and it also leads to the decrease of this enzyme's activity [39].