## 3 Results and Discussion
### Assessment of Phytotoxicity  
#### 3.2.1 Foliar Application  
Table 4 shows the contents of chlorophyll a, b, total chlorophyll and carotenoids in wheat leaves upon their treatment with a foliar application of SPs and Cu NPs. As clear from the table and for SPs, chlorophyll (a) decreased significantly compared to the control upon increasing the SPs concentration to 0.06 mg/mL, recording 3.61 and 4.90 mg/g fresh weight after 7 and 14 days from application, respectively. Upon the exposure of wheat leaves to 0.06 mg/mL of Cu NPs, chlorophyll (a) decreased insignificantly relative to the control, recording 4.10 mg/g fresh weight after 7 days from application. However, it significantly decreased after 14 days from application, recording a fresh weight of 5.68 mg/g at the highest concentration of 0.06 mg/mL. This indicates that the inhibitory effect of Cu NPs on chlorophyll (a) could only be realized at the highest employed concentration and only after 14 days. Chlorophyll (b) followed the same behavior as chlorophyll (a), where its content decreased with increasing the concentration of SPs to 0.06 mg/mL and recorded respective fresh weight values of 2.82 and 4.06 mg/g after 7 and 14 days of applying SPs, respectively. Meanwhile, treatment with Cu NPs showed no significant effect on the chlorophyll (b) content except after 14 days of applying 0.06 mg/mL of the nanoformulation which resulted in a fresh weight of 4.60 mg/g of chlorophyll (b). In addition, total chlorophyll decreased significantly relative to the control upon increasing the concentration of SPs and Cu NPs to 0.06 mg/mL, recording 8.96 and 10.28 after 14 days of application, respectively. Similar trends have been reported in previous studies which examined the effect of 1 mg/L of CuO nanoparticles on total chlorophyll content, chlorophyll (a) and (b) of _Arabidopsis thaliana_ seedlings [45] and _Elsholtzia splendens_[46]. Additionally, in agreement with the current results are those obtained from studies conducted on Ag nanoparticles. In these studies, the effect of Ag nanoparticles (20 nm) was investigated on the photosynthetic pigments (chlorophyll a and b) of _Coriandrum sativum_ when exposed to a nanoparticle concentration of 800 mg/L [47], in addition to those of _V. radiata_ and _B. campestris_ seedlings upon their exposure to silver nanoparticles at a concentration of 1000 \(\upmu\)g/mL [48], as well as those of _Arabidopsis thaliana_ and _Dracocephalum moldavica_ plants when treated with 3 mg/L and 80 mg/L of Ag nanoparticles, respectively [49, 50]. The seeds of _Arabidopsis thaliana_ were commonly tested in the above studies since they represent a good model for determining the growth parameters, as they grow relatively faster and have a shorter life cycle than other species [45]. Carotenoids followed a similar trend to that of the total chlorophyll after 14 days of SPs or Cu NPs application since it significantly decreased relative to the control when the concentration of either SPs or Cu NPs increased to 0.06 mg/mL. Under these conditions, the carotenoids content decreased when compared to the control and recorded 0.97 and 1.09 mg/g fresh weight upon treatment with SPs and Cu NPs, respectively. This behavior resembles that previously reported for the effect of silver nanoparticles (47 nm) on the carotenoids content of mustard (_Brassica_ sp.) seedlings [51]. After 7 days of application of 0.06 mg/mL of either SPs or Cu NPs, an insignificant decrease in the carotenoids content was, however, observed.