Pb and Cd concentrations in leaves and roots
When plants were exposed to Pb, the concentration of Pb in their leaves and roots increased significantly. The highest Pb amount obtained in Pb-exposed plants without foliar NP application was 8.83 mg g-1 DW. Nonetheless, NPs reduced Pb accumulation in sage plant roots and shoots. In Pb-exposed plants, Se, Si, and Zn NPs reduced Pb accumulation by 23, 30, and 22% for roots and 35, 43, and 40% for shoots, respectively, when compared to the control. Cadmium toxicity followed a similar pattern, with remarkable decreases in its accumulations in sage tissues following NPs. Silicon NPs reported the greatest reduction in Cd shoot (39%), followed by Zn NPs (36%), and Se NPS (29%). As a result, NPs may inhibit the accumulation of Cd and Pb in sage tissues, particularly in the leaves (Table 1).
Plant weight
Heavy metals (Pb and Cd) significantly (P0.05) decreased plant weight, but foliar-applied NPs modulated oxidative stresses by increasing plant weight. When compared to non-polluted soils, Cd and Pb stresses reduced shoot weight by 41 and 35% (Fig. 1a), respectively, and root weight by 50 and 33% (Fig. 1b). However, NPs played a significant role in increasing plant weight. In comparison to non-sprayed plants, Se, Si, and Zn NPs caused 25, 40, and 44% increases in shoot weight (Fig. 1a) and 11, 25, and 16% increases in root weight (Fig. 1b). Therefore, Cd was more toxic than Pb, and Si and Zn NPs were more effective in increasing sage plant weight.
Relative water content (RWC) and chlorophyll content
Plants exposed to Pb and Cd stress had noticeable reductions in RWC, whereas NPs had remarkable effects on improving RWC. In this regard, Cd and Pb-exposed plants experienced 28 and 22% decreases in RWC, respectively, compared with the control. In contrast, Se, Si, and Zn NPs enhanced RWC in Cd-stressed plants by 18, 23, and 22%, respectively, when compared with non-NPs application (Fig. 2a). Total chlorophyll followed the RWC trend after the treatments in this study. Compared with the non-polluted treatment, remarkable reductions of total chlorophyll were observed in Cd (36%) and Pb (29%) contaminated soils without foliar-applied NPS. However, NPs especially Si NPs improved total chlorophyll in Cd (37%) and Pb (31%) exposed plants (Fig. 2b). Totally, Cd and Pb toxicity led to decreased RWC and chlorophyll but NPs, particularly Si NPs, improved these variables.
Malondealdehyde (MDA) and electrolyte leakage (EL)
Oxidative stress caused by Cd and Pb increased MDA and EL in sage plants, whereas NPS decreased these variables. Malondealdehyde and EL levels were highest in plants exposed to Cd toxicity without foliar NPs. Cadmium and Pb toxicity increased MDA by 46 and 34% in non-sprayed plants, respectively (Fig. 3a), and EL by 30 and 19%. (Fig. 3b). The most intriguing results were obtained for NPs by decreasing MDA and EL. For example, in plants with Cd toxicity, 14, 22, and 20% declines in MDA (Fig. 3a) and 16, 17, and 18% enhancements in EL (Fig. 3b) were observed compared with non-foliar application of NPs.
Essential oil (EO) content and EO yield
The EO content and EO yield of sage plants decreased by the heavy metals but improved by the NPs. Upon non-foliar application, 20 and 15% reductions in EO content were observed in Cd and Pb-exposed plants in comparison to the control. In contrast, NPs elevated EO content, with 15, 31, and 24% increases for Se, Si, and Zn NPs relative to non-foliar NPs in plants experiencing Cd stress (Fig. 4a). The EO yield followed the pattern of EO content upon heavy metals and NPs. In non-NP plants, the 2.1 and 1.8-fold increases were observed in Cd and Pb-exposed plants, respectively. In non-stressful plants, Se, Si, and Zn NPS elevated EO yield by 36, 37, and 43%, respectively, compared with non-NPs (Fig. 4b).
Essential oil (EO) profile
The GC/MS analysis revealed 25 compounds, which accounted for more than 98% of the total EO profile. The main EO constituents were 1,8 Cinoele, α-thujone, β-thujone, and camphor with different amounts of heavy metals and NPs. The Cd and Pb toxicity led to elevated 1,8 Cinoele, ranging from 9.45% in Se NPs without heavy metal stress to 13.42% in Pb stress and Si NPs. The amount of α-thujone was obtained in a range of 27.43% to 38.76%, with increasing upon the NPs. Like α-thujone, β-thujone increased when plants were sprayed with NPs. it differed from 10.14% without heavy metals toxicity and NPs (control) to 12.94% in Cd stress and Zn application. Camphor mainly increased with NPs as Se, Si, and Zn NPs increased it by 20, 12, and 21%, respectively, compared with control. Relative to sesquiterpene, the monoterpenes described the major amount of EO compositions in sage plants.
Multivariate analysis
According to PCA eigenvalues, F1 justified -thujone and camphore, while F2 explained 1,8 cineole and -thujone (Fig. 5a). Based on AHC for physiological traits, three distinct clusters were identified: T5, T6, T8, T1, T9, and T12 in one cluster, T2 and T3 in another, and T10, T4, and T7 in yet another. As a result, three distinct clusters of main EO compounds were discovered, with T2, T3, and T4 significantly different from others (Fig. 5b).