Figure 1 displays how the cold plasma treatments in an exposure time-dependent manner was associated with morphological and anatomical changes in the Datura seedlings. These changes included changes in stem length, root length, root biomass, numbers of leaves produced, leaf area, and leaf biomass. The Plasma treatments of 60, 120 and 180 s improved the growth performance of seedlings, while the plasma treatment of 300 s drastically declined growth performance. The plasma treatments for 60, 120, and 180 s increased the stem length by 43.5%, 27.2%, and 74.5%, respectively, over than the control (Fig. 2a). While, the treatment for 300 s decreased the stem length by 71.2% compared to the control (Fig. 2a). The P60 and P120 groups had higher root length amounts compared to the control (Fig. 2b). In contrast, The P300 treatment restricted the root length by 72.6% compared to the control. The most pronounced response to the plasma treatments was on root fresh weight (Fig. 2c). The P60, P120, and P180 treatments resulted in the significant drastic increase (about two-fold) in the root fresh mass compared with the control. In contrast with these groups, the P300 treatments adversely influenced root fresh mass by 52.4% in comparison with the control (Fig. 2c). The number of leaves displayed an upward trend (39.3%) in response to the plasma treatment for 180 s, while extending the exposure time to 300 s decreased this trait by 53.6% compared to the control (Fig. 2d). The P60 and P120 treatments led to a slight increase in leaf area by 12.8% and 21%, respectively, while the plasma treatment for 180 s did not make a significant change relative to the control (Fig. 2e). The lowest leaf area (28.1% fewer than the control group) was recorded in the P300 group (Fig. 2e). The plasma of 60, 120, and 180 s significantly increased leaf fresh mass by 33.6%, 12.4%, and 37.6%, respectively (Fig. 2f). However, the leaf fresh mass was significantly reduced in the P300 group by 67.9% (Fig. 2f).
The proline concentrations in leaves displayed a linear significant upward trend in response to the plasma treatments (Fig. 3a). The proline concentrations in roots were also exhibited a similar trend to that of the proline content in leaves (Fig. 3b). The plasma treatment for 180s was the most effective method to increase alkaloids in leaves by 2-fold over the control group (Fig. 3c). With increasing the plasma duration time from 60 to 300 s, the soluble phenols in leaves were linearly enhanced when compared with the control group (Fig. 3d). The P60, P120, and P180 treatments respectively augmented total protein concentrations by 23%, 28%, and 47.6%, while the P300 treatments significantly diminished total protein content by 27.2% (Fig. 3e). In comparison with the control group, the P120, P180, and P300 treatments significantly enhanced the soluble sugars in leaves by 38.7%, 64.8%, and 40.6%, respectively (Fig. 3f).
The plasma priming was associated with changes in photosynthetic pigments, including Chla, Chlb, and carotenoids. The highest amounts of photosynthetic pigments were recorded in the P120 and P180 treatment groups by an average of 26% over the control group (Fig. 4a, b, c). In contrast with these groups, the plasma treatment for 300 s reduced photosynthetic pigments by an average of 49.8% compared with the untreated control group. The moderate significant upregulation (about 62%) in the leaf catalase activities resulted from the P60 and P120 treatments, while the P60 and P120 treatments led to the drastic promotions in this parameter by an average of 2.3-fold over the control group (Fig. 4d). with increasing the exposure time from 60 s to 300 s, the peroxidase activity in leaves showed a significant linear upward trend and increased by an average of 49.5% (Fig. 4e). The P60, P120, P180, and P300 treatments improved the activity of PAL enzyme by 23.5%, 80.7%, 2-fold, and 58%, respectively (Fig. 4f).
The accumulation of alkaloids strongly correlated with several variables, including PAL activity, soluble phenols, and sugars (Fig. 5). It was found that concentration of alkaloids is moderately correlated with variables, such as number of leaves, root biomass, leaf fresh mass, carotenoids, proteins, proline content in leaves and roots (Fig. 5). There was positive correlation between the majority of growth-related characteristics explored (Fig. 5). The statistical analysis also confirmed the positive correlation between the proline content in leaves and roots with the activities of catalase, peroxidase, and PAL, as well as soluble phenols (Fig. 5). Figure 5 displays how the plasma priming contributed to the anatomical variations in stem apical meristem (SAM). Differential staining in the SAM area indicates variations in the mitotic activity. In the plasma-primed samples, the vegetative meristem is more voluminous, elongated, and domed.