Interactive effect of biogenic nanoparticles and UV-B exposure on physio-biochemical behavior and secondary metabolism of Artemisia annua L

Biosynthesized silver nanoparticles (AgNPs) are key nanomaterials with unique physio-chemical characteristics and diverse applications. Their strong absorption potential and antibacterial activity make them useful for agriculture, medicine and other industries. AgNPs boost plant growth and metabolism, especially under stress. However, the combined effects of AgNPs and UV-B exposure on plants are unknown. To elucidate the interactive effects of biosynthesized silver nanoparticles (AgNPs) and exposure of ultraviolet B (UV-B) on plant growth and metabolic processes, this study assessed the response of Artemisia annua under controlled in vitro conditions. In total, eight sets of plants were used with the alone/combined treatment of AgNPs and UV-B. For this purpose, spherical and averaged ∼ 31.8 nm in size AaAgNPs were synthesized. The photosynthetic pigments were calculated maximum with the alone treatment of 0.5 mg L⁻¹ AaAgNPs and combined treatment of 0.5 mg L⁻¹ AaAgNPs with 3 h UV-B, respectively. The results evidenced that the co-exposure of AaAgNPs and UV-B led to a significant balance in ROS production of A. annua; as well as improved antioxidative enzyme activity. Fluorescence and scanning electron microscopic (SEM) analysis indicated the enhancement of glandular trichomes (GT) area and density with the combined treatment of AaAgNPs and 3 h UV-B. In accordance with correlation between microscopic GT results, high concentration of artemisinin and up-regulation of related transcripts were found in A. annua plants treated with low concentrations of AaAgNPs and UV-B. Thus, it may be inferred that two distinct plant growth modulators, namely low-concentration biosynthesized AgNPs and short-term UV-B exposure, can enhance the physio-biochemical characteristics and production of secondary metabolites (specially artemisinin) in A. annua synergistically.