Structural alterations of Cymbopogon citratus (DC.) Stapf leaves and roots caused by silicon nanoparticles during in vitro propagation

Cymbopogon citratus (DC.) Stapf (lemongrass or citronella) is a herb of therapeutic potential highly sought by various industries due to the presence of essential oil. In vitro propagation of commercial crops is highly desirable; it is an alternative approach for the production of quality planting materials. But the plantlets encounter certain morpho-structural and physiological disorders under in vitro conditions resulting in suppressed growth and reduced survival. The present study aimed to analyze the effect of silicon nanoparticles (SiNPs) on the in vitro morphometric and structural developments, rooting, and acclimatization efficiency in C. citratus. Murashige and Skoog (MS) medium supplemented with 4.0 mg/L of 6-benzylaminopurine (BAP) was effective for bud breaking. The shoot proliferation was further accelerated with the addition of 0.25 mg/L NAA (α-naphthalene acetic acid) in subsequent subcultures (after 3rd subculture, 21.0 shoots with 4.9 cm length per explants per culture vessel). Such shoots were characterized by thin leaf blades, reduced leaf area, and shoot tip necrosis, which negatively affected the life of cultures, ex vitro rooting, and acclimatization efficiency. Microscopic evaluation of those leaves showed underdeveloped stomata, epidermis, and reduced photosynthetic and vascular tissues. The incorporation of optimal concentration of SiNPs (40 mg/L) with the optimized growth regulators (4.0 mg/L BAP + 0.25 mg/L NAA) significantly increased shoot proliferation (38.0), shoot length (6.4 cm), robust leaf, and biomass (5.2 g fresh weight; 1.9 g dry weight). Shoot tip necrosis was reversed by the addition of SiNPs, and the developed shoots were morphologically thick with well-developed tissue systems. These C. citratus shoots performed better during ex vitro rooting (100% rooting, 8.0 roots/shoot) when treated with indole-3-butyric acid (IBA) at the concentration of 200 mg/L and acclimatization.