Biostimulation of Biogenic Zinc Oxide Nanoparticles on Morpho-Physiological Development of Basil Seedlings

Nanomaterials derived from essential nutrients such as zinc enable the synthesis of nanocomposite materials and nano-fertilizers, offering broader agricultural applications and improved human nutrition. In this study, thyme leaf extract was used to synthesize biogenic zinc-oxide nanoparticles (BZO-NPs), and their effects on the micro-morphological and biochemical parameters of sweet basil (Ocimum basilicum L.) were investigated. The synthesized BZO-NPs were characterized using UV-Vis spectroscopy, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDXS). The BZO-NPs exhibited a crystalline spherical structure with sizes ranging from 50 to 100 nm. Different BZO-NP concentrations (25, 50, 100, and 200 mg L-1) were applied to basil plants during the vegetative growth stage. The relative growth rate, total chlorophyll content, and relative water content ratio increased at all BZO-NP concentrations except 200 mg L-1, with the highest values observed at 50 mg L-1 BZO-NP. Stomata density decreased at all BZO-NP concentrations except 50 mg L-1 BZO-NP, and stomata sizes also decreased at all BZO-NP concentrations. The number of peltate trichomes increased on both leaf surfaces with higher BZO-NP concentrations, with a more pronounced increase on the upper leaf surface. Changes in peltate trichomes were associated with the presence of three phenolic compounds: caffeic acid, rosmaniric acid, and chlorogenic acid. The treatment of BZO-NP concentrations also influenced the activity of antioxidant enzymes (SOD, CAT, GR and APX) in sweet basil. Treatment with BZO-NPs at all concentrations reduced oxidative stress by decreasing hydrogen peroxide levels compared to the control, while malondialdehyde (MDA) content remained unchanged. In conclusion, BZO-NPs, being economically viable and environmentally sustainable, demonstrate significant potential as nano-based nutrient sources for basil cultivation.