Zinc Oxide Nanoparticles Applied Topically Reduce Cadmium Stress and Enhance Periwinkle (Catharanthus roseus L.) Growth Performance

Abstract

Worldwide, the growth of attractive plants is restricted by the non-essential and extremely hazardous metal cadmium (Cd). A new method for acting as nano-fertilizers and directly reducing the Cd stress is the use of nanoparticles (NPs). However, little is known about how beautiful and medicinal plants, particularly Catharanthus roseus (periwinkle), defend themselves. Through the enhancement of antioxidant activities, physiological improvements, and elemental status in periwinkle plant parts under Cd stress (0.5 mM), the current experiment aims to examine the effects of zinc oxide nanoparticles (ZnO——NPs; 25 mg l-1) on the reduction of oxidative stress. One week following transplanting, the periwinkle plants were subjected to Cd stress through soil soaking, whereas ZnO——NPs were added topically 14 days later. The periwinkle plants' morphological characteristics were greatly diminished by the Cd toxicity, which also had an adverse effect on the pigments and photosynthetic apparatus, inhibited the activities of antioxidant enzymes, and decreased the accumulation of Cd. However, in Cd-stressed plants, exogenous ZnO——NPs supplementation resulted in increased plant height, flower number, root length, fresh and dry biomass, and levels of carotenoid and chlorophyll. Similarly, in Cd-polluted periwinkles, the ZnO——NPs have similarly controlled the levels of free proline, soluble protein, antioxidant enzymes (SOD, CAT, and APX), and gaseous exchange rates. The treatment of ZnO——NPs also significantly decreased the levels of malondialdehyde (—47%) and hydrogen peroxide (—25%) that were triggered by Cd stress. Additionally, ZnO——NPs supplied Cd-stressed plants with higher Zn and lower Cd levels, respectively. In metal-hoarded soil conditions, the current experiment suggests that exogenous ZnO——NPs supplements are a viable and sustainable method of improving the development characteristics and lowering the Cd levels in periwinkle plants.