Alleviation of cadmium stress and improved growth performance of periwinkle (Catharanthus roseus L.) by foliar application of zinc oxide nanoparticles

Cadmium (Cd) is a nonessential and very toxic element that confines the growth of ornamental plants worldwide. Nanoparticles (NPs) have been used as a novel approach to act as nano-fertilizers and directly alleviate the Cd stress. However, its defensive mechanisms are not well understood in ornamental/medicinal plants, especially Catharanthus roseus (periwinkle). The objectives of the current experiment are intended to examine the impacts of zinc oxide nanoparticles (ZnONPs; 25 mg l^-1) on the reduction of oxidative stress by enhancing antioxidant activities, physiological improvements, and elemental status in periwinkle plant parts under Cd stress (0.5 mM). The periwinkle plants were transplanted and exposed to Cd stress one week later by soil drenching, whereas, ZnONPs were applied after 14 days by foliar supplementation. The Cd toxicity significantly reduced the morphological traits, negatively affected the pigments and photosynthetic apparatus, abridged antioxidant enzyme activities, and Cd accrual in periwinkle plants. However, exogenous ZnONPs supplementation produced elevated plant height, flower numbers, root length, plant fresh and dry biomass, chlorophyll, and carotenoid contents in Cd-stressed plants. Likewise, the ZnONPs have also regulated the gaseous exchange rates, antioxidant enzymes (SOD, CAT, APX), soluble protein, and free proline contents in Cd-polluted periwinkles. The application of ZnONPs also considerably reduced the hydrogen peroxide (−25 %) and malondialdehyde (−47 %), activated by Cd stress. Furthermore, the Zn and Cd contents were also elevated and reduced, respectively, in ZnONPs supplied Cd-stressed plants. The present experiment recommends that the exogenous supplementations of ZnONPs are a feasible and sustainable strategy for enhancing the growth attributes and reducing the Cd levels in periwinkle plants in metal-hoarded soil conditions.