Potency of Titanium Dioxide Nanoparticles, Sodium Hydrogen Sulfide and Salicylic Acid in Ameliorating the Depressive Effects of Water Deficit on Periwinkle Ornamental Quality

Abstract

In this study, the optimal concentration of sodium hydrosulfide (NaSH), salicylic acid (SA), and titanium dioxide nanoparticles (TiO2NPs), and their relative effectiveness on alleviating the adverse effects of water deficit on ornamental quality, were investigated in periwinkle. Plants were cultivated under three water deficit levels (80, 50, and 20% available water content) and received two foliar applications of TiO2NPs (0, 0.5 and 1 mM), NaSH (0.5 and 1 mM), or SA (1 and 2 mM). Water deficit deteriorated ornamental quality, amplified the risk of buckling (lower stem strength) and suppressed longevity. It decreased both light interception (leaf area) and carbon assimilation. Besides impaired hydration status, water-stressed plants underwent oxidative damage as indicated by reduced chlorophyll content, elevated membrane degradation, and lipid peroxidation. Spray treatments improved all traits, besides stem strength and proline content. Additionally, they enhanced carotenoid content and the activities of catalase and peroxidase. Their relative effectiveness (TiO2NPs > NaSH > SA) and optimal concentration (i.e., 0.5 mM (TiO2NPs, NaSH), and 1 mM (SA)) was independent of water deficit level. In conclusion, this study provides practices for improved ornamental quality and longevity independently of water availability, with their positive effect being stronger under irregular or limited water supply.