Titanium dioxide nanoparticles treatment on morphological and physiological characteristics of licorice (Glycyrrhiza glabra L.) under drought stress

Drought stress is one of the factors limiting growth and development in plants, which negatively affects the morphological traits and physiological processes of plants. These effects are reduced using a variety of compounds and nanomaterials, including titanium dioxide nanoparticles (TiO2 NPs). In recent years, the use of TiO2 NPs has been the focus of plant physiologists due to their special biological properties. This beneficial nanoparticle stimulates the growth and quality of crops.  The foliar application effects of TiO2 NPs on morphological and physiological traits of licorice (Glycyrrhiza glabra L.) under drought stress were investigated in a factorial experiment with a completely randomized design with three replications under greenhouse cultivation at Malayer University in spring 2019. TiO2 NPs were used at concentrations of 0, 0.02, and 0.04 mM with the application of drought stress and irrigation cut-off at 24 h, 7 days, and 14 days. The measured morphological and physiological traits were root length, shoot length, root diameter, stem diameter, root fresh weight (RFW), shoot fresh weight (SFW), root dry weight (RDW), shoot dry weight (SDW), chlorophyll content (a, b, and total) (Chl. a, Chl. b) and, carotenoids, anthocyanin, proline, total phenol, total flavonoids, soluble carbohydrates, and insoluble carbohydrates. The results indicated that values of all traits, except root length, shoot length, and SDW, decreased with drought stress, while it increased physiological traits, including anthocyanins, carotenoids, flavonoids, and soluble and insoluble carbohydrates. TiO2 NPs positively influenced all physiological traits, except insoluble carbohydrates and total phenols. Key words: Licorice (Glycyrrhiza glabra L.), titanium dioxide nanoparticles, morphological and physiological characteristics, drought stress.