Agrobiological, chemical and antioxidant properties of saffron (Crocus sativus L.) exposed to TiO2 nanoparticles and ultraviolet-B stress

Saffron (Crocus sativus L.) is one of the most commonly known and expensive medicinal and aromatic plants in the world from which dried stigmas are consumed. Saffron includes 85 species and has a special place among industrial and export commodities. Ultraviolet-B (UV-B) radiation causes the generation of oxygen free radicals, which disrupt the balance of metabolism in cells. The present study aimed to explore the application of titanium dioxide nanoparticles (TiO2 NPs) on saffron exposed to harmful UV-B radiation, in order to evaluate their effect against photo – oxidative stress. Saffron plants were grown in the hydroponic system in a greenhouse for 45 days. After the three-leaf stage, they were exposed to UV-B radiation for 30 and 45 min on a daily basis for one month. TiO2 NPs were used at two concentrations of 25 and 50 mg/L as the foliar application before UV-B exposure every day. The plants were harvested 75 days later and their growth, chemical and antioxidant parameters were measured. The results showed that UV-B exposure was related to lower plant length, fresh and dry weight, and leaf number. The simultaneous UV-B exposure and TiO2 NPs application resulted in the loss of dissolved sugars and the increased content of total anthocyanins and malondialdehyde (MDA) in saffron leaves. Besides, content of UV-B absorbents (total phenolics and total flavonoids) and radical scavenging activity ((DPPH) in saffron stigmas were increased. The foliar application of TiO2 NPs counterbalanced some plant traits impaired by UV-B exposure as compared with plants only exposed to UV-B radiation. Due to the increased antioxidant activity of saffron stigmas, it could be assumed that the use of TiO2 NPs enhances the nutritive value of saffron.