The impact of TiO2 nanoparticles treatment, developmental, and environmental factors on phenolic content and antioxidant capacity of grapevine (Vitis vinifera L.) leaves

Over the last decades, researchers used several elicitors to increase secondary metabolite synthesis (D'Amelia et al., 2018; Anjum et al., 2019). Several studies are now using a variety of nanoparticles (NPs) as unique and effective secondary metabolite elicitors in planta of several plant species. The most frequent "nano-elicitors" include carbon nanotubes (CNT), silver (Ag), gold (Au), copper (Cu), zinc oxide (ZnO), and titanium dioxide nanoparticles (TiO2 NPs) (Anjum et al., 2019; Khan et al., 2021; Lala, 2021). TiO2 is one of the most popular commercially available nano-size materials that has found application in a variety of fields due to its wide availability, biocompatibility, low cost, non-toxicity, and high chemical stability. In nature, TiO2 exists in four polymorphs: anatase, rutile, brookite, and TiO2 (B). The physical and chemical features of TiO2 depend on the crystal phase, size, and shape of the particles. For example, different phases of crystalline TiO2 have varied band gaps, such as rutile and anatase TiO2, which have 3.0 eV and 3.2 eV, respectively, and these band gaps impact TiO2's photocatalytic activity. The activation of TiO2 NPs by photon energy equal to or more than the TiO2 band gap energy drives an electron from the valence band to the conduction band, leaving a hole in the valence band; electron-hole pairs (the charge carriers) are formed. The electron and hole participate in redox reactions with species adsorbed on the surface of TiO2 such as H2O and O2 to generate reactive oxygen species (ROS). ROS are efficient against pathogens and the degradation of hazardous organic compounds (Kőrösi et al., 2019b). Furthermore, they play a crucial role as signal molecules for upregulating antioxidant defense in plants

Nanostructured titanium dioxide as an antimicrobial agent on grapevine (Vitis Vinifera L.) leaves: a phytotoxicological study

In the past two decades, nanostructured materials including colloidal nanocrystals, semiconductor nanoparticles, nanotubes, nanowires and porous materials have received a great attention thanks to their unique physicochemical properties. Titanium dioxide nanoparticles (TiO2 NPs) excited by UV light can produce different reactive oxygen species (ROS) such as hydroxyl radical, superoxide radical anion and singlet oxygen. This special feature of TiO2 NPs so-called photocatalytic property can be exploited in numerous fields, especially in water treatment technologies for removing toxic compounds or inactivation various pathogens. In this work we applied directly TiO2 NPs on the grapevine (Vitis vinifera cv. Cabernet sauvignon) leaves as potential antimicrobial agent. Experiments were performed under field conditions where the plants were exposed to sunlight. Physiological responses, flavonol profile and micro- macroelements of the leaves were studied. We found that TiO2 NPs with the concentration of 250 3 00 mg kg-1 increased the stomatal conductance whereas decreased the photosynthetic rate. Despite of their negative effect on photosynthesis, flavonol profile as a stress sensitive factor showed only minor changes after the foliar exposure as revealed by HPLC-DAD measurements. Elevated level of K, Mg, Ca, P and B were detected in the treated leaves which may be related to the increased stomatal opening. Our results indicate that TiO2 NPs with the applied concentration can be phytotoxic in the presence of UV irradiation which probably stem from the excess of ROS production of nanoparticles. Consequently, further studies are necessary for determining the parameters which allows safety and efficient field applications of TiO2 NPs

Fotoreaktív nanorészecskék hatása vörösborszőlő-fajták levelének polifenol összetételére és tápelemtartalmára

A különleges tulajdonságokkal rendelkező nanoszerkezetű anyagok hasznosítása az iparban, a mezőgazdaságban és gyógyászatban egyaránt folyamatosan növekszik. A fotoreaktív titán-dioxid (TiO2) nanorészecskék sajátsága, hogy UV-fény hatására reaktív oxigén származékokat (ROS generálnak, melyek jelentős antimikrobiális hatással bírnak, így a növényre kijuttatva potenciális növényvédőszerként funkcionálhatnak. A növényekben keletkező ROS a növények élettani folyamatainak szabályozásában is részt vesznek, ezért a mesterségesen, TiO2 nanorészecskék segítségével keltett ROS a célzott antimikrobiális aktivitás mellett a levelek metabolizmusára is hatással lehet. Ez a hatás lehet negatív, mivel a ROS nagy mennyiségben sejtkárosító, de lehet pozitív is, a természetes úton keletkező ROS hatásához hasonlóan a stresszvédő utakat aktiváló. Habár a TiO2, mint alternatív növényvédőszer a gyakorlatban nagy érdeklődésre tarthat számot, ftotoxicitásáról még csak nagyon kevés információ áll rendelkezésünkre. Ebben a munkában azt tanulmányoztuk, hogy a levelek felszínére juttatott és ott napsugárzásnak kitett TiO 2 nanorészecskék miként befolyásolják a szőlőlevelek teljes fenolos tartalmát(antioxidáns kapacitását) és polifenol proflját. Ezek a paraméterek érzékenyen jelzik a növény oxidatív stresszre adott válaszreakcióit.Nyomon követtük továbbá a levelek makro- és mikroelem összetételének változását is. Szabadföldi kísérletben öt vörösborszőlő-fajtát (Cabernet sauvignon, Cabernet franc, Merlot, Kékfrankos és Kadarka) vizsgáltunk. Nagyhatékonyságú folyadékkromatográfás mérésekkel kimutattuk, hogy szőlőfajtától függően a levelek kaftársav és flavonol-glikozid tartalma a kezelést követően szignifkánsan emelkedett. A levelek teljes fenolos tartalmának növekedése szintén szignifkáns volt. Mindemellett ICP-AES méréseink azt mutatták, hogy TiO2 nanorészecskék a levelek főbb makro- és mikroelemeinek (Ca, Mg, K, B és Mn) koncentrációját ugyancsak növelték

Highly-efficient photocatalytic generation of superoxide radicals by phase-pure rutile TiO2 nanoparticles for azo dye removal

The photocatalytic activity of TiO2 polymorphs has been frequently debated in literature. Numerous studies reported that rutile TiO2 exhibits low photocatalytic activity, and it is generally accepted that rutile has lower photoactivity than the anatase phase. Herein, we studied the photocatalytic activity of phase-pure rutile TiO2 nanoparticles prepared via microwave-assisted hydrothermal method (MW-R NPs). The syntheses were performed with relatively short reaction time (1−3h) at 180 °C using a microwave digestion system. The samples were characterized in detail and then tested in the photodegradation of methyl orange (MO). We demonstrate that the photodegradation of MO with MW-R NPs is highly efcient in the presence of H2O2. By employing 4.4 mM H2O2, ~90% of total decolorization was achieved after 2 min of UV-A irradiation. At the same experimental conditions, MO degradation with Degussa P25 TiO2 was only ~7%. The superior photoactivity of MW-R NPs was related to the effective photogeneration of O2•− radicals as revealed by EPR investigation. These rutile nanoparticles are excellent photocatalysts in the presence of H2O2, signifying that this oxygen source react easily with the photogenerated holes on the MW-R NPs, and thus the interfacial charge transfer lead to the formation of a large amount of O2•− radicals

Nanostructured TiO2-induced photocatalytic stress enhances the antioxidant capacity and phenolic content in the leaves of Vitis vinifera on a genotype-dependent manner

Over the past decades, nanotechnology has received great attention and brought revolutionary solutions for a number of challenges in scientific fields. Industrial, agricultural and medical applications of engineered nanomaterials have increased intensively. The ability of titanium dioxide nanoparticles (TiO2 NPs) to produce reactive oxygen species (ROS), when excited by ultra-violet (UV) light, makes them useful for effectively inactivate various pathogens. It is known that ROS also have signalling role in living organisms, therefore, TiO2 NPs-induced ROS can influence both enzymatic and non-enzymatic defence systems, and could play a role in the resistance of plants to pathogens. Herein, we studied the photocatalytic stress responses of grapevine (Vitis vinifera L.) as model plant, when exposed to a well-known photocatalyst, Degussa P25 TiO2 NPs. The photocatalytically produced ROS such as superoxide anion, hydroxyl radical and singlet oxygen were confirmed by electron paramagnetic resonance spectroscopy. Foliar exposure of five red cultivars (Cabernet sauvignon, Cabernet franc, Merlot, Kékfrankos and Kadarka) was carried out in blooming phenophase under field condition where plants are exposed to natural sunlight with relatively high UV radiation (with a maximum of ~ 45 W m−2). After two weeks of exposure, the effects of photogenerated ROS on the total phenolic content, antioxidant capacity, flavonol profile and the main macro-, microelements of the leaves were studied in detail. We found that foliar application of TiO2 NPs boosted the total phenolic content and biosynthesis of the leaf flavonols depending on the grapevine variety. Photocatalytically active TiO2 NPs also increased K, Mg, Ca, B and Mn levels in the leaves as shown by ICP-AES measurements