**1. Introduction**

Nanotechnology is a multidisciplinary field, which includes a wide range of processes, materi‐ als, and applications. The main aims of this new discipline are the characterization, fabrication, and manipulation of material at nanoscale level [1]. The reason why these new materials are so widely used is linked to their unique and novel properties principally related with the increase of the surface area to volume ratio. Nowadays, a lot of products are based on nanotechnology; at the beginning, these materials were applied in construction materials, new devices and techniques in

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electronics, cosmetics, sporting equipment, wastewater treatment, medicine, and more recently in agriculture and the food industry [2]. The agri‐food was the last sector in terms of succession to be interested by this technological revolution but at the same time it would be far reaching in the next years [1]. In fact, the nanotechnology has recently emerged as the technological advancement to develop and transform the entire agri‐food sector, in terms of increasing global food produc‐ tion and nutritional value, quality and safety of food [3]. The type of nanoparticles (NPs) or nano‐ materials (NMs) used in plant science are quite wide, but they could be clustered in two principal groups: the carbon nanomaterial (CBNMs) and the metal‐based nanomaterials (MBNMs) [4]. In the group of MBNMs, the most common NPs are TiO<sup>2</sup> , CeO2 , Fe3 O4 , ZnO, and AgNO3 [5]. Our experiments were focused on TiO2 nanoparticles (*n*TiO2 ) that represent the most used nanoma‐ terial between the MBNMs. Several papers demonstrate the positive effects of *n*TiO2 on plants [6–9]. More recently, Dehkourdi and Mosavi [10] used nano‐anatase to treat parsley seeds, which resulted in an increase in the percentage of germination, the germination rate index, the root and shoot length, the fresh weight, the vigor index, and the chlorophyll content of the seedlings. Also, Feizi et al. [11] observed that the germination rate of *Salvia officinalis* improved when the seeds were exposed to *n*TiO2 . Previous studies demonstrate a positive effect also during the plant veg‐ etative growth, for example, Hong et al. [7] demonstrate an acceleration in the rate of evolution of oxygen by chloroplasts in spinach plants. Another experiment on spinach demonstrated a gain in the photosynthetic carbon reaction in treated plants [9]. More recently, Qi et al. [12] treated tomato plants with *n*TiO2 and put them in a mild heat stress, the plants resulted to have an improvement in the photosynthetic rate with respect to the control ones. Currently, the application of nano‐ materials in the field of primary production is still under investigation, and therefore, it may take many years before specific nanoproducts for agriculture are commercialized worldwide [1]. Since the studies performed up to now have been conducted in a very simplified experimental condition, we still lack accurate information on what is happening in the soil. Further research is required to ensure complete success for these applications of nanotechnologies [13].
