###### Abstract  
In recent years, there has been an impressive development of nanotechnology. This has resulted in the increasing release of nanomaterials (NM) into the environment, thereby causing the risk of an uncontrolled impact on living organisms, including plants. More studies indicated the biotoxic effect of NM on plants, including crops. The interaction of nanoparticles (NP) with food crops is extremely important as they are a link to the food chain. The objective of this study was to investigate the effect of negatively charged gold nanoparticles (-) AuNP (at two concentrations; 25 \(\mu\)g/mL or 50 \(\mu\)g/mL) on barley (_Hordeum vulgare_ L.) root development. Morphological, histological and ultrastructural analyses (with the use of stereomicroscope, bright filed microscope and transmission electron microscope) revealed that regardless of the concentration, (-) AuNP did not enter into the plant body. However, the dose of (-) AuNP proved to be important for the plant's response because different morphological, histological and ultrastructural changes were observed in the treated roots. The NP treatment caused: red root colouration, a local increase in the root diameter and a decreased formation of the root hair cells (on morphological level), damage to the rhizdermal cells, vacuoulisation of the cortical cells, a detachment of the cell files between the cortical cells, atypical divisions of the cells, disorder of the meristem organisation (on the histological level), the appearance of periplasmic space, numerous vesicles and multivesicular bodies, electron-dense spots in cytoplasm, alterations in the structure of the mitochondria, breakdown of the tonoplast and the plasmalemma (on the ultrastructural level). b 25 February 2022  
Accepted: 19 March 2022  
Published: 23 March 2022  
[[http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci)]([http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci))  
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Information on the impact of manufactured nanomaterials on food crops is increasing. This knowledge is important in connection with increasing production and use of manufactured nanomaterials, including nanopesticides. The toxic effects of CuO NP on cultivated crop plants by inhibiting seed germination, decreasing shoot and root lengths, reducing photosynthesis and the respiration rate and morphological as well enzymatic changes were also proven (for a review, see [12]). The effect of NP on crops also includes a decrease in the germination rate, a reduction in the biomass and the length of roots and shoots, an alteration in the process of photosynthesis and the transpiration rate and an increase in the chromatin condensation and lipid peroxidation [12]. The influence of AgNP on wheat plants revealed severe phytotoxicity and a decrease in the content of micronutrients such as Fe, Cu and Zn [13]. A significant part of the publication describes the effect of NP on the growth and physiological parameters of crop plants [14; 15; 16]. Despite numerous studies in this field, there is still no complete picture of the impact of NP on crops. Thus, on the one hand, nanofertilisers and nanopesticides are necessary to obtain the right yields, but on the other hand, the effects of NP may be detrimental to plant growth. Nanofertilisers provide nutritional management benefits due to their strong potential for increasing the efficacy of nutrient utilisation. When used alone or in combination, the nutrients are bound to nano-sized adsorbents that release nutrients very slowly compared to conventional fertilisers [17].