NANOSTRATEGIES IN FE SUPPLY TO PLANTS

Modern agriculture is characterised by the employment of novel approaches, strategies, implements, products and tools aimed at improving crop yields to fulil the need for food of the increasing human population and reducing the impact on environment and natural resources. To achieve this goal, novel types of fertilisers with greater eficiency and lower impact are necessary. Recently, more natural strategies and eco-friendly materials have been employed. Iron is a metal element that is essential for the metabolic activities of living organisms, especially in mitochondria and chloroplasts. It is required by organisms in traces and for this reason it is considered a micronutrient but beyond thresholds, depending on the organism, iron results toxic. The chemical species of iron depend on the redox condition of the environment. In the prevalently oxic conditions of terrestrial ecosystems, iron is mostly present in the ferric form Fe(III). This oxidised form, however, is mostly insoluble in water solutions, except for very acidic conditions. The absorption of this essential element is then dificult for plants and microorganisms; however, the latter have evolved various mechanisms on purpose, under iron limited conditions. In a case, organic compounds named siderophores are released, which act as speciic and eficient ferric iron chelating agents that can be transported into the cytoplasm where they release iron. Plants can also release organic compounds with similar attitude (phytosiderophores). Electrospinning is a versatile nanotechnology providing the possibility to create ibrous matrices in both freestanding and ilm coating forms for a large number of applications. Such versatility results from the multitude of polymers (potentially mixed in blends either) that can be electrospun to obtain ibres in the range from nano to microscale, arranged in 2D and 3D frameworks. These nanoibrous scaffolds can retain a variety of properties (physical, chemical and biological) that can be further implemented by post-processing functionalisations. In the present study, a PCL/PHB biodegradable electrospun matrix was used to load various classes of siderophores to be used as biostimulants to provide iron to plants. Speciically, duckweeds (Lemna gibba L.), the smallest representative of vascular plants and ecological indicator of chemical contaminations in aquatic environments, were used to evaluate the potential toxic effects of the nanoibrous products (NSs) created. Distinct treatments were ixed to test the effectiveness and toxicity of the NSs in hydroponic culturing conditions. Plants were tested for limiting iron (Fe3+) concentrations and starved plants were resupplied with soluble Fe3+ to test the recovery capacity of plants. Two strategies for nanoproducts were investigated for their capacity to provide iron to starved plants: i) addition of siderophore-loaded NSs (SLNSs); ii) addition of Fe-chelating SLNSs (FeSLNSs). Spatiotemporal changes in photosynthetic eficiency were monitored by imaging chlorophyll luorescence to evaluate Fe deiciency and the potential toxic effects of the nanoproducts on plants. Results are here reported and discussed.