What is missing to advance foliar fertilization using nanotechnology?

Recent advances within bionanotechnology pave the way for development of biocompatible foliar nanofertilizers with superior nutrient use efficiency. Emerging evidence shows that nanoparticle physicochemical properties and formulation are key for effective penetration of all major plant barriers, including the cuticle, stomata, cell walls, and plasma membrane. Nanoparticles can be targeted to specific cell organelles and be programmed to release their nutrients in a time-dependent manner or as a response to cellular stimuli. Nanoparticles can translocate from exposed leaves to unexposed tissue. This highlights a clear potential for designing phloem-mobile nanofertilizers, containing nutrients that are currently immobile. Manipulating the phloem mobility of nutrients would constitute a major landmark within plant science. An urgent challenge within agriculture is to improve fertilizer efficiency in order to reduce the environmental footprint associated with an increased production of crops on existing farmland. Standard soil fertilization strategies are often not very efficient due to immobilization in the soil and losses of nutrients by leaching or volatilization. Foliar fertilization offers an attractive supplementary strategy as it bypasses the adverse soil processes, but implementation is often hampered by a poor penetration through leaf barriers, leaf damage, and a limited ability of nutrients to translocate. Recent advances within bionanotechnology offer a range of emerging possibilities to overcome these challenges. Here we review how nanoparticles can be tailored with smart properties to interact with plant tissue for a more efficient delivery of nutrients. An urgent challenge within agriculture is to improve fertilizer efficiency in order to reduce the environmental footprint associated with an increased production of crops on existing farmland. Standard soil fertilization strategies are often not very efficient due to immobilization in the soil and losses of nutrients by leaching or volatilization. Foliar fertilization offers an attractive supplementary strategy as it bypasses the adverse soil processes, but implementation is often hampered by a poor penetration through leaf barriers, leaf damage, and a limited ability of nutrients to translocate. Recent advances within bionanotechnology offer a range of emerging possibilities to overcome these challenges. Here we review how nanoparticles can be tailored with smart properties to interact with plant tissue for a more efficient delivery of nutrients. chemical compounds with the ability to modify the properties of solutions, including reducing the surface tension to increase adhesion of aerosol droplets to the hydrophobic leaf surface. the space between plasma membranes of adjacent cells, composed of both the cell wall matrix and cavities filled with air and fluid. a β-1,3-glucan polysaccharide found in the cell walls of many higher plants, especially around plasmodesmata and sieve plate pores. multilayered matrix composed mainly of polysaccharides, lignin, and minor amounts of structural proteins, surrounding the plasma membrane of plant cells. peptides with enhanced capacity for penetrating biological membranes due to their ability to, for example, trigger endocytosis or transient pore formation. specialized parenchyma cells that are closely associated with sieve elements. a protective hydrophobic layer covering the epidermis; it is composed primarily of lipids and hydrocarbons. a tube-like structure, present in most plasmodesmata, connecting the endoplasmic reticulum of two adjacent cells. waxes deposited on the cuticle, contributing to the hydrophobic properties of the cuticle. application of a fertilizer directly to plant leaves, most commonly in the form of an aerosol containing essential plant nutrients and adjuvants. a group of essential plant nutrients with little or no ability to enter the phloem and translocate from source to sink tissue (Mn, B, Ca). a tissue rich in chloroplasts, and the main tissue responsible for photosynthesis in plants; it is located between the two epidermal cell layers of a leaf. small particles of various shapes and composition, with at least one dimension <100 nm. a phrase that describes how efficiently the applied nutrients are utilized by the crop. short signal peptides carrying the information required for selective transport of proteins into their target organelle. the structure that constitutes the boundary between the interior and exterior environment of a cell; it is composed of lipids and proteins. nanosized channels that span across the cell walls and create a cytoplasmic continuum between neighboring cells. plasmodesmata-derived pores connecting companion cells and sieve elements. They are asymmetrically branched with multiple channels towards the CC and one opening towards the SE. semiconductor NPs which exhibit size- and composition-dependent optical properties (e.g., photoluminescence). cells that are connected end-to-end via perforated sieve plates to form long sieve tubes, conducting phloem transport of solutes from source to sink organs. the upper size limit for NPs able to cross a biological barrier. nonphotosynthetic tissue or tissues that do not produce sufficient photosynthates to support their own development (e.g., fruits). ‘Source’ organs (e.g., leaves), which produce photosynthates in excess of their own needs, export photosynthates to ‘sink’ organs via the plant vasculature. the space, inside the plasma membrane, which encompasses the cytoplasm and all cell organelles. hair-like structures on the leaf surface involved in plant defense; they affect leaf-surface properties such as hydrophobicity and roughness. the electrokinetic potential in colloidal systems, for example, NP dispersions. It provides information about the magnitude of the surface charge of NPs in solution.