Optimising the foliar uptake of zinc oxide nanoparticles: Do leaf surface properties and particle coating affect absorption?

Abstract

Foliar absorption of zinc (Zn) is limited by several barriers, the first of which is the leaf cuticle. In this study, we investigated the absorption of Zn from Zn oxide nanoparticles (ZnO-NPs) in wheat (Triticum aestivum cv Gladius) and sunflower (Helianthus annuus cv Hyoleic 41) to determine the importance of NP surface coating for Zn absorption. Fourier transform infrared (FTIR) spectroscopy showed a higher polysaccharide content in the wheat cuticle than sunflower, indicated by a more pronounced glycosidic bond at 1020 cm −1 , but wax and cutin content were similar. Scanning electron microscopy (SEM) revealed that trichome density was twice as high in wheat (3600 AE 900 cm −2) as in sunflower (1600 cm −2) and stomatal density four times higher in sunflower (6400 AE 800 cm −2 in wheat and 22 900 cm −2 in sunflower). Suspensions of ZnO-NPs with coatings of different hydrophobicity were applied to leaves to compare Zn absorption using X-ray fluorescence microscopy (XFM) and inductively coupled plasma mass spectroscopy (ICP-MS). Absorption of Zn was similar between wheat and sunflower when Zn was applied at 1000 mg Zn l −1 , but much less Zn was absorbed from all ZnO products than from soluble Zn fertiliser. Particle coating did not affect Zn absorption, but it may facilitate particle adhesion to leaves, providing a longer-term source of resupply of Zn ions to the leaves. Differences in leaf surface characteristics did not affect Zn absorption, indicating that the cuticle is the main pathway of absorption under these conditions.

Nanobiofertilization as a novel technology for highly efficient foliar application of Fe and B in almond trees

“…This protective effect and process could have occurred under both sets of conditions in our experiment (growth chamber and field). This effect was observed recently for Zn nanoparticles in two different types of leaf, wheat and sunflower, for which the authors indicated that coating may facilitate particle adhesion to leaves, providing a long-term source of uptake of Zn ions into leaves [52]. Furthermore, this process probably did not occur with the Fe vesicles since some elements (such as Fe), due to their chemical properties, can compete for water, causing dehydration of the pore and cutting the flow between the two sides of the structure [53].…”

Insight into the Prospects for Nanotechnology in Wheat Biofortification

“…The Zn accumulated in leaves from foliar supply of ZnO NFs can be efficiently utilized in metabolic processes of plants [ 80 , 81 ]. This accumulation can be attributed to the direct absorption of ZnO NPs by the leaf cuticles of wheat plants and their movement across the leaf epidermis via stomata, their release in apoplast and then adhesion to the mesophyll cells irrespective of the particle coating [ 54 , 82 ].…”

Metabolomic Response of Early-Stage Wheat (Triticum aestivum) to Surfactant-Aided Foliar Application of Copper Hydroxide and Molybdenum Trioxide Nanoparticles

“…In another short-term exposure study (24 h), wheat leaves exposed to zinc salts containing 0.05 wt% of Tween20 resulted in about six times greater Zn content in wheat leaves than the ZnO NMs-Tween20 foliar exposure. However, no significantly Zn content differences were found among ZnO NMs-Tween20 suspensions with different coatings [29]. The authors proposed that ionic adsorption was likely the dominant mechanism for passing through the cuticular pathway.…”

“…Many factors can affect the effectiveness of NMs foliar application processes, including NM properties (e.g., size [28][29][30], concentration [31][32][33], zeta potential [30], response duration [31], and coating [29,30]), leaf surface characteristics (e.g., wax thickness, pores, trichomes, and epidermis maturity) [34,35], NM uptake pathways (i.e., stomata [32,36,37] vs. cuticle [29,30]), and environmental factors [2,[27][28][29]. For example, Avellan et al, (2019) investigated the effects of Au NMs sizes and coatings for wheat foliar exposure without the assistance of surfactants [30].…”