The Dimensional Increase of Cu-Based Nanomaterials Boosts Cu Accumulation and Reprograms Biosynthesis of Fatty Acids in the Cuticle and Wax of Crops

Copper oxide nanoparticles are commonly used in nanoscale agrochemicals. However, how morphological differences influence the behavior of copper nanomaterials (NMs) on leaves and their environmental impact remain unclear. Here, 50 mg/L of different dimensional Cu NM (nanoparticles, NPs; nanosheets, NSs; nanowires, NWs) suspensions were foliar applied to Cucumis sativus L. and Zea mays L. at a dose of 3 mL/plant for 21 days with a 7-day interval. Cu NS nanosuspension exhibited the smallest contact angle on the leaf surface, resulting in the greatest Cu accumulation in the leaves, especially in the cuticle. Cu NMs on the surface of epidermal cells demonstrated that NMs penetrated the cuticle. Compared to NPs, larger-sized NSs resulted in a 47–52% increase of total Cu accumulation in cuticle and wax of cucumber and maize. The Cu NMs upregulated hub genes, including ACCB, which are involved in leaf fatty acid synthesis and elongation, resulting in lipid accumulation in the cuticle, especially with Cu NSs and NWs, which enhance leaf tolerance to stress. Overall, the copper nanosheets and nanowires are more suitable for foliar application than copper nanoparticles. This study provides new insights into how modulating the nanoscale dimensions of materials can influence their foliar behavior and ecological effects.