Department of Civil Engineering, McGill University, Montreal, Quebec H3A 0C3, Canada.
Department of Plant and Environmental Sciences, University of Copenhagen, Frederiksberg 1871, Denmark.
Environ Sci Technol. 2023 Dec 26;57(51):21704-21714. doi: 10.1021/acs.est.3c06424. Epub 2023 Dec 11.
Foliar application of nutrient nanoparticles (NPs) is a promising strategy for improving fertilization efficiency in agriculture. Phloem translocation of NPs from leaves is required for efficient fertilization but is currently considered to be feasible only for NPs smaller than a cell wall pore size exclusion limit of <20 nm. Using mass spectrometry imaging, we provide here the first direct evidence for phloem localization and translocation of a larger (∼70 nm) fertilizer NP comprised of ZnO encapsulated in mesoporous SiO (ZnO@MSN) following foliar deposition. The Si content in the phloem tissue of the petiole connected to the dosed leaf was ∼10 times higher than in the xylem tissue, and ∼100 times higher than the phloem tissue of an untreated tomato plant petiole. Direct evidence of NPs in individual phloem cells has only previously been shown for smaller NPs introduced invasively in the plant. Furthermore, we show that uptake and translocation of the NPs can be enhanced by their application on the abaxial (lower) side of the leaf. Applying ZnO@MSN to the abaxial side of a single leaf resulted in a 56% higher uptake of Zn as well as higher translocation to the younger (upper) leaves and to the roots, than dosing the adaxial (top) side of a leaf. The higher abaxial uptake of NPs is in alignment with the higher stomatal density and lower density of mesophyll tissues on that side and has not been demonstrated before.
叶面施用营养纳米颗粒（NPs）是提高农业施肥效率的一种很有前途的策略。 NPs 从叶片中经韧皮部转运是实现高效施肥所必需的，但目前认为只有小于细胞壁孔大小排除限制(<20nm)的 NPs 才可行。本文利用质谱成像技术，首次直接证明了较大（约 70nm）肥料 NPs ZnO@MSN（ZnO 封装在介孔 SiO 中）在叶面沉积后，可通过韧皮部定位和转运。与施药叶片相连的叶柄韧皮组织中的 Si 含量比木质部组织高约 10 倍，比未经处理的番茄叶柄韧皮组织高约 100 倍。只有以前通过对植物进行侵入性处理才能证明较小的 NPs 可以在单个韧皮细胞中存在。此外，我们还证明了 NPs 的吸收和转运可以通过将其施用到叶片的下（背面）侧来增强。将 ZnO@MSN 施用到单个叶片的下侧，与将其施用到叶片的上（正面）侧相比，叶片中 Zn 的吸收增加了 56%，并且向更年轻（上部）叶片和根部的转运也增加了。 NPs 在背面的更高吸收与该侧更高的气孔密度和更低的叶肉组织密度相一致，以前尚未证明过这一点。
