He-Yi
Zhang
and
Wen-Hao
Su
*
College of Engineering, China Agricultural University, 17 Qinghua East Road, Haidian, Beijing 100083, China. E-mail: wenhao.su@cau.edu.cn
First published on 17th April 2024
Nanotechnology offers a viable solution to enhancing agricultural sustainability by supporting seed germination and crop growth. Besides augmenting crop yields and mitigating the effects of abiotic stresses on crops, nanoparticles (NPs) can also serve as carriers to amplify the effectiveness of fertilizers and pesticides by facilitating their gradual or highly targeted release. However, application of NPs in agricultural systems can result in interaction with crops and pave the way for transfer along the food chain, which raises concerns for consumers. To address these matters, this article provides a comprehensive review of the tracking of various NPs delivered to crops through different uptake pathways. Three types of NPs (including inorganic, carbon-based, and organic NPs) are highlighted for uptake, transport, and their impact on crop growth in agricultural crops. NPs can enter the plant via seeds, roots, and leaves, while the translocation of NPs mainly involves the apoplastic and symplastic pathways. The influence of NPs on plant growth highly depends on the specific plant species as well as the type, size, charge, and concentration of NPs. NPs emit fluorescence through inherent photoluminescence or in combination with fluorescent dyes, which enables monitoring of their distribution within the crop. The benefits and challenges of NPs are discussed, establishing signposts for future research that will enable NPs to contribute to precise and sustainable agriculture.
Environmental significanceApplication of NPs in agricultural systems can result in interaction with crops and pave the way for transfer along the food chain, which raises concerns for consumers. It is necessary to fully characterize the potential risks of NPs to avoid negative impacts on the environment, plant health and human health. To address these matters, this article provides a comprehensive review of the tracking of various NPs delivered to crops through different uptake pathways. The benefits and challenges of NPs are discussed, establishing signposts for future research that will enable NPs to contribute to precise and sustainable agriculture. |
With the introduction of nanotechnology into modern agriculture, traditional agricultural strategies are shifting towards precision farming to ensure cost-effective and sustainable forms of food security.12 The classification of NPs is a prerequisite for studying the effect of NPs on crops as the same types of NPs have similar properties. Usually, researchers divide NPs into organic, inorganic, and carbon-based NPs.1,13 When the plant is exposed to the NPs, it will absorb the NPs through seeds, roots, and leaves as well as translocate them to other parts internally via apoplastic and symplastic pathways. Although applying NPs could increase crop yield, the accumulation of NPs in plants may adversely affect crops and may be transferred along the food chain, therefore it is necessary to understand whether NPs pose a risk to humans and the environment.14 Research focusing on the traces and effects of NPs in crops is still in the developmental stage. The application of NPs requires a thorough understanding of the mechanisms by which NPs are taken up and transported. However, tracking the different NPs entering the crop is difficult and requires proper monitoring strategies. The method of detecting NPs varies depending on the type of NPs. Fluorescence provides a powerful tool for tracking and imaging NPs in plants. In addition to relying on their own photoluminescence to generate fluorescence, NPs can also bind to functionalized probes.15 NPs with photoluminescence can be referred to as luminescent NPs (LNPs), including mainly semiconductor quantum dots, carbon dots, single-walled carbon nanotubes, graphene quantum dots and nanodiamonds.16 Apart from tracing their location in the planta using a range of analytical and imaging techniques, it is possible to track whether they escape from the plant into the soil or even to quantify them.17 A detailed understanding of the transport pathways of NPs will help researchers to better explore their mode of action and assess the possible hazards of NPs.18
This paper provides a comprehensive review of the tracking and influence of different NPs delivery to crops based on different uptake pathways. There are many previous review articles related to this topic. For example, Su et al. review critical plant morphological and physiological indices for NP transport, and examine the efficacy of various delivery methods for NPs (foliar application, root application, and feeding/injecting directly into plant tissue) with an emphasis on NP transport efficiency throughout the entire plant.19 Gao et al. described uptake and translocation of NPs in plants, and summarized impacts of NPs on plants.20 Wang et al. focused on the effect of size, surface charge and chemical composition of NP on the absorption and transportation in leaf and root through different ways.21 Shrivastava et al. highlighted existing as well as promising developments in the area of ENPs detection and quantifications in soil–plant system.22 Unlike the aforementioned literature, the uptake and translocation of three types of NPs (inorganic, carbon-based, and organic NPs) in plants are highlighted in this article. The mechanisms and differences in uptake (seeds, roots, and leaves) and transport pathways (apoplastic and symplastic pathways) are analysed and compared to understand how NPs enter the plant and are transported to other regions. The effect of NPs on plants depends upon the plant species and the physicochemical properties of NPs (such as type, size, shape, and charge of NPs). Methods of NPs detection after uptake and translocation (direct observation, analyses of elemental content, and novel technologies) are summarized. The photoluminescence of NPs and the fluorescence produced by NPs in combination with fluorescent dyes provide an effective way to traces of NPs in crop plants. This paper compiles the latest literature in the field of crop NPs technology and identifies the gaps in current research and future directions. The content of this article is expected to guide the application of NPs in agricultural production.
Fig. 1 Preferred reporting items for systematic reviews and meta-analyses flow chart (PRISMA 2020)23 of this review. |
Treatment | Advantages | Disadvantages |
---|---|---|
Foliar | Rapid uptake by plants | Potential phytotoxicity |
Targeted delivery of nutrients or pesticides to specific plant parts | Limited systemic effects as NPs may not distribute evenly throughout the plant | |
Enhanced effectiveness of pesticides through improved adhesion and penetration | Regulatory concerns regarding toxicity and environmental impact | |
Root | Enhanced nutrient uptake by plant roots. | Limited root absorption for some nanoparticles |
Reduced nutrient leaching and improved fertilizer efficiency | Potential interactions with soil components, affecting mobility and bioavailability | |
Increased plant resilience to environmental stresses | Uncertain regulatory status and compliance requirements | |
Contributes to sustainable agriculture by reducing fertilizer usage | Long-term effects on soil health and ecosystem functioning require further study | |
Seed | Improved seed germination rates and seedling vigor | Potential seed damage or inhibition of germination with improper formulation |
Protection against seedborne and soilborne pathogens | Concerns about nanoparticle residues accumulating in soil and water ecosystems | |
Reduction in the need for chemical pesticides and fertilizers | Regulatory requirements for safety assessments and compliance | |
Cost-effectiveness compared to conventional seed priming |
The other absorption pathway is through the cuticle covering the leaf surface. This pathway is also considered to be an important pathway as it has a larger area compared to the stomata. The cuticle has very small channels, which limits the size of NPs passively absorbed into the plant to <5 nm.42 Foliar application of ZnO NPs with different coatings to wheat and sunflower, respectively, was carried out by Read et al.49 The results showed that the cuticle of the plant leaves was the main route of uptake. However, characterization of the NPs used in this study revealed particle sizes of 40–50 nm, all of which were larger than 5 nm. The larger NPs were able to be absorbed by the plants through the cuticle probably due to the surfactant effect of the NP coating. The cuticle is a waxy porous layer while the surfactant can dissolve the epidermal wax, thus promoting the uptake of NPs by the leaves.50,51 The reason why such NPs, which are larger than the cuticle pores, are absorbed by plants through the cuticle has not been well explained, so more intensive studies on the role of the foliar cuticle in NP absorption are needed.
NPs entering the leaf via the two methods mentioned above transport to vasculature through several barrier (epidermis, palisade mesophyll, and spongy mesophyll) after passing through the cuticle. The NPs are transported to the bundle sheath cells that are connected to companion cells by either the apoplastic or symplastic pathway, and further to sieve-tube elements (STE) of the phloem. The apoplastic pathway is the passage through the cell wall pore followed by diffusion into the space between the cell wall and the plasma membrane or through the intercellular space without crossing the cell membrane.52 The symplastic pathway is a mode of transport from the interior of one cell to the interior of another through plasmodesmata.53 Currently, there is no consensus as to which is the major route of NPs transport.54 NPs reaching bundle sheath cells transport to vasculature through plasmodesmata. Then, NPs can be transported through the phloem to the roots, internalized with water and nutrients, and then transferred through the xylem to the aerial parts.55 The vasculature, consisting of xylem (apoplast) and phloem (symplast), determines the extent of NP translocation, making it essential to understand about the vasculature.46,56 The vasculature is the tube-like structure that connects the plant roots to the leaves, as shown in Fig. 2(C). The xylem channels allow the upward flow of water absorbed by the roots, while the phloem permits the transport of photosynthetic products from their source (photosynthetic organs producing sugars and amino acids) to their sink (developing tissues).54 The sieve tubes of the phloem have a higher local concentration of photosynthates compared to the surrounding xylem cells, leading to an osmotic exchange between xylem and phloem.57 The transport of NPs takes place during the osmotic exchange. A more detailed understanding of the transport after foliar uptake is essential to improve the efficiency of NP transport.
Fig. 3 Traces of NPs in crops. (A) Transmission electron microscopy of cross sections of roots containing FeNPs (yellow arrows indicate FeNPs).82 (B) Scanning electron microscope (SEM) images of leaf surfaces (bright white patches represent adherent graphene quantum dots modified with positively charged amino functional groups).83 (C) Confocal images of stems and roots of lettuce after carbon dots (CDs) treatment.84 (D) Fluorescence microscopy images of CDs in maize leaves (arrows show CDs).85 |
Tables 2–4 show the uptake, transport, and impact of crops on inorganic, carbon-based, and organic NPs, respectively. Plants can take up NPs and transport them systemically through root, seed, and foliar treatments. Internalization of NPs by plants may cause phytotoxicity. Understanding the uptake and transport of NPs is therefore fundamental to studying their toxic effects on plants. It has been reported that AgNPs were able to translocate from roots to shoots of soybean and wheat.86,87 Afzal et al. studied the transport of foliar absorbed FeO NPs in rice (Oryza sativa L.) which revealed that FeO NPs were absorbed by rice leaves and biodistributed throughout the plant by the vasculature.88 Hala et al. proposed TiO2 NPs as a medium for seed-priming.89 They studied the translocation of NPs in pomegranate seeds observing that TiO2 NPs could translocate cross the seed coat into the seed embryo. Recently, studies have focused on the use of mesoporous silica NPs as delivery systems for pesticides and fungicides in plants. Pan et al. found that bimodal mesoporous silica NPs can transport pesticide molecules for delivery to plants with excellent biological safety.90 Kou et al. treated tomato and lettuce seeds using CDs, showing that CDs were able to translocate to roots and stems.84 Ristroph et al. found that ZNPs could be taken up by soybean roots and biodistributed in the plant.91 Factors that influence absorption and transport are plant species, NP type, NP size, NP charge, and processing method. Malejko et al. found that radish, carrot, and lettuce all absorbed AuNPs, but the uptake was ranked from highest to lowest: radish, carrot, lettuce.92 Likewise, the translocation in each crop was different. This suggested that plant species affects nanoparticle uptake and transport. Yilmaz et al. found greater deposition of AgNPs with smaller sizes in the shoots and roots of maize seedlings, demonstrating the impact of nanoparticle size on uptake and transport.93 Similarly, Xu et al. found that the smaller the size of the MSN, the easier it was to be absorbed and transmitted by the cucumber roots.94 Surface modification can change the charge of the NPs, thereby affecting the uptake of the NPs by the crop. Milewska-Hendel et al. found that AuNPs could not enter Barley's roots, which may be due to their modification of the AuNPs surface using polyethylene glycol.95 Zhu et al. found that positively charged NPs were more evenly distributed within wheat leaves and that smaller size NPs were more likely to enter the crop.96 Afzal et al. found that foliar treatment enabled rice to absorb more NPs than root treatment.97
NPs | Size | Morphology | Plant species | Exposure method | Concentration | Treatment medium | Uptake and translocation | Detection technique | Effects | Ref. |
---|---|---|---|---|---|---|---|---|---|---|
“—” indicates that the information is not available. Abbreviations: R—reference; AgNP–PVP—silver nanoparticles coated with polyvinylpyrrolidone; AgNP–CTAB—silver nanoparticles coated with cetyltrimethylammonium bromide; AgNPs—silver nanoparticles; MS—Murashige and Skoog; ICP-MS—inductively coupled plasma mass spectrometry; SERS—surface-enhanced Raman spectroscopy; AAS—atomic absorption spectrometer; AuNPs—gold nanoparticles; ATR-FTIR—attenuated total reflectance-Fourier transform infrared spectroscopy; CuO NPs—copper oxide nanoparticles; ICP-OES—inductively coupled plasma optical emission spectroscopy; FeNPs—iron nanoparticles; SEM—scanning electron microscope; EDS—energy dispersive X-ray spectroscopy; FeO NPs—ferrous oxide nanoparticles; FM—fluorescence microscopy; Fe2O3 NPs—hematite nanoparticles; VSM—vibrating sample magnetometer; Fe3O4 NPs—magnetite nanoparticles; TEM—transmission electron microscope; XRD—X-ray diffraction; CLSM—confocal laser scanning confocal microscopy; ZnO NPs—zinc oxide nanoparticles; n-ZnO—nanosized zinc oxide; ZnO NFs—ZnO nanoflowers; ZnO QDs—zinc oxide quantum dots; TiO2 NPs—titanium dioxide nanoparticles; XRF—X-ray fluorescence; BMMs—bimodal mesoporous silicas; FL-MSNs—fluorescent mesoporous silica nanoparticles; MSNs—mesoporous silica nanoparticles. | ||||||||||
AgNPs | 6 nm | Spherical | Annual ryegrass (Lolium perenne L.) | Root treatment | 0, 1, 5, 10, 20, 40 mg L−1 | NP suspension | Internalized AgNPs | ICP-OES | Inhibited growth and caused cell damage at high doses (10, 20, 40 mg L−1) | 99 |
AgNPs | 20–50 nm | Circular | Soybean (Glycine max) | Root treatment | 5 mg L−1 | NP suspension | Transported from roots to shoots | SEM, EDS | Compromised the root integrity of soybeans | 87 |
AgNPs | 35 ± 15 nm | Round | Candy leaf (Stevia rebaudiana B.) | Root treatment | 0, 12.5, 25, 50, 100, 200 mg L−1 | Gelling medium | Deposited between the intercellular spaces and reached leaves | FM | Stimulated growth at low dose while inhibited at high doses (50, 100, 200 mg L−1) | 102 |
AgNP–PVP | 80 nm | — | Tobacco (Nicotiana tabacum L.) | Root treatment | 25, 50, 100 μM | MS medium | Absorbed by roots and translocated to leaves | ICP-MS | Lead the induction of oxidative stress | 98 |
AgNP–CTAB | 40 nm | — | Tobacco (Nicotiana tabacum L.) | Root treatment | 25, 50, 100 μM | MS medium | Absorbed by roots and translocated to leaves | ICP-MS | Lead the induction of oxidative stress | 98 |
AgNPs | 56 nm | — | Maize (Zea mays L.) | Root treatment | 7.5 ppm | Hoagland solution | Accumulated in shoots | SERS | Inhibited crop growth | 93 |
AgNPs | 30 nm | — | Maize (Zea mays L.) | Root treatment | 1 mg kg−1 | Soil medium | Taken up by roots | AAS | Found no significant effects | 103 |
AuNPs | 5 nm | — | Tobacco (Nicotiana tabacum L.) | Root treatment | 100 mg L−1 | NP suspension | Presented throughout the plant tissue cross section | ICP-MS | — | 104 |
AuNPs | 2 nm | — | Rice (Oryza sativa L.) | Root treatment | 0, 50 μM | NP suspension | Translocated into plant stems and leaves from roots | ICP-MS | — | 105 |
AuNPs | 5 nm | Spherical | Barley (Hordeum vulgare L.) | Root treatment | 0, 50 μg ml−1 | Hoagland solution | No AuNPs entered the roots from the external solution | TEM, SEM | — | 95 |
AuNPs | 90.0 ± 4.5 nm | — | Carrot (Daucus carota), radish (Raphanus sativus L.), lettuce (Lactucca sativa L.) | Root treatment | 0, 500 mg | Soil medium | Taken up by all plants, but varied among species | ICP-MS | — | 92 |
AuNPs | 20–30 nm | — | Broad bean (Vicia faba L.) | Root treatment | 0, 20, 50, 100, 200 mg L−1 | NP suspension | Absorbed by roots and transported to the aboveground part | AAS | Had the toxicity performance | 106 |
AuNPs | 1–5 nm | Spherical | Parsley (Petroselinum crispum) | Root treatment | 0, 1, 5, 10, 50, 100, 200 mg L−1 | Soil medium | Taken up by roots and translocated to leaves | ICP-MS | Increased the content of pigments at low concentrations (0, 1, 5, 10 mg L−1) | 107 |
CuO NPs | 39 ± 3 nm | Spherical | Leaf mustard (Brassica juncea) | Root treatment | 0, 200, 500, 1000, 1500 mg L−1 | Hoagland solution | Traveled from roots to shoot and up to the leaf | XRD | Accumulated reactive oxygen species at high doses (1000, 1500 mg L−1) | 108 |
CuO NPs | Around 46.1 nm | — | Rape (Brassica napus L.) | Root treatment | 10, 50, 100 mg kg−1 | Soil medium | Translocated from roots to leaves | ICP-OES | Damaged roots | 109 |
CuO NPs | 30–50 nm | — | Barley (Hordeum sativum L.) | Root treatment | 300, 2000, 10000 mg kg−1 | Soil medium | Accumulated in roots and transferred to stems | AAS | Impeded the development and productivity | 110 |
FeO2 NPs | 20–30 nm | Spherical | Rue (Ruta graveolens) | Root treatment | 50 μM | Hoagland solution | Accumulated in plant roots | AAS | Increased Fe bioavailability | 111 |
Fe2O3 NPs | — | — | Rice (Oryza sativa L.) | Root treatment | 50 mg L−1 | NP suspension | Accumulated in symplast and apoplast of roots | ICP-MS | Alleviated cadmium accumulation | 112 |
Fe2O3 NPs | 10 ± 3.2 nm | — | Rice (Oryza sativa L.) | Root treatment | 0, 2, 20, 200 mg L−1 | NP suspension | Penetrated the cell membrane and translocated to the shoots | ICP-MS, TEM | Decreased abscisic acid and indole-3-acetic acid concentrations in the roots | 113 |
Fe2O3 NPs | 14 nm | Spherical | Barley (Hordeum vulgare L.) | Root treatment | 50, 100, 200 mg L−1 | NP suspension | Absorbed by roots and reached leaves through stem | ICP-OES, VSM | Improved germination, plant growth, and biomass | 114 |
Fe3O4 NPs | 12 nm | Spherical | Barley (Hordeum vulgare L.) | Root treatment | 50, 100, 200 mg L−1 | NP suspension | Absorbed by roots and reached leaves through stem | ICP-OES, VSM | Improved germination, plant growth, and biomass | 114 |
Fe3O4 NPs | 10 nm | — | Common bean (Phaseolus vulgaris L.) | Root treatment | 0, 1000, 2000 mg L−1 | NP suspension | Absorbed by the roots, transported to stems and leaves | ICP-OES, VSM | Detected no toxicity visually | 115 |
Fe3O4 NPs | 17 nm | — | Hemp (Cannabis sativa L.) | Root treatment | 50, 100, 200, 500 mg L−1 | NP suspension | Dispersed throughout root cells | ICP-MS, TEM | Promoting hemp growth | 116 |
Fe3O4 NPs | 1–4 nm | Polydisperse | Mung bean (Vigna radiata) | Root treatment | 10, 100 mg L−1 | Hoagland solution | Absorbed by roots and translocated to shoots | ICP-MS | Had favorable effect on the photosynthetic parameters | 117 |
Fe3O4 NPs | 25 nm | Agglomerate | Barley (Hordeum vulgare L.) | Root treatment | 1, 10, 20 mg L−1 | NP suspension | Penetrated roots and translocated to leaves | CLSM | Increased the level of genotoxicity | 118 |
ZnO NPs | 386 ± 18.3 nm | — | Wheat (Triticum aestivum L.) | Root treatment | 100, 200, 400, 800 mg kg−1 | Soil medium | Transported to endodermis and vascular cylinder | CLSM | — | 119 |
ZnO NPs | <40 nm | — | Radish (Raphanus sativus L.) | Root treatment | 0, 0.1, 10, 100, 1000 mg L−1 | NP suspension | Absorbed by the seedlings | AAS | Shown toxic effects on root length, shoot length, and fresh weight | 120 |
ZnO NPs | 10–20 nm | Polydisperse | Mung bean (Vigna radiata) | Root treatment | 10, 100 mg L−1 | NP suspension | Absorbed by roots and translocated to shoots | ICP-MS | Observed no apparent benefit or toxicity | 117 |
ZnO NPs | 70 nm | — | Red perilla (Perilla frutescens) | Root treatment | 50, 100, 200 mg L−1 | Moss medium | Translocated to leaves | AAS | Increased plant biomass at low doses (50, 100 mg L−1) | 121 |
ZnO NPs | 37 ± 2 nm | Face-centered cubic | Rice (Oryza sativa L.) | Root treatment | 10, 50, 100, 500 mg L−1 | Hoagland solution | Biodistributed throughout the plant | AAS | Promoted plant protein and sugar content at low doses (10, 50 mg L−1) | 88 |
ZnO NPs | 20–30 nm | Spherical | Rice (Oryza sativa L.) | Root treatment | 10, 20, 50, 100 mg L−1 | NP suspension | Translocated from roots to shoots | ICP-MS | Decreased as accumulation | 122 |
ZnO NPs | 51 ± 18 nm | — | Pea (Pisum sativum L.) | Root treatment | 100, 200 mg L−1 | Hoagland solution | Clustered in the roots with limited transit | AAS | Decreased photosynthetic pigments | 123 |
TiO2 NPs | 14 nm | — | Wheat (Triticum aestivum L.) | Root treatment | 10 g L−1 | NP suspension | Accumulated in seedlings | XRF | Induced increased root elongation | 124 |
TiO2 NPs | 20–160 nm | — | Tomato (L. esculentum) | Root treatment | 0, 20 μg mL−1 | Soil medium | Absorbed and accumulated in roots | ICP-OES | Decreased the leaf dry matter | 125 |
TiO2 NPs | 32–171 nm | Agglomerate | Wheat (Triticum aestivum L.) | Root treatment | 0, 10, 100, 1000 mg L−1 | Hoagland solution | Translocated to shoots from roots | ICP-MS | Increased abscisic acid content | 126 |
TiO2 NPs | 30 nm | — | Radish (Raphanus sativus L.) | Root treatment | 0, 5 mg L−1 | NP suspension | Translocated up to aboveground organs | ICP-MS | — | 127 |
TiO2 NPs | 35.7 ± 1.2 nm | Spherical | Wheat (Triticum aestivum L.) | Root treatment | 0, 5, 10, 30 mg L−1 | NP suspension | Taken up by roots | ICP-MS | Shifted the trend of ionic flux | 128 |
TiO2 NPs | — | — | Spinach (Spinacia Oleracea L.) | Root treatment | — | Soil medium | Translocated from roots to shoots | SEM, EDS | Enhanced photosystem II | 129 |
TiO2 NPs | 23.0 ± 1.6 nm | Spherical | Fenugreek (Trigonella foenum-graecum L.) | Root treatment | 0, 50, 100 mg L−1 | Hoagland solution | Transported to stem and leaves | ICP-OES | Damaged root cellular membranes | 130 |
SiO2 NPs | — | — | Rice (Oryza sativa L.) | Root treatment | 0, 50 μg ml−1 | NP suspension | Observed an upward translocation to the shoot system | FM | Detected no negative effects on germination | 131 |
SiO2 NPs | 30 ± 10 nm | — | Cotton (Gossypium hirsutum L.) | Root treatment | 0, 10, 100, 500, 2000 mg L−1 | NP suspension | Transported from roots to shoots via xylem sap | ICP-OES, TEM | Decreased plant height and biomass | 132 |
SiO2 NPs | 13.3 ± 0.1 nm | Spherical | Wheat (Triticum aestivum L.) | Root treatment | 0, 10, 50, 100 mg L−1 | NP suspension | Taken up by roots | FM | Caused root damage | 133 |
MSNs | 20 nm | Spherical | Lupin (Lupinus Linn) | Root treatment | 0, 0.1 mg mL−1 | MS medium | Taken up by roots and translocated in the vascular system | CLSM | Had no effect on seed germination and radicle length | 134 |
MSNs | 20 nm | Spherical | Wheat (Triticum aestivum L.) | Root treatment | 0, 0.2 mg mL−1 | NP suspension | Penetrated the root cell wall, entered to the vascular tissue, and transported to the aerial parts | CLSM, TEM | Observed no negative effects on seed germination | 135 |
MSNs | 15 nm | Spherical | Cucumber (cucumis sativus L.) | Root treatment | 0, 0.3 mg mL−1 | NP suspension | Entered plant and translocated upward to other parts | CLSM | — | 94 |
FeNPs | 10–80 nm | Chain, spherical, semi-spherical or ellipsodial | Spring wheat (Longchun 29) | Seed treatment | 5, 10, 15 mg L−1 | NP suspension | Absorbed by seeds | TEM, EDS | Enhanced growth performance | 82 |
CuO NPs | 79.9 nm | — | Soybean (Glycine max L.) | Root and foliar treatment | 75, 300 mg kg−1 | Soil medium | Absorbed through the medium, but limited transit | ICP-OES | Found plant growth-promoting effect | 136 |
BMMs | 20–50 nm | Spherical | Tomato (Solanum lycopersicum L.) | Root and foliar treatment | 0, 5 mg mL−1 | NP suspension | Absorbed and translocated in plants | FM | — | 90 |
AgNPs | 15–100 nm | Spherical | Wheat (Triticum aestivum L.) | Seed treatment | 0, 8 mg L−1 | NP suspension | Accumulated in roots and translocated to aerial parts | AAS | Reduced root growth significantly | 86 |
AuNPs | 10 nm | — | Chickpea (Cicer arietinum L.) | Seed treatment | 0, 2.15 mg mL−1 | NP suspension | Transferred from root system to upper part | ATR-FTIR | — | 137 |
CuO NPs | <50 nm | Spherical | Buckwheat (F. esculentum) | Seed treatment | 0, 50, 500, 2000, 4000 mg L−1 | NP suspension | Entered the endodermis of buckwheat root cells | TEM | Inhibited root growth at high doses (2000, 4000 mg L−1) | 138 |
CuO NPs | 42.80 nm | — | Cucumber (Cucumis sativus L.) | Seed treatment | 50, 100, 200 mg kg−1 | Soil medium | Translocated to shoots and leaves | ICP-OES | Stimulated cucumber growth | 139 |
Fe2O3 NPs | — | — | Chickpea (Cicer arietinum L.) | Seed treatment | 0, 0.022, 1.1 g L−1 | NP suspension | Transported through the shoot and localized in the leaves | ATR-FTIR, ICP-OES | Increased plant growth and fruit production | 140 |
Fe3O4 NPs | 14 nm | — | Soybean (Glycine max L.) | Seed treatment | 50, 100 mg L−1 | Hoagland solution | Accumulated in plant roots | VSM, XRD | Found positive effects on root hair formation | 141 |
ZnO NPs | 30 ± 10 nm | — | Rice (Oryza sativa L.) | Seed treatment | 25, 50, 100 mg L−1 | NP suspension | Transferred from seeds to seedling | TEM, EDS | Had no effects on seed germination | 142 |
ZnO NPs | 15–40 nm | — | Wheat (Triticum aestivum L.) | Seed treatment | 50, 100, 150, 200 mg L−1 | NP suspension | Accumulated in roots and shoots | AAS | Decreased α-amylase activity at high doses (150, 200 mg L−1) | 143 |
TiO2 NPs | 45.14 nm | Irregular | Pomegranate (Punica granatum L.) | Seed treatment | 0, 40 mg L−1 | NP suspension | 144 | TEM | — | 89 |
SiO2 NPs | 17.23 nm | AgglomerateIrregular | Arugula (Eruca sativa) | Seed treatment | 0, 100, 250, 500, 1000 μg L−1 | NP suspension | Found in root, shoot and leaf tissues | EDS | Improved plant biometrics and physiology | |
CuO NPs | 18.51 ± 1.56 nm | — | Lettuce (Lactuca sativa L.) | Foliar treatment | 0, 1 mg L−1 | NP suspension | Entered leave via the stomata | ICP-MS | — | 145 |
CuO NPs | 40–200 nm | — | Lettuce (Lactuca sativa L.) | Foliar treatment | 100, 1000 mg L−1 | NP suspension | Absorbed by leaves and translocated to roots | AAS | Triggered oxidative burst | 146 |
FeO NPs | 27 ± 2 nm | Face-centered cubic | Rice (Oryza sativa L.) | Foliar treatment | 10, 50, 100, 500 mg L−1 | NP suspension | Biodistributed throughout the plant | AAS, FM | Inhibited plant growth at high doses (100, 500 mg L−1) | 88 |
Fe2O3 NPs | 34.48 nm | Spherical | Watermelon (Citrullus lanatus L.) | Foliar treatment | 10, 50, 100, 500 ppm | Aerosol | Passed through the shoots and reached the roots | ICP-OES | — | 147 |
Fe2O3 NPs | 20.2 ± 11.3 nm | Spherical | Pomelo (Citrus maxima) | Foliar treatment | 20, 50, 100 mg L−1 | NP suspension | Absorbed by leave, but no downward transported from shoots to roots | AAS | Observed no phytotoxicity at lower concentrations (20 and 50 mg L−1) | 148 |
n-ZnO | 13.3 ± 0.3 nm | Spherical | Alfalfa (Medicago sativa L.) | Foliar treatment | 30, 60, 90 mg L−1 | NP suspension | Found in vacuoles of the mesophyll cells | ICP-MS, TEM | Upregulated alfalfa growth under heat stress | 149 |
ZnO NFs | 18.1 ± 0.7 nm | — | Lettuce (Lactuca sativa L.) | Foliar treatment | — | NP suspension | Trapped on the leaves | FM | Showed higher photosynthetic parameters | 150 |
ZnO NPs | 40 nm | Spherical | Wheat (Triticum aestivum L.) | Foliar treatment | 2 mmol L−1 | NP suspension | Distributed homogeneously on and within the leaf | CLSM | — | 96 |
ZnO QDs | — | Spherical | Tomato (Solanum lycopersicum L.) | Foliar treatment | 0, 1, 5, 15, 25, 50 mg L−1 | NP suspension | Translocation from shoots to roots via phloem | CLSM | Enhanced seedling fitness and leaded to higher biomass | 151 |
ZnO QDs | 3.76 nm | Mono-disperse | Lettuce (Lactuca sativa L.) | Foliar treatment | 0, 50, 100, 200, 500 mg L−1 | NP suspension | Absorbed by root | CLSM | Improved biomass and nutritional quality at low doses (0, 50, 100, 200 mg L−1) | 152 |
FL-MSNs | — | — | Tomato (Solanum lycopersicum L.) | Foliar treatment | 0, 22.5 g ai hm−2 | NP suspension | Entered tomato plant tissues from root effectively. | FM | — | 153 |
FL-MSNs | — | — | Pakchoi (Brassica chinensis L.) | Foliar treatment | 0, 22.5 g ai hm−2 | NP suspension | Found in various parts of the plant. | FM | — | 154 |
MSNs | 20–50 nm | Spherical | Rice (Oryza sativa L.) | Foliar treatment | 0, 0.1 mg mL−1 | NP suspension | Translocated to different parts of the rice plants | CLSM | — | 155 |
NPs | Size | Morphology | Plant species | Exposure method | Concentration | Treatment medium | Uptake and translocation | Detection techniques | λ ex/λem (nm) | Influence | Ref. |
---|---|---|---|---|---|---|---|---|---|---|---|
“—” indicates that the information is not available. Abbreviations: R—reference; CDs—carbon dots; MWCNT—multi-walled carbon nanotubes; SWCNTs—single-walled carbon nanotubes; NH2-GQDs—graphene quantum dots modified with positively charged amino functional groups; OH-GQDs—graphene quantum dots modified with negatively charged hydroxyl functional groups; TEM—transmission electron microscope; FM—fluorescence microscopy; CLSM—confocal laser scanning confocal microscopy; ATY-FTIR—attenuated total reflectance-Fourier transform infrared spectroscopy; EDS—energy dispersive X-ray spectroscopy; SEM—scanning electron microscope. | |||||||||||
CDs | 2–6 nm | Spherical, or semi-spherical | Pumpkin | Root treatment | 0, 200, 400 and 800 mg L−1 | Hoagland solution | Entered the leaf cells | FM | — | Triggered the defense mechanisms | 156 |
CDs | 2 nm | — | Maize (Zea mays L.) | Root treatment | 1, 5, 10 mg L−1 | NP suspension | Passed through the whole plant | FM | 558/580 | Raised photosynthetic pigments | 85 |
CDs | 1.5–2.7 nm | — | Tomato (Solanum lycopersicum L.), lettuce (Lactuca sativa L.) | Root treatment | 0.033, 0.066, 0.132 mg mL−1 | NP suspension | Translocated to root and stem | CLSM | 289/410 | Improved absorbance of mineral elements and photosynthesis | 84 |
MWCNTs | 37.84 nm | Long tubes | Malabar spinach (Basella alba) | Root treatment | 50, 100, 150, 200 μg mL−1 | NP suspension | Absorbed and accumulated in leaves | EDS | — | Increased plant protein and chlorophyll content | 157 |
CDs | 3.07 ± 0.55 nm | — | Maize (Zea mays L.) | Seed treatment | 250, 500, 1000, 2000 mg L−1 | NP suspension | Translocated in maize | FM | 330–380/— | High concentration (1000, 2000 mg L−1) inhibited the growth. | 101 |
CDs | 4–6 nm | Spherical | Mung bean | Seed treatment | 0.02, 0.04, 0.12 mg mL−1 | NP suspension | Translocated to stems and leaves. | LSCFM, TEM | 405/— | Enhanced the photosynthesis | 158 |
Fullerol | 5.0 ± 0.7 nm | — | Bitter melon (Momordica charantia) | Seed treatment | 0.943, 4.72, 9.43, 10.88, 47.2 nM | NP suspension | Translocated to stem, petiole, leaf, and flower | FTIR | — | Increased biomass yield, fruit yield and phytomedicine content in fruits | 159 |
SWCNTs | — | Bundle | Chickpea (Cicer arietinum L.) | Seed treatment | 1.25 mg mL−1 | NP suspension | Transferred from root system to upper part | ATR-FTIR | — | — | 137 |
CDs | 3.25 ± 0.58nm | Tori-spherical | Rice (Oryza sativa L.) | Foliar treatment | 300μg mL−1 | NP suspension | Absorbed by leaves and evenly distributed | TEM | — | Increased chlorophyll content and shoot length | 160 |
CDs | 3.8 nm | Spherical | Tobacco (Nicotiana tabacum) | Foliar treatment | 0.01, 0.05, 0.1, 0.3 mg mL−1 | NP suspension | Absorbed by root and transported to stems and leaves | CLSM | 420/680 | Promoted plant growth and strengthened photosynthesis | 161 |
NH2-GQDs | 13.0 ± 1.8 nm | — | Maize (Zea mays L.) | Foliar treatment | 10 mg L−1 | NP suspension | Translocated to stems and roots | FM, SEM | 326/415 | Impaired the photosynthesis | 83 |
OH-GQDs | 14.1 ± 2.3 nm | — | Maize (Zea mays L.) | Foliar treatment | 10 mg L−1 | NP suspension | Translocated to stems and roots | FM, SEM | 300/393 | Impaired the photosynthesis | 83 |
NPs | Size | Morphology | Plant species | Exposure method | Concentration | Growth medium | Uptake and translocation | Detection techniques | Fluorescent labeling | λ exc/λem (nm) | Influence | Ref. |
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“—” indicates that the information is not available. Abbreviations: R—reference; ZNPs—zein nanoparticles; FITC—fluorescein isothiocyanate; FLNPs—fluorescent lignin nanoparticles; FM—fluorescence microscopy; FZNP–D—fluorescent zein nanoparticles synthesized with didodecyldimethylammonium bromide; LNPs—lignin-graft-poly(lactic-co-glycolic) acid nanoparticles; LNCs—lignin nanocapsules; FY088—fluorol yellow 088; PSI-NPs—polysuccinimide nanoparticles; PS—polystyrene; CLSM—confocal laser scanning confocal microscopy; Py-GC/MS—pyrolysis gas chromatography–mass spectrometry. | ||||||||||||
ZNPs | 135 ± 3 nm | Mono-disperse | Soybean (Glycine max L.) | Root treatment | 0.88 and 1.75 mg mL−1 | Hoagland solution | Biodistributed within the plant | — | FITC | 485/535 | — | 91 |
LNPs | 113.8 ± 3.4 nm | Spherical | Soybean (Glycine max L.) | Root treatment | 0.02, 0.20, 2.00 mg mL−1 | NP suspension | — | — | — | — | High doses increased root biomass | 162 |
LNCs | 200–250 nm | — | Eragrostis tef | Root treatment | — | NP suspension | Translocated to leaves. | FM | FY088 | 450/515 | — | 163 |
PS nanospheres | Around 80 nm | — | Rice (Oryza sativa L.) | Root treatment | 40 mg L−1 | NP suspension | Translocated from roots to aerial parts | CLSM | Nile blue | 620/680 | — | 164 |
PS nanoplastics | 63.82 ± 0.57 nm | — | Wheat (Triticum aestivum L.) | Root treatment | 100 mg L−1 | Hoagland solution | Translocated to stem, leaf, and root | FM | — | 620/680, 480/525 | Affected carbohydrate metabolism | 165 |
PS nanoplastics | 33.9–58.8 nm | — | Cucumber (Cucumis sativus) | Root treatment | 50 mg L−1 | NP suspension | Absorbed by root and transported to upper part | Py-GC/MS | — | — | — | 166 |
FLNPs | 52.9 ± 0.2 nm | — | Soybean (Glycine max L.) | Seed treatment | 5, 10 mg mL−1 | NP colloids | Entered between seed coat and cotyledons | FM | FITC | 480/535 | Plant viability was not affected | 167 |
FZNP-D | 138.8 ± 0.9 nm | — | Soybean (Glycine max L.) | Seed treatment | 5, 10 mg mL−1 | NP colloids | Entered under the seed coat | FM | FITC | 480/535 | Plant viability was not affected | 167 |
PSI-NPs | 14.2 ± 0.5 nm | — | Maize (Zea mays L.) | Seed treatment | 50, 100, 200, 400, 800 mg L−1 | NP suspension | — | — | — | — | Improved seedling growth | 75 |
The impact of NPs on crops varies depending on NP type, size, and concentration. Košpić et al. treated tobacco roots with AgNPs with different surface coatings found that AgNP–PVP treatment increased superoxide dismutase (SOD) activity and proline content, while AgNP–CTAB activated more catalase (CAT) and ascorbate peroxidase (APX).98 Different types of NPs have different effects on different indicators of plants. Yin et al. found that smaller AgNP particles (6 nm) more strongly affected plant growth than similar concentrations of larger (25 nm) particles.99 Smaller AgNPs with higher surface areas can better interfere with cell membrane function by directly reacting with the membrane and allowing many atoms localized at the surface to interact with cells. Generally, NPs have a hormesis effect on crops, which means that they promote crop growth at low concentrations and inhibit crop growth at high concentrations. Biocompatible carbon-based NPs and readily biodegradable polymeric NPs have higher critical concentrations than metal-based NPs. Castro-González et al. found that low doses (12.5, 25 mg L−1) of AgNPs simulated the growth of candy leaf, while high doses (50, 100, 200 mg L−1) inhibited the growth.100 Chen et al. found that CDs at 250 and 500mg L−1 showed no toxicity to maize, while 1000 and 2000mg L−1 CDs significantly reduced the fresh weight.101
Detection method | Strengths | Shortcomings |
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Abbreviations: SEM—scanning electron microscope; TEM—transmission electron microscope; EDS—energy dispersive X-ray spectroscopy; ICP-OES—inductively coupled plasma optical emission spectroscopy; ICP-MS—inductively coupled plasma mass spectrometry; AAS—atomic absorption spectrometry; XRD—X-ray diffraction; VSM—vibrating sample magnetometer; MPS—magnetic particle spectrometry; FM—fluorescence microscopy; CLSM—confocal laser scanning confocal microscopy; ATR-FTIR—attenuated total reflectance-Fourier transform infrared spectroscopy; SERS—surface-enhanced Raman spectroscopy; Py-GC/MS—pyrolysis gas chromatography–mass spectrometry. | ||
SEM | High-resolution | Destructive |
Suitable for elemental analysis by complementary techniques (EDS) | Incompatible with wet and liquid samples, which may require coatings | |
TEM | High-resolution | Destructive |
Suitable for elemental analysis by complementary techniques (EDS) | Incompatible with wet and liquid samples, which may require coatings | |
EDS | Generation of the elemental composition of individual particles | Biased towards heavy elements |
ICP-OES | Detection of the composition of tens of elements simultaneously with high sensitivity | Destructive |
Requirement for acid digestion | ||
ICP-MS | Detection of the composition of tens of elements simultaneously with high sensitivity | Destructive |
Requirement for acid digestion | ||
Provision of better selectivity than ICP-OES | ||
AAS | High sensitivity | Requirement for pre-concentration step prior to analysis |
Long detection time | ||
XRD | Provision of structural information | Requirement for a large amount of sample 1–3% weight limit |
VSM | Ability to distinguish between different magnetic behaviors | Destructive |
Detection of magnetic nanoparticles only | ||
MPS | Sensitive | Destructive |
Effective | Detection of magnetic nanoparticles only | |
FM | Direct observation | Need for fluorescent dye labelling |
Non-destructive | Understanding the wavelengths of excitation light and filters for dyes | |
CLSM | Direct observation | Need for fluorescent dye labelling |
Non-destructive | Understanding the wavelengths of excitation light and filters for dyes | |
ATR-FTIR | Little or no sample preparation required | Overlapping between NPs and other substances |
Fast analysis | ||
SERS | High sensitivity and selectivity | Not suitable for the determination of many complex samples |
Need for pretreatment | ||
Py-GC/MS | Sensitive to complex environments and low concentrations | Risk of misinterpretation, because different polymers have similar pyrolysis products |
The previous study demonstrated that crops can take up NPs through seeds, roots and leaves and transport them systematically in the crop, which then interacts with the crop. The data on the effect of NPs on plants are diverse and insufficient, making it difficult to draw general conclusions. What is certain is that it is related to plant species and the physicochemical properties of the NPs (such as type, size, and charge of NPs). In addition, most NPs have a dose effect on the crop, with high concentrations inhibiting crop growth and low concentrations promoting it. The threshold concentrations of biocompatible carbon-based NPs and readily biodegradable polymeric NPs are higher than those of metal-based NPs, which means that the dose must be selected according to the different species when using the corresponding NPs. This provides insight into the future application of NPs to agricultural systems.
Tracking of NPs in crops is necessary to reveal the principles of nanoparticle-crop interactions. Direct observation and analysis of elemental content are common testing techniques for tracking NPs. The latter is done by comparison with a control group which is not exposed to NPs. If the test part of the plant exposed to NPs contains more of the corresponding element, it proves that the part can absorb NPs or that NPs can be transferred from the absorbing part to the test part. However, since it is not possible to analyse the morphology of the NPs in the plant, it is not possible to determine whether the absorbed NPs are converted to the ionic state. If the morphology is to be analysed, a specific digestion procedure is required, which adds to the difficulty of the test. Another method uses the fluorescence produced by NPs for tracking, which has the advantages of simple operation, adjustable fluorescence, fast detection speed, and good reproducibility. Specifically, NPs produce fluorescence by photoluminescence and fluorescent dye labelling. Combined with laser confocal scanning microscopy or fluorescence microscopy, the position of fluorescent NPs in the crop can be quickly obtained. In addition, different doses of NPs produce different fluorescence intensities, so fluorescence intensity can be used for quantitative measurements. If fluorescence is detected in time after treatment, the path of NPs in the crop can be demonstrated. This provides a powerful means of tracing the pathways of NPs through the crop.
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