Plant enrichment effects of quantum dots in agroecosystems: a double-edged sword

Abstract

Quantum dots (QDs) are increasingly used in diverse fields, and thus they inevitably spread unintentionally into the farmland ecosystem through (i) environmental release and (ii) intentional application in fertilizers, pesticides or growth promoters in agriculture. Several studies have shown that QDs can enter plants through leaf and root absorption and translocate throughout the plant, potentially affecting plant growth and development. At appropriate concentrations, QDs have been found to stimulate plant growth, enhance nutritional quality, improve resilience to abiotic stressors, and facilitate disease management. However, inappropriate concentrations of QDs, particularly those containing heavy metals or functional moieties such as hydroxyl and amino groups, may exert adverse effects including oxidative stress, cellular damage, growth retardation, and genetic toxicity. This review synthesizes the enrichment effect of QDs on plants in the farmland ecosystem from aspects such as the absorption pathway, transport mechanism, and its impact on plant growth, photosynthesis, stress resistance and yield. Accordingly, we propose that future research should be based on this “double-edged effect” to develop agricultural applications of QDs. Focus should be on elucidating the specific uptake and transport mechanisms of different types of QDs in different plant species, refining the preparation methods and application technologies of QDs, and rigorously assessing their ecological risks, to provide a sound scientific basis for the safe and effective use of QDs in agroecosystems aligned with determining their full agricultural potential.

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Environmental significance

The increase in production and application has resulted in a significant influx of quantum dots (QDs) into farmland ecosystems, potentially influencing plant growth and development. Crops are capable of absorbing these nanoparticles via leaves and roots and subsequently transporting them throughout their systems. At appropriate concentrations, QDs can stimulate crop growth, enhance nutritional quality, strengthen resistance to abiotic stress, and facilitate disease management. The strategic development and rational utilization of this beneficial effect could reduce reliance on agricultural chemicals, thereby minimizing traditional agricultural pollution. This approach offers precise and environmentally friendly solutions for plant disease management, addressing the challenges of food security and environmental sustainability in the context of climate change.

1 Introduction

Quantum dots (QDs) are semiconductor nanocrystals composed of elements from groups II–IV or III–V in the periodic table, with typical diameters ranging from 2 to 20 nanometers.¹ Based on composition, QDs can be broadly classified into metal-based QDs, carbon-based QDs, and perovskite QDs, each exhibiting distinct physicochemical and environmental behaviors.² Key physicochemical properties, such as particle size, crystal structure, surface functionalization and composition, determine their characteristics like emission wavelength, quantum yield and biocompatibility, all of which are crucial to their behavior in the ecosystems.³ For instance, surface functionalization with groups such as carboxyl, amino, or hydroxyl can enhance water dispersibility and reduce potential toxicity. Furthermore, QDs demonstrate strong size-tunable optical properties, characterized by narrow emission peaks and high quantum yields, which make them widely used in bioimaging, sensing, medicine and agriculture.^4–6 As the utilization of QDs has increased, global production reached 55 tons per year in 2012,⁷ and projections indicate a projected annual growth rate of 200% over the next few decades.⁸ However, the increased production of QDs unavoidably results in their prevalence in the environment due to the nature of the manufacturing process and the potential improper disposal.¹ A probabilistic analysis of material flow in electronic devices suggests that the majority of the QDs employed in these devices may be released into their surrounding environments during recycling. In contrast, about 20% of the QDs used in medical devices may eventually accumulate in soil at levels ranging from ng kg⁻¹ to μg kg⁻¹.⁹ Furthermore, based on the effectiveness of QDs in promoting plant growth and improving stress resistance, the intentional application of QD-based fertilizers, pesticides, or growth promoters inevitably results in the introduction of QDs into the farmland ecosystem. Therefore, soil serves as a potential destination for engineered nanomaterials (ENMs),¹⁰ and, likely, QDs will eventually accumulate either in soil or even in agricultural fields.

Plants are a vital component of terrestrial ecosystems¹¹ and significantly influence the environmental fate of various QDs. Kong et al. highlighted the crucial pathways for QDs and their ubiquitous transfer in the environment represented in plant uptake and bioaccumulation of QDs.¹² QDs could enter whole plants and seedlings through multiple plant sites (including plant leaves and roots) and reach each other through plant uptake and translocation.¹³ Concurrently, QDs exhibiting distinct surface attributes can modulate many plant-associated pathways such as physiological, biochemical, and physicochemical processes.¹⁴ This, in turn, could detrimentally influence plant growth, products, and metabolism. Consequently, when QDs enter farmland, a plant enrichment effect inevitably ensues, impacting the morphology and physiology of the plant,¹⁵ and may impact crop growth, yield, and the resistance to pests and diseases.

Thus, we review the environmental content and environmental fate of QDs and discuss the uptake and translocation of QDs by plants, considering both root-to-leaf and leaf-to-root perspectives. Subsequently, we examined the documented effects of QDs on plants in recent years, illustrating both beneficial and detrimental outcomes. Finally, a proposal was put forth regarding the rational utilization of the beneficial effects of QDs to regulate the growth of crops in agroecosystems, thereby mitigating any associated environmental risks.

2 Environmental content and environmental fate of QDs

2.1 Environmental content of QDs

According to Gallagher et al., the potential for environmental release exists throughout the entire life cycle of QD or QD-enabled products, such as encompasses synthesis, manufacturing, application, and end-of-life stages.¹⁶ The environmental concentration of QDs was expected to increase as the range of applications for QDs expands and the lifespan of specific QD species and devices using QDs lengthens.¹⁷ Nevertheless, owing to limitations in analytical capabilities, there have been no reports of experimentally derived environmental concentrations of nanoparticles.¹⁸ However, model-based estimates and predictions have been published in the relevant literature. For example, Gottschalk et al. employed a modeling approach to predict concentrations of QDs between various samples of water as follows: 0.2 and 45 μg kg⁻¹ in freshwater sediments, between 0.04 and 2 μg kg⁻¹ in seawater sediments, and 0.0001–0.013 μg kg⁻¹ QDs in sludge-treated soils, in Denmark, for the years 2000–2014.¹⁹ Based on accumulation of data from 1990 to 2014, Wang et al. projected that the range of QD concentrations in surface waters across seven European regions may fall within the range of 9.6–530 fg L⁻¹.⁹ On a global scale, the aggregate QD input to wastewater treatment facilities was estimated to range from 0.0057 to 0.456 metric tons per annum.

Furthermore, given the indiscriminate disposal of electronic products containing QDs, soil seems to be the most significant environmental sink for these particles.²⁰ Indeed, global emissions of QDs into the soil have been estimated to range between 6.1 and 30.9 tonnes per year as of 2021.⁸ However, the amount of QDs discharged from wastewater and deposited in sludge is considerably greater, with global emissions estimated to reach 55.29 tons per year by 2021.⁸ The disposal of QD-containing devices in landfill sites and their incineration have resulted in the expansion of landfills into a significant repository for QDs. During the combustion process, cadmium selenide quantum dots (CdSe-QDs) are released in the form of particles, and a proportion of the QDs are retained in the bottom ash or residue produced following incineration.²¹ More recently, Chopra et al. have demonstrated that products containing QDs, when discarded in landfills, result in the release of approximately 0.077 μg L⁻¹ QDs into the surrounding environment.²⁰ Moreover, the model developed by Wang et al. indicated that compared with natural soil (0.003–0.027 ng kg⁻¹), sewage-treated soils presented considerably elevated concentrations of QDs (0–17 ng kg⁻¹).⁹ Therefore, these findings suggest that QDs may be introduced into terrestrial ecosystems through treated sewage and sludge. However, the environmental concentrations of these expected QDs are orders of magnitude lower than those of most other commonly used nanoparticles (e.g., carbon nanotubes, TiO₂, ZnO, and Ag) due to the yield of QDs relative to other ENMs, lower solubility in the natural environment, and lower minimized environmental exposures designed into the use of QD products.^22,23 Consequently, it is noteworthy that the present concentration of QDs in the environment may exceed the predicted concentration.

2.2 Environmental fate of QDs

QDs that are released into or remain in the surrounding environment may be ingested by organisms and undergo dissolution in their bodies.²⁴ For instance, some QDs that enter freshwater environments could enter algal plants through macropinocytosis and be solubilized due to redox reactions, electrostatic attraction, or hydrogen bonding between QDs and biomolecules.²⁵ Furthermore, QDs present in the soil may be absorbed by root-bearing plants during nutrient uptake or water intake, subsequently accumulating in their bodies. For example, Whiteside et al. reported that after introducing QDs into fungus-inoculated bluegrass, the QDs were subsequently transported into the plant root tissues through the organic nitrogen uptake pathway facilitated by the plant root system.²⁶ For their part, Al-Salim et al. found that soil water-soluble QDs (cadmium selenide/zinc sulfide core–shell quantum dots (CdSe/ZnS-QDs)) could be taken up by onions, ryegrass, and chrysanthemums along with limited transport observed in the vascular system of their cut stems.²⁷

Concurrently, QDs with particular coatings may interact with compounds produced within plant tissues, such as proteins, amino acids, organic acids, sugars, and phenols, thus increasing aggregation. For instance, CdSe/Cd/ZnS-QDs with anionic coatings exhibit a relatively stable and uniform distribution in Arabidopsis leaves after uptake by Arabidopsis leaf axes and roots, whereas cationic and relatively neutral-coated QDs accumulate in Arabidopsis tissues.²⁸ Sun et al., in contrast, discovered that negatively charged polyethylene glycol-carboxyl-functionalized CdS/ZnS quantum dots (PEG-COOH-CdS/ZnS-QDs) as well as QDs functionalized with a neutral coating were able to undergo significant aggregation and form aggregates on the surfaces of primary, lateral, and fibrous roots of maize seedlings.⁴

Moreover, researchers found that after caterpillars were fed Arabidopsis leaves containing QDs, fluorescence from the QDs was detected in both the bodies and the debris of the caterpillars.²⁸ Similarly, Al-Salim et al. detected the fluorescence of QDs in the intestines and hemolymph of four different Lepidoptera after feeding on QD-containing plants for 2–4 days.²⁷ Lee et al. also observed the tertiary trophic transfer of QDs from protozoa to zooplankton to fish using bioimaging.²⁹ These results suggest that consumers have ingested QDs from water, plants, or animals through the food chain, which may be another home for QDs in the environment.

Additionally, the QDs that enter the environment may also be degraded by microorganisms or enzymes. For example, functionalized QDs may be degraded by fungal processes, specifically via the Fenton reaction.³⁰ In addition to fungi, researchers have shown that the human myeloperoxidase enzyme, expressed by neutrophils and eosinophils, could also degrade graphene quantum dots (GQDs).³¹ At the same time, carbon quantum dots (CQDs) could also be catalytically degraded in the presence of lipases.³² Nevertheless, few in-depth studies have evaluated the biodegradability of QDs within living organisms.

3 Uptake, translocation and biotransformation of QDs by plants

The specialized structures of terrestrial plants (such as stomata in leaves, pores, and fissures in roots) permit the exchange of gases and the uptake of nutrients from the external environment, thereby enabling plant growth and development³³ and providing potential avenues for the entry of QDs into land plants. Terrestrial plants are in direct contact with soil, water, and even the atmosphere, which represent the primary environmental components of agroecosystem QDs. Consequently, terrestrial plants may be exposed to QDs from many sources. Airborne QDs could be deposited on the surface of plant leaves or other air-contacted plant parts, where they may accumulate and enter the plant tissue through stomatal channels.^6,10 In contrast, QDs adsorbed on soil and sediment can penetrate root epidermal cell walls and cell membranes, enter the plant's vascular bundles (xylem) through a complex series of processes, and move toward the columnar structure through sympathetic transport and then into the leaf, as shown in (Fig. 1).³⁴

Fig. 1 QDs penetration in plant tissues and biotransformation pathways in plant cells. (a) Penetration pathway of QDs via plant tissue. (b) Biotransformation pathways of QDs in plant cells.

3.1 Root uptake and root-to-leaf translocation

3.1.1 Pathways for root uptake. In soil, QDs are transferred to aboveground parts after interacting with plant roots and accumulating in cells or suborganelles. It can be posited that the absorption of QDs from soil by plant roots represents the initial stage of bioaccumulation.³⁵ The initial contact between QDs and plant roots is achieved through the process of adsorption, which occurs on the root surface.^6,10 According to Khan et al., the root hairs could secrete chemicals such as mucus or organic acids (green shading in the lower right part of Fig. 1), which impart anionic charges to the root surface and facilitate the accumulation of cationic QDs on the root surface and increase their absorption.³⁶ Concurrently, the development of lateral roots furnished a novel adsorption interface for the QDs, thereby facilitating their penetration into the root column.³⁷ However, the root tips and root hair epidermis of primary and secondary roots have not yet reached full development. Following exposure, the QDs might directly contact the root epidermis and, subsequently, pass through it, as mentioned in ref. 38. Once within plant tissues, QDs could be internalized by cells through various mechanisms including ionic transport, endocytosis, binding to membrane proteins, and physical disruption of the cell membrane.¹⁵

The epidermal cells that constitute the root cell wall exhibit semipermeability, as evidenced by the presence of minute pores that impede the passage of nanoparticles with a diameter greater than a certain threshold. As a result, some QDs may stimulate the development of novel stomata within the epidermal cell wall, thereby facilitating their entry.³⁹ However, the restricted pore size of QDs restricts their access to cells via this pathway. Therefore, plant cells can internalize large-sized QDs through endocytosis. Endocytosis could result in the invagination of the plant cell membrane, thereby facilitating the internalization of QDs into the cell. For instance, plant protoplasts have been shown to take up QDs with a diameter less than 1 μm via endocytosis.⁴⁰ Li et al. reported that the root surface cells of woody plants facilitate the penetration of cadmium sulfide/zinc sulfide quantum dots (CdS/ZnS-QDs) through the plant cell wall/membrane via endocytosis, thus enabling their cellular uptake.⁷ Moreover, the increased specific surface area of QDs allows them to form complexes with different carrier proteins or root secretions and carry them inside the root cells.³⁶ For example, as demonstrated by Lian and Majumdar et al., the specific transporters present in soybean and rice plants can facilitate the effective translocation of cadmium sulfide quantum dots (CdS-QDs) and cadmium telluride quantum dots (CdTe-QDs) within the plants themselves.^41,42

3.1.2 Transport pathway of QDs at roots. As illustrated in (Fig. 1), when QDs are internalized by the root hair cells of land plants, they initially traverse a series of root barriers including the cuticle and epidermis. Afterwards, they pass through the cortex, endodermis, root cell wall, Casparian strip, and finally through the xylem system to reach the stems of the plant.³⁶ During this process, QDs usually selectively traverse the cell wall and subsequently enter the endodermis via apoplastic or symplastic transport.⁴³

Apoplastic and symplastic pathways are the two main routes for nanoparticle transport in the roots of land plants,⁴⁴ with the apoplast comprising the cell walls, intercellular spaces, and vascular tissues. QDs could migrate through extraplastidial plasmodesmata, traversing root cell walls, intercellular spaces, and xylem lumens, ultimately reaching the vascular bundle.⁴⁵ Nevertheless, when QDs are transported through the epidermis to the endodermis, they encounter Casparian bands, which impede their progression. Some QDs are deposited in the endodermis, whereas others undergo radial transportation along the Casparian strip, but not across it. However, the absence of fully developed Casparian strips at the lateral root junction resulted in reliance on the vascular system for QD transport.⁴⁶ An additional pathway is symplastic transport, which is how nanoparticles are transported between plant cells. Notwithstanding the relative autonomy and resilience of plant cells, cytoplasmic hyphae can establish intercellular connections across cell walls. Furthermore, the utility of cytoplasmic hyphae enables the transportation of QDs to continuous root cells and into endothelial cells.⁴⁷

3.2 Foliar uptake and leaf-to-root translocation

3.2.1 Pathways for foliar uptake. The cuticle and stomata serve as the primary routes of nanomaterial delivery to the leaves. The surface of the leaf is made up of a layer of wax called the cuticle, which contains nanoscale (2 nm) hydrophilic stomata and micron-sized stomata.¹⁵ Therefore, atmospheric QDs are readily adsorbed onto the surface of terrestrial plant leaves, where they are then absorbed by the plant via the cuticle or stomata on the leaf surface. The waxy cuticle found on the surface of leaves is primarily composed of lipid compounds, including long-chain fatty acids and monohydric alcohols.⁴⁸ It provides protection to plant leaves against water loss during the process of growth and acts as a natural barrier that prevents the intrusion of external pollutants into the leaves themselves.⁴⁹ However, the surface of the stratum corneum contains two distinctive channels,⁵⁰ which exhibit hydrophilic and lipophilic properties.

The diameter range of the hydrophilic and lipophilic channels is between 0.6 nm and 4.8 nm.⁵⁰ Hydrophilic channels permit the diffusion of hydrophilic QDs with a diameter of less than 4.8 nm; lipophilic channels, in contrast, allow lipophilic QDs to enter plant leaves through diffusion and osmosis.⁵¹ In a recent study, Hu et al. demonstrated that CQDs with a diameter of less than 2 nm could enter cotton leaves via the epidermal pathway.¹³ Nevertheless, the absorptive capacity of plants for QDs through the epidermal layer is limited by the narrow dimensions of the pore channels within the cuticle. Accordingly, it has been proposed that QDs may be taken up by plants through the stomatal pathway (Fig. 1).

Stomata are located on the surface of leaves and serve as gas exchange organs in terrestrial plants, allowing for the efficient transfer of ENPs from the leaf surface into chloroplasts.⁵² For example, Sun et al. discovered that GQDs primarily enter leaves through stomata, forming aggregates that gradually increase in size within the stomata.⁵³ In addition, Wang et al. employed laser confocal scanning microscopy to observe the entry of CdTe-QDs into plants via stomata, subsequently demonstrating their diffusion into anthers and ovules through vascular bundles.⁵⁴ Typically, the diameter of a single stomatal pore ranges from 10 to 100 μm on average, with considerable variation observed among different plant species. Nevertheless, the specific size exclusion limits for stomatal apertures and QD diffusion remain uncertain because of the distinctive geometry and physiological function of these structures.⁵⁵

3.2.2 Transport pathway of QDs in leaves. As with the root transport pathway, when QDs enter the chloroplast via the cuticle and stomata, they could be transported over considerable distances within the plant via the extracellular or plastidial pathway, ultimately reaching the roots.⁵⁶ The extracellular pathway primarily involves the movement of substances through the extracellular space. This method typically involves the diffusion of QDs within the interstitial space of cells and their subsequent movement through the cell wall. The movement of QDs through a cell wall is dependent upon the dimensions of the particles and the nature of their surface charge. They could be transported via the extracellular milieu, which encompasses the cell wall, the longitudinal channels that traverse the cell walls, the interlamellar regions, and the xylem.⁵⁵ For instance, GQDs could swiftly traverse the leaf–stem–root pathway in the direction of the root system within a single day following their initial entry into the plant conductance system.⁵³ The protoplast pathway involves transport primarily through intercellular channels and intercellular ligaments with diameters of approximately 2–20 nm.⁵⁷ Upon traversing the intercellular connecting filaments, QDs accumulate within the cytoplasm, where they are subsequently transported to both the endodermis and the Casparian strips of plants (Fig. 1).⁵⁸ The substances are subsequently transported from the leaves to the roots via the vascular system–plastid transport pathway. Furthermore, the substantial diameter of the phloem sieve tubes allows for straightforward transportation of some relatively large-sized QDs.⁵¹ Xu et al. observed the transport of QDs from the foliar surface of pumpkin after uptake through the plastidic pathway along the leaf–stem–root pathway and their accumulation in the plastidic ectodomain, which is taken up by chloroplasts, via confocal laser scanning microscopy.⁵⁹ These findings are also consistent with the transport of nitrogen-doped carbon quantum dots (N-CQDs) and CQDs in Arabidopsis thaliana and Pleurotus ostreatus.^60,61

3.3 Biotransformation of QDs by plants

Once internalized, QDs are not inert entities; instead, during their translocation across roots, stems, and leaves, they undergo a cascade of physicochemical transformations, including changes in chemical speciation, surface reconstruction, and the formation of biomolecular coronas.⁶² These transformations critically determine their bioavailability, tissue distribution, toxicological outcomes, and ecological risks while also influencing perturbations to photosynthetic and respiratory metabolism.⁶³ For instance, Marmiroli et al. demonstrated that CdS-QDs, upon interacting with oxygen- and sulfur-containing ligands such as organic acids, sulfur metabolites, proteins, and secondary metabolites, undergo progressive lattice destabilization.⁶⁴ This process generates trace Cd(II) and CdS_n clusters, which subsequently form stable complexes with thiol-rich molecules like glutathione and phytochelatins; the complexes are further compartmentalized in vacuoles, depicting a nano-specific biotransformation pathway distinct from the fate of ionic Cd. Furthermore, Pagano et al. emphasized that the core–shell architecture and surface ligand stability of QDs are decisive factors in determining whether particles undergo partial dissolution, surface redox reactions, or ligand rearrangements in planta.⁶⁵ Such transformations are intimately linked to the activation of oxidative stress signaling, induction of antioxidant defenses, and detoxification mechanisms, particularly those involving glutathione metabolism. Overall, the interplay between QD integrity and plant defense capacity determines biotransformation outcomes, and surface engineering offers a viable path toward safer agricultural applications.

4 Effects of QDs on plants

Once internalized by plants, QDs interact with cellular and subcellular structures, thereby altering plant morphology and physiological status.⁶⁶ As highlighted by Ma et al. in their discussion of plant responses to nanoparticle exposure—which is also applicable to QD–plant interactions—the effects of nanoparticles are inherently biphasic.⁶⁷ At low or optimal concentrations, they may promote seed germination,⁶⁸ enhance photosynthesis, stimulate growth,⁶⁹ and improve tolerance to abiotic stresses (Fig. 2). Conversely, at higher concentrations or in combination with certain chemical constituents, they can induce oxidative stress, DNA damage, chromosomal aberrations, and growth inhibition. Moreover, the magnitude and direction of these responses are strongly governed by the physicochemical properties of the nanoparticles, including their size, concentration, surface charge, and surface coatings as well as the developmental stage or species of the host plant. A unifying mechanistic basis underlying phytotoxicity involves the overproduction of reactive oxygen species (ROS) and subsequent metabolic reprogramming, which can disrupt both primary and secondary metabolism. For example, exposure to CdSe-QDs can lead to oxidative stress within plants, which in turn can result in physical damage⁷⁰ including cytotoxicity and genotoxicity.⁷¹

Fig. 2 Enrichment effect of soil plants on QDs. (a) The positive and negative effects mediated by QDs. (b) The mechanism of promoting seed germination and seedling growth mediated by the biotransformation of QDs in plants.

4.1 Positive effects

In recent years, researchers have studied the positive effects of QDs on soil plants, such as rice, corn, and wheat. The positive effects include the promotion of seed germination and root growth, enhancement of photosynthesis and biomass accumulation, and improvement of plant resistance to abiotic stresses and diseases,⁷² as described in Table 1.

Table 1 Positive effects of QDs on soil plants

Type of QDs	Plant species	Effects of QDs on plant	QD concentration applied	Mechanism of action	Reference
CQDs	Rice	Improved disease resistance and food production	0.56 g L^−1	Increased expression of thionin genes; degradation of CQDs to form phytohormone analogs and CO2; 42% increase in RuBisCO enzyme activity	73
CQDs	Rice	Promoted photosynthesis in rice plants, resulting in a significant increase in plant growth	300 mg L^−1	The electron transport rate and photosynthetic efficiency of photosystem II exhibit a notable increase, reaching 29.81% and 29.88%, respectively; the chlorophyll content and RuBisCO enzyme activity demonstrate a significant rise, reaching 64.53% and 23.39%, respectively	74
CQDs	Rice	In the presence of CQDs, photosynthetic rate and stomatal conductance were increased by 56% and 18% in rice and maize, respectively	150 mg L^−1	Promoted electron transfer rate during photosynthesis and increased the fluorescence quantum efficiency and CO2 assimilation rate and stomatal conductance were also improved	75
Magnesium–nitrogen co-doped carbon dots (Mg,N-CQDs)	Rice	The height, fresh biomass, and chlorophyll a and b content of rice seedlings were significantly increased	300 mg L^−1	The expression of genes associates with the biosynthesis of chlorophyll is increased; the levels of chlorophyll a and b are elevated by 14.39% and 26.54%, respectively; and the activity of the enzyme RuBisCO exhibits a 46.62% increase	76
Water-soluble carbon nano-dots (wsCND)	Wheat	Increased root and shoot growth	0.75 g L^−1	Easily crosses biological barriers in seedlings, carrying more nutrients and water for wheat plant growth	77
Cerium-doped carbon dots “”(CDs:Ce)	Wheat	Promoted the growth and development of wheat in the concentration range of 0.01–0.4 mg mL^−1, resulting in a 45% increase in root number, a 57% increase in root length, a 28% increase in leaf length and a 46% increase in plant height	0.01–0.025 g L^−1	Increased the accumulation of chlorophyll, enhanced light absorption, promoted photosynthesis, reduced MDA content, and improve POD activity	78
N-CQDs	Maize	Increased maize photosynthesis by 44.48%, maize yield by 24.50% and 1000 kernel weight by 15.03%	5–50 mg L^−1	Resulted in a significant increase in light conversion efficiency, chlorophyll content, psbA gene expression, ATPase activity, and NADPH production in maize; N doping led to a high separation efficiency of electrons and holes, thereby increasing light conversion and electron supply during photosynthesis	79
CQDs	Maize	Resulted in 20.9% and 39.6% increase in height and spike weight, respectively, as well as an increase in yield	150 mg L^−1	The hydroxyl and carboxyl groups on the surface of CQDs provided abundant binding sites for water molecules to enter the plant together with the CQDs and increased the maize CO2 assimilation rate and stomatal conductance by 16% and 18%, respectively	75
Orange carbon dots (O-CDs)	Maize	Increased the net photosynthetic rate of maize	1 mg L^−1 foliarly; 5 mg L^−1 rootly	O-CDs can increase the photosynthetic parameters of maize leaves and enhance photosynthetic pigments	80
N-CQDs	Maize	Increased the biomass of maize, promoted root growth, ensured the survival of maize under drought stress, and enhanced the drought tolerance of maize	5 mg L^−1	Increased superoxide dismutase activity and decreased malondialdehyde enzyme activity; improved light use efficiency, upregulated the expression of psbA gene, and promoted the rapid synthesis of D1 protein, thus repairing photosystem II under drought stress	81
CQDs	Maize	Increased root exudates, improved photosynthesis, increased the abundance of rhizosphere microorganisms, promoted nutrient uptake, and enhanced drought tolerance	5 mg L^−1	Improved the photo use efficiency and ability to contribute electrons to promote plant photosynthesis, scavenge ROS, upregulated the gene encoding isocitrate dehydrogenase, increased the synthesis of succinic acid	69
Silicon quantum dots (Si-QDs)	Cucumber	Increased the total fresh weight of seedlings by 51.91% and root water absorption by 74.6%	0.01–0.3 g L^−1	Induced a significant increase in the expression of water channel protein genes in the root system of cucumber seedlings and improved hydraulic conductance and transport in the root system	82
Zinc oxide quantum dots (ZnO-QDs)	Lettuce	Promoted the absorption and accumulation of Ca, Mg, Fe, Mn, Zn, and B in lettuce; increased the soluble sugar content of lettuce; and improved the biomass and nutritional quality of lettuce	50–200 mg L^−1	The low concentration of ZnO-QD treatment significantly increased lettuce soluble protein and soluble sugar content, induced antioxidant, improved plant resistance, promoted chlorophyll synthesis, and facilitated lettuce nutrient uptake	83
Si-QDs	Lettuce	Root length, seedling height and biomass of lettuce seedlings were significantly increased when the concentration of Si-QDs was less than 30 mg L^−1	<30 mg L^−1	Concentrations of Si-QDs less than 30 mg L^−1 resulted in increased chlorophyll production in lettuce, enhanced water and nutrient uptake by the root system, promoted photosynthesis in lettuce, and maintained the concentration of reactive oxygen species at a beneficial level	84
La2O3 + CdS-QDs	Zucchini	The stem length of zucchini was increased by 13–25%	500 mg L^−1	La2O3 stimulated cell elongation	85

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4.1.1 Promotion of seed germination and root growth. Seed germination constitutes the initial and most critical stage of plant growth, and the promotion of good seed germination is conducive to the advancement of overall plant development. The absorption of water is a prerequisite at all stages of seed germination.⁸⁶ It seems reasonable to suggest that one of the reasons that enable QDs to facilitate seed germination and enhance seed vigor is their capacity to traverse the impermeable seed coat and enhance water penetration, thereby promoting water absorption and seed germination.⁸⁷ For instance, Li et al. concluded via confocal microscopy that CQDs penetrated mung bean seed coats through gaps of thin-walled cells, diffusing into cotyledons and aggregating, thereby accelerating germination.⁸⁸

Wang et al. demonstrated that CQDs could facilitate mung bean seed development by increasing the permeability of the seed coat and enhancing seedling hydration.⁸⁹ Moreover, hydrophilic groups, namely –OH and –COOH, which are present on the QD surface, have been demonstrated to be involved in multiple crucial processes during seed germination including the development of roots, seed water content, and seedling length.^86,90 The presence of hydrophilic groups provides numerous binding sites for water, which is subsequently absorbed by the plant. Accordingly, sufficient water uptake could facilitate seed germination and accelerate seedling growth.^73,90 Also, Li et al. discovered that the hydrophilic groups on the surface of CQDs could readily bind to water molecules, facilitating transportation to rice seeds and ensuring adequate water levels in the seeds to promote germination and accelerate the growth of rice plants.⁷³

In addition to functioning as water adsorption sites, QDs may also stimulate aquaporin-related gene expression, facilitate cell growth by regulating the cell cycle, and thereby enhance seed germination and plant growth.⁹¹ Kou et al. observed that the hydrophilic groups of CQDs may facilitate enhanced water and mineral element uptake, promote root and hypocotyl elongation in seedlings, and accelerate seed germination by increasing the expression of genes associated with aquaporins.⁹² Therefore, it can be surmised that QDs may promote plant uptake of mineral nutrients in addition to promoting water absorption. The hydrophilic groups present on the surface of QDs can adsorb a diverse array of nutrient ions (including K⁺, Ca²⁺, Mg²⁺, Cu²⁺, Zn²⁺, Mn²⁺, and Fe³⁺) that are indispensable for optimal plant growth. These hydrophilic groups engage in both hydrogen bonding and electrostatic interactions with the nutrient ions, subsequently facilitating their adsorption onto the surface of the QDs. The nutrient ions enter the plant together with the QDs, resulting in an increased concentration of nutrient ions within the plant.⁹³ Li et al. elevated levels of nutrient ions in Arabidopsis treated with CQDs in comparison with the control, indicating that CQDs facilitate plant growth by adsorbing water and metal ions through their surface functional groups (–OH and –COOH) and transporting them to the plant.⁹⁰ Hu et al. demonstrated that the effect of CQDs was significantly dose-dependent. They reported notable increases in the levels of soluble sugars, proteins, vitamin C, minerals, and plant yields after being subjected to CQDs at concentrations exceeding 30 mg L⁻¹.⁹⁴

In conclusion, QDs have the potential to activate water channel proteins and lower the inter-root pH, which in turn could facilitate the uptake of water and nutrients, enhance the inter-root microbial environment, and stimulate seed germination and growth.⁹⁵ Nevertheless, the specific molecular mechanisms by which enzymes and phytohormones control seed germination remain unidentified. Consequently, future studies should focus on investigating alterations in related enzymes and phytohormones at the molecular level.

4.1.2 Enhance photosynthesis and crop yield. Distinctive nanostructures and atomic compositions, in conjunction with quantum binding effects, endow QDs with exceptional optical and electronic attributes, thereby enabling their utilization as electron donors and acceptors. Moreover, the uncomplicated functional alteration of their surfaces highlights their considerable potential for enhancing plant photosynthesis.⁹⁶ A substantial body of research has demonstrated that QDs could enhance plant photosynthesis through three principal mechanisms (Fig. 3): (1) accelerating the rate of electron transfer to chloroplasts and subsequently to light-trapping pigments results in an acceleration of the light reaction process; (2) promotion of the conversion of light or energy into chloroplasts, thereby increasing their photosynthetic activity; (3) facilitation of the synthesis of chlorophyll and the assimilation of CO₂ in plants.

Fig. 3 Principle of the mechanism by which QDs enhance plant photosynthesis.

In general, QDs, and CQDs in particular, exhibit exceptional luminescence properties, typically demonstrating pronounced absorption in the UV region (200–400 nm). The light absorption range of these materials can extend into the visible range due to the specific characteristics of their surface groups and the abundance of oxygen and nitrogen present in their carbon nuclei. Additionally, in the 500–800 nm range, QDs demonstrate longwave absorption, which has the potential to convert UV light that is not utilized by plants into visible light.^97,98 Therefore, QDs can enhance solar efficiency, increase the concentration of light-trapping pigments, and expedite electron transfer.⁹⁹ For example, in 2010, Nabiev et al. discovered that CdTe-QDs possess an “antenna effect” that could enhance the efficiency of chlorophyll photosynthesis by approximately threefold through resonant energy transfer with photopigments.¹⁰⁰ Additional research by Li et al. discovered that Si-QDs increased the contents of chlorophyll a and chlorophyll b in lettuce by 41.04% and 114.83%, respectively, and augmented the photosynthetic activity and electron transfer rate of chloroplasts, thus enhancing photosynthesis in lettuce.⁸⁴ Furthermore, QDs, as highly efficacious electron donors and acceptors, could augment plant photosynthesis through accelerated electron transfer efficiency, whereby electrons are transported to chloroplasts and subsequently to light-trapping complexes.⁸⁷ For instance, amine-functionalized CQDs are markedly coupled at the surface of chloroplasts, facilitating photon uptake and electron transfer to the chloroplasts, thereby accelerating the electron transfer chain within the photosynthetic reaction and consequently enhancing photosynthetic activity.¹⁰¹ Also, in 2021, Wang et al. demonstrated that N-doped CQDs are efficacious light-converting materials and electron donors that can augment light conversion and electron supply during maize photosynthesis, which could lead to a substantial increase of 122.80% in the photoelectron transfer rate.⁷⁹

In addition to facilitating the processes of photosynthesis that occur in the presence of light, QDs have been demonstrated to accelerate the dark reactions of this metabolic pathway. Carbon assimilation is understood to be the process by which CO₂ is reduced to sugar through absorptive forces (ATP and NADPH), which are the result of light reactions. This process is similarly crucial for plant growth. Ribulose bisphosphate carboxylase oxygenase (RuBisCO) is a pivotal enzyme within the Calvin cycle that has a decisive influence on the dark reaction of photosynthesis.¹⁰² Consequently, the activity of this enzyme directly impacts the rate of photosynthesis. It has been demonstrated that QDs could enhance their activity, accelerate the carbon reaction process, and improve their photosynthetic efficiency, thereby increasing their carbohydrate content.¹⁰³ According to Wang et al., the activity of the RuBisCO enzyme in mung bean seedlings treated with CQDs was 30.9% greater than that in mung bean seedlings than in the control group.⁸⁹ Similarly, CQDs were found to increase RuBisCo enzyme activity in other plants, including rice and A. thaliana. This increase in activity coincided with an increase in photosynthesis in these plants.^73,90 Li et al. reported that when various dicotyledonous plants were treated with CQDs, the activity of the RuBisCO enzyme increased by 30.9%, the quantity of carbohydrates increased, and the total yield of the plants increased by 20%.⁹⁰ Consistent with the findings of Zhang et al., their study examined the effects of distinct chiral CQDs on mung bean and found that D-chiral carbon quantum dots (D-CQDs) increased RuBisCo enzyme activity by 67.5%, which in turn enhanced carbohydrate production and promoted plant growth.¹⁰⁴ Furthermore, QDs could undergo degradation in plants, forming phytohormone analogs and releasing CO₂. The degradation of these hormones could promote growth in plants, while the released CO₂ could be incorporated into carbohydrates through the Calvin cycle, leading to an increase in carbohydrate accumulation.⁹⁰

4.1.3 Strengthening abiotic stress and disease resistance. In practice, crops are being exposed to a multitude of adverse abiotic environmental conditions including, but not limited to, drought, extreme temperature conditions, nutrient imbalances, elevated soil salinity, and heavy metal levels.¹⁰⁵ During periods of stress, plant cells undergo physiological and biochemical changes that could have detrimental effects on various aspects of plant growth, development, and productivity.¹⁰⁶ For example, post-flowering drought stress in rice and wheat could causes premature plant aging, a decline in material yield, a shorter seed filling period, and a reduction in seed weight.¹⁰⁷

The enhanced production of ROS constitutes a crucial mechanism by which abiotic stresses affect plant growth, and the accumulation of ROS within cells frequently results in damage to essential biomolecules, including proteins, lipids, carbohydrates, and DNA.¹⁰⁸ QDs enriched by plants may act as antioxidants with the ability to scavenge excess free radicals generated by abiotic stressors. As shown by Farhangi-Abriz et al., CQDs accumulation under drought stress induces a decrease in ROS production, lipid peroxidation, and osmotic stress in soybean, leading to an increase in the concentration of proline, soluble carbohydrates, and proteins, which in turn leads to improved osmoregulation and increased yield in soybean.¹⁰⁹ Concurrently, QDs have the potential to enhance the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), while simultaneously reducing the levels of ROS and malondialdehyde (MDA).¹¹⁰ In their investigations into the mitigating effects of CQDs on heat stress in lettuce, Wang et al. discovered that CQDs enhanced antioxidant enzyme activities and osmoregulation while simultaneously reducing lipid peroxidation damage to plant cells, thus improving the heat tolerance of the plant.¹¹¹ Thereafter, in 2022, Wang et al. discovered that under conditions of drought, CQDs could upregulate the GmNRT (mediates nitrate uptake in soybean roots), GmAMT (involved in ammonium uptake, especially during nodulation), GmLB (facilitates O₂ transport/homeostasis in root nodules), and GmAQP (regulates water and some solutes transport under stress) genes within the root system of soybean crops, leading to a notable increase in the N content and water uptake capacity of soybeans, thus enhancing the drought tolerance of soybean plants.¹¹² Additional research by Chai et al. illustrated that ZnO-QDs could reduce the levels of H₂O₂ and MDA, increase antioxidant enzyme activity, reduce the Na/K ratio, and modulate the expression of genes related to stress response pathways under salt stress in Salvia miltiorrhiza, thus jointly alleviating salt stress.¹¹³

Recent studies have indicated that the presence of QDs in plants may also enhance their resistance to pests and diseases, thereby reducing the overall incidence of yield loss and associated environmental risks. For instance, Wang et al. observed that ZnO-QDs induced the production of hydroxyl radicals in pathogenic bacteria, amplified the expression of genes associated with oxidative stress, and compromised intracellular defenses, culminating in cell lysis and death of the bacteria.¹¹⁴ This led to a substantial decrease in the prevalence of bacterial fruit blotch disease in melons. Luo et al. discovered that foliar uptake of N-CQDs induced the expression of jasmonic acid- and salicylic acid-dependent resistance pathways in tomato plants, which effectively inhibited pathogen growth and led to a 71.19% reduction in the symptoms associated with greening disease.¹¹⁵

Furthermore, studies have shown that QDs exhibit diverse effects on plant and microbial systems, which are highly dependent on their composition, concentration, and surface functionalization characteristics. At high concentrations or when using heavy metal-based QDs (e.g., CdTe-QDs, CdSe-QDs), QDs can generate ROS or induce photodynamic effects under light activation, causing broad-spectrum antibacterial and antifungal activity by disrupting cell membranes, damaging microbial DNA/RNA, and impairing cell wall integrity.^116,117 Such effects have been observed against both Gram-positive and Gram-negative pathogens.¹¹⁸ In contrast, at low or environmentally relevant concentrations, particularly for carbon-based (e.g., CQDs) and N-CQDs, these nanomaterials have demonstrated beneficial effects on plants and the rhizobiome. For instance, Luo et al. reported that foliar application of 10 mg L⁻¹ N-CQDs significantly suppressed tomato bacterial wilt by 71%, enhanced fresh shoot biomass by ∼56%, activated ROS scavenging systems, induced salicylic acid- and jasmonic acid-dependent systemic acquired resistance (SAR), and stimulated the tricarboxylic acid (TCA) cycle and fatty acid synthesis in tomato cells.¹¹⁵ Similarly, Kou et al. showed that spray treatment with CQDs at 240 mg L⁻¹ reduced the incidence of gray mold in Nicotiana benthamiana and tomato by 44% and 12%, respectively, and under simulated sunlight (480 mg L⁻¹), achieved broad-spectrum antifungal activity—up to 100% inhibition of Botrytis cinerea—by damaging fungal hyphae and spore structures while activating antioxidant enzyme responses in treated tissues.¹¹⁹

4.1.4 Improving the rhizosphere microbial community. The plant microbiome and the inter-root soil microbiome are both integral to the health of the plant and the yield of the crop. They are composed of bacteria and fungi in addition to other groups of organisms, including viruses, archaea, and protists.¹²⁰ These microorganisms play pivotal roles in the biogeochemical cycling of essential nutrients, including nitrogen, phosphorus, potassium, carbon, and sulfur. They are also instrumental in biochemical reactions that regulate crucial processes within ecosystems, including nutrient uptake, the production of antibiotics, biomass decomposition, biodegradation, the maintenance of soil structure, and the stimulation of plant tolerance. It is therefore inevitable that QDs enriched in plants will be exposed to these microorganisms, with a consequent impact on their communities.

A healthy plant-associated microbiome has been shown to enhance many important plant functions, including growth, nutrient uptake, and resistance to pathogens.¹²¹ In recent years, researchers have reported that the enrichment of QDs in plants can affect plant growth by modulating soil microbial activity at the level of root-to-root interactions. On the one hand, QDs exposed to the plant root system can act directly on the microbial community. For example, the presence of Si-QDs in radish rhizosphere soil, by enriching microorganisms mainly associated with the nitrogen cycle, can change the structure of soil bacterial communities and establish a healthy inter-root microenvironment, thus providing sufficient nitrogen resources for plant growth and defense against subterranean herbivores.¹²² A study by Yin et al. revealed that tomato rhizosphere exposed to 2.5 mg kg⁻¹ selenium-doped carbon quantum dots (Se-CQDs) showed a significant increase in the soil Actinobacteria and mycorrhizal phyla increased significantly in diversity and prevalence, while the inter-root soil microenvironment was also optimized to enhance the uptake of selenium (and other mineral nutrients), which ultimately promotes root development and plant growth.¹²³

On the other hand, the uptake of QDs by plants through leaves may affect the inter-root microbial community and soil metabolism, thereby improving soil microbiology and promoting plant growth. For example, Xu et al. observed that when pumpkin leaves were exposed to ZnO-QDs, the inter-root fungal community was altered through coordinated host–microbe and microbe–microbe interactions.¹²⁴ This resulted in the accumulation of beneficial microorganisms in endophytic and inter-root environments, which promoted plant growth, nutrient uptake, and adversity tolerance.^125,126 Furthermore, experimental evidence has demonstrated that foliar exposure to QDs results in a decrease in inter-root organic acid abundance. This phenomenon, in turn, has been shown to promote the growth of soil microorganisms associated with carbon and nitrogen, thereby exerting an effect on soil fertility and plant health.¹²⁷

4.2 Negative effects

As demonstrated in Table 2, the adverse impact of QDs on plants, particularly those with heavy metals, hydroxyl and amino functional groups, or relatively high concentrations, cannot be overlooked. The toxicity of QDs may cause damage to plants via several mechanisms including the stimulation of oxidative stress in the plant, which could result in physical damage, or the induction of oxidative damage, which might have toxic effects on the plant, thereby inhibiting growth and development.¹²⁸ Recent studies have consistently demonstrated that especially CdS-QDs exhibit phytotoxic effects across a wide range of concentrations, indicating that their toxicity is not limited to high-dose exposures. Multiple studies have reported that CdS-QDs disrupt fundamental metabolic pathways such as glutathione metabolism, the tricarboxylic acid cycle, and amino acid biosynthesis in soybean and other crops, leading to oxidative stress, impaired growth, and cellular damage.⁴² Similar observations have been made in wheat and maize, where CdS-QD exposure resulted in DNA damage, alterations in antioxidant enzyme activity, and inhibition of seed germination regardless of the applied concentration.^4,129 Similarly, Lian et al. reported that rice plants exposed to CdS QDs exhibited inhibited root development, altered antioxidative enzyme activity, and elevated cadmium accumulation regardless of the applied concentration.⁴¹ In A. thaliana, Marmiroli et al. discovered that CdS-QD toxicity followed a mechanism distinct from ionic cadmium toxicity, involving unique gene expression responses in resistant mutants, such as alterations in photosynthetic regulatory genes.¹³⁰ Further, Marmiroli et al. reported that 40–60 mg L⁻¹ CdS-QDs induced oxidative stress in A. thaliana, reduced chlorophyll and carotenoid content, and caused alterations in plant morphology.¹³¹

Table 2 Negative effects of QDs on plants

Type of QDs	Plant species	Effects of QDs on plant	QD concentration applied	Mechanism of action	Reference
CdTe-QDs	Wheat	Plant height, root length and total biomass were significantly reduced	25–400 mg L^−1	Causes antioxidant defense and programmed cell death in roots and shoots of wheat seedlings, leading to apoptotic body formation and DNA breaks	132
GQDs	Wheat	The contents of globulin, lamin, amylose, amylopectin and mineral elements in wheat grains decreased	0.5–50 μg kg^−1	Downregulation of the levels of proteins with nutrient reserve activity thus leads to changes in the protein structure of wheat grain and downregulation of α-amylase inhibitors, thus interfering with metabolic processes	133
CdS-QDs	Soybean	QDs accumulate in soybean roots and shoots and cause phytotoxicity	200 mg L^−1	Disrupts major metabolic pathways such as glutathione metabolism, the tricarboxylic acid cycle, glycolysis, fatty acid oxidation, and the biosynthesis of phenylpropanes and amino acids in soybeans	42
ZnO-QDs	Lettuce	When the concentration of ZnO-QDs increased (up to 500 mg L^−1), plant biomass decreased	500 mg L^−1	High concentrations of ZnO-QDs induced stress and altered the activity of antioxidant enzymes in lettuce, leading to membrane lipid peroxidation as well as an increase in MDA content, which disrupted the chloroplast membranes and led to a decrease in chlorophyll content	83
Si-QDs	Lettuce	At concentrations greater than 100 mg L^−1, the plants become greener but photosynthesis was also inhibited which in turn inhibits seedling growth and biomass production	>30 mg L^−1	When the concentration of Si-QDs was greater than 100 mg L^−1, the water uptake capacity of seedlings was inhibited, which led to oxidative damage and increased SOD activity and MDA content	84
Amino-functionalized graphene quantum dots (N-GQDs)	Lettuce	At a concentration of 50 mg L^−1, N-GQDs reduced the root elongation degree by 40%. When the concentration was increased to 100 mg L^−1, N-GQDs reduced the root elongation degree by 32%	50 mg L^−1, 100 mg L^−1	Causes oxidative damage, disrupts mineral and organic nutrient homeostasis, impairs plant photosynthesis and regulates phytohormone levels and causes light-triggered production of reactive oxygen species and oxidation of antioxidants in plants	134
Carboxyl-functionalized graphene quantum dots (C-GQDs)		At a concentration of 50 mg L^−1, C-GQDs reduced the root elongation degree by 36%, the root dry weight by 39%, the stem dry weight by 44%, the root fresh weight by 55%, and the leaf moisture by 74%, and the leaf moisture by 75%. When the concentration was increased to 100 mg L^−1, C-GQDs reduced the root elongation degree by 41%	50 mg L^−1, 100 mg L^−1
Hydroxyl-functionalized graphene quantum dots (O-GQDs)		When the concentrations were 1 and 10 mg L^−1, O-GQDs reduced the stem dry weight by 36% and 47% respectively, the root fresh weight by 74%, and the leaf moisture by 76%. When the concentration was 50 mg L^−1, O-GQDs reduced the root elongation by 41%, the stem elongation by 39%, the seed germination rate by 39%, the root dry weight by 43%, the stem dry weight by 55%, the fresh root weight by 31%, the stem fresh weight by 89%, and the leaf moisture by 90%. When the concentration was increased to 100 mg L^−1, the root elongation degree decreased by 85%, the stem elongation degree decreased by 88%, and the seed germination rate decreased by 71%	1 mg L^−1, 10 mg L^−1, 50 mg L^−1, 100 mg L^−1
CdTe/CdS/ZnS-QDs	Allium cepa L.	The adsorption of QDs on the surface of plant roots caused cadmium to accumulate in the roots and caused a reduction in plant root growth	30 μM, 100 μM	Cd-based QDs lack chemical stability when subjected to prolonged exposure. The release of Cd from QDs into the exposure medium occurs in the form of Cd^2+, which is subsequently absorbed and utilized by onion roots. The internalization of nuclear/shell QDs into plants is limited or negligible due to the plant cell wall thickness, the large size and aggregation of QDs, and the lack of endocytic capacity in the selected plant species	135
CdS-QDs	Zucchini	The fresh weight of the above-ground part was significantly reduced by approximately 21.9%	100 mg L^−1	High accumulation and transport of Cd lead to excessive generation of ROS and downregulation of photosynthetically related genes, thereby inhibiting carbon assimilation	85
CeO2 + CdS-QDs		Zucchini fresh weight was reduced by 23.4%	CeO2 500 mg L^−1 CdS-QDs 100 mg L^−1	Cd toxicity was dominant, and the transport pattern of Ce was significantly altered (Ce in the stem increased to 576 mg kg^−1), exacerbating metabolic interference

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4.2.1 Genotoxicity and oxidative stress damage. The transport and accumulation of QDs in plants have the potential to induce phytotoxicity. Furthermore, the interaction of QDs with plants leads to increased production of ROS, potentially resulting in oxidative damage and genotoxicity.¹³⁶ The genotoxicity of QDs was demonstrated by their ability to induce DNA damage, interfere with gene expression, and affect the cell cycle. Various studies have demonstrated that QDs induce single-strand and double-strand DNA breaks through the induction of oxidative stress in plant cells.¹³¹ Moreover, specific QDs, such as O-GQDs, have the potential to interact directly with DNA, thereby disrupting essential processes such as DNA replication and repair.⁷¹ Additionally, it is plausible that QDs may disrupt the expression of essential genes within plant cells, particularly those associated with DNA repair and cell cycle regulation, which might result in impaired cellular function.⁸⁸

In addition to their genotoxic effects, QDs have been demonstrated to induce ROS and trigger hormonal changes in plants. Presumably in all aerobic organisms, plant cells could be stimulated by environmental changes, thereby activating the production of ROS.¹³⁷ When ROS levels surpass the capacity of defensive mechanisms, a state of “oxidative stress” is initiated within the cellular milieu, resulting in indiscriminate damage to proteins and nucleic acids.¹³⁸ Verma et al. mentioned that QDs have been demonstrated to induce oxidative stress and ultimately lead to programmed cell death in plant systems.¹³⁹ For example, research by Shi et al. discovered that CdTe-QDs can decompose into highly toxic Cd within rice root cells, disrupting the redox homeostasis of the roots and leading to excessive accumulation of ROS and subsequent cell death.¹²⁹ This ultimately results in the inhibition of root and shoot growth. Recently, researchers evaluated the detrimental impacts of CdS-QDs on soybean plants and indicated that CdS-QDs induced oxidative stress and impaired amino acid metabolism in soybean leaves, resulting in the formation of lignin and hardening of the cell wall and reduced root growth.¹⁴⁰ Additionally, high concentrations of QDs may induce apoptosis in plant cells, which could have a detrimental impact on plant growth and development.¹³¹ Also, in 2010, Hu et al. showed that the internalization of QDs by plants predominantly influences their oxidative stress processes, and that high concentrations of QDs (>312.8 μM) exhibit cytotoxicity, specifically affecting maize seed germination and root growth.¹⁴¹

4.2.2 Inhibition of plant growth. The presence of QDs in soil can exert a considerable influence on the structural integrity and physiological functions of plants, with the potential for adverse effects on their growth and development. Upon entering the root epidermis, QDs were observed to cause root blockage, which in turn resulted in the deformation, swelling, and breakage of plant roots,^131,142 and the continued transport of QDs into the roots via the conduit may result in the formation of lesions on the leaves or other tissues,²⁸ leading to alterations in the cellular structure and subsequent effects on plant development.

Furthermore, after entering plant cells, QDs may disrupt the integrity of the cellular membrane, leading to the leakage of ions and an increase in membrane permeability. In response to the oxidative stress induced by QDs, plant cells typically initiate the antioxidant defense system and enhance the activity of antioxidant enzymes. However, this process results in the exhaustion of substantial quantities of antioxidant resources, which can impair cellular function and, consequently, plant growth and development.¹³¹ Additionally, it has been demonstrated that the presence of heavy metal QDs in soil may lead to a reduction in chlorophyll levels in plants.^131,132 As a consequence of this reduction, plant photosynthesis is adversely affected, which consequently affects plant growth and development.

5 Perspectives and future outlook

QDs are now widely detected in agroecosystems, and their enrichment by plants has become an unavoidable reality. In recent years, substantial advances have already been made in clarifying the uptake and transport pathways of QDs in plants, their regulatory effects on photosynthesis and stress tolerance, and their interactions with rhizosphere microbial communities. Likewise, numerous studies have revealed both the beneficial roles of QDs in stimulating seed germination, promoting growth, and enhancing stress resistance, and their adverse effects involving oxidative stress, DNA damage, and growth inhibition. These findings suggest that QD–plant interactions are not simply prospective issues but represent an active research field with a rapidly growing body of evidence.

Despite these advances, a critical gap remains in defining the precise conditions under which QDs exert positive versus negative effects on plant agroecosystems. Factors such as QDs' concentration, particle size, functionalization, and environmental context are decisive in shaping outcomes. Moreover, the outcome of QD exposure is strongly species-dependent, as an enhancement of photosynthetic efficiency or stress resilience in one crop species may, in another species, result in toxicity and growth inhibition. This plant-specific variability highlights the urgent need for systematic, comparative studies across representative crops to establish boundary conditions for safe and beneficial use.

Future research should therefore prioritize disentangling the molecular and biochemical mechanisms by which QDs regulate enzyme activity, phytohormone signaling, and DNA repair or cell cycle processes. At the same time, there is a pressing need to investigate the long-term transport, transformation, and ecological fate of QDs in soils and water bodies as well as their impacts on non-target organisms such as soil microbiota and insects. Rigorous risk assessments, including both acute and chronic toxicity tests, will be indispensable to ensure the safe deployment of QDs in agroecosystems. By integrating these mechanistic insights with ecological evaluations, future work can move beyond proof-of-concept studies to establish a rational framework for exploiting the beneficial effects of QDs while minimizing environmental risks.

Author contributions

Hao Cheng: writing – original draft, data curation, methodology. Yanxing Xu: writing – review & editing. Abdelrahman Ibrahim: writing – review & editing. Yanzheng Gao: writing – review & editing, conceptualization, supervision, funding acquisition. Hefei Wang: writing – review & editing, methodology, supervision. Ahmed Mosa: writing – review & editing, methodology, supervision. Wanting Ling: writing – review & editing, methodology, supervision.

Conflicts of interest

There are no conflicts of interest to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analyzed as part of this review.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (42261144738, U22A20590, 42207025, 42430703, 42577012).

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