Table 1.
Expanded direct and supporting evidence for brassinosteroid-mediated mitigation of micro- and nanoplastic stress in plants.
| Evidence type | Plant/system | Plastic particle details | Plastic dose and exposure | BR treatment: compound, dose, application | Key observations | Mechanistic interpretation and cautions | Reference |
|---|---|---|---|---|---|---|---|
| Direct mitigation; edible-plant NP uptake and seedling phytotoxicity | Tomato (Solanum lycopersicum) seedlings and fruit; preliminary PS-NP accumulation screen across ten edible plant species. | Polystyrene nanoplastics (PS-NPs), non-surface-modified; nominal about 60 nm. In Hoagland solution: about 63.69 nm for non-fluorescent PS-NPs and 95.07 nm for fluorescent PS-NPs; zeta potential about -25.3 and -28.3 mV, respectively. PS-NPs accumulated mainly in xylem regions of edible tissues. | Main tomato assay: 50 mg L-1 PS-NPs for 14 d. Toxicity screen also included 10, 50, and 100 mg L-1. Aquaporin inhibition assay: 50 mg L-1 PS-NPs plus 0.05 mM AgNO3 for 7 d. | Reported as exogenous brassinosteroids (BRs); the available article text does not identify the analogue as BL or 24-epiBL; 10, 50, and 250 nM were screened; 50 nM was selected because it reduced PS-NP accumulation, whereas 250 nM suppressed tomato growth. Treatment was supplied exogenously in the culture system, not as a foliar spray in the described seedling assay. | 50 nM BRs reduced PS-NP fluorescence in tomato fruit to near-control levels; mitigated PS-NP-induced reductions in fresh weight and plant height; decreased H2O2 and MDA; lowered stress-elevated SOD, POD, and CAT activities relative to PS-NP exposure alone. | BRs appear to reduce NP accumulation through aquaporin-associated transport control and redox stabilization. PS-NPs upregulated TIP2-1, TIP2-2, PIP2-6, PIP2-8, SIP2-1, and NIP1-2, whereas BRs downregulated TIP2-1, TIP2-2, PIP2-6, PIP2-8, PIP2-9, SIP2-1, and NIP1-2. Interpret aquaporins as transport/hydraulic regulators, not necessarily as pores through which intact NPs pass. | Gao et al. (2023) |
| Direct mitigation; medicinal plant physiology and secondary metabolism | Pinellia ternata pot experiment; leaves, tubers, photosynthesis, ROS metabolism, AsA-GSH cycle, and secondary metabolites were measured. | Polyethylene microplastics (PE-MPs), 13 µm particles/granules used as an agricultural PE model. | Soil amendment with 1% PE-MPs (w/w). PE-MPs and air-dried soil were mixed evenly and stabilized for 10 d before transplanting. Experimental design: MP 0/1% x BR 0/0.1 mg L-1. | 0.1 mg L-1 BL (reported as BR in the paper) foliar spray for 7 d after the three leaves were fully unfolded; samples were collected 30 d after spraying. | MP reduced plant height (15.0%), Fv/Fm (3.2%), SOD (15.0%), and APX (5.1%), but increased O2.- production (29.6%), GSH (4.4%), flavonoids (6.8%), alkaloids (75%), and β-sitosterol (26.5%). Under MP stress, BL increased plant height (15.7%), aboveground biomass (16.1%), underground biomass (10.3%), carotenoids (11.8%), GSH (4.2%), Fv/Fm (2.9%), SOD (32.2%), GR (21.08%), and MDHAR (20.9%). | BL functions as a rescue regulator rather than a plastic detoxifier. It improves PSII photochemistry, carotenoid-linked photoprotection, redox homeostasis, and AsA-GSH cycling, while moderating stress-related carbon allocation into secondary metabolism. | Zhang et al. (2024) |
| Direct mitigation; germination and early seedling growth | Rice (Oryza sativa, cultivar Zhe Fu No. 7) seed germination in Petri dishes for 7 d at 25 °C. | Polystyrene particles: micro-sized PS microspheres (50 µm MPs) and nano-sized PS microspheres (50 nm NPs). Stock suspension contained 2.5% solids; working solutions were sonicated for 30 min. | MP/NP treatments used 0, 200, 500, 1000, and 1500 mg L-1 in the germination assay; the combined BR plus plastic test used the high PS dose of 1500 mg L-1. Each dish contained 20 seeds and 5 mL treatment solution; three replicates. | 0.01, 0.10, and 1.00 mg L-1 24-epibrassinolide (24-epiBL), combined treatment used 0.01 mg L-1 24-epiBL plus 1500 mg L-1 MPs or NPs. | NPs were more inhibitory than MPs. At 1500 mg L-1, NPs reduced root length, shoot length, fresh weight, dry weight, and vigor index by about 26%, 14%, 18%, 18%, and 22%, respectively. Adding 0.01 mg L-1 24-epiBL to NPs increased root length, shoot length, fresh weight, dry weight, and vigor index by 43%, 27%, 20%, 13%, and 44% relative to NPs alone; BR+MPs also improved biomass indices. | 24-epiBL protects early development mainly by redox regulation. BR+MP/NP treatments reduced POD, CAT, and MDA toward control levels and normalized SOD activity. The response is consistent with BR-mediated antioxidant priming and ROS homeostasis, not plastic degradation. | Gui et al. (2025) |
| Direct plant-soil interface evidence; rhizosphere microecology | Pinellia ternata rhizosphere/pot experiment; root morphology, soil physicochemical properties, enzymes, and bacterial/fungal communities were assessed. | Polyethylene microplastics (PE-MPs), 13 µm; SEM showed fragments, fibers, and irregular particles with rough surfaces and cracks. | 1% PE-MPs (w/w) mixed with dried soil and stored/equilibrated for 10 d before planting. Plants were harvested on day 30 after transplanting. | 0.1 mg L-1 brassinolide (BL; reported as BR) foliar spraying for one week after full leaf unfolding. Soil was covered during spraying to prevent direct BR addition to the soil. | BR+MP reduced root length (35.8% vs control) but maintained/increased root diameter, suggesting architectural reprogramming. Under MP stress, BL decreased soil CAT activity and increased urease activity; BL partially mitigated microbial dysbiosis by reducing pathogenic Rhizoctonia and improving the relative abundance of beneficial or less detrimental fungal groups compared with MP alone. | BL effects extend from plant tissues to the rhizosphere, probably through altered root architecture, exudation, nutrient demand, and stress signaling. The row should be framed as rhizosphere stabilization, not simple root-growth promotion, because root elongation decreased while radial/root-soil traits shifted. | Zhang et al. (2025) |
| Supporting evidence; hormone-network context, no exogenous BR rescue | Cucumber (Cucumis sativus, Jinyou No. 1); hydroponic and soil systems combined with transcriptomics and metabolomics. | Hydroponics: fluorescent PS microspheres of 0.1 µm and 5 µm. Soil: PVC, PE, and PS microplastics sieved to <13 µm; DOP used as a representative phthalate plasticizer. | Hydroponics: 10 mg L-1 PS. Soil: 0.05 g kg-1 PVC, PE, or PS; PS+DOP treatment combined 0.05 g kg-1 PS with 10 mg kg-1 DOP. Plants were cultivated for 74 d; seven replicates per treatment. | No exogenous BR applied. Endogenous BR-related regulation was inferred from BR biosynthesis/homeostasis genes, including DET2, CYP92A6, and CYP734A1. Metabolomics showed no significant accumulation of BRs, suggesting homeostatic compensation. | Microplastics and DOP primarily affected tryptophan-dependent auxin biosynthesis, CK de novo synthesis, GA metabolism, ABA-related ABA2 expression, ethylene biosynthesis, JA accumulation, and BR homeostasis. Smaller 0.1 µm PS was more readily absorbed/translocated than larger PS and was associated with reduced IAA biosynthesis efficiency. PE and PS affected hormone biosynthesis more strongly than PVC; PS+DOP synergistically enhanced JA. | This study supports the review concept that plastic stress rewires hormone networks, including endogenous BR homeostasis, and therefore provides rationale for BR-centered crosstalk experiments. It should not be cited as direct evidence that exogenous BR mitigates MP/NP stress. | Zhuang et al. (2025) |
24-epiBL, 24-epibrassinolide; ABA, abscisic acid; AgNO3, silver nitrate; APX, ascorbate peroxidase; AsA-GSH, ascorbate-glutathione; BL, brassinolide; BR, brassinosteroid; CAT, catalase; CK, cytokinin; DOP, di-n-octyl phthalate; GA, gibberellin; GR, glutathione reductase; GSH, reduced glutathione; H2O2, hydrogen peroxide; IAA, indole-3-acetic acid; JA, jasmonic acid; MDA, malondialdehyde; MDHAR, monodehydroascorbate reductase; MP, microplastic; NP, nanoplastic; PE, polyethylene; POD, peroxidase; PS, polystyrene; PSII, photosystem II; PVC, polyvinyl chloride; ROS, reactive oxygen species; SOD, superoxide dismutase; Fv/Fm, maximum quantum efficiency of PSII.