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Ploidy-dependent carbon nanotube mitigation of polystyrene microplastic stress safeguards medicinal quality in Salvia miltiorrhiza cultures
Summary
Researchers tested whether carbon nanotubes could protect the medicinal herb Salvia miltiorrhiza from polystyrene microplastic stress in a controlled culture system. The study found that microplastics reduced key medicinal compounds by about 50% and inhibited growth, but carbon nanotube co-treatment restored metabolite production, reactivated biosynthetic pathways, and reduced oxidative stress, with triploid plants showing stronger recovery than diploids.
Microplastics threaten plant productivity and medicinal quality by disrupting physiological and metabolic functions. Using the medicinal herb Salvia miltiorrhiza, we established a controlled in vitro culture system with defined ploidy (diploid NY and triploid 810) to test how multi-walled carbon nanotubes (MWCNTs) mitigate polystyrene microplastics (PSMPs) stress in a ploidy-dependent manner, assessing impacts on regeneration, whole-plant growth, hairy-root metabolism and targeted gene expression. In hairy roots, PSMPs reduced dihydrotanshinone and salvianolic acid B contents by about 50 %, whereas MWCNTs restored and even enhanced metabolites with levels exceeding controls by more than 17 %. Targeted gene expression analyses showed that PSMPs downregulated key biosynthetic checkpoints for phenolic acids and tanshinones, while MWCNTs reactivated these pathways, with triploids showing greater recovery. PSMP exposure caused clear, dose-dependent inhibition of plant height and shoot induction: at 15 mg·L, plant height decreased by 40 % in NY and 33 % in 810, and shoot induction declined by more than 60 %. MWCNT co-treatments shortened shoot formation by six days, with triploid plants showing stronger recovery. PSMPs also increased reactive oxygen species by about 30 % and reduced photosystem II efficiency by 10 %, whereas 5 mg·L MWCNTs lowered oxidative markers by nearly 20 % and restored photosynthetic performance to 95 % of control levels. Overall, MWCNTs mitigated PSMP-induced phytotoxicity by reducing internal PSMP accumulation and stabilizing redox, hormonal, photosynthetic, and developmental balance in a ploidy-sensitive manner. These findings provide a ploidy-aware, plant-compatible framework for understanding microplastic-induced phytotoxicity, suggesting practical strategies for mitigating microplastic hazards and safeguarding biomass and medicinal output in contaminated environments.