Nanomaterial-induced modulation of hormonal pathways enhances plant cell growth

Abstract

In this study, Bright Yellow 2 (BY-2) tobacco (Nicotiana tabacum L.) cell suspensions exposed to manganese ferrite nanoparticles (nMnFe₂O₄) or nitrogen-doped carbon dots (N-CDs) were analyzed for hormonal pathways. The dose response trial (0.05–1 mg L⁻¹, 2–72 h) showed that N-CDs (2.9 ± 0.5 nm) at 0.1 mg L⁻¹ and nMnFe₂O₄ (28.7 ± 7.7 nm) at 1 mg L⁻¹ significantly promoted the cell viability by 11.6% and 30.4%, respectively. Meanwhile, no growth improvement was observed in an ionic control (FeSO₄·7H₂O + MnSO₄·H₂O). On this basis, the cell morphology, hormone contents, fluxes of H⁺, K⁺ and IAA, gene expression, and metabolite profiles were measured for select samples. nMnFe₂O₄ exposure increased the fresh weight (FW) and cytokinin level by 48.2% and 70.2%, respectively, while N-CDs elevated the FW and IAA level by 30.8% and 37.2%, respectively. Specifically, nMnFe₂O₄ increased the efflux of H⁺ (by 75.7%) and influx of K⁺ (by 278%), consequently enhancing the expression of expansin (EXP, by 3.3 fold) for cell enlargement. N-CDs led to an early (2 h) expression of CYCB (by 4.9 fold) for the cell cycle and a late (until 24 h) extrusion of H⁺. The metabolomic analysis further revealed that nMnFe₂O₄ enhanced the metabolism in cytokinin signaling (by 5.4–17.0%), ATP synthesis (by 22.6–200%), and cell expansion (27.5%), while N-CDs contributed to the resistance to stress (by 41.8–121%) and synthesis of IAA (by 63.3%). Together, it seems that nMnFe₂O₄ initiated the signaling pathway of SCF^TIR1/AFB-AUX/IAA, while N-CDs may activate the IAA-mediated cell cycle for promoting cell growth.