Mn3O4 nanoparticles maintain ROS homeostasis to modulate stomatal aperture to improve cotton drought tolerance†

Drought is a global issue causing severe reductions in crop yields. The use of nanobiotechnology to increase plant resistance to drought is widely reported. However, the mechanisms underlying nanomaterial improvement of crop drought tolerance are not well understood. Herein, we reported that poly(acrylic) acid coated manganese oxide (Mn₃O₄) nanoparticles (PMO, 5.43 nm, −31.6 mV) increase cotton fresh weight (74.9%) under drought stress relative to controls by catalytically scavenging ROS and modulating stomatal aperture. PMO treated cotton leaves showed significantly lower ROS levels (60–70%) determined by confocal microscopy and biochemical and histochemical staining analysis. Also, plants exposed to PMO experienced less oxidative damage than controls under drought, as indicated by their lower malondialdehyde (MDA) content (2.02 ± 0.15 μmol L⁻¹vs. 3.25 ± 0.27 μmol L⁻¹) and electrolyte leakage rate (31.13% ± 5.51 vs. 64.83% ± 4.29). PMO treated cotton plants also maintained stomatal aperture and had higher photosynthetic performance (160%) under drought stress. Furthermore, we set up a portable monitoring system with low cost which can allow the real-time imaging of stomatal aperture and chlorophyll fluorescence in plants treated with nanomaterials. Overall, our results suggested that PMO could be a biocompatible and scalable tool for improving crop drought tolerance.