ROS-scavenging Mn3O4 nanozymes increase cotton alkaline tolerance by increasing the stability of actin filaments and reducing Na+ content

Alkaline stress in saline soil limits cotton production that may be improved by using emerging nanobiotechnology approaches. Here, we applied poly acrylic acid coated Mn 3 O 4 nanoparticles (PMO) on cotton leaves which showed higher chlorophyll content (up to 100.0 %) and fresh weight (46.9 %) and lower electrolyte leakage rate (up to 6.8 %) and cell death rate (up to 84.8 %) than controls. Further investigation showed that PMO can maintain ROS (reactive oxygen species) homeostasis, increase the stability of actin filament (AF), and reduce Na + content. Confocal imaging and ROS content measurement showed that PMO foliar application effectively alleviated ROS over-accumulation (up to 16.4 % decrease for H 2 O 2 and 45.3 % decrease for O 2 •- ) in cotton leaves. Moreover, under alkaline stress, genes for AF depolymerization such as GhADF1/8 and GhADF6 were significantly upregulated whereas those for AF polymerization such as GhADF5 and GhADF7 were significantly down-regulated in PMO treated cotton lines relative to those in the control, consistent with the fluorescence intensities of AFs. Furthermore, our results showed that PMO mitigated Na + toxicity under alkaline stress, as indicated by the reduced Na + fluorescence intensity and Na + content. Furthermore, relative to those of the control, PMO treatment increased seed yield and lint yield by 65.0 % and 66.3 % respectively. Together, our work demonstrates that ROS scavenging PMO alleviated alkaline stress by stabilizing actin filaments and reducing Na + toxicity.