Alkaline stress in saline soil limits cotton production that may be improved by using emerging nanobiotechnology approaches. Here, we applied poly acrylic acid coated Mn₃O₄ 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 reactive oxygen species (ROS) 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 H₂O₂ and 45.3% decrease for O₂^•-) in cotton leaves. Moreover, under alkaline stress, genes for AF depolymerization such as GhADF1/8 and GhADF6 and for AF polymerization such as GhADF5 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.

Use of nanomaterials (NMs) to improve plant abiotic stress tolerance (AST) is a hot topic in NM-enabled agriculture. Previous studies mainly focused on the physiological and biochemical responses of plants treated with NMs under abiotic stress. To use NMs for improving plant AST, it is necessary to understand how they act on this tolerance at the omics and epigenetics levels. In this review, we summarized the knowledge of NM-improved abiotic stress tolerance in relation to omics (such as metabolic, transcriptomic, proteomic, and microRNA), DNA methylation, and histone modifications. Overall, NMs can improve plant abiotic stress tolerance through the modulation at omics and epigenetics levels.

Soil salinity is a big environmental issue affecting crop production. Although seed nanopriming has been widely used to improve seed germination and seedling growth under salinity, our knowledge about the underlying mechanisms is still insufficient. Herein, we newly synthesized selenium-doped carbon dots nanoparticles coated with poly acrylic acid (poly acrylic acid coated selenium doped carbon dots, PAA@Se-CDs) and used it to prime seeds of rapeseeds. The TEM (transmission electron microscope) size and zeta potential of PAA@Se-CDs are 3.8 ± 0.2 nm and −30 mV, respectively. After 8 h priming, the PAA@Se-CDs nanoparticles were detected in the seed compartments (seed coat, cotyledon, and radicle), while no such signals were detected in the NNP (no nanoparticle control) group (SeO₂ was used as the NNP). Nanopriming with PAA@Se-CDs nanoparticles increased rapeseeds germination (20%) and seedling fresh weight (161%) under saline conditions compared to NNP control. PAA@Se-CDs nanopriming significantly enhanced endo-β-mannanase activities (255% increase, 21.55 µmol h⁻¹ g⁻¹ vs. 6.06 µmol h⁻¹ g⁻¹, at DAS 1 (DAS, days after sowing)), total soluble sugar (33.63 mg g⁻¹ FW (fresh weight) vs. 20.23 mg g⁻¹ FW) and protein contents (1.96 µg g⁻¹ FW vs. 1.0 µg g⁻¹ FW) to support the growth of germinating seedlings of rapeseeds under salt stress, in comparison with NNP control. The respiration rate and ATP content were increased by 76% and 607%, respectively. The oxidative damage of salinity due to the over-accumulation of reactive oxygen species (ROS) was alleviated by PAA@Se-CDs nanopriming by increasing the antioxidant enzyme activities (SOD (superoxide dismutase), POD (peroxidase), and CAT (catalase)). Another mechanism behind PAA@Se-CDs nanopriming improving rapeseeds salt tolerance at seedling stage was reducing sodium (Na⁺) accumulation and improving potassium (K⁺) retention, hence increasing the K⁺/Na⁺ ratio under saline conditions. Overall, our results not only showed that seed nanopriming with PAA@Se-CDs could be a good approach to improve salt tolerance, but also add more knowledge to the mechanism behind nanopriming-improved plant salt tolerance at germination and early seedling growth stage.

Nano-enabled agriculture is an emerging hot topic. To facilitate the development of nano-enabled agriculture, reviews addressing or discussing the applications, knowledge gap, future research needs, and possible new research field of plant nanobiotechnology in agricultural production are encouraged. Here we review the following topics in plant nanobiotechnology for agriculture: 1) improving stress tolerance, 2) stress sensing and early detection, 3) targeted delivery and controlled release of agrochemicals, 4) transgenic events in non-model crop species, and 5) seed nanopriming. We discuss the knowledge gaps in these topics. Besides the use of nanomaterials for harvesting more electrons to improve photosynthetic performance, they could be used to convert nIR and UV to visible light to expand the light spectrum for photosynthesis. We discuss this approach to maintaining plant photosynthesis under light-insufficient conditions. Our aim in this review is to aid researchers to learn quickly how to use plant nanobiotechnology for improving agricultural production.