Soil salinization is a critical challenge for worldwide agriculture, impairing crop growth and reducing yields while hindering sustainable agricultural development (Bui, 2013). Climate change further exacerbates soil salinization through rising sea levels, deteriorating irrigation water quality, and increased evaporation rates (Zulfiqar and Hancock, 2020). According to the Food and Agriculture Organization of the United Nations (FAO), salt stress threatens around 1 billion hectares of arable land, with projections predicting that salinization may damage half of available arable land by 2050. Therefore, enhancing plant salt tolerance is crucial for improving crop yield and quality in saline soils.
Salt stress usually damages plants by inducing osmotic stress, ionic toxicity, and oxidative stress caused by reactive oxygen species. (Ibrahimova et al., 2021, Zhou et al., 2024). Enhancing antioxidant enzyme activity and maintaining cytosolic sodium and potassium ion (Na+/K+) homeostasis are critical strategies for improving plant salt tolerance (Yan et al., 2020, Li et al., 2022, Verma et al., 2021). Because of its amazing physiological effects, hydrogen (H2) has recently demonstrated promising use in agricultural productivity (Zulfiqar et al., 2021). The rise of “hydrogen agriculture” has transformed agricultural development strategies and promoted environmentally friendly farming techniques (Zulfiqar et al., 2024). Research on H2 in plant stress regulation has received a lot of interest (Shen and Sun, 2019). Due to its electrical neutrality, H2 can quickly pass through cell and organelle membranes to exert biological effects (Cheng et al., 2023, Ishaq et al., 2022). Numerous studies have demonstrated that H2 can increase crop productivity, promote growth, and improve plant sterss tolerance (Wu et al., 2021, Lv et al., 2024, Su et al., 2021, Guan et al., 2019). Currently, H2 is primarily provided in agricultural applications by traditional electrolysis-generated hydrogen-rich water (HRW). Despite the fact that traditional HRW provides a safe and effective method of delivering H2 biological effects, agricultural H2 applications are limited by the short HRW half-life caused by the poor solubility and high diffusivity of H2 in solution (Shen and Sun, 2019).
Because of their remarkable physicochemical properties, nanomaterials present new opportunities for tackling intricate biological issues (Zulfiqar and Ashraf, 2021). As a result, developing slowly H2-releasing nanomaterials utilizing nanotechnology has significant research and practical application value for achieving long-term H2 release in agricultural applications. Unlike traditional H2 supply methods, certain nanomaterials have the ability to sustainably and responsively release H2 over long periods of time in solution (Fan et al., 2019, Zhao et al., 2018, Zhang et al., 2019). For example, magnesium-based nanomaterials can release H2 in acidic solutions in a pH-dependent manner (Fan et al., 2019). He’s group synthesized PdH0.2 nanocrystals that can release H2 under near-infrared light irradiation (Zhao et al., 2018). However, the potential application of these nanoparticles in agriculture remains uncertain. Previous studies have shown that solid hydrogen storage materials loaded onto nanocarriers can effectively generate H2 and extend its release duration (Zhang et al., 2019, Yuan et al., 2021). This strategy improves the biological effects of H2 while also decreasing the frequency of use of solid-state hydrogen storage materials. Ammonia borane (AB), an efficient hydrogen storage material, contains a high hydrogen content (19.6 wt%). Shen’s group demonstrated that low concentrations of AB could improve oilseed rape seedling resistance to salt, drought, and cadmium stress. They also discovered that AB stimulated lateral root meristem development in tomatoes via phytomelatonin signaling (Wang et al., 2021, Wang et al., 2024, Zhao et al., 2021). Conversely, high concentrations of AB limited agricultural applications by inhibiting plant growth. Hollow mesoporous silica nanoparticles (HMSN) are widely used in medicine and agriculture because they have a outstanding stability, large specific surface area, superior biocompatibility, and regulated guest molecule release capabilities (Cao et al., 2018, Liu et al., 2019, Wang et al., 2021). Importantly, the vast cavities of HMSN greatly enhance the ability to load guest molecules. Encapsulating AB into HMSN not only achieves sustained release of H2 but it also mitigates the adverse effects of high-concentration AB on plants.
In this study, we synthesized a H2-releasing nanomaterial, AB@HMSN, using AB as the hydrogen storage material and HMSN as the carrier. AB@HMSN exhibited ultrahigh AB loading capacity (811 mg·g−1) and sustained acid-responsive H2 release in solution for over 3 days. Subsequently, sweetpotato was used as a model plant to investigate the effects of AB@HMSN on plant growth under salt stress, as well as the underlying mechanisms. The results demonstrated that AB@HMSN significantly increased photosynthetic efficiency and antioxidant capacity in sweetpotato seedlings. Mechanistic investigations revealed that AB@HMSN enhanced the activity of sodium-proton (Na+/H+) antiporters and plasma membrane proton-pumping ATPase (PM H+-ATPase), which promoted Na+ efflux and H+ influx while inhibiting K+ efflux in sweetpotato seedling roots under salt stress. This response is primarily attributed to the production of endogenous melatonin (MT) in the sweet potato roots induced by AB@HMSN.
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