Although the sources of molecular hydrogen (H₂) synthesis in plants remain to be fully elucidated, ample evidence shows that plant-based H₂ can regulate development and stress responses. Here, we present genetic and molecular evidence indicating that nitrate reductase (NR) might be a target of H₂ sensing that positively regulates nitrogen use efficiency (NUE) and seed size in Arabidopsis (Arabidopsis thaliana). The expression level of NR and changes of NUE under control and, in particular, low nitrogen supply, were positively associated with H₂ addition supplied exogenously or through genetic manipulation. The improvement in nitrate assimilation achieved by H₂ was also mediated via NR dephosphorylation. H₂ control of seed size was impaired by NR mutation. Further genetic evidence revealed that H₂, NR, and nitric oxide can synergistically regulate nitrate assimilation in response to N starvation conditions. Collectively, our data indicate that NR might be a target for H₂ sensing, ultimately positively regulating nitrate uptake and seed size. These results provide insights into H₂ signaling and its functions in plant metabolism.

Improvement of the storage quality of rice is a critical challenge for the scientific community. This study assesses the effects of the irrigation with hydrogen nanobubble water (HNW) on the storage quality of rice (Oryza sativa ‘Huruan1212’). Compared with ditch water control, after one year of storage at 25 °C and 70% RH, the HNW-irrigated rice had higher contents of essential amino acids, especially lysine. Importantly, the generation of off-flavors in the stored rice was significantly decreased, which was confirmed by the lower levels of volatile substances, including pentanal, hexanal, heptanal, octanal, 1-octen-3-ol, and 2-heptanone. The subsequent results showed that the HNW-irrigated rice not only retained lower levels of free fatty acid values, but also had increased antioxidant capacity and decreased lipoxygenase activity and transcripts, thus resulting in decreased lipid peroxidation. This study opens a new window for the practical application of HNW irrigation in the production and subsequent storage of crops.

Argon, a non-polar molecule, easily diffuses into deeper tissue and interacts with larger proteins, protein cavities, or even receptors. Some of the biological effects of argon, notably its activity as an antioxidant, have been revealed in animals. However, whether and how argon influences plant physiology remains elusive. Here, we provide the first report that argon can enable plants to cope with salinity toxicity. Considering the convenience of the application, argon gas was dissolved into water (argon-rich water (ARW)) to investigate the argon’s functioning in phenotypes of alfalfa seed germination and seedling growth upon salinity stress. The biochemical evidence showed that NaCl-decreased α/β-amylase activities were abolished by the application of ARW. The qPCR experiments confirmed that ARW increased NHX1 (Na⁺/H⁺ antiporter) transcript and decreased SKOR (responsible for root-to-shoot translocation of K⁺) mRNA abundance, the latter of which could be used to explain the lower net K⁺ efflux and higher K accumulation. Subsequent results using non-invasive micro-test technology showed that the argon-intensified net Na⁺ efflux and its reduced Na accumulation resulted in a lower Na⁺/K⁺ ratio. NaCl-triggered redox imbalance and oxidative stress were impaired by ARW, as confirmed by histochemical and confocal analyses, and increased antioxidant defense was also detected. Combined with the pot experiments in a greenhouse, the above results clearly demonstrated that argon can enable plants to cope with salinity toxicity via reestablishing ion and redox homeostasis. To our knowledge, this is the first report to address the function of argon in plant physiology, and together these findings might open a new window for the study of argon biology in plant kingdoms.

Although emerging evidence revealed that molecular hydrogen (H₂) positively regulates numerous physiological responses, understanding the synthesis of H₂ and its functions is a challenge for biology. The correct timing of flowering is controlled by environmental stimuli and endogenous signals. We report that endogenous H₂ facilitates the floral transition in Arabidopsis. The Nuclear Architecture Related 1 (NAR1) gene of Arabidopsis was prokaryotic expressed and purified, and its H₂-synthesizing activity was subsequently detected. Furthermore, mutation experiments were used to investigate the catalytic roles of conserved sequences and Cys sites. Biochemistry and molecular approaches were employed to investigate the role of H₂ in regulating floral transition. Similar to [Fe-Fe] hydrogenase (HYD1) from Chlamydomonas reinhardtii, NAR1 protein is a H₂-synthesizing enzyme in Arabidopsis thaliana. Protein mutation experiments in vitro show that four Cys residues are important for the inducible catalyzing activity upon hypoxia. Accordingly, NAR1-dependent circadian-rhythmic H₂ was observed under light/dark cycles, which was accompanied with contrasting changes in nitric oxide (NO) signal. Knockdown of NAR1 by CRISPR or RNAi reduced H₂ production and delayed flowering. Whereas, exogenous H₂ supply and overexpressing NAR1 or CrHYD1 promoted early flowering. These early flowering phenotypes were aggravated by the removal of endogenous NO, but abolished by NO addition. Since the mutant (mms19) defective in Fe-S cluster assembly function displays early flowering regardless of H₂ addition, we further deduce that NAR1 control of early flowering is largely achieved by H₂. Biochemical and genetic evidences show that NAR1-driven floral transition is functionally linked to the modulation of circadian oscillators via NO signaling. Since H₂ production is modulated by circadian rhythms and constitutively produced, it may integrate external and internal cues into floral transition, and the modulation of its production might be a promising strategy for crop breeding cultivation.