Shimane University

The successful development of a magnetic field-free objective lens for high-resolution imaging has enabled the acquisition of atomic-resolution scanning transmission electron microscopy (STEM) images under magnetic field-free conditions around the sample. Utilizing this magnetic field-free objective lens for conventional transmission electron microscopy (TEM) observations is expected to offer advantages for the comprehensive characterization of magnetic materials. This approach is particularly significant in the context of in-situ observations. To obtain conventional TEM images, such as bright- and dark-field images, it is important to position the objective lens aperture in a diffraction plane, typically the back focal plane of the objective lens. However, positioning the objective lens aperture around the back focal plane, which is surrounded by multiple magnetic poles, is not feasible for the magnetic field-free objective lens. In this study, we describe the development of an image-forming system that can position the aperture in a diffraction plane conjugate to the back focal plane. In addition, the development of a wide-gap pole piece for the magnetic field-free objective lens has enabled the use of sample holders with thick tips for in-situ observations. The magnetic field-free electron microscope, which integrates a newly developed pole piece and image-forming system with higher-order aberration correctors, offers not only atomic-resolution TEM/STEM observations but also a versatile approach for the characterization of magnetic materials in a magnetic field-free environment.

Ascorbate is a key antioxidant that protects plant cells from oxidative damage. While plants actively synthesize ascorbate during the day, its degradation becomes prominent under prolonged dark conditions. Since ascorbate degradation begins with its oxidized form, dehydroascorbate (DHA), this process inherently requires ascorbate oxidation. However, the molecular mechanisms underlying dark-induced ascorbate oxidation and subsequent degradation remain unclear. In this study, we investigated the role of intracellular and extracellular ascorbate redox regulation in controlling this process. Using Arabidopsis knockout mutants for key enzymes involved in ascorbate oxidation and recycling, including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), and ascorbate oxidase (AO), as well as NADPH oxidases (rbohD and rbohF), we found that none of these enzymes significantly influenced the dark-induced decrease in ascorbate levels. Notably, ascorbate levels decreased similarly in newly generated multiple mutants, including a quintuple mutant (∆dhar pad2 mdar5), which has severely impaired ascorbate recycling capacity, and the ao2 rbohD double mutant, which is strongly expected to exhibit a highly altered apoplastic redox state. Furthermore, we examined the potential involvement of senescence signaling, including ORESARA1 and ethylene signaling components, but found no evidence for their contribution. These findings indicate that the dark-induced decrease in ascorbate levels is not governed by conventional pathways for ascorbate oxidation and recycling or senescence signaling processes, suggesting an unidentified regulatory mechanism.

A hypoxic water mass in Mikawa Bay, a semi-enclosed coastal area in Japan, dissipated significantly on August 20, 2020. Observational data suggest that the dissipation resulted from the advection of oxygen-rich water masses from the bay mouth and/or the open sea. However, the precise mechanism driving the dissipation of hypoxia remains unclear. In this study, using an ecological hydrodynamic model, we aimed to simulate the short-term dissipation of hypoxic water masses in Mikawa Bay. Sensitivity analysis was conducted to examine the interplay between density-, wind-driven, and tidal currents in the dissipation of hypoxic water masses and to identify the contributing factors. Although the modeled bottom-layer dissolved oxygen (DO) concentrations in the inner bay did not fully align with the observational data, the timing of increased DO levels was consistent between the observations and simulations, with a correlation coefficient of 0.78, root mean square error of 1.27 mg/L, and bias of -0.57 mg/L, indicating that the ecological hydrodynamic model effectively replicates the reduction of bottom-layer hypoxia in Mikawa Bay. Factor analysis revealed that density currents, driven by high salinity near the bay mouth, are the primary contributors to increased bottom-layer DO concentrations. Wind-induced and tidal currents influence DO distribution but are not primary drivers of elevated bottom-layer DO levels. Our findings highlight the importance of density currents in reducing hypoxic conditions, with significant implications for ecosystem dynamics and hypoxia management in coastal areas. These results could guide future studies and strategies to mitigate hypoxic events in similar environments.