小椋 康光

Boron is an essential micronutrient required for plant cell wall integrity, as it is necessary for crosslinking the pectic polysaccharide rhamnogalacturonan II. Reproductive organs require a greater amount of boron for development and growth compared to vegetative organs. However, the mechanism by which plants distribute boron to specific organs is not fully understood. Under boron-limited conditions, the borate exporter BOR1 plays a central role in transporting boron from the roots to the shoots in Arabidopsis (Arabidopsis thaliana). Here, we found that BOR1 is expressed in the tapetal cells of young anthers in unopened buds, showing polar localization toward the locule where microspores develop. Tapetum-localized BOR1 undergoes endocytosis and is subsequently degraded during anther development. BOR1 degradation occurs independently of the lysine residue at position 590 of BOR1, which is responsible for high boron-induced ubiquitination and degradation. Loss-of-function bor1 mutants exhibit disrupted pollen structure, causing reduced fertility under boron-sufficient conditions in the wild type. These phenotypes were rescued by supplementing with high boron concentrations. Furthermore, inflorescence stem grafting experiments suggested that BOR1-dependent boron transport in the flower is necessary for pollen development and subsequent fertilization under boron-sufficient conditions. Our findings suggest the borate exporter BOR1, together with the previously described boric acid channel NIP7;1, facilitates boron transport in tapetal cells toward the locule, thereby supporting pollen development in young anthers under boron-limited conditions.

The body mitigates the toxic effects of metals through diverse detoxification mechanisms that are activated depending on the chemical species and the burden of metals in each tissue. In this regard, analytical methods that can obtain information on the chemical form and the abundance of metals are required to elucidate the full range of detoxification mechanisms. Laser ablation (LA) is used to trim a specific microregion from tissue sections and visualize elements in it. Speciation analysis by liquid chromatography (LC) hyphenated to inductively coupled plasma mass spectrometry (ICP-MS) has been optimized for microvolume samples from small tissue sections. In this study, we developed a combined method of LA and LC-ICP-MS (LA/LC-ICP-MS) and applied it to rat brain and kidney tissues. Differences in copper (Cu) and zinc (Zn) abundance in each brain tissue region are reflected in the peak intensities of metallothioneins (MTs) detected by LC-ICP-MS analysis. In addition to revealing differences in the distribution and the concentration of mercury (Hg) in the kidneys of rats exposed to inorganic mercury (iHg) or methylmercury (MeHg) by LA-ICP-MS, we also revealed differences in the type of proteins that bind these Hg species by LC-ICP-MS. We found that in the iHg-exposed group, MT induction occurred mainly in the renal cortex and the outer medulla with elevated Cu and Zn, whereas in the MeHg-exposed group, Hg was mainly bound to hemoglobin (Hb). LA/LC-ICP-MS can simultaneously provide qualitative and quantitative information on metals in a small tissue region.

Rare earth elements, comprising 17 elements including 15 lanthanides, are essential components in numerous high-tech applications. While physicochemical methods are commonly employed to remove toxic heavy metals (e.g., cadmium and mercury) from industrial wastewater, biological approaches offer increasingly attractive alternatives. Biomining, which utilizes microorganisms to extract valuable metals from ores and industrial wastes, and bioremediation, which leverages microorganisms to adsorb and transport metal ions into cells via active transport, provide eco-friendly solutions for resource recovery and environmental remediation. In this study, we investigated the potential of three recently identified lanthanide-binding proteins-SPL2, lanpepsy, and lanmodulin-for applications in these areas using single-cell inductively coupled plasma mass spectrometry (scICP-MS). Our results demonstrate that SPL2 exhibits superior characteristics for lanthanide and cadmium bioremediation. Heterologous expression of a cytosolic fragment of SPL2 in bacteria resulted in high expression levels and solubility. Single-cell ICP-MS analysis revealed that these recombinant bacteria accumulated lanthanum, cobalt, nickel, and cadmium, effectively sequestering lanthanum and cadmium from the culture media. Furthermore, SPL2 expression conferred enhanced bacterial tolerance to cadmium exposure. These findings establish SPL2 as a promising candidate for developing recombinant bacterial systems for heavy metal bioremediation and rare earth element biomining.

Due to its toxicity, contamination with arsenic, a Group 1 carcinogen, is a significant environmental and public health issue. The toxicity of arsenic varies with its chemical form. For example, inorganic species like arsenite (AsO33-) and arsenate (AsO43-) are generally more toxic than organoarsenic compounds. However, some organoarsenic species exhibit higher toxicity than inorganic species. Therefore, the precise quantification and speciation of arsenic is necessary. Chromatographic techniques, particularly liquid chromatography coupled with inductively coupled plasma mass spectrometry (LC-ICP-MS), are widely used for arsenic speciation owing to their high sensitivity and accuracy. Gas chromatography-mass spectrometry (GC-MS) is another effective technique for detecting arsenic species after derivatization. In addition to chromatographic methods, more straightforward and cost-effective techniques are available for inorganic arsenic speciation. These include adsorption techniques, colorimetric assays such as the molybdenum blue method, hydride generation reactions, and voltammetry. Emerging technologies, such as microfluidic and electrochemical devices, enable rapid and portable analysis, facilitating in situ detection of arsenite and arsenate in environmental samples. While LC-ICP-MS remains the gold standard for comprehensive arsenic speciation, other advanced technologies provide a practical, rapid, and cost-effective approach.

A μDG was installed into a sample introduction system of scICP-MS to achieve efficient and quantitative elemental analysis of cultured mammalian cells at the single-cell level.