ORCID Profile
0000-0002-2369-1313
Current Organisation
University of Tskuba
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Publisher: American Association for the Advancement of Science (AAAS)
Date: 14-07-2023
Abstract: Preliminary analyses of asteroid Ryugu s les show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu s les that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (~235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously uns led outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryugu’s rubble pile origin.
Publisher: Wiley
Date: 28-06-2023
DOI: 10.1111/NPH.19109
Abstract: Carotenoids are photoprotectant pigments and precursors of hormones such as strigolactones (SL). Carotenoids are produced in plastids from geranylgeranyl diphosphate (GGPP), which is erted to the carotenoid pathway by phytoene synthase (PSY). In tomato ( Solanum lycopersicum ), three genes encode plastid‐targeted GGPP synthases ( SlG1 to SlG3 ) and three genes encode PSY isoforms ( PSY1 to PSY3 ). Here, we investigated the function of SlG1 by generating loss‐of‐function lines and combining their metabolic and physiological phenotyping with gene co‐expression and co‐immunoprecipitation analyses. Leaves and fruits of slg1 lines showed a wild‐type phenotype in terms of carotenoid accumulation, photosynthesis, and development under normal growth conditions. In response to bacterial infection, however, slg1 leaves produced lower levels of defensive GGPP‐derived diterpenoids. In roots, SlG1 was co‐expressed with PSY3 and other genes involved in SL production, and slg1 lines grown under phosphate starvation exuded less SLs. However, slg1 plants did not display the branched shoot phenotype observed in other SL‐defective mutants. At the protein level, SlG1 physically interacted with the root‐specific PSY3 isoform but not with PSY1 and PSY2. Our results confirm specific roles for SlG1 in producing GGPP for defensive diterpenoids in leaves and carotenoid‐derived SLs (in combination with PSY3) in roots.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 24-02-2023
Abstract: Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. S les of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measured the mineralogy and bulk chemical and isotopic compositions of Ryugu s les. The s les are mainly composed of materials similar to those of carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The s les consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37° ± 10°C, about 5.2 − 0.7 + 0.8 million (statistical) or 5.2 − 2.1 + 1.6 million (systematic) years after the formation of the first solids in the Solar System. After aqueous alteration, the Ryugu s les were likely never heated above ~100°C. The s les have a chemical composition that more closely resembles that of the Sun’s photosphere than other natural s les do.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-11-2022
Abstract: Little is known about the origin of the spectral ersity of asteroids and what it says about conditions in the protoplanetary disk. Here, we show that s les returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the Main Belt. In this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 16-12-2022
Abstract: The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16 O-rich (associated with refractory inclusions) and 16 O-poor (associated with chondrules). Both the 16 O-rich and 16 O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16 O-rich to 16 O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.
No related grants have been discovered for Izumi Nakai.