Memories of the Distant Voyages of Umitaka Maru

東京海洋大学　名誉教

Initial incorporation of phytoplankton into young ice in Saroma Ko lagoon, Hokkaido, Japan

The initial incorporation of phytoplankton into young ice was examined on February 25-28,1998 in Saroma Ko lagoon, Hokkaido, Japan to test our hypothesis that some physical selection would occur to establish the ice algal assemblages during the formation of young sea ice and the development of fast sea ice. An open pool (2×2m) was employed for the experiment. Young sea ice was collected for a 24hr experiment. Relative brine volume in the young sea ice might be related to air temperature. Incorporated contents of chlorophyll α, biogenic silica, particulate organic carbon and nitrogen were directly related to the relative brine volume. The larger than 2μm fractions of chlorophyll α and biogenic silica were 95% and 78%, respectively. The most abundant species incorporated into the young sea ice were Navicula transitans (33%) and Achnanthes taeniata (12%). Those species were originated from a water column where they were released from the bottom surface of seasonal sea ice in the vicinity of the experimental pool. Cell density of the incorporated phytoplankton ranged from 46 to 154 cells ml^ into the young sea ice and 17±5 cells ml^ in the sea water under the young sea ice. Those microscopic observations suggested the selective incorporation of phytoplankton into the young sea ice at the beginning of ice formation and it might accelerate selective development of establish the ice algal assemblages with the growth of fast sea ice

Photosynthetic characteristics of phytoplankton off Adelie Land, Antarctica, during the austral summer

The photosynthesis-irradiance characteristics (P-E curves) and quantum yields of natural phytoplankton were investigated in the Southern Ocean off Adelie Land, Antarctica, during the austral summer. Data were acquired at eight stations during a cruise of T/V Umitaka-Maru III. The photosynthetic P-E curves showed low light adaptation of phytoplankton. Mean value (±standard deviation) of the P-E curve parameters, α^*, and I_k, were 0.014 (±0.013) mgC (mg chl. α)^ h^1 (μmol photons m^ s^)^ and 76 (±55) μmol photons m^ s^, respectively. Although phytoplankton were adapted to low irradiance, the phytoplankton in the SCM were not fully adapted to the low irradiance prevailing at those depths. P^*_ in the studied region was low (mean of 0.66 (±0.37) mgC (mg chl. α)^ h^) and generally lower than the previously reported values in waters near the Antarctic Peninsula. The maximum quantum yield varied widely, ranging from 0.001 to 0.038mol C (mol photons absorbed)^ at the surface and from 0.007 to 0.092mol C (mol photons absorbed)^ near the bottom of the euphotic zone. These values were within the range of published data. Comparison of photosynthetic parameters with historical data indicated that primary productivity from remotely sensed data for the whole of the Southern Ocean, based on these field estimates of photosynthetic parameters, has been overestimated

Sexual dimorphism in body shape of Antarctic krill (Euphausia superba) and its influence on target strength

AbstractSexual dimorphism in the body shape of Antarctic krill (Euphausia superba) was investigated and its influence on target strength (TS) was clarified using a theoretical scattering model. The TS which is used to convert acoustic backscatter to krill density was also presented. Body shape data were obtained from 456 specimens (54 juveniles, 200 males, and 202 females) collected off Adélie Land using a Rectangular Midwater Trawl. The sexual dimorphism manifested as a swollen cephalothorax in female krill with body lengths exceeding 40 mm. The TS of female krill was higher than those of male krill at low frequencies, even when body lengths were the same. This is because of the Rayleigh scattering region and the transition region to the geometric scattering region. The influence of the sexual dimorphism on the TS was small at frequencies exceeding 70 kHz, which are close to the geometric scattering region. The regression curve derived from the predicted TS of 456 specimens was in reasonable agreement with the measured TS in other previous studies, and the regression curve could be applied to the acoustic surveys of Antarctic krill

Spatio-temporal variability in life cycle strategy of four pelagic Antarctic copepods: Rhincalanus gigas, Calanoides acutus, Calanus propinquus and Metridia gerlachei

Spatio-temporal variability in life cycle strategy of four pelagic Antarctic copepods, Rhincalanus gigas, Calanoides acutus, Calanus propinquus and Metridia gerlachei was studied, including their copepodite stage composition, using the multiyear samples taken off east Antarctica (90-160°E) in March 1988-1996. Except for R. gigas, the rare occurrence of adults indicated that the spawning activities ceased by mid-March in this research area. Younger copepodite stages appeared for C. propinquus compared to C. acutus, suggesting the late reproduction or slow growth in the former. Multiple regression analysis on the relationship between environmental variables and the copepodite stage composition showed that the population matured earlier in the warmer area for C. acutus, C. propinquus and M. gerlachei. The study demonstrated that the three species flexibly changed timing of the reproduction and development, and shifted their life cycle from one year to two years in the southern Antarctic Circumpolar Current (ACC) area, responding to spatio-temporal environmental change caused by meandering of the ACC

Aurora-A controls pre-replicative complex assembly and DNA replication by stabilizing geminin in mitosis

Geminin, an essential factor for DNA replication, directly binds to the licensing factor Cdt1 and inhibits pre-replicative complex formation to prevent re-replication. In G1, geminin levels are controlled by the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase complex, which targets geminin for proteasomal degradation to allow pre-replicative complex formation. Conversely, from S to G2, geminin is stabilized due to APC/C ubiquitin ligase complex inhibition, ensuring the inhibition of pre-replicative complex formation. However, mitotic regulation of geminin has hitherto not been described. Here we show that Aurora-A phosphorylates geminin on Thr25 during M phase, and this event induces geminin stabilization by preventing its APC/C ubiquitin ligase complex-mediated degradation during mitosis. In turn, stabilized geminin inhibits SCFSkp2-mediated degradation of Cdt1 to ensure pre-replicative complex formation in the ensuing S phase. The Aurora-A–geminin–Cdt1 axis therefore represents a critical regulator of proper DNA replication

OsYSL16 plays a role in the allocation of iron

Graminaceous plants acquire iron by secreting mugineic acid family phytosiderophores into the rhizosphere and taking up complexes of iron and phytosiderophores through YSL (yellow stripe 1-like) transporters. Rice OsYSL15 is a transporter of the iron(III)-2′-deoxymugineic acid complex. OsYSL16 has 85 % similarity to both OsYSL15 and the iron(II)-nicotianamine transporter OsYSL2. In the present study, we show that OsYSL16 functionally complemented a yeast mutant defective in iron uptake when grown on medium containing iron(III)-deoxymugineic acid, but not when grown on medium containing iron(II)-nicotianamine. OsYSL16-knockdown seedlings were smaller than wild-type seedlings when only iron(III)chloride was supplied as an iron source. The iron concentration in shoots of OsYSL16-knockdown plants was similar to that of the wild type; however, they showed more severe chlorosis than wild-type plants under iron-deficient conditions. Furthermore, OsYSL16-knockdown plants accumulated more iron in the vascular bundles of the leaves. Expression of the OsYSL16 promoter fused to the β-glucuronidase gene showed that OsYSL16 is expressed in the root epidermis and vascular bundles of whole plants. The expression was typically observed around the xylem. In the vascular bundles of unelongated nodes, it was detected in the xylem of old leaves and the phloem of new leaves. Graminaceous plants translocate iron from the roots to old leaves mainly via the xylem and to new leaves mainly via the phloem. Our results suggest that OsYSL16 plays a role in the allocation of iron(III)-deoxymugineic acid via the vascular bundles. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11103-012-9930-1) contains supplementary material, which is available to authorized users

Roles for B[a]P and FICZ in subchondral bone metabolism and experimental temporomandibular joint osteoarthritis via the AhR/Cyp1a1 signaling axis

Bone loss due to smoking represents a major risk factor for fractures and bone osteoporosis. Signaling through the aryl hydrocarbon receptor (AhR) and its ligands contributes to both bone homeostasis and inflammatory diseases. It remains unclear whether the same AhR signaling axis affects the temporomandibular joint (TMJ). The aim of this study was to investigate possible mechanisms which mediate bone loss in the TMJ due to smoking. In particular, whether benzo[a]pyrene (B[a]P), a carcinogen of tobacco smoke, induces expression of the AhR target gene, Cyp1a1, in mandibular condyles. Possible functions of an endogenous ligand of FICZ, were also investigated in a TMJ-osteoarthritis (OA) mouse model. B[a]P was administered orally to wild-type and AhR−/− mice and bone metabolism was subsequently examined. TMJ-OA was induced in wild-type mice with forceful opening of the mouth. Therapeutic functions of FICZ were detected with μCT and histology. Exposure to B[a]P accelerated bone loss in the mandibular subchondral bone. This bone loss manifested with osteoclastic bone resorption and upregulated expression of Cyp1a1 in an AhR-dependent manner. In a mouse model of TMJ-OA, FICZ exhibited a dose-dependent rescue of mandibular subchondral bone loss by repressing osteoclast activity. Meanwhile, in vitro, pre-treatment with FICZ reduced RANKL-mediated osteoclastogenesis. B[a]P regulates mandibular subchondral bone metabolism via the Cyp1a1. The AhR ligand, FICZ, can prevent TMJ-OA by regulating osteoclast differentiation