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

Color morphs of the coral, Acropora tenuis, show different responses to environmental stress and different expression profiles of fluorescent-protein genes

Corals of the family Acroporidae are key structural components of reefs that support the most diverse marine ecosystems. Due to increasing anthropogenic stresses, coral reefs are in decline. Along the coast of Okinawa, Japan, three different color morphs of Acropora tenuis have been recognized for decades. These include brown (N morph), yellow green (G), and purple (P) forms. The tips of axial polyps of each morph exhibit specific fluorescence spectra. This attribute is inherited asexually, and color morphs do not change seasonally. In Okinawa Prefecture, during the summer of 2017, N and P morphs experienced bleaching, in which many N morphs died. Dinoflagellates (Symbiodiniaceae) are essential partners of scleractinian corals, and photosynthetic activity of symbionts was reduced in N and P morphs. In contrast, G morphs successfully withstood the stress. Examination of the clade and type of Symbiodiniaceae indicated that the three color-morphs host similar sets of Clade-C symbionts, suggesting that beaching of N and P morphs is unlikely attributable to differences in the clade of Symbiodiniaceae the color morphs hosted. Fluorescent proteins play pivotal roles in physiological regulation of corals. Since the A. tenuis genome has been decoded, we identified five genes for green fluorescent proteins (GFPs), two for cyan fluorescent proteins (CFPs), three for red fluorescent proteins (RFPs), and seven genes for chromoprotein (ChrP). A summer survey of gene expression profiles under outdoor aquarium conditions demonstrated that (a) expression of CFP and REP was quite low during the summer in all three morphs, (b) P morphs expressed higher levels of ChrP than N and G morphs, (c) both N and G morphs expressed GFP more highly than P morphs, and (d) GFP expression in N morphs was reduced during summer whereas G morphs maintained high levels of GFP expression throughout the summer. Although further studies are required to understand the biological significance of these color morphs of A. tenuis, our results suggest that thermal stress resistance is modified by genetic mechanisms that coincidentally lead to diversification of color morphs of this coral

Negative Correlation between Brain Glutathione Level and Negative Symptoms in Schizophrenia: A 3T 1H-MRS Study

BACKGROUND: Glutathione (GSH), a major intracellular antioxidant, plays a role in NMDA receptor-mediated neurotransmission, which is involved in the pathophysiology of schizophrenia. In the present study, we aimed to investigate whether GSH levels are altered in the posterior medial frontal cortex of schizophrenic patients. Furthermore, we examined correlations between GSH levels and clinical variables in patients. METHODS AND FINDINGS: Twenty schizophrenia patients and 16 age- and gender-matched normal controls were enrolled to examine the levels of GSH in the posterior medial frontal cortex by using 3T SIGNA EXCITE (1)H-MRS with the spectral editing technique, MEGA-PRESS. Clinical variables of patients were assessed by the Global Assessment of Functioning (GAF), Scale for the Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scale (BPRS), Drug-Induced Extra-Pyramidal Symptoms Scale (DIEPSS), and five cognitive performance tests (Word Fluency Test, Stroop Test, Trail Making Test, Wisconsin Card Sorting Test and Digit Span Distractibility Test). Levels of GSH in the posterior medial frontal cortex of schizophrenic patients were not different from those of normal controls. However, we found a significant negative correlation between GSH levels and the severity of negative symptoms (SANS total score and negative symptom subscore on BPRS) in patients. There were no correlations between brain GSH levels and scores on any cognitive performance test except Trail Making Test part A. CONCLUSION: These results suggest that GSH levels in the posterior medial frontal cortex may be related to negative symptoms in schizophrenic patients. Therefore, agents that increase GSH levels in the brain could be potential therapeutic drugs for negative symptoms in schizophrenia

The Constrained Maximal Expression Level Owing to Haploidy Shapes Gene Content on the Mammalian X Chromosome.

X chromosomes are unusual in many regards, not least of which is their nonrandom gene content. The causes of this bias are commonly discussed in the context of sexual antagonism and the avoidance of activity in the male germline. Here, we examine the notion that, at least in some taxa, functionally biased gene content may more profoundly be shaped by limits imposed on gene expression owing to haploid expression of the X chromosome. Notably, if the X, as in primates, is transcribed at rates comparable to the ancestral rate (per promoter) prior to the X chromosome formation, then the X is not a tolerable environment for genes with very high maximal net levels of expression, owing to transcriptional traffic jams. We test this hypothesis using The Encyclopedia of DNA Elements (ENCODE) and data from the Functional Annotation of the Mammalian Genome (FANTOM5) project. As predicted, the maximal expression of human X-linked genes is much lower than that of genes on autosomes: on average, maximal expression is three times lower on the X chromosome than on autosomes. Similarly, autosome-to-X retroposition events are associated with lower maximal expression of retrogenes on the X than seen for X-to-autosome retrogenes on autosomes. Also as expected, X-linked genes have a lesser degree of increase in gene expression than autosomal ones (compared to the human/Chimpanzee common ancestor) if highly expressed, but not if lowly expressed. The traffic jam model also explains the known lower breadth of expression for genes on the X (and the Z of birds), as genes with broad expression are, on average, those with high maximal expression. As then further predicted, highly expressed tissue-specific genes are also rare on the X and broadly expressed genes on the X tend to be lowly expressed, both indicating that the trend is shaped by the maximal expression level not the breadth of expression per se. Importantly, a limit to the maximal expression level explains biased tissue of expression profiles of X-linked genes. Tissues whose tissue-specific genes are very highly expressed (e.g., secretory tissues, tissues abundant in structural proteins) are also tissues in which gene expression is relatively rare on the X chromosome. These trends cannot be fully accounted for in terms of alternative models of biased expression. In conclusion, the notion that it is hard for genes on the Therian X to be highly expressed, owing to transcriptional traffic jams, provides a simple yet robustly supported rationale of many peculiar features of X's gene content, gene expression, and evolution

Photosynthetic nature of ice-algae under fast ice near Syowa Station, Antarctica

The photosynthetic nature of the ice-associated microalgal assemblages (ice-algae) was investigated in the annual sea ice area near Syowa Station (69°00′S, 39°35′E), Antarctica. The maximum photosynthetic rate of 1.23mgO_2/mg chl. α/h was obtained under the light intensity of 25μE/m^2/s. In a higher light condition above 80μE/m^2/s, a depression of the rate caused by photo-inhibition was observed. These results demonstrated the low-light-adaptation of Antarctic ice-algae under the exceedingly low light conditions. The light condition under the ice was largely controlled by the thickness of snow covering the fast ice as well as by the variation of solar radiation. The optimum temperature for photosynthesis of the ice-algae was about 8℃, while the rates of photosynthesis reduced at higher temperatures. In the present area, an average specific growth rate (μ) of the ice-algae was 0.25 div./day

Siliceous cysts from Kita-no-seto Strait,north of Syowa Station, Antarctica

Siliceous cysts of 29 different morphological shapes were observed in the sea ice and sea water at the Kita-no-seto Strait, north of Syowa Station, Antarctica. Twenty species of those were newly discovered in the Antarctic waters. Cysts collected were in the size range of 3 to 10μm. They were tentatively classified into four groups based on their morphological characteristics; Sphaerica, Ovoidea, Hemisphaerica, and Tri/quadrihedra. Twelve cysts representative of each group and a cyst of Paraphysomonas imperforata confirmed newly were described. Cysts appeared from March to May, and in December (summer to autumn season) and the species diversity was highest in December with 18 species. Among 29 species, 20 appeared in the sea ice, eight in both sea ice and sea water, and one in sea water only. Main habitat of them seemed to be the brine pockets or channels of the sea ice