The derivation of the formyl-group oxygen of chlorophyll b in higher plants from molecular oxygen.

The mechanism of formation of the formyl group of chlorophyll b has long been obscure but, in this paper, the origin of the 7-formyl-group oxygen of chlorophyll b in higher plants was determined by greening etiolated maize leaves, excised from dark-grown plants, by illumination under white light in the presence of either H218O or 18O2 and examining the newly synthesized chlorophylls by mass spectroscopy. To minimize the possible loss of 18O label from the 7-formyl substituent by reversible formation of chlorophyll b-71-gem-diol (hydrate) with unlabelled water in the cell, the formyl group was reduced to a hydroxymethyl group during extraction with methanol containing NaBH4: chlorophyll a remained unchanged during this rapid reductive extraction process. Mass spectra of chlorophyll a and [7-hydroxymethyl]-chlorophyll b extracted from leaves greened in the presence of either H218O or 18O2 revealed that 18O was incorporated only from molecular oxygen but into both chlorophylls: the mass spectra were consistent with molecular oxygen providing an oxygen atom not only for incorporation into the 7-formyl group of chlorophyll b but also for the well-documented incorporation into the 131-oxo group of both chlorophylls a and b [see Walker, C. J., Mansfield, K. E., Smith, K. M. & Castelfranco, P. A. (1989) Biochem. J. 257, 599–602]. The incorporation of isotope led to as much as 77% enrichment of the 131-oxo group of chlorophyll a: assuming identical incorporation into the 131 oxygen of chlorophyll b, then enrichment of the 7-formyl oxygen was as much as 93%. Isotope dilution by re-incorporation of photosynthetically produced oxygen from unlabelled water was negligible as shown by a greening experiment in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The high enrichment using 18O2, and the absence of labelling by H218O, unequivocally demonstrates that molecular oxygen is the sole precursor of the 7-formyl oxygen of chlorophyll b in higher plants and strongly suggests a single pathway for the formation of the chlorophyll b formyl group involving the participation of an oxygenase-type enzyme

Time trends in placenta-mediated pregnancy complications after assisted reproductive technology in the Nordic countries

Background The use of assisted reproductive technology (ART) is increasing worldwide and conception after assisted reproduction currently comprises 3-6% of birth cohorts in the Nordic countries. The risk of placenta-mediated pregnancy complications is higher after ART compared to spontaneously conceived pregnancies. Whether the excess risk of placenta-mediated pregnancy complications in pregnancies following assisted reproduction has changed over time, is unknown. Objectives To investigate whether time trends in risk of pregnancy complications (hypertensive disorders in pregnancy, placental abruption and placenta previa) differ for pregnancies after ART compared to spontaneously conceived pregnancies during three decades of assisted reproduction treatment in the Nordic countries. Study Design In a population-based cohort study, with data from national health registries in Denmark (1994-2014), Finland (1990-2014), Norway (1988-2015) and Sweden (1988-2015), we included 6,830,578 pregnancies resulting in delivery. Among these, 146,998 (2.2%) were pregnancies after assisted reproduction (125,708 singleton pregnancies, 20,668 twin pregnancies and 622 of higher order plurality) and 6,683,132 (97.8%) pregnancies were conceived spontaneously (6,595,185 singleton pregnancies, 87,106 twin pregnancies and 1,289 of higher order plurality). We used logistic regression with post-estimation to estimate absolute risks and risk differences for each complication. We repeated analyses for singleton and twin pregnancies, separately. In sub-samples with available information, we also adjusted for maternal body mass index, smoking during pregnancy, previous cesarean section, culture duration and cryopreservation. Results The risk of each placental complication was consistently higher in pregnancies following ART compared to spontaneously conceived pregnancies across the study period, except for hypertensive disorders in twin pregnancies, where risks were similar. Risk of hypertensive disorders increased over time in twin pregnancies for both conception methods, but more strongly for pregnancies following ART (risk difference 1.73 percentage points per 5 years, 95% confidence interval 1.35 to 2.11) than for spontaneously conceived twins (risk difference 0.75 percentage points, 95% confidence interval 0.61 to 0.89). No clear time trends were found for hypertensive disorders in singleton pregnancies. Risk of placental abruption decreased over time in all groups (risk difference -0.16 percentage points, 95% confidence interval -0.19 to -0.12 and -0.06 percentage points, 95% confidence interval -0.06 to -0.05 for pregnancies after assisted reproduction and spontaneously conceived pregnancies, respectively, for singletons and multiple pregnancies combined). Over time, the risk of placenta previa increased in pregnancies after assisted reproduction among both singletons (risk difference 0.21 percentage points, 95% confidence interval 0.14 to 0.27) and twins (risk difference 0.30 percentage points, 95% confidence interval 0.16 to 0.43), but remained stable in spontaneously conceived pregnancies. When adjusting for culture duration, the temporal increase in placenta previa became weaker in all groups of ART pregnancies, whereas adjustment for cryopreservation moderately attenuated trends in ART twin pregnancies. Conclusions The risk of placenta-mediated pregnancy complications following ART remains higher compared to spontaneously conceived pregnancies, despite declining rates of multiple pregnancies. For hypertensive disorders in pregnancy and placental abruption, pregnancies after assisted reproduction follow the same time trends as the background population, whereas for placenta previa, risk has increased over time in pregnancies after ART.Peer reviewe

Psychological and physical correlates of musculoskeletal symptoms in male professional divers and offshore workers

Background: Underwater divers are more likely to complain of musculoskeletal symptoms than a control population. Accordingly, we conducted a study to determine whether musculoskeletal symptoms reflected observable physical disorder, to ascertain the relationship between symptoms and measures of mood, memory and executive function and to assess any need for future screening. Methods: A 10% random sample of responders to a prior postal health questionnaire was examined (151 divers, 120 non-diving offshore workers). Participants underwent physical examination and a neuropsychological test battery for memory and executive function. Participants also completed the Hospital Anxiety and Depression Scale for anxiety (HADSa) and depression (HADSd), and questionnaires for physical health-related quality of life (SF36 PCS), mental health-related quality of life (SF36 MCS), memory (Cognitive Failures Questionnaire (CFQ), Prospective and Retrospective Memory Questionnaire (PRMQ)), executive function (dysexecutive syndrome questionnaire (DEX)), musculoskeletal symptoms (MSS) and general unrelated symptom reporting. Results: Of participants with moderate/severe musculoskeletal symptoms, 52% had physical signs, and of participants with no symptoms, 73% had no physical signs. There was no difference in the prevalence of signs or symptoms between groups. Musculoskeletal symptoms were associated with lower SF36 PCS for both groups. In divers, musculoskeletal symptoms were associated with higher general unrelated symptom reporting and poorer scoring for HADSa, PRMQ, CFQ and DEX with scores remaining within the normative range. A positive physical examination was associated with general unrelated symptom reporting in divers. There were no differences in neuropsychological test scores attributable to either group or musculoskeletal symptoms. Conclusions: Musculoskeletal symptoms were associated with physical signs, but this was not a strong effect. Reporting of musculoskeletal symptoms by the divers studied was also associated with a tendency to report symptoms generally or somatisation, and caution should be exercised regarding their interpretation as an indication of physical disease or their use for health screening

Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1

In order to identify the sources of the observed diffuse high-energy neutrino flux, it is crucial to discover their electromagnetic counterparts. IceCube began releasing alerts for single high-energy ($E > 60$ TeV) neutrino detections with sky localisation regions of order 1 deg radius in 2016. We used Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for any optical transients that may be related to the neutrinos. Typically 10-20 faint ($m < 22.5$ mag) extragalactic transients are found within the Pan-STARRS1 footprints and are generally consistent with being unrelated field supernovae (SNe) and AGN. We looked for unusual properties of the detected transients, such as temporal coincidence of explosion epoch with the IceCube timestamp. We found only one transient that had properties worthy of a specific follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of astrophysical origin of $\sim$50 %), we found a SN PS16cgx, located at 10.0' from the nominal IceCube direction. Spectroscopic observations of PS16cgx showed that it was an H-poor SN at z = 0.2895. The spectra and light curve resemble some high-energy Type Ic SNe, raising the possibility of a jet driven SN with an explosion epoch temporally coincident with the neutrino detection. However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously difficult. Based on all available data we conclude that the transient is more likely to be a Type Ia with relatively weak SiII absorption and a fairly normal rest-frame r-band light curve. If, as predicted, there is no high-energy neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence, and unrelated to the IceCube-160427A. We find no other plausible optical transient for any of the five IceCube events observed down to a 5$\sigma$ limiting magnitude of $m \sim 22$ mag, between 1 day and 25 days after detection.Comment: 20 pages, 6 figures, accepted to A&

Neutrinos below 100 TeV from the southern sky employing refined veto techniques to IceCube data

Many Galactic sources of gamma rays, such as supernova remnants, are expected to produce neutrinos with a typical energy cutoff well below 100 TeV. For the IceCube Neutrino Observatory located at the South Pole, the southern sky, containing the inner part of the Galactic plane and the Galactic Center, is a particularly challenging region at these energies, because of the large background of atmospheric muons. In this paper, we present recent advancements in data selection strategies for track-like muon neutrino events with energies below 100 TeV from the southern sky. The strategies utilize the outer detector regions as veto and features of the signal pattern to reduce the background of atmospheric muons to a level which, for the first time, allows IceCube searching for point-like sources of neutrinos in the southern sky at energies between 100 GeV and several TeV in the muon neutrino charged current channel. No significant clustering of neutrinos above background expectation was observed in four years of data recorded with the completed IceCube detector. Upper limits on the neutrino flux for a number of spectral hypotheses are reported for a list of astrophysical objects in the southern hemisphere.Comment: 19 pages, 17 figures, 2 table