Vitamin B12 amplifies circadian phase shifts induced by a light pulse in rats

Vitamin B₁₂ (VB₁₂) is a putative modulator of the human circadian clock, improving entrainability to the 24 h light-dark cycle. The present study was intended to elucidate the mechanism of VB₁₂ action in an animal model. In male rats free-running under constant dim illumination, a single light pulse of 50–1000 lux for 20 min given at circadian time (CT) 20 induced a 0.28 to 1.08 h phase advance and at CT 14 induced a 0.54 to 2.10 h phase delay. A 3 h intracerebroventricular (icv) infusion of 30 nmol VB₁₂ starting 2 h prior to a 20 min 200 lux light pulse significantly amplified phase shifts in comparison with saline-treated or untreated controls. The mean phase advance (1.13 h) was 1.8-fold greater than that of saline-infused controls, whereas the mean phase delay (2.28 h) was 2.9-fold greater. These values were comparable to the maximal phase shifts caused by 1000 lux light pulses in untreated rats. Since the same VB₁₂ treatment alone had failed to induce a phase shift in a previous experiment, these results indicate that VB₁₂ strongly enhanced light pulse-induced phase shifts and thus augmented the entrainability of the circadian clock to light.     

Cyclic electron flow around photosystem I is essential for photosynthesis

Photosynthesis provides at least two routes through which light energy can be used to generate a proton gradient across the thylakoid membrane of chloroplasts, which is subsequently used to synthesize ATP. In the first route, electrons released from water in photosystem II (PSII) are eventually transferred to NADP+ by way of photosystem I (PSI). This linear electron flow is driven by two photochemical reactions that function in series. The cytochrome b6f complex mediates electron transport between the two photosystems and generates the proton gradient (DeltapH). In the second route, driven solely by PSI, electrons can be recycled from either reduced ferredoxin or NADPH to plastoquinone, and subsequently to the cytochrome b6f complex. Such cyclic flow generates DeltapH and thus ATP without the accumulation of reduced species. Whereas linear flow from water to NADP+ is commonly used to explain the function of the light-dependent reactions of photosynthesis, the role of cyclic flow is less clear. In higher plants cyclic flow consists of two partially redundant pathways. Here we have constructed mutants in Arabidopsis thaliana in which both PSI cyclic pathways are impaired, and present evidence that cyclic flow is essential for efficient photosynthesis.     

Ferroelectricity from iron valence ordering in the charge-frustrated system LuFe2O4

Ferroelectric materials are widely used in modern electric devices such as memory elements, filtering devices and high-performance insulators. Ferroelectric crystals have a spontaneous electric polarization arising from the coherent arrangement of electric dipoles (specifically, a polar displacement of anions and cations). First-principles calculations and electron density analysis of ferroelectric materials have revealed that the covalent bond between the anions and cations, or the orbital hybridization of electrons on both ions, plays a key role in establishing the dipolar arrangement. However, an alternative model-electronic ferroelectricity-has been proposed in which the electric dipole depends on electron correlations, rather than the covalency. This would offer the attractive possibility of ferroelectric materials that could be controlled by the charge, spin and orbital degrees of freedom of the electron. Here we report experimental evidence for ferroelectricity arising from electron correlations in the triangular mixed valence oxide, LuFe(2)O(4). Using resonant X-ray scattering measurements, we determine the ordering of the Fe(2+) and Fe(3+) ions. They form a superstructure that supports an electric polarization consisting of distributed electrons of polar symmetry. The polar ordering arises from the repulsive property of electrons-electron correlations-acting on a frustrated geometry.     

Oxygen permeability of the chorion in relation to diapause termination in Bombyx eggs

Oxygen permeability of the chorion of the silkworm, Bombyx mori, was measured in relation to embryonic diapause. It did not change appreciably when the eggs were freed from diapause by being kept under long chilling. This finding suggests that the increase in oxygen permeability of the chorion is not a pre-requisite for the termination of the diapause and resynthesis of glycogen from 2 polyols.     

Novel double-cyclization reaction ofTrans-β-ionylidene acetic acid as a model for conjugated polyenoic acids

Zusammenfassung Es wird eine neuartige Doppel-Zyklisierungs-Reaktion an einer konjugierten Polyencarbonsäure beschrieben.