Aromatic and aliphatic mono- and bis-nitroxides: A study on their radical scavenging abilities

Nitroxide radicals are an emerging class of interesting compounds with versatile antioxidant and radioprotective properties. All literature studies have so far concentrated on compounds bearing only one nitroxide function. Here, we now investigate and compare the radical scavenging behaviour and antioxidant activity of aromatic indolinonic and aliphatic piperidine bis-nitroxides, i.e compounds bearing two nitroxide functions. Their corresponding mono-derivatives were also studied for comparison. Radical scavenging activity was investigated using EPR and UV–Vis spectroscopy by following spectral changes in acetonitrile of the nitroxides in the presence of alkyl and peroxyl radicals generated, respectively, under anoxic or aerobic conditions from thermal decomposition of AMVN [2,2′-azobis(2,4-di-methylvaleronitrile)]. Antioxidant activity of the nitroxides was evaluated by monitoring conjugated dienes (CD) formation during methyl linoleate micelles peroxidation and by measuring carbonyl content in oxidized bovine serum albumin (BSA). The results show that: (a) each nitroxide moiety in bis-nitroxides scavenges radicals independent of each other; (b) aliphatic nitroxides do not scavenge peroxyl radicals, at least under the experimental conditions used here, whereas indolinonic aromatic ones do: their stoichiometric number is 1.14 and 2.17, respectively, for mono- and bis-derivatives; (c) bis-nitroxides are roughly twice more efficient at inhibiting lipid peroxidation compared to their corresponding mono-derivatives. Although this study provides only comparative information on the relative radical-scavenging abilities of mono- and bis-nitroxides, it helps in understanding further the interesting reactivity of these compounds especially with regards to peroxyl radicals where many controversies in the literature exist.     

Temperature stress and survival ability of Mediterranean sclerophyllous plants

ABSTRACT

The Mediterranean climate with hot and dry summer periods, and low winter temperatures and episodic frosts in northern, altitudinal and continental districts, demands from evergreen broadleaved woody plants an adequate and flexible acclimation to the climatic constraints.

In this brief survey on some responses of Mediterranean sclerophylls to temperature stress, the following is presented and discussed: criteria for cold and heat limits of photosynthetic function; winter depression and summer photoinactivation of photosynthesis; peculiar patterns of tissue freezing of scleromorphous leaves and limits of frost resistance of various plant parts and ontogenetic stages; heat impairment of chloroplasts and thermotolerance of sclerophyllous species; survival capacity and recovery after damage. Risks of damage to plants in relation to stressful temperatures in Mediterranean regions are estimated. Cold stress and drought stress indices, according to Mitrakos (1980), have been applied to characterise different localities in Italy. Additionally, a heat stress index for the Mediterranean region is proposed. Future research topics are suggested.     

Effect of spatial and temporal patterns of stress and disturbance intensities in a sub-Mediterranean grassland

Abstract

The present study examined a sub-Mediterranean pastoral system in the central Apennines (Italy) with a long history of grazing, where winter cold stress is alternated with summer drought stress. The research goals were to ascertain whether different floristic structures correspond to different stress conditions (xeric and semimesic), and whether peculiar functional plant traits (such as avoidance and tolerance mechanisms) respond to stress/disturbance intensities, and understand how vegetation reacts to changeable livestock pressure (through floristic and plant trait variations). Cluster analysis indicated that separate communities develop under different stress intensities. Other analyses highlighted how avoidance strategies predominate within the pastoral system. Observations of grazed and ungrazed patches conducted in 10-m transects revealed spiny cushion formation in semimesic grassland, where a brief period of overgrazing occurs in late summer, causing variations in plant community structure. All these results confirm the importance of historical grazing and current land use, showing how small disturbances and stress variations cause ecosystem responses. Best practices for management were identified. In xeric conditions, it is advisable that the intensity of disturbance be lessened, while in semimesic grassland overgrazing should be forbidden during the dry period, because it could facilitate the development of spiny patches, and subsequent spread of Brachypodium rupestre.     

Upward ant distribution shift corresponds with minimum,not maximum,temperature tolerance

Rapid climate change may prompt species distribution shifts upward and poleward, but species movement in itself is not sufficient to establish climate causation. Other dynamics, such as disturbance history, may prompt species distribution shifts resembling those expected from rapid climate change. Links between species distributions, regional climate trends and physiological mechanism are needed to convincingly establish climate‐induced species shifts. We examine a 38‐year shift (1974–2012) in an elevation ecotone between two closely related ant species, Aphaenogaster picea and A. rudis. Even though A. picea and A. rudis are closely related with North American distributions that sometimes overlap, they also exhibit local‐ and regional‐scale differences in temperature requirements so that A. rudis is more southerly and inhabits lower elevations whereas A. picea is more northerly and inhabits high elevations. We find considerable movement by the warm‐habitat species upward in elevation between 1974 and 2012 with A. rudis, replacing the cold‐habitat species, A. picea, along the southern edge of the Appalachian Mountain chain in north Georgia, USA. Concomitant with the distribution shifts, regional mean and maximum temperatures remain steady (1974–2012), but minimum temperatures increase. We collect individuals from the study sites and subject them to thermal tolerance testing in a controlled setting and find that maximum and minimum temperature acclimatization occurs along the elevation gradient in both species, but A. rudis consistently becomes physiologically incapacitated at minimum and maximum temperatures 2 °C higher than A. picea. These results indicate that rising minimum temperatures allow A. rudis to move upward in elevation and displace A. picea. Given that Aphaenogaster ants are the dominant woodland seed dispersers in eastern deciduous forests, and that their thermal tolerances drive distinct differences in temperature‐cued synchrony with early blooming plants, these climate responses not only impact ant‐ant interactions, but might have wide implications for ant‐plant interactions.     

The western painted turtle genome,a model for the evolution of extreme physiological adaptations in a slowly evolving lineage

Background

We describe the genome of the western painted turtle, Chrysemys picta bellii, one of the most widespread, abundant, and well-studied turtles. We place the genome into a comparative evolutionary context, and focus on genomic features associated with tooth loss, immune function, longevity, sex differentiation and determination, and the species'' physiological capacities to withstand extreme anoxia and tissue freezing.

Results

Our phylogenetic analyses confirm that turtles are the sister group to living archosaurs, and demonstrate an extraordinarily slow rate of sequence evolution in the painted turtle. The ability of the painted turtle to withstand complete anoxia and partial freezing appears to be associated with common vertebrate gene networks, and we identify candidate genes for future functional analyses. Tooth loss shares a common pattern of pseudogenization and degradation of tooth-specific genes with birds, although the rate of accumulation of mutations is much slower in the painted turtle. Genes associated with sex differentiation generally reflect phylogeny rather than convergence in sex determination functionality. Among gene families that demonstrate exceptional expansions or show signatures of strong natural selection, immune function and musculoskeletal patterning genes are consistently over-represented.

Conclusions

Our comparative genomic analyses indicate that common vertebrate regulatory networks, some of which have analogs in human diseases, are often involved in the western painted turtle''s extraordinary physiological capacities. As these regulatory pathways are analyzed at the functional level, the painted turtle may offer important insights into the management of a number of human health disorders.     

REV7 is required for anaphase-promoting complex-dependent ubiquitination and degradation of translesion DNA polymerase REV1

REV1 is a Y-family polymerase specialized for replicating across DNA lesions at the stalled replication folk. Due to the high error rate of REV1-dependent translesion DNA synthesis (TLS), tight regulation of REV1 activity is essential. Here, we show that human REV1 undergoes proteosomal degradation mediated by the E3 ubiquitin ligase known as anaphase-promoting complex (APC). REV1 associates with APC. Overexpression of APC coactivator CDH1 or CDC20 promotes polyubiquitination and proteosomal degradation of REV1. Surprisingly, polyubiquitination of REV1 also requires REV7, a TLS accessory protein that interacts with REV1 and other TLS polymerases. The N-terminal region of REV1 contains both the APC degron and an additional REV7-binding domain. Depletion of REV7 by RNA interference stabilizes REV1 by preventing polyubiquitination, whereas overexpression of REV7 augments REV1 degradation. Taken together, our findings suggest a role of REV7 in governing REV1 stability and interplay between TLS and APC-dependent proteolysis.     

Understanding the origins of UV-induced recombination through manipulation of sister chromatid cohesion

Ultraviolet light (UV) can provoke genome instability, partly through its ability to induce homologous recombination (HR). However, the mechanism(s) of UV-induced recombination is poorly understood. Although double-strand breaks (DSBs) have been invoked, there is little evidence for their generation by UV. Alternatively, single-strand DNA lesions that stall replication forks could provoke recombination. Recent findings suggest efficient initiation of UV-induced recombination in G₁ through processing of closely spaced single-strand lesions to DSBs. However, other scenarios are possible, since the recombination initiated in G₁ can be completed in the following stages of the cell cycle. We developed a system that could address UV-induced recombination events that start and finish in G₂ by manipulating the activity of the sister chromatid cohesion complex. Here we show that sister-chromatid cohesion suppresses UV-induced recombination events that are initiated and resolved in G₂. By comparing recombination frequencies and survival between UV and ionizing radiation, we conclude that a substantial portion of UV-induced recombination occurs through DSBs. This notion is supported by a direct physical observation of UV-induced DSBs that are dependent on nucleotide excision repair. However, a significant role of nonDSB intermediates in UV-induced recombination cannot be excluded.     

UV light phototransduction depolarizes human melanocytes

Exposure of human skin to low doses of solar UV radiation (UVR) causes increased pigmentation, while chronic exposure is a powerful risk factor for skin cancers. The mechanisms mediating UVR detection in skin, however, remain poorly understood. Our recent studies revealed that UVR activates a retinal-dependent G protein-coupled signaling pathway in melanocytes. This phototransduction pathway leads to the activation of transient receptor potential A1 (TRPA1) ion channels, elevation of intracellular calcium (Ca²⁺) and rapid increase in cellular melanin content. Here we report that physiological doses of solar-like UVR elicit a retinal-dependent membrane depolarization in human epidermal melanocytes. This transient depolarization correlates with delayed inactivation time of the UVR-evoked photocurrent and with sustained Ca²⁺ responses required for early melanin synthesis. Thus, the cellular depolarization induced by UVR phototransduction in melanocytes is likely to be a critical signaling mechanism necessary for the protective response represented by increased melanin content.