Membranes as targets of ultraviolet radiation

In non-photosynthetic cells, evidence for UV (ultraviolet radiation) damage to membranes comes from electron microscopy, chemical analysis and observations of transport processes. Specific perturbations in transport across membranes occur quickly after a relatively low fluence of UV. As an example, irradiation of suspension-cultured rose cells with 500-2000 J m^?2 (at 254 nm) causes an appearance of K⁺ in the extracellular medium at the rate of 5 × 10^?10μmol cell^?1 min^?1 for 30 to 60 min and more slowly thereafter. The early, rapid phase of appearance of K⁺ reflects both an increase in efflux and a decrease in influx. The appearance of K⁺ is matched by an appearance of HCO^?₃ in the medium. The HCO^?₃ comes from respiratory CO₂, which hydrates and dissociates in the cytoplasm, leading to a decrease in cytoplasmic pH. Overall, these results not only demonstrate UV damage to membrane function, but also suggest several ways by which UV may alter the general metabolic state of the cell. A demonstration of direct effects of UV on membrane components requires a purified system. At lower fluence, < 1800 J m^?2 (254 nm), the ATPase of membrane vesicle preparations is inactivated in a two-phase process that suggests the presence of enzymes with different UV sensitivities. The existence of two non-mitochondrial enzymes in rose cell vesicles has been confirmed by solubilizing the vesicle proteins with 1% cholic acid and separating the components on G-150 Sephadex. One component of relatively high molecular weight is especially sensitive. The fact that it is still sensitive when it is dissolved in cholic acid strongly suggests that its sensitivity is intrinsic and does not depend on sensitization by other membrane components. The action spectrum for the inactivation of the ATPase has a major peak at 290 nm and extends into the UV-C and UV-A regions. The physiological effects of UV-stimulated membrane changes are uncertain. There is little evidence that the UV damage to membranes is responsible for cell death. A UV-induced loss of K⁺ from guard cells may result in lower stomatal conductance. UV-stimulated membrane changes may play a role in the UV-induced synthesis of anthocyanins.     

Sociopathy as an adaptation

Sociopathy in males and hysteria (Briquet's syndrome) in females very closely fit predictions from a model of characteristics of cheaters or nonreciprocators in a complex social system. Such a model is discussed and characteristics of sociopaths and hysterics are described. Since a successful cheating adaptation should require, above all else, concealment of the trait, recognition and diagnosis of these traits in humans will always be difficult and ambiguous at the level of language and interpersonal interaction.     

Resistance of 5,10-methenyltetrahydrofolate to ultraviolet radiation

Aeration of aqueous solutions of 5,10-methenyltetrahydrofolic acid (MTHF) during exposure to ultraviolet irradiation (=300–390 nm, 240 W/m², 30 min) slowed down photolysis in comparison with deaerated solutions. The rate of photolysis in the presence of oxygen depended on the ionic strength of the buffer composition. MTHF degradation did not exceed 6% of the starting amount of MTHF. Photolysis of MTHF included opening of the imidazoline ring, dehydrogenation of the tetrahydropterin heterocycle, and elimination of the p-aminobenzoylglutamate moiety. 6,7-Dimethyltetrahydropterin was used as a model compound to show that protonation of the reduced pterin heterocycle increased its resistance to oxidation, and UV irradiation did not accelerate this process. The stabilizing effect of protonation of the pterin portion and the presence of the positively charged imidazoline moiety are assumed to hamper MTHF oxidation and photolysis. It is assumed that these factors favored the choice of MTHF molecules as photosensors in radiation-sensitive proteins in the course of evolution.__________Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 3, 2005, pp. 315–323.Original Russian Text Copyright © 2005 by Telegina, Lyudnikova, Zemskova, Sviridov, Kritsky.     

Tolerance of 5,10-methenyltetrahydrofolate to ultraviolet radiation

Aeration of aqueous solutions of 5,10-methenyltetrahydrofolic acid (MTHF) during exposure to ultraviolet irradiation (lambda 300-390 nm, 240 W/m2, 30 min) slowed down photolysis in comparison with deaerated solutions. The rate of photolysis in the presence of oxygen depended on buffer composition. It did not exceed 6% of the starting amount of MTHF. Photolysis of MTHF included opening of the imidazoline ring, dehydrogenation of the tetrahydropterin portion, and elimination of the p-aminobenzoylglutamate moiety. 6,7-Dimethyltetrahydropterin was used as a model compound to show that protonation of the reduced pterin heterocycle increased its tolerance to oxidation, and UV irradiation did not accelerate this process. The stabilizing effect of protonation of the pterin portion and the presence of the positively charged imidazoline moiety are assumed to hamper MTHF oxidation and photolysis. It is assumed that these factors favored the choice of MTHF molecules as photosensors in light-sensitive proteins in the course of evolution.     

Susceptibility of Legionella pneumophila to ultraviolet radiation

Distilled water suspensions of Legionella pneumophila were found to be sensitive to low doses of germicidal ultraviolet radiation.     

Long-term exposure to solar ultraviolet radiation as a risk factor for age-related macular degeneration

A clinical epidemiological study has been conducted as apart of research project investigating chronic exposure to solar ultraviolet radiation (UVR) as a factor contributing to the onset of age-related macular degeneration (ARMD). The study included 623 subjects older than 50 from two different geographic areas, one with high solar radiation (the island of Solta - Region 1) and the other (Zagreb and its surroundings - Region 2) with low solar radiation. Individual exposure to UVR was assessed according to global exposure to sunlight, on the basis detailed history of life-long exposure to sunlight, with special reference to professional history and geophysical specificities of the respective areas. Different grades of ARMD were based on the fundus photographs and flourescein angiography. Statistically significant relation was found between ARMD and mean daily exposure (in hours) to solar radiation in Region 1 (chi2 = 186.22; p = 0.000), Region 2 (chi2 = 25.66; p = 0.000) and in both regions together (chi2 = 216.43; p = 0.000). ARMD is more frequent in the subjects belonging to the Region 1 and with the same exposure to sunlight (8 hours and more) which goes in favor of their increased UVR exposure. The results support a relationship between long-term sunlight exposure and increased risk of ARMD.     

Ultraviolet radiation induces dose-dependent pigment dispersion in crustacean chromatophores

Pigment dispersion in chromatophores as a response to UV radiation was investigated in two species of crustaceans, the crab Chasmagnathus granulata and the shrimp Palaemonetes argentinus. Eyestalkless crabs and shrimps maintained on either a black or a white background were irradiated with different UV bands. In eyestalkless crabs the significant minimal effective dose inducing pigment dispersion was 0.42 J/cm(2) for UVA and 2.15 J/cm(2) for UVB. Maximal response was achieved with 10.0 J/cm(2) UVA and 8.6 J/cm(2) UVB. UVA was more effective than UVB in inducing pigment dispersion. Soon after UV exposure, melanophores once again reached the initial stage of pigment aggregation after 45 min. Aggregated erythrophores of shrimps adapted to a white background showed significant pigment dispersion with 2.5 J/cm(2) UVA and 0.29 J/cm(2) UVC. Dispersed erythrophores of shrimps adapted to a black background did not show any significant response to UVA, UVB or UVC radiation. UVB did not induce any significant pigment dispersion in shrimps adapted to either a white or a black background. As opposed to the tanning response, which only protects against future UV exposure, the pigment dispersion response could be an important agent protecting against the harmful effects of UV radiation exposure.     

Senescence as an adaptation to limit the spread of disease

Aging has the hallmarks of an evolved adaptation. It is controlled by genes that have been conserved over vast evolutionary distances, and most organisms are able to forestall aging in the most challenging of environments. But fundamental theoretical considerations imply that there can be no direct selection for aging. Senescence reduces individual fitness, and any group benefits are weak and widely dispersed over non-relatives. We offer a resolution to this paradox, suggesting a general mechanism by which senescence might have evolved as an adaptation. The proposed benefit is that senescence protects against infectious epidemics by controlling population density and increasing diversity of the host population. This mechanism is, in fact, already well-accepted in another context: it is the Red Queen Hypothesis for the evolution of sex. We illustrate the hypothesis using a spatially explicit agent-based model in which disease transmission is sensitive to population density as well as homogeneity. We find that individual senescence provides crucial population-level advantages, helping to control both these risk factors. Strong population-level advantages to individual senescence can overcome the within-population disadvantage of senescence. We conclude that frequent local extinctions provide a mechanism by which senescence may be selected as a population-level adaptation in its own right, without assuming pleiotropic benefits to the individual.     

Fantastic animals as an experimental model to teach animal adaptation

Background

Science curricula and teachers should emphasize evolution in a manner commensurate with its importance as a unifying concept in science. The concept of adaptation represents a first step to understand the results of natural selection. We settled an experimental project of alternative didactic to improve knowledge of organism adaptation. Students were involved and stimulated in learning processes by creative activities. To set adaptation in a historic frame, fossil records as evidence of past life and evolution were considered.

Results

The experimental project is schematized in nine phases: review of previous knowledge; lesson on fossils; lesson on fantastic animals; planning an imaginary world; creation of an imaginary animal; revision of the imaginary animals; adaptations of real animals; adaptations of fossil animals; and public exposition. A rubric to evaluate the student's performances is reported. The project involved professors and students of the University of Modena and Reggio Emilia and of the "G. Marconi" Secondary School of First Degree (Modena, Italy).

Conclusion

The educational objectives of the project are in line with the National Indications of the Italian Ministry of Public Instruction: knowledge of the characteristics of living beings, the meanings of the term "adaptation", the meaning of fossils, the definition of ecosystem, and the particularity of the different biomes. At the end of the project, students will be able to grasp particular adaptations of real organisms and to deduce information about the environment in which the organism evolved. This project allows students to review previous knowledge and to form their personalities.

     

The penetration of ultraviolet radiation to the ground

The evolution of analytic formulas for characterizing the ultraviolet spectral ir-radiance penetrating to the ground is briefly described. Analytic spectral functions for the extraterrestrial solar spectral irradiance, the ozone absorption coefficient, Rayleigh scattering coefficients and aerosol scattering and absorption coefficients, which are used as basic inputs, are given. With Beer's law, these give immediately the direct solar spectral irradiance. A ratio technique described in quantitative detail gives a procedure for calculating the skylight component of the UV radiation reaching the ground. The influence of ground reflectivity, clouds and a possible connection between photobiology and radiological physics are discussed. Finally the advantages of multiwavelength monitoring are described, using monochromators similar to those used in satellite ozone sounding to serve the needs of the photobiology and the atmospheric science communities.     

Cardiac regeneration as an environmental adaptation

Heart failure is a devastating disease that affects more than 26 million individuals worldwide and has a 5-year survival rate of less than 50%, with its development in part reflecting the inability of the adult mammalian heart to regenerate damaged myocardium. In contrast, certain vertebrate species including fish and amphibians, as well as neonatal mammals, are capable of complete cardiac regeneration after various types of myocardial injury such as resection of the ventricular apex or myocardial infarction, with this regeneration being mediated by the proliferation of cardiomyocytes, dissolution of temporary fibrosis, and revascularization of damaged tissue. In an effort to identify regulators of cardiac regeneration and to develop novel therapeutic strategies for induction of myocardial regeneration in the adult human heart, recent studies have adopted an approach based on comparative biology. These studies have pointed to cellular or tissue responses to environmental cues—including activation of the immune system, the reaction to mechanical stress, and the adoption of oxidative metabolism—as key determinants of whether the heart undergoes regeneration or nonregenerative scar formation after injury. We here summarize recent insight into the molecular mechanisms as well as environmental and systemic factors underlying cardiac regeneration based on the findings of inter- or intraspecific comparisons between regenerative and nonregenerative responses to heart injury. We also discuss how recent progress in understanding the molecular, systemic, and environmental basis of cardiac regeneration in a variety of organisms may relate to multiple scientific fields including ecology, evolutionary as well as developmental biology.     

A Pseudomonas aeruginosa biosensor responds to exposure to ultraviolet radiation

We fused the Pseudomonas aeruginosa recA promoter to a promoterless Vibrio fisherilux operon. This recA–lux fusion (pMOE15) was introduced into wild-type P. aeruginosa strain FRD1 and recA expression was monitored by measuring 490-nm light production. The RM4440 strain responded to increasing doses of ultraviolet radiation by an increase in its bioluminescence. RM4440 has the potential to be useful as a biosensor for the presence of DNA-damaging agents in the environment. Received: 18 February 1998 / Received revision: 18 June 1998 / Accepted: 27 June 1998     

Damage to macrophage membranes by exposure to middle-wave ultraviolet radiation

An influence of middle-wave ultraviolet radiation (lambda max = 306 nm) on plasma membranes of mice peritoneal macrophages was studied by microfluorimetry analysis. It was found that a percentage of cells with damaged plasma membranes in the irradiated macrophage population reliably increased with the UVB dose starting with 6 J/cm2. Irradiation of cells with 4.2 J/cm2 UVR dose which does not cause evident damage to plasma membranes led to the latent damage which was detected by treatment with detergent digitonin (4.5 micrograms/ml).     

Differential enzyme targeting as an evolutionary adaptation to herbivory in carnivora

Not all members of the order Carnivora are carnivorous. Some are omnivorous, and a few, such as the giant panda, Ailuropoda melanoleuca, are almost exclusively herbivorous. Although a number of adaptations to increased plant-eating are recognized within Carnivora, few have been studied at the molecular level. One molecular adaptation to diet that is spread widely across Mammalia is the differential intracellular targeting of the intermediary metabolic enzyme alanine:glyoxylate aminotransferase (AGT), which tends to be mitochondrial in carnivores, peroxisomal in herbivores, and both mitochondrial and peroxisomal in omnivores. In the present study, we have analyzed the targeting of AGT in Carnivora in relation to species' natural diets. We show not only that there has been an adaptive shift in AGT targeting from the mitochondrion toward the peroxisome as diets have shifted from being mainly carnivorous to ones that are more omnivorous and herbivorous but also that in one lineage, namely that of the giant panda, there is evidence for positive selection pressure at the molecular level on the AGT mitochondrial targeting sequence to decrease its efficiency, thereby allowing more AGT to be targeted to the peroxisomes.     

Methods for exposure of laboratory animals to ultraviolet radiation

Two different sources of ultraviolet B (UVB) radiation, an electronically controlled UVB exposure unit, containing FS40 tubes, and a hand-held Kromayer lamp, were evaluated for actual irradiance in W/m2 and spectra (physical dosimetry and biological dosimetry (skin effects in rodents)). The technical studies of the FS40 sources demonstrated that the flux intensity of the lamps could be changed electronically, without affecting the spectrum. Thus it was possible to standardize UVB exposure electronically. The biologically effective doses of these sources were analysed in RIV-Tox Wistar rats and BALB/c mice. After low doses of UVB radiation, histopathological changes such as acanthosis, hyperkeratosis and dermal inflammation were observed in the skin without the presence of major side effects such as erythema and oedema. After higher doses of UVB radiation erythema and oedema were clearly visible. Quantitative studies showed that the minimal erythema dose, as a biological parameter, correlated well to the emission in J/m2. In addition, biological parameters such as acanthosis and inflammation in the skin correlated well to the actual exposure in J/m2 and were sensitive biomarkers for UVB-induced skin toxicity. Thus, in addition to minimal erythemal doses, acanthosis and inflammation may also be applied as biologically relevant doses for studies of the biological effects of UVB radiation.