Plant response to solar ultraviolet-B radiation in a southern South American Sphagnum peatland

1. Plant growth and pigmentation of the moss Sphagnum magellanicum and the vascular plants Empetrum rubrum, Nothofagus antarctica and Tetroncium magellanicum were measured under near-ambient (90% of ambient) and reduced (20%) ultraviolet-B (UV-B) radiation for three growing seasons in a Sphagnum peatland in Tierra del Fuego, Argentina (55°S). 2. Reduction of solar UV-B increased height growth but decreased volumetric density in S. magellanicum so that biomass production was not influenced during the 3 years. The morphology of vascular plants tended not to respond to UV-B reduction. 3. A 10-20% decrease in UV-B-absorbing compounds occurred in T. magellanicum under solar UV-B reduction. No effects were seen on chlorophyll or carotenoids in S. magellanicum, although, for UV-B-absorbing compounds, a significant interaction between UV-B and year suggests some response to solar UV-B reduction. 4. The climate-related growth of the dwarf shrub E. rubrum was assessed retrospectively by correlating an 8-year record of annual stem elongation with macroclimatic factors including solar UV-B and visible radiation, precipitation and temperature. 5. No significant negative correlations were found between annual E. rubrum stem elongation and ambient solar UV-B, the ratio of UV-B: visible radiation, or the 305-nm: 340-nm irradiance ratio for an 8-year record (1990-91 to 1997-98), nor was stem elongation affected by solar UV-B reduction in our experimental field plots after 3 years. 6. The role of solar UV-B radiation on plant growth in Sphagnum peatlands in Tierra del Fuego, Argentina, is likely to depend on the severity of stratospheric ozone depletion over the next several decades. The increases in ambient solar UV-B associated with ozone depletion over the last 20 years are less than the difference between our radiation treatments. Therefore, providing that the ozone layer substantially recovers by the middle of this century, only modest effects of increased solar UV-B on plant growth may be expected.Fil: Searles, Peter Stoughton. State University of Utah; Estados UnidosFil: Flint, Stephan D.. State University of Utah; Estados UnidosFil: Diaz, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; ArgentinaFil: Rousseaux, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Ballare, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Caldwell, Martyn M.. State University of Utah; Estados Unido

Effects of ultraviolet radiation on aquatic bryophytes

The depletion of the stratospheric ozone layer as a result of anthropogenic activities increases the ultraviolet-B (UV-B) irradiance at ground level. This may lead to harmful biological consequences affecting photosynthetic organisms. Mountain streams are especially exposed to a UV-B increase, and bryophytes play a key ecological role in them. In this paper, the effects of enhanced UV-B radiation on photosynthetic organisms in general and on bryophytes in particular are described. Hereafter, some results obtained by our group on the effects of UV-B on bryophytes from mountain streams are presented. Laboratory and field experiments show that these effects depend on the species, the environmental factors (such as temperature), and the origin of the samples (sun or shade conditions, low or high altitude). Among the variables measured, the maximum quantum yield of photosystem II (Fv/Fm) and the level of UV-absorbing compounds seem to be the most responsive to enhanced UV-B, but no variable responded in the same manner in every species. The potential use of aquatic bryophytes as bio-indicators of changes in ambient UV-B radiation would require an adequate selection of both variables and species. Promising variables are Fv/Fm, the concentration of UV-absorbing compounds (especially if they are analyzed individually) and DNA damage, whereas the liverwort Jungermannia exsertifolia subsp. cordifolia has been revealed to be a good bio-indicator species. Globally, the responses of aquatic bryophytes to UV-B radiation and their protecting systems are still poorly characterized, and thus further study is required under both controlled and field conditions.La degradación antropogénica de la capa de ozono estratosférico provoca un aumento de la radiación ultravioleta-B (UV-B) en la superficie de La Tierra. Esto puede causar consecuencias biológicas nocivas en los organismos fotosintéticos. Los arroyos de montaña están especialmente expuestos al aumento de UV-B, y los briófitos desempeñan un papel ecológico crucial en estos ecosistemas. En el presente artículo, se describen los efectos de un aumento de radiación UV-B sobre los organismos fotosintéticos en general y sobre los briófitos en particular. A continuación, se presentan algunos resultados obtenidos por nuestro grupo de investigación sobre los efectos de la radiación UV-B en briófitos de arroyos de montaña. Los experimentos realizados tanto en campo como en laboratorio muestran que dichos efectos dependen de la especie considerada, de los factores ambientales (como la temperatura) y de la procedencia de las muestras (aclimatadas a condiciones de sol o sombra, provenientes de baja o elevada altitud). Entre las variables analizadas, el rendimiento cuántico máximo del fotosistema II (Fv/Fm) y el nivel de compuestos absorbentes de radiación UV parecen ser las que mejor responden a un aumento de UV-B, pero ninguna variable responde de la misma manera en todas las especies. El uso potencial de los briófitos acuáticos como bioindicadores de cambios en los niveles naturales de radiación UV-B requiere una selección adecuada tanto de las variables analizadas como de las especies empleadas. Fv/Fm y la concentración de compuestos absorbentes de radiación UV (en especial si éstos son analizados individualmente), junto con los daños en el ADN, parecen ser las variables más prometedoras en este campo, mientras que la hepática Jungermannia exsertifolia subsp. cordifolia podría resultar una buena especie bioindicadora. Desde un punto de vista global, las respuestas de los briófitos acuáticos a la radiación UV-B, y los mecanismos protectores que utilizan para hacerle frente, están todavía poco caracterizados, y en consecuencia se necesita una mayor investigación en condiciones controladas y en campo

Exobiology and Future Mars Missions

Scientific questions associated with exobiology on Mars were considered and how these questions should be addressed on future Mars missions was determined. The mission that provided a focus for discussions was the Mars Rover/Sample Return Mission

UV-B and abscisic acid effects on grape berry maturation and quality

This review provides an overview of existing literature on the effects of ultraviolet-B (UV-B) radiation and abscisic acid (ABA) on physiological and biochemical aspects affecting grape berry (Vitis vinifera L.) growth, maturation and their quality for winemaking. The UV-B (280?315 nm) comprises only a small fraction of sunlight that reaches the Earth?s surface, but has enough energy to cause large photobiological effects on higher plants. The UV-B levels are greater in the tropics than in upper latitudes and also increase with altitude, hence some vineyards are exposed to high UV-B but photoprotection and repair mechanisms are usually sufficient to prevent the occurrence of damage in grapevine tissues. ABA is a phytohormone that, aside to control stomatal aperture, regulates acclimation to adverse environmental conditions, and controls grape berry maturation (non-climacteric). A promotive effect of UV-B on ABA biosynthesis has been found in grapevine leaves. Accumulation of phenols (namely phenolic acids, stilbenes and flavonoids) is an acclimation and protective response against UV-B, either directly by absorbing UV-B in epidermal tissues and/or by reducing its penetration through underlying tissues, or indirectly by scavenging free radicals so acting as antioxidants. High UV-B and ABA applications increase total phenols in grape berries, but those with higher antioxidant capacity (i.e. dihydroxylated anthocyanidins and flavonols like quercetin) are increased relatively more. These treatments also hasten berry sugar and phenol accumulation, but reduce berry growth and sugar per berry at harvest, and therefore decrease yield. The quality of grape berries for winemaking integrates various aspects, but for red wines, it has a high correlation with accumulation of phenolics stimulated by UV-B and ABA.Fil: Berli, Federico Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mendoza. Instituto de Biologia Agricola de Mendoza; Argentina;Fil: Bottini, Ambrosio Ruben. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mendoza. Instituto de Biologia Agricola de Mendoza; Argentina

Origin of Life

The evolution of life has been a big enigma despite rapid advancements in the fields of biochemistry, astrobiology, and astrophysics in recent years. The answer to this puzzle has been as mind-boggling as the riddle relating to evolution of Universe itself. Despite the fact that panspermia has gained considerable support as a viable explanation for origin of life on the Earth and elsewhere in the Universe, the issue remains far from a tangible solution. This paper examines the various prevailing hypotheses regarding origin of life like abiogenesis, RNA World, Iron-sulphur World, and panspermia; and concludes that delivery of life-bearing organic molecules by the comets in the early epoch of the Earth alone possibly was not responsible for kick-starting the process of evolution of life on our planet.Comment: 32 pages, 8 figures,invited review article, minor additio

Seasonal and inter-annual variation in the chlorophyll content of three co-existing Sphagnum species exceeds the effect of solar UV reduction in a subarctic peatland

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USSR Space Life Sciences Digest, issue 6

This is the sixth issue of NASA's USSR Space Life Sciences Digest. It contains abstracts of 54 papers recently published in Russian language periodicals and bound collections and of 10 new Soviet monographs. Selected abstracts are illustrated with figures and tables from the original. Additional features include a table of Soviet EVAs and information about English translations of Soviet materials available to readers. The topics covered in this issue have been identified as relevant to 26 areas of aerospace medicine and space biology. These areas are adaptation, biospherics, body fluids, botany, cardiovascular and respiratory systems, developmental biology, endocrinology, enzymology, exobiology, genetics, habitability and environment effects, health and medical treatment, hematology, human performance, immunology, life support systems, mathematical modeling, metabolism., microbiology, morphology and cytology, musculoskeletal system, neurophysiology, nutrition, perception, personnel selection, psychology, radiobiology, reproductive biology, and space medicine

Review on Nonoccupational Personal Solar UV Exposure Measurements

Solar ultraviolet (UV) radiation follows people during their whole life. Exposure to UV radiation is vital but holds serious risks, too. The quantification of human UV exposure is a complex issue. UV exposure is directly related to incoming UV radiation as well as to a variety of factors such as the orientation of the exposed anatomical site with respect to the sun and the duration of exposure. The use of badge-sensors allows assessing the UV exposure of differently oriented body sites. Such UV devices have been available for over 40 years, and a variety of measuring campaigns have been undertaken since then. This study provides an overview of those studies which reported measurements of the personal UV exposure (PE) during outdoor activities of people not related to their occupation. This overview is given chronologically to show the progress of knowledge in this research and is given with respect to different activities. Special focus is put on the ratio of personal exposure to ambient UV radiation. This ratio, when given as a function of solar elevation, allows estimating PE at any other location or date if ambient UV radiation is known