Stephen De Mora

INTRACELLULAR DIMETHYLSULFOXIDE (DMSO) IN UNICELLULAR MARINE ALGAE : SPECULATIONS ON ITS ORIGIN AND POSSIBLE BIOLOGICAL ROLE

Recent studies have established that aqueous phase concentrations of dimethylsulfoxide (DMSO) often exceed those of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS). Yet, in comparison to DMSP and DMS, DMSO remains a poorly understood component of the marine sulfur cycle. Much of what is known about the mechanisms for the formation and loss for DMSO is inferred from laboratory experiments, and no explanation exists to rationalize how a large pool of DMSO is maintained. One formation pathway that, until very recently, has been ignored involves the direct synthesis of DMSO by marine phytoplankton. This review examines some of the circumstantial evidence for DMSO in marine particulate material and recent reports containing preliminary data for particulate DMSO (DMSOp) in the marine environment. Drawing on literature from a range of scientific disciplines, speculations on the possible origins and biological functions of intracellular DMSO are also made. On the basis of its physicochemical properties, intracellular DMSO could have a potential role as a cryoprotectant, a specialist cryo‐osmoregulator in extreme environments, an intracellular electrolyte modifier, and a free‐radical scavenger. The review also assesses the impact of DMSOp at both the organism and the global level. Consideration is given to the marine biogeochemical cycling of sulfur and potential links to climate control.

The effects of UV radiation in the marine environment: Enhanced UV radiation – a new problem for the marine environment

UV irradiance at the earth’s surface is intimately related to stratospheric ozone. This gas tends to be concentrated in the lower stratosphere (hence the notion of an ozone layer) and is primarily responsible for the absorption of solar UV radiation (UVR). UVR has been recognised for many years (e.g. Worrest, Dyke & Thomson, 1978; Worrest et al., 1981; Calkins, 1982) as a potential stress for organisms in a variety of environments and as a factor in biogeochemical cycling (Zepp, Callaghan & Erickson, 1995). The trend in recent years of an intensifying, but periodic, anthropogenic-induced decline in stratospheric ozone concentrations with concurrent enhanced UV-B radiation is quite alarming. Altered solar radiation regimes can potentially upset established balances in marine ecosystems and thus presents a new problem. Most attention has been given to the ‘ozone hole’ over Antarctica that has been recorded annually since the 1980s. However, recent observations have confirmed measurable ozone losses over other regions, including the development of an Arctic ozone hole. The major factor responsible for the destruction of the ozone layer is anthropogenic emissions of chlorofluorocarbons (CFCs). These gases, having no natural sources, are non-toxic and inert in the troposphere, but are photolysed in the stratosphere, thereby releasing reactive chlorine atoms that catalytically destroy ozone. Other anthropogenic contributions to ozone depletionmay include global changes in land use and the increased emission of nitrogen dioxide as a result of fertiliser applications (Bouwman, 1998). Paradoxically, the anthropogenic emissions of greenhouse gases that tend to cause a temperature increase at the earth’s surface also produce a decrease in stratospheric temperatures. This decrease in stratospheric temperatures leads to enhanced formation of polar stratospheric clouds and may serve to increase ozone

PARTICULATE DIMETHYLSULFOXIDE IN ARCTIC SEA-ICE ALGAL COMMUNITIES: THE CRYOPROTECTANT HYPOTHESIS REVISITED

The particulate‐phase concentrations of dimethyl sulfoxide (DMSOp) and dimethylsulfoniopropionate (DMSPp) in sea‐ice algal communities from the North Water, northern Baffin Bay, were examined from April to June 1998. The concentrations of these compounds were measured in the bottom 2 cm of the ice at 36 locations throughout this region and are compared with results from water‐column samples collected for a complementary study. In general, levels of DMSPp (8.66–987 nmol·L−1, average 126 nmol·L−1) in sea‐ice algal communities were slightly less than those found in bottom sea‐ice algal communities from other polar locations but greater than those found in phytoplankton in other polar environments or at more temperate latitudes. Furthermore, DMSPp  :chl a ratios (0.02–14.8 nmol·μg−1, average 1.91 nmol·μg−1) in the sea‐ice algal community were slightly less than those found in other polar environments. DMSOp was measured for the first time in sea‐ice algal communities. DMSOp concentrations varied from 1.35 to 102 nmol·L−1 (average 13.7 nmol·L−1). DMSOp:chl a ratios varied from 0.01 to 4.5 nmol·μg−1 (average 0.22 nmol·μg−1) and were significantly lower than the DMSPp:chl a ratios observed in this study. It has been hypothesized that DMSO can act as a cryoprotector in phytoplankton cells. However, the low concentrations of DMSO observed in the ice algae during this study indicate that intracellular concentrations of DMSO are unlikely to have a significant influence on the freezing point depression of intracellular fluids.

The effects of UV radiation in the marine environment: Index

Preface Stephen de Mora 1. Enhanced UV radiation - a new problem for the marine environment Robert Whitehead, Stephen de Mora and Serge Demers 2. UV physics and optics Susana Diaz, John Morrow and Charles Booth 3. Spectral weighting functions for quantifying effects of ultraviolet radiation in marine ecosystems Patrick Neale 4. Marine photochemistry and its impact on carbon cycling Kenneth Mopper and David Kieber 5. Photochemical production of biological substrates David Kieber 6. Mechanisms of UV damage to aquatic organisms Warwick Vincent and Patrick Neale 7. Strategies for the minimisation of UV-induced damage Suzanne Roy 8. Ultraviolet radiation effects on heterotrophic bacterioplankton and viruses in marine ecosystems Wade Jeffrey, Jason Kase and Steven Wilhelm 9. Effects of ultraviolet radiation on the physiology and ecology of marine phytoplankton Maria Vernet 10. Impact of solar UV radiation on zooplankton and fish Horacio Zagarese and Craig Williamson 11. Implications of UV radiation on the food web structure and consequences on the carbon flow Behzad Mostajir, Serge Demers, Stephen de Mora, Robert Bukata and John Jerome.

The effects of UV radiation in the marine environment: The Effects of UV Radiation in the Marine Environment

Preface Stephen de Mora 1. Enhanced UV radiation - a new problem for the marine environment Robert Whitehead, Stephen de Mora and Serge Demers 2. UV physics and optics Susana Diaz, John Morrow and Charles Booth 3. Spectral weighting functions for quantifying effects of ultraviolet radiation in marine ecosystems Patrick Neale 4. Marine photochemistry and its impact on carbon cycling Kenneth Mopper and David Kieber 5. Photochemical production of biological substrates David Kieber 6. Mechanisms of UV damage to aquatic organisms Warwick Vincent and Patrick Neale 7. Strategies for the minimisation of UV-induced damage Suzanne Roy 8. Ultraviolet radiation effects on heterotrophic bacterioplankton and viruses in marine ecosystems Wade Jeffrey, Jason Kase and Steven Wilhelm 9. Effects of ultraviolet radiation on the physiology and ecology of marine phytoplankton Maria Vernet 10. Impact of solar UV radiation on zooplankton and fish Horacio Zagarese and Craig Williamson 11. Implications of UV radiation on the food web structure and consequences on the carbon flow Behzad Mostajir, Serge Demers, Stephen de Mora, Robert Bukata and John Jerome.