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• 1. [Article] Prospectus for Future Research: Temperature Effects on Green Macroalgae

  Research on temperature change has received attention from scientists. Not only has temperature change attracted scientists who study the Earth’s weather and climate, but also those who study plants and ...

  Citation × Citation Citation Abstract Copy Title: Prospectus for Future Research: Temperature Effects on Green Macroalgae Author: Gonzalez Pelayo, Ana Year: 2016 Research on temperature change has received attention from scientists. Not only has temperature change attracted scientists who study the Earth’s weather and climate, but also those who study plants and animals on land and in oceans. The research being conducted looks at how these temperature changes affect the anatomy and physiology of organisms, but other research also studies how terrestrial and aquatic ecosystems have changed and the types of responses that have occurred as a result. For many years, research in terrestrial ecosystems has dominated research in aquatic ecosystems. Limited research has been conducted in aquatic ecosystems involving green macroalgae, which are primary producers and an essential part of these ecosystems. Within the last fifteen years, research regarding the effects of temperature change on green macroalgae has shown that temperature affects photosynthesis and biochemistry. Overall, photosynthesis is almost completely inhibited after sufficient exposure due to damage in Photosystem II. There is also a substantial change in the production of chemical molecules known as reactive oxygen species that caused physical damage to the algal cells as well as a change in structure for proteins that is essential for function. I reviewed the literature within the past fifteen years, regarding the effects of temperature on a variety of green macroalgae species. The results indicated that after sufficient exposure, the photosynthetic rate of macroalgae is reduced significantly and that the change in chemistry lead to alterations in the physiology of green macroalgae. In this thesis, I propose two possible directions for algae research that involves genetic sequencing of a model species to identify a possible temperature tolerance gene, as well as the potential use of green macroalgae in photobioreactors as a source of renewable energy. Title: Prospectus for Future Research: Temperature Effects on Green Macroalgae Author: Gonzalez Pelayo, Ana Year: 2016 Research on temperature change has received attention from scientists. Not only has temperature change attracted scientists who study the Earth’s weather and climate, but also those who study plants and animals on land and in oceans. The research being conducted looks at how these temperature changes affect the anatomy and physiology of organisms, but other research also studies how terrestrial and aquatic ecosystems have changed and the types of responses that have occurred as a result. For many years, research in terrestrial ecosystems has dominated research in aquatic ecosystems. Limited research has been conducted in aquatic ecosystems involving green macroalgae, which are primary producers and an essential part of these ecosystems. Within the last fifteen years, research regarding the effects of temperature change on green macroalgae has shown that temperature affects photosynthesis and biochemistry. Overall, photosynthesis is almost completely inhibited after sufficient exposure due to damage in Photosystem II. There is also a substantial change in the production of chemical molecules known as reactive oxygen species that caused physical damage to the algal cells as well as a change in structure for proteins that is essential for function. I reviewed the literature within the past fifteen years, regarding the effects of temperature on a variety of green macroalgae species. The results indicated that after sufficient exposure, the photosynthetic rate of macroalgae is reduced significantly and that the change in chemistry lead to alterations in the physiology of green macroalgae. In this thesis, I propose two possible directions for algae research that involves genetic sequencing of a model species to identify a possible temperature tolerance gene, as well as the potential use of green macroalgae in photobioreactors as a source of renewable energy. Close

• 2. [Article] Stomatal Responses of Douglas-Fir Seedlings to Elevated Carbon Dioxide and Temperature During the Third and Fourth Years of Exposure

  Two major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water ...

  Citation × Citation Citation Abstract Copy Title: Stomatal Responses of Douglas-Fir Seedlings to Elevated Carbon Dioxide and Temperature During the Third and Fourth Years of Exposure Author: Lewis, James D., Lucash, Melissa S., Olszyk, David M., Tingey, David T. Year: 2002 Two major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2] and temperature on seasonal patterns of stomatal conductance (gs), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO2 (AC) or ambient + 180 µmol mol-1 CO2 (EC), and at ambient temperature (AT) or ambient + 3.5° C (ET) in a full-factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO2] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO2] significantly increased with seasonal increases in the needle-to-air vapour pressure deficit (D). Across CO2 treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO2] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO2 supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between gs and net photosynthetic rates. This study suggests that elevated [CO2] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle-level water loss and water use efficiency of Douglas-fir seedlings. Title: Stomatal Responses of Douglas-Fir Seedlings to Elevated Carbon Dioxide and Temperature During the Third and Fourth Years of Exposure Author: Lewis, James D., Lucash, Melissa S., Olszyk, David M., Tingey, David T. Year: 2002 Two major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2] and temperature on seasonal patterns of stomatal conductance (gs), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO2 (AC) or ambient + 180 µmol mol-1 CO2 (EC), and at ambient temperature (AT) or ambient + 3.5° C (ET) in a full-factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO2] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO2] significantly increased with seasonal increases in the needle-to-air vapour pressure deficit (D). Across CO2 treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO2] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO2 supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between gs and net photosynthetic rates. This study suggests that elevated [CO2] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle-level water loss and water use efficiency of Douglas-fir seedlings. Close

• 3. [Article] Photosynthetic response models for a terrestrial plant community

  Photosynthetic response to light and temperature was modeled using data from a small red alder (Alnus rubra B. ) community growing in a controlled environment chamber linked to the computer. This new system ...

  Citation × Citation Citation Abstract Copy Title: Photosynthetic response models for a terrestrial plant community Author: Webb, Warren Lewis, 1935- Photosynthetic response to light and temperature was modeled using data from a small red alder (Alnus rubra B. ) community growing in a controlled environment chamber linked to the computer. This new system controls air temperature, root temperature, and vapor pressure over a wide range, and both light intensity and spectral quality are comparable with natural sunlight. Net photosynthetic rates are measured by continuously monitoring atmospheric CO in the gas-tight environment chamber. Photosynthetic measurements were taken between 0.06 ly/min and 0.68 ly/min (total short-wave radiation) at temperatures from 6° to 30°C. A stepwise multiple linear regression analysis accounted for 98% of the variation in steady-state net photosynthesis using light and temperature plus two interaction terms as independent variables. Non-linear models were constructed based on the known light curve for photosynthesis of single plants. The weighted average deviation of the data from the best non-linear model was + 3.7%. Extrapolation of predicted photosynthetic response appears reliable except for an inconsistency at light energies below 5% full sunlight for temperatures less than 6°C. Title: Photosynthetic response models for a terrestrial plant community Author: Webb, Warren Lewis, 1935- Photosynthetic response to light and temperature was modeled using data from a small red alder (Alnus rubra B. ) community growing in a controlled environment chamber linked to the computer. This new system controls air temperature, root temperature, and vapor pressure over a wide range, and both light intensity and spectral quality are comparable with natural sunlight. Net photosynthetic rates are measured by continuously monitoring atmospheric CO in the gas-tight environment chamber. Photosynthetic measurements were taken between 0.06 ly/min and 0.68 ly/min (total short-wave radiation) at temperatures from 6° to 30°C. A stepwise multiple linear regression analysis accounted for 98% of the variation in steady-state net photosynthesis using light and temperature plus two interaction terms as independent variables. Non-linear models were constructed based on the known light curve for photosynthesis of single plants. The weighted average deviation of the data from the best non-linear model was + 3.7%. Extrapolation of predicted photosynthetic response appears reliable except for an inconsistency at light energies below 5% full sunlight for temperatures less than 6°C. Close

• 4. [Article] Relationships Between Needle Nitrogen Concentration and Photosynthetic Responses of Douglas-Fir Seedlings to Elevated CO2 and Temperature

  Here we examined correlations between needle nitrogen concentration ([N]) and photosynthetic responses of Douglas-fir (Pseudotsuga menziesii) seedlings to growth in elevated temperatures and atmospheric ...

  Citation × Citation Citation Abstract Copy Title: Relationships Between Needle Nitrogen Concentration and Photosynthetic Responses of Douglas-Fir Seedlings to Elevated CO2 and Temperature Author: Lewis, James D., Lucash, Melissa S., Olszyk, David M., Tingey, David T. Year: 2004 Here we examined correlations between needle nitrogen concentration ([N]) and photosynthetic responses of Douglas-fir (Pseudotsuga menziesii) seedlings to growth in elevated temperatures and atmospheric carbon dioxide concentrations ([CO2]). Seedlings were grown in sunlit, climate-controlled chambers at ambient or ambient+3.5° C and ambient or ambient +180 μmol mol-1 CO2 in a full factorial design. Photosynthetic parameters and needle [N] were measured six times over a 21-month period. Needle [N] varied seasonally, and accounted for 30–50% of the variation in photosynthetic parameters. Across measurement periods, elevated temperature increased needle [N] by 26% and light-saturated net photosynthetic rates by 17%. Elevated [CO2] decreased needle [N] by 12%, and reduced net photosynthetic rates measured at a common [CO2], maximum carboxylation activity (Vc,max) and electrontransport capacity (Jmax), indicating photosynthetic acclimatization. Even so, elevated [CO2] enhanced net photosynthesis, and this effect increased with needle [N]. These results suggest that needle [N] may regulate photosynthetic responses of Douglas-fir to climate change. Further, needle [N] may be altered by climate change. However, effects of elevated [CO2] on photosynthesis may be similar across growth temperatures. Title: Relationships Between Needle Nitrogen Concentration and Photosynthetic Responses of Douglas-Fir Seedlings to Elevated CO2 and Temperature Author: Lewis, James D., Lucash, Melissa S., Olszyk, David M., Tingey, David T. Year: 2004 Here we examined correlations between needle nitrogen concentration ([N]) and photosynthetic responses of Douglas-fir (Pseudotsuga menziesii) seedlings to growth in elevated temperatures and atmospheric carbon dioxide concentrations ([CO2]). Seedlings were grown in sunlit, climate-controlled chambers at ambient or ambient+3.5° C and ambient or ambient +180 μmol mol-1 CO2 in a full factorial design. Photosynthetic parameters and needle [N] were measured six times over a 21-month period. Needle [N] varied seasonally, and accounted for 30–50% of the variation in photosynthetic parameters. Across measurement periods, elevated temperature increased needle [N] by 26% and light-saturated net photosynthetic rates by 17%. Elevated [CO2] decreased needle [N] by 12%, and reduced net photosynthetic rates measured at a common [CO2], maximum carboxylation activity (Vc,max) and electrontransport capacity (Jmax), indicating photosynthetic acclimatization. Even so, elevated [CO2] enhanced net photosynthesis, and this effect increased with needle [N]. These results suggest that needle [N] may regulate photosynthetic responses of Douglas-fir to climate change. Further, needle [N] may be altered by climate change. However, effects of elevated [CO2] on photosynthesis may be similar across growth temperatures. Close

• 5. [Article] Comparative photosynthesis and respiration rates of Douglas-fir seedlings from Vancouver Island and Montana under various conditions of light and temperature

  Citation × Citation Citation Abstract Copy Title: Comparative photosynthesis and respiration rates of Douglas-fir seedlings from Vancouver Island and Montana under various conditions of light and temperature Author: Krueger, Kenneth W. Title: Comparative photosynthesis and respiration rates of Douglas-fir seedlings from Vancouver Island and Montana under various conditions of light and temperature Author: Krueger, Kenneth W. Close

• 6. [Article] Spinach peroxidase and the photo-oxidation of managanese by isolated chloroplasts

  Manganese has been known to be essential for photosynthesis for almost 30 years. Subsequent experimentation indicated a definite function for manganese in oxygen evolution. However, the mode of action ...

  Citation × Citation Citation Abstract Copy Title: Spinach peroxidase and the photo-oxidation of managanese by isolated chloroplasts Author: McKenna, John Michael Manganese has been known to be essential for photosynthesis for almost 30 years. Subsequent experimentation indicated a definite function for manganese in oxygen evolution. However, the mode of action of manganese and further localization of its site of action have not been determined. Ten years ago it was demonstrated that illuminated chloroplasts were capable of oxidizing manganese. The role of manganese in photosynthesis and the observed photooxidation of manganese by chloroplasts have often been correlated theoretically but never experimentally. Peroxidase was secondarily implicated since it is a stimulant for the manganese oxidizing reaction. The experiments presented in this thesis were conducted in order to determine more about the manganese oxidizing reaction and its relation to photosynthesis, and to characterize spinach peroxidase both as a stimulant in manganese oxidation and as a separate entity. If added, excess manganese replaces water in the photo-oxidizing system, the reaction should have properties similar to those of the Hill reaction. Results presented herein show the photo-oxidation to be sensitive to DCMU and simazine. Also the light saturation is practically identical to that of Hill reaction as is the response to temperature. Unlike the Hill reaction, the system is inhibited by acriflavin and KCN and is stimulated by FMN. Since the system requires oxygen as the oxidant and is stimulated by peroxidase, the latter results are to be expected. Additional information on the requirement for plastoquinone and other cofactors is presented. It appears that manganese is a redox intermediate acting at a site in photosynthetic electron transport between the point of oxygen evolution and the site of DCMU and simazine inhibition. Peroxidase is known to be present in almost all plants. The specific function of the enzyme is not known. It has been studied extensively in extracts from horseradish roots but not from green leaf tissue. Therefore, a preliminary study of spinach peroxidase was conducted. This study includes a purification procedure and an elementary characterization including pH optimum, substrate reactivity, and inhibitor studies. Although the results may contribute something to the multitudinous in vitro studies on peroxidase, no evidence for a specific in vivo function for this enzyme was obtained. Title: Spinach peroxidase and the photo-oxidation of managanese by isolated chloroplasts Author: McKenna, John Michael Manganese has been known to be essential for photosynthesis for almost 30 years. Subsequent experimentation indicated a definite function for manganese in oxygen evolution. However, the mode of action of manganese and further localization of its site of action have not been determined. Ten years ago it was demonstrated that illuminated chloroplasts were capable of oxidizing manganese. The role of manganese in photosynthesis and the observed photooxidation of manganese by chloroplasts have often been correlated theoretically but never experimentally. Peroxidase was secondarily implicated since it is a stimulant for the manganese oxidizing reaction. The experiments presented in this thesis were conducted in order to determine more about the manganese oxidizing reaction and its relation to photosynthesis, and to characterize spinach peroxidase both as a stimulant in manganese oxidation and as a separate entity. If added, excess manganese replaces water in the photo-oxidizing system, the reaction should have properties similar to those of the Hill reaction. Results presented herein show the photo-oxidation to be sensitive to DCMU and simazine. Also the light saturation is practically identical to that of Hill reaction as is the response to temperature. Unlike the Hill reaction, the system is inhibited by acriflavin and KCN and is stimulated by FMN. Since the system requires oxygen as the oxidant and is stimulated by peroxidase, the latter results are to be expected. Additional information on the requirement for plastoquinone and other cofactors is presented. It appears that manganese is a redox intermediate acting at a site in photosynthetic electron transport between the point of oxygen evolution and the site of DCMU and simazine inhibition. Peroxidase is known to be present in almost all plants. The specific function of the enzyme is not known. It has been studied extensively in extracts from horseradish roots but not from green leaf tissue. Therefore, a preliminary study of spinach peroxidase was conducted. This study includes a purification procedure and an elementary characterization including pH optimum, substrate reactivity, and inhibitor studies. Although the results may contribute something to the multitudinous in vitro studies on peroxidase, no evidence for a specific in vivo function for this enzyme was obtained. Close

• 7. [Article] Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide

  The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. ...

  Citation × Citation Citation Abstract Copy Title: Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide Author: Mehari, Tetemke Year: 1990 The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. The Photosystem I core protein has retained > 90% of Fx and 100% of P700 (determined by optical spectroscopy) but is totally devoid of iron-sulfur centers Fᴀ and Fв (determined by optical and ESR spectroscopy). SDS-PAGE indicates the retention of the 82-and 83-kDa reaction center polypeptides. The loss of Fᴀ and Fв is further reflected in the decline of acid labile sulfide from 11.8 ± 0.4 S²-/P700 in the Photosystem I complex to 4.6 ± 0.3 S²-/P700 in the Photosystem I core.protein. This preparation represents the first isolation of an intact reaction center core incorporating the redox centers P700 through Fx but totally lacking Fᴀ and Fʙ. Complete restoration of electron flow from P700 to Fᴀ/Fв was achieved by incubating a P700 and Fx-containing Photosystem I core protein with a freshly isolated 8.9-kDa, Fᴀ/Fв polypeptide. When illuminated during freezing, both Fᴀ and Fв become quantitatively reduced, and the ESR spectrum is nearly indistinguishable from Fᴀ and Fв in the control Photosystem I complex. In the reconstituted Photosystem I complex Fx is photochemically reduced only in the presence of Fᴀ- and Fв- and the broad high field resonance of Fx in the core protein appears upon reconstitution to be indistinguishable from Fx in the control Photosystem I complex. Optical flash photolysis after extensive washing confirms the complete restoration of the P700+ [Fᴀ/Fв]- backreaction, indicating quantitative rebinding of the 8.9-kOa polypeptide. This procedure.represents the first reconstitution of the Photosystem I complex from a purified Photosystem I core protein and a freshly isolated 8.9 kDa Fᴀ/Fв holoprotein, and makes possible independent manipulation of the two subunits that carry the entire electron acceptor system of Photosystem I. The Fᴀ/Fв iron-sulfur clusters in the 8.9 kDa polypeptide are easily degraded to the level of zero-valence sulfur during isolation from the Photosystem I complex. The level of degradation is minimized by working under anaerobic conditions and low temperature. It has been found that incubation of the purified Photosystem I core protein and the low molecular mass polypeptides (which includes the 8.9-kDa Fᴀ/Fв apoprotein) with a solution of FeCI₃, Na₂S and B-mercaptoethanol restores the light induced charge separation between P700 and Fᴀ/Fв. The optical and spectroscopic properties are indistinguishable from the control Photosystem one I complex. When a rebuilt spinach or Synechococcus sp. PeC 6301 Fᴀ/Fв polypeptide is rebound to a Photosystem I core protein from the same species, the reconstituted complexes show light-induced ESR spectra of Fᴀ/Fв with g-values identical to their respective controls. However, when the rebuilt spinach Fᴀ/Fв polypeptide is rebound to a Synechococcus sp. PCC 6301 Photosystem I core protein, the hybrid spinach Synechococcus sp. PCC 6301 Photo system complex shows a light-induced ESR spectrum of Fᴀ/Fв with g- values that differ slightly, but characteristically, from those of both spinach and Synechococcus sp. PCC 6301 control complexes. The hybrid spinach-Synechococcus sp. PCC 6301 Photosystem I complex was completely functional in light-induced charge separation between P700 and Fᴀ/Fв and showed a normal 30-ms room temperature charge recombination between P700+ and [Fᴀ/Fв]-. Accordingly, rebuilding of the Fᴀ and Fв iron-sulfur clusters is now possible and reconstitution of the Fᴀ/Fв holoprotein after chemical modification of the Fᴀ/Fв apoprotein or genetic modification of the psaC gene should reveal new findings about Photosystem I structure and function. Title: Resolution and Reconstitution of the Photosystem I Reaction Center: Structure and Function of the Terminal Electron Acceptor FA/FB Polypeptide Author: Mehari, Tetemke Year: 1990 The Photosystem I core protein containing P700, A₀, A₁, and Fx has been isolated from Synechococcus sp. PCC 6301 and spinach Photosystem I complexes with 6.8 M urea followed by sucrose density ultracentrifugtion. The Photosystem I core protein has retained > 90% of Fx and 100% of P700 (determined by optical spectroscopy) but is totally devoid of iron-sulfur centers Fᴀ and Fв (determined by optical and ESR spectroscopy). SDS-PAGE indicates the retention of the 82-and 83-kDa reaction center polypeptides. The loss of Fᴀ and Fв is further reflected in the decline of acid labile sulfide from 11.8 ± 0.4 S²-/P700 in the Photosystem I complex to 4.6 ± 0.3 S²-/P700 in the Photosystem I core.protein. This preparation represents the first isolation of an intact reaction center core incorporating the redox centers P700 through Fx but totally lacking Fᴀ and Fʙ. Complete restoration of electron flow from P700 to Fᴀ/Fв was achieved by incubating a P700 and Fx-containing Photosystem I core protein with a freshly isolated 8.9-kDa, Fᴀ/Fв polypeptide. When illuminated during freezing, both Fᴀ and Fв become quantitatively reduced, and the ESR spectrum is nearly indistinguishable from Fᴀ and Fв in the control Photosystem I complex. In the reconstituted Photosystem I complex Fx is photochemically reduced only in the presence of Fᴀ- and Fв- and the broad high field resonance of Fx in the core protein appears upon reconstitution to be indistinguishable from Fx in the control Photosystem I complex. Optical flash photolysis after extensive washing confirms the complete restoration of the P700+ [Fᴀ/Fв]- backreaction, indicating quantitative rebinding of the 8.9-kOa polypeptide. This procedure.represents the first reconstitution of the Photosystem I complex from a purified Photosystem I core protein and a freshly isolated 8.9 kDa Fᴀ/Fв holoprotein, and makes possible independent manipulation of the two subunits that carry the entire electron acceptor system of Photosystem I. The Fᴀ/Fв iron-sulfur clusters in the 8.9 kDa polypeptide are easily degraded to the level of zero-valence sulfur during isolation from the Photosystem I complex. The level of degradation is minimized by working under anaerobic conditions and low temperature. It has been found that incubation of the purified Photosystem I core protein and the low molecular mass polypeptides (which includes the 8.9-kDa Fᴀ/Fв apoprotein) with a solution of FeCI₃, Na₂S and B-mercaptoethanol restores the light induced charge separation between P700 and Fᴀ/Fв. The optical and spectroscopic properties are indistinguishable from the control Photosystem one I complex. When a rebuilt spinach or Synechococcus sp. PeC 6301 Fᴀ/Fв polypeptide is rebound to a Photosystem I core protein from the same species, the reconstituted complexes show light-induced ESR spectra of Fᴀ/Fв with g-values identical to their respective controls. However, when the rebuilt spinach Fᴀ/Fв polypeptide is rebound to a Synechococcus sp. PCC 6301 Photosystem I core protein, the hybrid spinach Synechococcus sp. PCC 6301 Photo system complex shows a light-induced ESR spectrum of Fᴀ/Fв with g- values that differ slightly, but characteristically, from those of both spinach and Synechococcus sp. PCC 6301 control complexes. The hybrid spinach-Synechococcus sp. PCC 6301 Photosystem I complex was completely functional in light-induced charge separation between P700 and Fᴀ/Fв and showed a normal 30-ms room temperature charge recombination between P700+ and [Fᴀ/Fв]-. Accordingly, rebuilding of the Fᴀ and Fв iron-sulfur clusters is now possible and reconstitution of the Fᴀ/Fв holoprotein after chemical modification of the Fᴀ/Fв apoprotein or genetic modification of the psaC gene should reveal new findings about Photosystem I structure and function. Close

• 8. [Article] Spring Thaw Ionic Pulses Boost Nutrient Availability and Microbial Growth in Entombed Antarctic Dry Valley Cryoconite Holes

  The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only ...

  Citation × Citation Citation Abstract Copy Title: Spring Thaw Ionic Pulses Boost Nutrient Availability and Microbial Growth in Entombed Antarctic Dry Valley Cryoconite Holes Author: Telling, Jon, Anesio, Alexandre M., Tranter, Martyn, Fountain, Andrew G., Nylen, Thomas H., Hawkings, Jon, Singh, Virendra B., Kaur, Preeti, Musilova, Michaela, Wadham, Jemma L. Year: 2014 The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only occasionally exceed 0°C during the Austral summer. Here we follow temporal changes in cryoconite hole biogeochemistry on Canada Glacier from fully frozen conditions through the initial stages of spring thaw toward fully melted holes. The cryoconite holes had a mean isolation age from the glacial drainage system of 3.4 years, with an increasing mass of aqueous nutrients (dissolved organic carbon, total nitrogen, total phosphorus) with longer isolation age. During the initial melt there was a mean nine times enrichment in dissolved chloride relative to mean concentrations of the initial frozen holes indicative of an ionic pulse, with similar mean nine times enrichments in nitrite, ammonium, and dissolved organic matter. Nitrate was enriched twelve times and dissolved organic nitrogen six times, suggesting net nitrification, while lower enrichments for dissolved organic phosphorus and phosphate were consistent with net microbial phosphorus uptake. Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability. There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation. Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher. This study demonstrates that ionic pulses significantly alter the timing and magnitude of microbial activity within entombed cryoconite holes, and adds credence to hypotheses that ionic enrichments during freeze-thaw can elevate rates of microbial growth and activity in other icy habitats, such as ice veins and subglacial regelation zones. Title: Spring Thaw Ionic Pulses Boost Nutrient Availability and Microbial Growth in Entombed Antarctic Dry Valley Cryoconite Holes Author: Telling, Jon, Anesio, Alexandre M., Tranter, Martyn, Fountain, Andrew G., Nylen, Thomas H., Hawkings, Jon, Singh, Virendra B., Kaur, Preeti, Musilova, Michaela, Wadham, Jemma L. Year: 2014 The seasonal melting of ice entombed cryoconite holes on McMurdo Dry Valley glaciers provides oases for life in the harsh environmental conditions of the polar desert where surface air temperatures only occasionally exceed 0°C during the Austral summer. Here we follow temporal changes in cryoconite hole biogeochemistry on Canada Glacier from fully frozen conditions through the initial stages of spring thaw toward fully melted holes. The cryoconite holes had a mean isolation age from the glacial drainage system of 3.4 years, with an increasing mass of aqueous nutrients (dissolved organic carbon, total nitrogen, total phosphorus) with longer isolation age. During the initial melt there was a mean nine times enrichment in dissolved chloride relative to mean concentrations of the initial frozen holes indicative of an ionic pulse, with similar mean nine times enrichments in nitrite, ammonium, and dissolved organic matter. Nitrate was enriched twelve times and dissolved organic nitrogen six times, suggesting net nitrification, while lower enrichments for dissolved organic phosphorus and phosphate were consistent with net microbial phosphorus uptake. Rates of bacterial production were significantly elevated during the ionic pulse, likely due to the increased nutrient availability. There was no concomitant increase in photosynthesis rates, with a net depletion of dissolved inorganic carbon suggesting inorganic carbon limitation. Potential nitrogen fixation was detected in fully melted holes where it could be an important source of nitrogen to support microbial growth, but not during the ionic pulse where nitrogen availability was higher. This study demonstrates that ionic pulses significantly alter the timing and magnitude of microbial activity within entombed cryoconite holes, and adds credence to hypotheses that ionic enrichments during freeze-thaw can elevate rates of microbial growth and activity in other icy habitats, such as ice veins and subglacial regelation zones. Close