• Cold tolerance in Arabidopsis kamchatica and related species

      Armstrong, Jessica J.; Wolf, Diana; Takebayashi, Naoki; Olson, Matthew (2013-05)
      Cold is a major limiting factor in the development and distribution of plants. Many plants increase cold tolerance via cold acclimation. We determined the cold tolerance strategy of Arabidopsis thaliana and A. kamchatica by comparing the extent that plants cooled below the freezing point without freezing, the supercooling capacity, to the temperatures at which 50% of freeze damage occurred (LT50). In A. kamchatica LT50 and supercooling values were similar before cold acclimation; after acclimation LT50 was much colder than supercooling, indicating non-acclimated A. kamchatica avoids freezing by supercooling but after acclimation appears to tolerate freezing. In A. thaliana, LT50 and supercooling were not different, regardless of acclimation, indicating this species avoids freezing year-round. We compared cold hardiness in populations from five Arabidopsis taxa by measuring freeze induced electrolyte leakage. There were differences among taxa; A. kamchatica, A. lyrata subspecies lyrata, and A. lyrata subspecies petraea were more cold tolerant, whereas A. thaliana and A. halleri subspecies gemmifera were less tolerant. There was no correlation between latitude of population origin and cold tolerance for any of the species we tested. Our results indicate a shared evolutionary history may be more important than latitude of origin as a predictor of cold hardiness.
    • Methods of temperature & metabolism reduction in rats and possible influence on human health

      Bailey, Isaac R.; Drew, Kelly L.; Kuhn, Thomas B.; Rasley, Brian T. (2017-10)
      Spaceflight poses unique and significant hazards; the maintenance of human health remains a large part of the National Aeronautic and Space Administration (NASA) strategic goals and work remains to be done if we wish to maintain a long-term presence in space. The effects of ionizing radiation and bone density loss are some of the primary health related problems which need to be addressed. One of the main purposes of this research is to translate aspects of thermoregulation and metabolism reduction in hibernating species to a non-hibernating species in- order to devise alternative methods of preventing DNA damage and loss of bone density in astronauts. A second purpose for this research applies the same approach in emergency medicine, having potential as conjunctive therapy for cardiac arrest victims. Targeted temperature management (TTM; formerly known as therapeutic hypothermia) is the standard of care for these patients and is applied to increase survival rates and reduces neurological deficit. Stimulating Central Nervous System (CNS) A1 adenosine receptors inhibits shivering and non-shivering thermogenesis, inducing a hibernation-like response in hibernating species. A similar phenomenon occurs when using this technique in non-hibernating species such as rats. The adenosine A1 agonist, N6-cyclohexyladenosine (CHA) was utilized in all 3 of the experiments to determine how dose, diet, ambient temperature, and finally surface temperature affects the thermoregulatory response in Sprague-dawley rats. In addition to CHA, the partial agonist capadenoson was also tested for thermolytic efficacy (that is, the efficacy to abolish thermogenesis). Surface temperature control using a temperature controlled cage designed and built by myself in combination with IV CHA was found to be most effective in maintaining a target temperature of 32°C without risk of over-cooling. Results from these experiments suggests that the new standard technique in studying TTM using small animals should be similar to what is currently used in clinics; surface temperature modulation.
    • Oxidative stress is transient and tissue-specific during cold acclimation of threespine sticklebacks

      Kammer, Aaron R. (2010-08)
      We sought to determine if oxidative stress occurs in liver, oxidative muscle or glycolytic muscle of threespine sticklebacks during cold acclimation. Fishes were held at 20°C for 12 wks and then acclimated to 8°C for 9 wks or held at 20°C for an additional 9 wks. Animals were harvested during the first four days of cold acclimation, and at wk 1, 4 and 9. Protein carbonyls were quantified as an indirect measure of the production of reactive oxygen species (ROS). The activity of superoxide dismutase (SOD), levels of SOD mRNA, and glutathione levels were quantified as indices of protection against ROS. All measurements were made in liver, glycolytic muscle and oxidative muscle. Protein carbonyl levels increased in livers of fishes after 1 wk at 8°C and decreased after wk 4. Total glutathione levels increased in livers on day 3 of cold acclimation and then decreased by wk 4. Measured at a common temperature, SOD activity increased early in all tissues and remained elevated throughout cold acclimation. Measured at the acclimation temperature, SOD activity increased only in oxidative muscle after 9 wks of cold acclimation. Together, these results indicate that oxidative stress is transient and tissue-specific during cold acclimation of fishes.
    • Roles of neighboring plants and temperature on growth and survival of white spruce seedlings along elevational gradients in Alaska

      Okano, Kyoko; Bret-Harte, M. Syndonia; Mulder, Christa P. H.; Juday, Glenn P. (2018-05)
      Seedlings are the most vulnerable stage of a tree's life and their successful survival and growth are critical to support future forests. Recent rapid warming in Alaska has promoted the movement of treeline upward in elevation, while trees at low elevations have decreased their growth. Understanding the direct effects of warming and the indirect effects induced by warming, such as species interactions, on the dominant treeline species, white spruce (Picea glauca) is key to sustaining boreal forests, from low elevations to above current treeline. The objectives of my thesis were to assess the roles that warming, neighboring interaction, habitat type, elevation and season play in the survival and growth of white spruce in Denali National Park and Preserve and Fairbanks, Alaska, USA. I planted spruce seedlings where I manipulated summer temperature and neighbor plants at seven sites (forest or tundra) along an elevational gradient that crossed treeline. I measured survival after winter and summer seasons, and harvested the seedlings for biomass after the third growing season. I found that competition -- particularly light competition where seedlings were shaded -- was the most important factor for seedling growth, while along elevational gradients, temperature and season had inverse effects on their survival: more seedlings at high elevations survived in summer and under warming, but more seedlings at low elevations survived in winter and under ambient temperatures. More seedlings with neighbors survived in summer and in forests, suggesting facilitation through shading. I found some evidence for a trade-off between growth and survival. Seedlings with a high relative growth in height (RGR height) in 2012 had a lower survival rate than seedlings with a low RGR height in the following hot and dry summer of 2013. More seedlings planted with neighbors that had a small diameter in 2012 also survived in 2013, but not without neighbors. These results suggest that a trade-off between survival and growth occurred only when competition for water can be expected. No difference in survival was found after the second winter and third summer. Altogether, I concluded the most important factor affecting seedling growth in my experiment was light competition, while the most important factors for seedling survival were warming and water availability for the first two years in the subarctic montane and interior Alaska.