Heat acclimation increases the local heat loss responses of sweating and skin blood flow which is thought to persist for up to 3 weeks post-acclimation. However, the extent to which increases in local heat loss affect whole-body heat loss as a function of increasing levels of heat stress remains unresolved. Using direct calorimetry, we examined changes in whole-body evaporative heat loss (EHL) during progressive increases in metabolic heat production 1) prior to (Day 0), during (Day 7) and following a 14-day heat acclimation protocol (Day 14) – Induction phase, and; 2) at the end of a 1-week (Day 21) and 2-week decay period (Day 28) – Decay phase. Ten males performed intermittent exercise (3 x 30-min (min) bouts of cycling at 300 (Ex1), 350 (Ex2), and 400 watts•meters2 (W•m2) (Ex3) separated by 10 and 20 min rest periods, respectively). During the induction period, EHL at Day 7 was increased at each of the three exercise bouts (Ex1: + 6%; Ex2 +8%; Ex3: +13%, all p≤0.05) relative to Day 0 (EHL at Ex1: 529 W; Ex2: 625 W; Ex3: 666 W). At Day 14, EHL was increased for all three exercise bouts compared to Day 0 (Ex1: 9%; Ex2: 12%; Ex3: 18%, all p≤0.05). As a result, a lower cumulative change in body heat content (ΔHb) was measured at Day 7 (-30%, p≤0.001) and Day 14 (-47%, p≤0.001). During the decay phase, EHL at Day 21 and 28 was only reduced in Ex 3 (p≤0.05) compared to Day 14. In parallel, ΔHb increased by 39% (p=0.003) and 57% (p≤0.001) on Day 21 and Day 28 relative to Day 14, respectively. When Day 28 was compared to Day 0, EHL remained elevated in each of the exercise bouts (p≤0.05). As such, ΔHb remained significantly lower on Day 28 compared to Day 0 (-16%, p=0.042). We show that 14 days of heat acclimation increases whole-body EHL during exercise in the heat which is maintained 14 days post-acclimation.

Human beings have been exposed to different cold conditions throughout time, and have through cold acclimation developed mechanisms to survive in these conditions. Cold acclimation can be elicited through exposure to natural cold climates, or artificially induced in a laboratory to study the body’s response to repeated cold exposures. Several studies looking at the effects of cold acclimation in humans have been conducted during the last 50 years, and have reported that cold acclimation can lead to a change in skin and core temperature, heat production and shivering. An accurate quantification of shivering thermogenesis (ST) during cold acclimation has not been done before, and most previous measurements of shivering during cold acclimation have been inaccurate and inadequate. In this study a Liquid Condition Suits (LCS) was used to elicit cold acclimation (10°C, 2hr daily, for 4 weeks) while an accurate measurement of the effect of cold acclimation on changes in muscle activity was conducted. In CHAPTER 2, results showed that four weeks of cold acclimation at 10°C did not change skin and core temperature, heat production or ST. The effects on shivering pattern and fuel selection were also analysed, but no effects of cold acclimation could be observed. These measurements were a part of a larger study, in which the effects of cold acclimation on changes in BAT were the main outcome measures. These data showed that an increase in BAT volume (45%) and activity (120%) were the only observed effects of cold acclimation. In CHAPTER 3, we set out to assess if changes in shivering from pre to post cold acclimation are associated with changes in BAT volume, and if the amount of BAT a participant possesses prior to cold acclimation can be used to predict changes in shivering intensity during cold acclimation. The interindividual variability in changes in thermal responses, heat production, shivering and BAT volume occurring between subjects during four weeks of cold acclimation was also addressed in this section.

Les microalgues ont développé des approches distinctes pour moduler l'absorption de la lumière et son utilisation par leurs photosystèmes en réponse à des stimuli environnementaux. Dans ce rapport de Thèse je présente les différentes stratégies employées par une algue d'eau douce (Chlamydomonas reinhardtii) et une algue marine (Phaeodactylum tricornutum) pour optimiser leur acclimatation à l'environnement.Dans la première partie de ce rapport, je propose un modèle de cellules entières de la diatomée marine Phaeodactylum tricornutum obtenue par analyses spectroscopiques et biochimiques ainsi que par l’obtention d’images par microscopie électronique et reconstitution 3-D. Ce modèle a été utilisé pour répondre aux questions suivantes i. comment est structuré un chloroplaste secondaire pour faciliter les échanges avec le cytosol à travers les quatre membranes qui le délimitent ii. comment sont structurées les membranes photosynthétiques afin d’optimiser l'absorption de lumière et le flux d'électrons et iii. comment les chloroplastes et les mitochondries sont organisés pour optimiser l'assimilation du CO2 par échange ATP / NADPH.La deuxième partie de ce rapport porte sur la régulation de la collection de la lumière et de sa dissipation chez Chlamydomonas grâce à l'étude d'une part du rôle de la perception de la couleur de la lumière et d'autre part du métabolisme sur la dissipation de l'excès de lumière par quenching non photochimique (NPQ). En utilisant des approches biochimiques et spectroscopiques, j'ai mis en évidence un lien moléculaire entre la photoréception, la photosynthèse et la photoprotection chez Chlamydomonas via le rôle du photorécepteur phototropine, démontrant ainsi que le métabolisme, en plus de la lumière, peut aussi affecter ce processus d'acclimatation.En conclusion, ce travail de thèse révèle l'existence et l'intégration des différentes voies de signalisation dans la régulation des réponses photoprotectrices mises en place chez les microalgues marines et d'eau douce. / Microalgae have developed distinct approaches to modulate light absorption and utilization by their photosystems in response to environmental stimuli. In this Ph.D Thesis, I characterised different strategies employed by freshwater (Chlamydomonas reinhardtii) and marine algae (Phaeodactylum tricornutum) to optimise their acclimation to the environment.In the first part of this work, I used spectroscopic, biochemical, electron microscopy analysis and 3-dimentional reconstitution to generate a model of the entire cell of the marine diatom Phaeodactylum tricornutum. This model has been used to address the following questions: i. how is a secondary chloroplast structured to facilitate exchanges with the cytosol via its four membranes envelope barrier ii. how have diatoms shaped their photosynthetic membranes to optimise light absorption and downstream electron flow and iii. how the cellular organelles interact to optimise CO2 assimilation via ATP/NADPH exchanges.In the second part, I have focused on the regulation of light harvesting and dissipation in Chlamydomonas by studying the role of perception of light colour and metabolism on excess light dissipation via the Non-Photochemical Quenching of energy (NPQ). Using biochemical and spectroscopic approaches, I found a molecular link between photoreception, photosynthesis and photoprotection in Chlamydomonas via the role of the photoreceptor phototropin on excess absorbed energy dissipation (NPQ) and also demonstrated that besides light, downstream metabolism can also affect this acclimation process.Overall this Ph.D work reveals the existence and integration of different signal pathways in the regulation of photoprotective responses by microalgae living in the ocean and in the land.

The ability of the heart and skeletal muscles to remodel to environmental demands, their plasticity, is of interest when studying animals’ adaptation to environment changes. Temperature variation due to seasonal change seems to lead to the development of a cold acclimated phenotype in small birds. To endure cold conditions a higher metabolism is required for shivering thermogenesis in aerobic skeletal muscles. This in turn leads to several physiological changes, including a heart and muscle hypertrophy as well as an increased oxygen carrying capacity of the blood. In this study were Red Junglefowls (Gallus gallus) bred indoors and outdoors and physiological aspects such as body size, growth rate, relative size of heart and skeletal muscles (pectoralis major and gastrocnemius maximus) as well as hematocrit and hemoglobin concentrations of the blood were compared between the groups. Observed significant differences included a slower growth rate in fowls bred outdoors, 2.5 (0.7) g/day than indoors, 3.8 (0.4) g/day, as well as a larger relative size of the heart and gastrocnemius muscle. The average relative size of the heart was more than twice as big in fowls bred outdoors, 0.97 (0.08) %, than indoors, 0.40-42 (0.05) %. The average relative size of the gastrocnemius muscle for the fowl bred outdoor was significantly larger than for fowl bred indoors (0.95 (0.11) %, vs. 0.58-0,63 (0.09) %). In addition, fowl bred outdoors showed an increased capacity for oxygen transportation, with blood hematocrit values of 43 (3) % higher than 35-37 (3) % for the indoor animals. Fowls bred outdoors also showed higher hemoglobin concentrations in the blood, 127 (7) g/l, than fowls bred indoors, 113 (7) g/l. Findings indicate a cold acclimated phenotype among the outdoor bred fowls.

Chronic changes in cardiac load can cause the vertebrate heart to remodel. For ectotherms, ambient temperature can directly alter cardiac load. Therefore, long-term ambient temperature change can initiate a dynamic cardiac remodelling response to preserve cardiac function. The aims of my PhD thesis were to study the effects of chronic temperature change on the ectothermic heart and cardiovascular system, using the cold-active rainbow trout and the cold-dormant freshwater turtle. In contrast to the majority of previous studies, my experiments focused on the passive, rather than active, properties of the heart. In results chapters 3, 4, 5 and 6, I studied the effects of thermal remodelling on the rainbow trout heart. Chronic cold caused a global increase in chamber stiffness, both at the whole chamber and micromechanical level, with an associated myocardial fibrosis. In the ventricle and atrium there was an up-regulation of collagen promoting genes. In the ventricle, I found cold-induced hypertrophy of the spongy myocardium with an up-regulation of hypertrophic growth factors, which was associated with an increase in tissue lipid suggesting an increase in fatty acid oxidation (FAO). In the atrium, there was no hypertrophy, but there was an increase in extra-bundular sinus, suggesting chronic dilation. Chronic warming initiated an opposite response, with increased cardiac compliance associated with an up-regulation of collagen degrading genes in the ventricle and atrium. In the outflow tract (OFT) and atrium, this increased activity of matrix metalloproteinase (MMPs) and in the OFT abundance of MMPs was increased. The warmed ventricle showed atrophy of the spongy myocardium with a decrease in lipid and an increase in glycogen suggesting a switch in cellular energetics from FAO to glycolytic pathways. In chapters 7, 8 and 9, I studied the effects of thermal remodelling on the freshwater turtle heart. I found an in vivo decrease in systemic resistance causing an increased right to left cardiac shunt flow, associated with an increased elastin content of the major outflow vessels. Cold acclimation increased cardiac sensitivity to preload as well as whole chamber passive stiffness and micromechanical stiffness of tissue sections, associated ventricular fibrosis and increased collagen coherency. In addition, chronic cold decreased the gelatinase activity of MMPs and increased mRNA expression of a tissue inhibitor of MMPs. Furthermore, chronic cold was associated with a decrease in tissue lipid and phosphates, but an increase in tissue protein, glycogen and lactate. These changes in tissue biochemistry suggest a switch in cellular energetics from FAO to glycolytic pathways, likely due to the decreased oxygen availability associated with winter inactivity. Overall, the chambers of the ectothermic heart show distinct remodelling phenotypes, which likely reflect their in cardiac function. Thermal remodelling of the fish ventricle serves both cardio-protection, from the haemodynamic strain of changes in cardiac preload and afterload, as well as compensation for the direct effects of temperature. In the turtle, changes in compliance and cellular energetics of the ventricle suggest a cardio-protective mechanism preparing the heart for increased haemodynamic stress and hypoxic or anoxic conditions during inactive winter hibernation.

Proteases play a crucial role in plant defence mechanisms as well as acclimation to changing metabolic demands and environmental cues. Proteases regulate the development of a plant from germination through to senescence and plant death. In this thesis the role of proteases and their inhibitors in plant response to cold stress and CO2 enrichment were investigated. The activity and inhibition of cysteine proteases (CP), as well as degradation of their potential target proteins was investigated in transgenic tobacco plants expressing the rice cystatin, OC-I. Expression of OC-I caused a longer life span; delayed senescence; significant decrease in in vitro CP activity; a concurrent increase in protein content; and protection from chilling-induced decreases in photosynthesis. An initial proteomics study identified altered abundance of a cyclophilin, a histone, a peptidyl-prolyl cis-trans isomerase and two RuBisCO activase isoforms in OC-I expressing leaves. Immunogold labelling studies revealed that RuBisCO and OC-I is present in RuBisCO vesicular bodies (RVB) that appear to be important in RuBisCO degradation in leaves under optimal and stress conditions. Plants need to respond quickly to changes in the environment that cause changes in the demand for photosynthesis. In this study the effect of CO2 enrichment on photosynthesis-related genes and novel proteases and protease inhibitors regulated by CO2 enrichment and/or development, was investigated. Maize plants grown to maturity with CO2 enrichment showed significant changes in leaf chlorophyll and protein content, increased epidermal cell size, and decreased epidermal cell density. An increased stomatal index in leaves grown at high-CO2 indicates that leaves adjust their stomatal densities through changes in epidermal cell numbers rather than stomatal numbers. Photosynthesis and carbohydrate metabolism were not significantly affected. Developmental stage affected over 3000 transcripts between leaf ranks 3 and 12, while 142 and 90 transcripts were modified by high CO2 in the same leaf ranks respectively. Only 18 transcripts were affected by CO2 enrichment exclusively. Particularly, two novel CO2 -modulated serine protease inhibitors modulated by both sugars and pro-oxidants, were identified. Growth with high CO2 decreased oxidative damage to leaf proteins. / Thesis (PhD)--University of Pretoria, 2009. / Plant Science / unrestricted

Heat acclimation increases the local heat loss responses of sweating and skin blood flow which is thought to persist for up to 3 weeks post-acclimation. However, the extent to which increases in local heat loss affect whole-body heat loss as a function of increasing levels of heat stress remains unresolved. Using direct calorimetry, we examined changes in whole-body evaporative heat loss (EHL) during progressive increases in metabolic heat production 1) prior to (Day 0), during (Day 7) and following a 14-day heat acclimation protocol (Day 14) – Induction phase, and; 2) at the end of a 1-week (Day 21) and 2-week decay period (Day 28) – Decay phase. Ten males performed intermittent exercise (3 x 30-min (min) bouts of cycling at 300 (Ex1), 350 (Ex2), and 400 watts•meters2 (W•m2) (Ex3) separated by 10 and 20 min rest periods, respectively). During the induction period, EHL at Day 7 was increased at each of the three exercise bouts (Ex1: + 6%; Ex2 +8%; Ex3: +13%, all p≤0.05) relative to Day 0 (EHL at Ex1: 529 W; Ex2: 625 W; Ex3: 666 W). At Day 14, EHL was increased for all three exercise bouts compared to Day 0 (Ex1: 9%; Ex2: 12%; Ex3: 18%, all p≤0.05). As a result, a lower cumulative change in body heat content (ΔHb) was measured at Day 7 (-30%, p≤0.001) and Day 14 (-47%, p≤0.001). During the decay phase, EHL at Day 21 and 28 was only reduced in Ex 3 (p≤0.05) compared to Day 14. In parallel, ΔHb increased by 39% (p=0.003) and 57% (p≤0.001) on Day 21 and Day 28 relative to Day 14, respectively. When Day 28 was compared to Day 0, EHL remained elevated in each of the exercise bouts (p≤0.05). As such, ΔHb remained significantly lower on Day 28 compared to Day 0 (-16%, p=0.042). We show that 14 days of heat acclimation increases whole-body EHL during exercise in the heat which is maintained 14 days post-acclimation.

Human beings have been exposed to different cold conditions throughout time, and have through cold acclimation developed mechanisms to survive in these conditions. Cold acclimation can be elicited through exposure to natural cold climates, or artificially induced in a laboratory to study the body’s response to repeated cold exposures. Several studies looking at the effects of cold acclimation in humans have been conducted during the last 50 years, and have reported that cold acclimation can lead to a change in skin and core temperature, heat production and shivering. An accurate quantification of shivering thermogenesis (ST) during cold acclimation has not been done before, and most previous measurements of shivering during cold acclimation have been inaccurate and inadequate. In this study a Liquid Condition Suits (LCS) was used to elicit cold acclimation (10°C, 2hr daily, for 4 weeks) while an accurate measurement of the effect of cold acclimation on changes in muscle activity was conducted. In CHAPTER 2, results showed that four weeks of cold acclimation at 10°C did not change skin and core temperature, heat production or ST. The effects on shivering pattern and fuel selection were also analysed, but no effects of cold acclimation could be observed. These measurements were a part of a larger study, in which the effects of cold acclimation on changes in BAT were the main outcome measures. These data showed that an increase in BAT volume (45%) and activity (120%) were the only observed effects of cold acclimation. In CHAPTER 3, we set out to assess if changes in shivering from pre to post cold acclimation are associated with changes in BAT volume, and if the amount of BAT a participant possesses prior to cold acclimation can be used to predict changes in shivering intensity during cold acclimation. The interindividual variability in changes in thermal responses, heat production, shivering and BAT volume occurring between subjects during four weeks of cold acclimation was also addressed in this section.

Acclimation of photosynthesis allows plants to adjust the composition of their photosynthetic apparatus to adapt to changes in the environment, and is important in maintaining fitness. Dynamic acclimation refers to acclimation of fully developed leaves, after developmental processes have ceased. Rates of photosynthesis fluctuate with environmental change, and this requires metabolic adjustments. It has previously been shown that acclimation requires the chloroplastic glucose 6-phosphate/ phosphate translocator GPT2. Using label-free proteomics we characterised the acclimation deficient gpt2 mutant. High light acclimation involves changes in the composition of the photosynthetic proteome and increases in many other metabolic enzymes, but in gpt2 plants, a reduced ability to alter protein composition, and enhanced stress responses were seen. Using a combined transcriptomics and proteomics approach we also analysed acclimation to low temperature. We show that photosynthetic acclimation requires the cytosolic fumarase, FUM2. In fum2 mutants, an enhanced transcriptional response to low temperature was seen, which was impaired at the level of the proteome, relative to the WT. We also identified a protein encoding a β-Amylase, BAM5, that strongly responded to high light acclimation. The role of this protein was further characterised, and we show a nonchloroplastic location. Furthermore, suppression of this gene resulted in plants that were unable to acclimate, and had a reduced sugar content. This research highlights novel and diverse roles for proteins in acclimation, and provides a comprehensive proteomic profiling of high light and low temperature acclimation that has previously been lacking.

Intertidal mussels regularly experience emersion-induced anoxia, in contrast to normoxic conditions experienced during submersion. We therefore hypothesized that acclimation to a tidal rhythm, as opposed to a rhythm of constant submersion, preconditions the proteome of the California mussel, Mytilus californianus, to respond differently to emersion-induced anoxia. Following acclimation, mussels either continued to receive the acclimation conditions (control) or were exposed to 100% nitrogengas (anoxia) during aerial emersion. We collected gill tissue for subsequent analysis of protein abundance with 2D gel electrophoresis and protein identification with tandem mass spectrometry. Relative to subtidally-acclimated mussels, tidally-acclimated mussels showed a greater propensity to respond to distrupted protein homeostasis during emersion through higher levels of several small heat shock protein isoforms, while they showed lower levels of several chaperones involved in redox-sensitive protein maturation in the endoplasmic reticulum during acute anoxia. Several metabolic proteins showed elevated levels in tidally-acclimated mussels, suggesting a compensatory response to reduced feeding times. However, changes in the abundance of several tricarboxylic acid cycle enzymes (e.g. aconitase, succinate dehydrogenase) suggest that tidally-acclimated mussels are also primed to sense reactive oxygen species (ROS) and limit their production, respectively. These findings are further supported by higher abundances of several aldehyde dehydrogenases and thioredoxin peroxidase, which function as scavengers of aldehydes and ROS, common products of lipid peroxidation. Finally, tidally-acclimated mussels are also more responsive to changes in cytoskeletal and vesicular trafficking dynamics in response to acute anoxia. Together, our analysis showed that proteostasis, energy metabolism, oxidative stress and cytoskeletal and trafficking processes are all involved in priming tidally-acclimated mussels to respond more dynamically to acute emersion-induced anoxia in Mytilus gill.