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PubMed1991

Acclimation of CO(2) Assimilation in Cotton Leaves to Water Stress and Salinity.

Cotton (Gossypium hirsutum L. cv Acala SJ2) plants were exposed to three levels of osmotic or matric potentials. The first was obtained by salt and the latter by withholding irrigation water. Plants were acclimated to the two stress types by reducing the rate of stress development by a factor of 4 to 7. CO(2) assimilation was then determined on acclimated and nonacclimated plants. The decrease of CO(2) assimilation in salinity-exposed plants was significantly less in acclimated as compared with nonacclimated plants. Such a difference was not found under water stress at ambient CO(2) partial pressure. The slopes of net CO(2) assimilation versus intercellular CO(2) partial pressure, for the initial linear portion of this relationship, were increased in plants acclimated to salinity of -0.3 and -0.6 megapascal but not in nonacclimated plants. In plants acclimated to water stress, this change in slopes was not significant. Leaf osmotic potential was reduced much more in acclimated than in nonacclimated plants, resulting in turgor maintenance even at -0.9 megapascal. In nonacclimated plants, turgor pressure reached zero at approximately -0.5 megapascal. The accumulation of Cl(-) and Na(+) in the salinity-acclimated plants fully accounted for the decrease in leaf osmotic potential. The rise in concentration of organic solutes comprised only 5% of the total increase in solutes in salinity-acclimated and 10 to 20% in water-stress-acclimated plants. This acclimation was interpreted in light of the higher protein content per unit leaf area and the enhanced ribulose bisphosphate carboxylase activity. At saturating CO(2) partial pressure, the declined inhibition in CO(2) assimilation of stress-acclimated plants was found for both salinity and water stress.

Journal Article↗

PubMed2004

Partitioning of evaporative water loss in white-winged doves: plasticity in response to short-term thermal acclimation.

We investigated changes in the relative contributions of respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) to total evaporative water loss (TEWL) in response to short-term thermal acclimation in western white-winged doves Zenaida asiatica mearnsii. We measured REWL, CEWL, oxygen consumption and carbon dioxide production in a partitioned chamber using flow-through respirometry. In doves housed for 2-4 weeks in a room heated to ca. 43 degrees C during the day, TEWL increased from 5.5+/-1.3 mg g(-1) h(-1) at an air temperature (T(a)) of 35 degrees C to 19.3+/-2.5 mg g(-1) h(-1) at T(a)=45 degrees C. In doves housed at room temperature for the same period, TEWL increased from 4.6+/-1.1 mg g(-1) h(-1) at T(a)=35 degrees C to 16.1+/-4.6 mg g(-1) h(-1) at T(a)=45 degrees C. The CEWL of heat-acclimated doves increased from 3.6+/-1.2 mg g(-1) h(-1) (64% of TEWL) at 35 degrees C to 15.0+/-2.1 mg g(-1) h(-1) (78% of TEWL) at T(a)=45 degrees C. Cool-acclimated doves exhibited more modest increases in CEWL, from 2.7+/-0.7 mg g(-1) h(-1) at T(a)=35 degrees C to 7.8+/-3.4 mg g(-1) h(-1) at T(a)=45 degrees C, with the contribution of CEWL to TEWL averaging 53% over this T(a) range. Cool-acclimated doves became mildly hyperthermic (body temperature T(b)=42.9+/-0.4 degrees C) and expended 35% more energy relative to heat-acclimated doves (T(b)=41.9+/-0.6 degrees C) at T(a)=45 degrees C, even though TEWL in the two groups was similar. In each of the two groups, metabolic rate did not vary with T(a), and averaged 7.1+/-0.5 mW g(-1) in cool-acclimated doves and 6.3+/-0.8 mW g(-1) in heat-acclimated doves. The differences in TEWL partitioning we observed between the two experimental groups resulted from a consistently lower skin water vapour diffusion resistance (r(v)) in the heat-acclimated doves. At T(a)=45 degrees C, r(v) in the cool-acclimated doves was 120+/-81 s cm(-1), whereas r(v) in the heat-acclimated doves was 38+/-8 s cm(-1). Our data reveal that in Z. a. mearnsii, TEWL partitioning varies in response to short-term thermal acclimation.

Acclimatization↗

PubMed1995

Enhanced hypo-osmoregulation induced by warm-acclimation in antarctic fish is mediated by increased gill and kidney Na+/K(+)-ATPase activities.

Serum osmolality and serum inorganic ion concentrations were studied in two antarctic fish species, Trematomus bernacchii and T. newnesi, during 5 weeks of acclimation to 4 degrees C and compared with control values for groups acclimated to -1.5 degrees C. Acclimation to 4 degrees C significantly decreased the serum osmolality of both species, thereby increasing their seawater-to-extracellular fluid (ECF) osmotic gradient. The decline in osmolality with acclimation to 4 degrees C was accompanied by significant and rapid losses of Na+ and Cl- during the first 14 days of acclimation and was maintained throughout the study period. At day 35 of acclimation, the lipid composition and microsomal Na+/K(+)-ATPase specific activities at 4 degrees C and 37 degrees C were determined in membranes from gill, kidney, liver and muscle tissues. No warm-induced decrease in fatty acid unsaturation was found in the tissues of either species. In the gills and kidneys of both species, the Na+/K(+)-ATPase activities assayed at 4 degrees C were increased after acclimation to 4 degrees C. The Na+/K(+)-ATPase activities at 37 degrees C increased at the higher acclimation temperature in T. newnesi kidneys and T. bernacchii gills, but in both species there was no compensation to temperature in the liver, regardless of assay temperature. Muscle Na+/K(+)-ATPase activity decreased in response to warm-acclimation in T. bernacchii and T. newnesi assayed at 4 degrees C and 37 degrees C, respectively. During acclimation to 4 degrees C, the discontinuity in the Arrhenius plot of the Na+/K(+)-ATPase activities of T. newnesi gill moved to a lower temperature, whereas that of kidney remained unchanged. The results indicate that acclimation to 4 degrees C induced a decrease in serum osmolality which resulted from the positive compensation of Na+/K(+)-ATPase in osmoregulatory tissues. The enhancement in Na+/K(+)-ATPase activity at 4 degrees C suggests that energy expenditure in antarctic fish may be lessened, in part, by maintaining a reduced seawater-to-ECF osmotic gradient.

Acclimatization↗

PubMed1996

Plasticity of fish muscle mitochondria with thermal acclimation

Short-horned sculpin Myoxocephalus scorpius were acclimated to 5 and 15 °C to evaluate the impact of thermal acclimation upon maximal rates of substrate oxidation by mitochondria and upon the thermal sensitivity of their ADP affinity. Cold acclimation virtually doubled maximal rates of pyruvate oxidation at all experimental temperatures (2.5, 7.5, 12.5 and 20 °C). Rates of palmitoyl carnitine oxidation were also enhanced by cold acclimation, but to a lesser degree. At their respective acclimation temperatures, the mitochondria attained similar rates of pyruvate oxidation. For warm-acclimated sculpin, the Q10 values for mitochondrial pyruvate and palmitoyl carnitine oxidation were higher between 2.5 and 7.5 °C than between 7.5 and 12.5 °C or between 12.5 and 20 °C. In contrast, for cold-acclimated fish, the Q10 values did not differ over these thermal ranges. The Arrhenius activation energy for pyruvate oxidation was reduced by cold acclimation (from 70 to 55 kJ mol-1), whereas that for palmitoyl carnitine oxidation was unchanged (approximately 75 kJ mol-1). Cold acclimation did not alter the ADP affinity of mitochondria at low temperatures but markedly increased the apparent Km for ADP (Km,app) at 12.5 and 20 °C. At the acclimation temperatures, mitochondrial ADP Km,app values did not differ. The loss of ADP affinity at higher temperatures may represent a cost of the enhanced maximal oxidative capacity achieved during cold acclimation.

Journal Article↗

PubMed2000

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation.

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.

Acclimatization↗

PubMed2002

Cold acclimation induces proliferation of sarcoplasmic reticulum without increase in Ca2+-ATPase activity in white axial muscle of striped bass (Morone saxatilis).

The effects of acclimation of striped bass to cold (5 degrees C) and warm (25 degrees C) temperatures upon ultrastructural features of white axial skeletal muscle are quantified. Surface density of sarcoplasmic reticulum (SR) increased by almost 30%, and SR volume density increased by about 20% during cold acclimation. Proliferation of SR suggests an increase in available SR surface for re-sequestration of Ca2+ and a decrease in diffusion path length for Ca2+ during cold acclimation. Average cross-sectional areas and cross-sectional perimeters of myofibrils situated in the center of muscle fibers decreased during cold acclimation by approximately 20% and 11%, respectively. Additionally, average major and minor axes of ellipses fit to central myofibrillar cross-sections decreased by approximately 12% and 8%, respectively, during cold acclimation. These measurements define a decrease in average myofibrillar diameter and suggest a decrease in diffusion path length for Ca2+ to and from myofibrillar activation sites. Measurements of peripheral myofibrils that had elongated profiles in cross-sections indicate that maximum profile length of these myofibrils decreases by about 17%. Peripheral myofibrils may break up into smaller myofibrils with more rounded cross-sectional profiles during cold acclimation. SR Ca2+-ATPase of white axial muscle was also measured in unfractionated homogenates and in crude SR-enriched subcellular fractions from cold- and warm-acclimated striped bass. No difference in SR Ca2+-ATPase activity per g wet weight was observed between cold- and warm-acclimated animals. Lack of increase in SR Ca2+-ATPase per g wet weight, despite a significant proliferation of SR, probably results in a decrease in average Ca2+-ATPase pump density within the SR membrane during cold acclimation. Thus, compensation for decreased diffusion coefficient of Ca2+ during cold acclimation appears due to the combined effects of proliferation of SR surface density and a decrease in average myofibrillar diameter.

Acclimatization↗

PubMed1988

Adaptation of intestinal morphology in the temperature-acclimated carp, Cyprinus carpio L.

The effects of temperature and photoperiod acclimation upon the morphology of carp intestinal mucosa have been studied using morphometric techniques. Carp intestine showed an absence of anatomical regionalisation. There was a gradual reduction in the dimensions of villi along the tract. The decrease in the dimensions of the villi was greatest in the anterior half. Temperature acclimation had no effect on intestinal-somatic indices. Acclimation to 10 degrees C or 30 degrees C resulted in large differences in the dimensions of villi. Cold acclimation produced significant increases in mean villus height and breadth along the entire intestine. These villus shape changes resulted in a 58% increase in total mucosal surface area and a 102% increase in total volume of villi in cold-acclimated fish relative to warm-acclimated fish. Surface area of the unmodified intestinal tube increased with cold acclimation by 28%. The total number of villi remained unchanged by thermal acclimation. Because normalisation to a nominal surface area does not take account of the possibility of differentially developed mucosal surfaces in differently acclimated animals, experiments comparing transepithelial transport rates of differently-acclimated fish, using unstripped preparations, overestimates the differences in area-specific transport capacity.

Adaptation, Physiological↗

PubMed2001

Cold acclimation increases basal heart rate but decreases its thermal tolerance in rainbow trout (Oncorhynchus mykiss).

Rainbow trout (Oncorhynchus mykiss, Walbaum) were acclimated to 4 degrees C and 17 degrees C for more than 4 weeks and heart rate was determined in the absence and presence of adrenaline to see how thermal adaptation influences basal heart rate and its beta-adrenergic control in a eurythermal fish species. The basal heart rate in vitro was higher in cold-acclimated than warm-acclimated rainbow trout at temperatures below 17 degrees C. On the other hand, adaptation to cold decreased thermal tolerance of heart rate so that the maximal heart rates were achieved at 17 degrees C (75 +/- 4 bpm) and 24 degrees C (88 +/- 2 bpm) in cold-acclimated and warm-acclimated trout, respectively. Beta-adrenergic response of the heart was enhanced by cold-adaptation, since adrenaline (100 nmol l(-1)) caused stronger stimulation of heart rate in cold-acclimated (29 +/- 14%) than in warm-acclimated fish (10 +/- 1%; P = 0.03). Furthermore, adrenaline strongly opposed the temperature-dependent deterioration of force production in cold-acclimated trout but not in warm-acclimated trout. The results indicate that adaptation to cold increases basal heart rate but decreases its thermal tolerance in rainbow trout. Cold acclimation up-regulates the beta-adrenergic system, and beta-adrenoceptor activation seems to provide cardioprotection against high temperatures in the cold-adapted rainbow trout.

Acclimatization↗

PubMed1990

Biliary excretion appears rate limiting for hepatic elimination of benzo[a]pyrene by temperature-acclimated rainbow trout.

Previous work demonstrated that mixed function oxidase activities of hepatic microsomes from cold- and warm-acclimated rainbow trout were similar when assayed at temperatures to which fish were acclimated. This "ideal temperature compensation" was partially explained by constitutive differences in microsomes. In the work reported here, rainbow trout were acclimated at 10 or 18 degrees C for 4 weeks and then ip injected with 10 mumol [3H] or [14C]benzo[a]pyrene (BP)/kg in one of two temperature regimens. First, fish were acclimated and exposed at the same temperature and killed after 4, 24, or 48 hr. Concentrations of [3H]BP equivalents in liver, bile, and fat but not in plasma, muscle, intestine, gill, or kidney increased with time. There were no differences in hexane or ethyl acetate extractable [3H] or [14C]BP tissue concentrations in 10 and 18 degrees C-acclimated fish exposed at their acclimation temperatures. At 24 hr after injection, biliary excretion of [3H]BP equivalents was about twofold higher at 18 degrees C than at 10 degrees C. Therefore, warmer temperature stimulated biliary excretion without a marked effect on in vivo BP metabolism. In the second regimen, 10 and 18 degrees C-acclimated fish were shifted to 14 degrees C, injected with [3H] or [14C]BP 1 hr later, and killed after an additional 24 hr. There were no differences in tissue concentrations of total [3H]BP equivalents between acclimation groups at 14 degrees C. However, the biliary concentration of [14C]BP not extracted by ethyl acetate was significantly higher in bile from 10 degrees C-acclimated fish than from 18 degrees C-acclimated fish when both groups were exposed at 14 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed2002

Diapause development and acclimation regulating enzymes associated with glycerol synthesis in the Shonai ecotype of the rice stem borer larva, Chilo suppressalis walker.

Overwintering larvae of the Shonai ecotype of the rice stem borer, Chilo suppressalis, enter diapause in early September and terminate diapause at the end of October. Cold acclimation at 0 degrees C did not influence glycerol, trehalose or glycogen content in larvae collected on 22 September. Acclimation at 0 degrees C increased the glycerol content and reduced the glycogen content significantly in larvae collected on 2 October and 22 November compared with acclimation at 15 degrees C. These results indicate that overwintering larvae at different phases of diapause development respond differently to the low temperature stimulus for glycerol synthesis. Thus, we evaluated the metabolic rearrangements associated with glycerol synthesis during diapause development and after temperature acclimation. Larvae collected on 2 October were acclimated at 15 degrees C for 15 and 60 days. Some of those acclimated at 15 degrees C were then moved to 0 degrees C for 15 days. The larvae acclimated at 15 degrees C for 15 days were in deep diapause and accumulated little glycerol, while larvae acclimated at 15 degrees C for 60 days were nearly ready to emerge from diapause and accumulated glycerol at 155.5 &mgr;mol/g. When larvae acclimated to 15 degrees C for 15 days were transferred to 0 degrees C, glycerol accumulation was stimulated to the same extent (ca 140 &mgr;mol/g) as it was in larvae that were acclimated to 15 degrees C for 60 days and then transferred to 0 degrees C. These results indicate that low temperature has a cumulative effect on glycerol production in larvae at different phases of diapause development. Glycerol accumulation was accomplished by activation of glycogen phosphorylase and inhibition of fructose-1,6-bisphosphatase, and activation of enzymes associated with glycerol synthesis, mainly glyceraldehyde-3-phosphatase and polyol dehydrogenase with glyceraldehyde activity.

Journal Article↗

PubMed2001

Seasonal patterns of photosynthetic response and acclimation to elevated carbon dioxide in field-grown strawberry.

Strawberry (Fragaria x ananassa) plants were grown in field plots at the current ambient [CO(2)], and at ambient + 300 and ambient + 600 mumol mol(-1) [CO(2)]. Approximately weekly measurements were made of single leaf gas exchange of upper canopy leaves from early spring through fall of two years, in order to determine the temperature dependence of the stimulation of photosynthesis by elevated [CO(2)], whether growth at elevated [CO(2)] resulted in acclimation of photosynthesis, and whether any photosynthetic acclimation was reduced when fruiting created additional demand for the products of photosynthesis. Stimulation of photosynthetic CO(2) assimilation by short-term increases in [CO(2)] increased strongly with measurement temperature. The stimulation exceeded that predicted from the kinetic characteristics of ribulose-1,5-bisphosphate carboxylase at all temperatures. Acclimation of photosynthesis to growth at elevated [CO(2)] was evident from early spring through summer, including the fruiting period in early summer, with lower rates under standard measurement conditions in plants grown at elevated [CO(2)]. The degree of acclimation increased with growth [CO(2)]. However, there were no significant differences between [CO(2)] treatments in total nitrogen per leaf area, and photosynthetic acclimation was reversed one day after switching the [CO(2)] treatments. Tests showed that acclimation did not result from a limitation of photosynthesis by triose phosphate utilization rate at elevated [CO(2)]. Photosynthetic acclimation was not evident during dry periods in midsummer, when the elevated [CO(2)] treatments conserved soil water and photosynthesis declined more at ambient than at elevated [CO(2)]. Acclimation was also not evident during the fall, when plants were vegetative, despite wet conditions and continued higher leaf starch content at elevated [CO(2)]. Stomatal conductance responded little to short-term changes in [CO(2)] except during drought, and changed in parallel with photosynthetic acclimation through the seasons in response to the long-term [CO(2)] treatments. The data do not support the hypothesis that source-sink balance controls the seasonal occurrence of photosynthetic acclimation to elevated [CO(2)] in this species.

Journal Article↗

PubMed1998

Time course of heat acclimation and its decay.

More is known about the time course for the acquisition of human heat acclimation during exercise than its decay or loss. Pioneering research in the 1940s led to our early understanding of the heat acclimation process and its subsequent decay with further knowledge concerning the associated physiological mechanisms in later years. For both hot-dry and hot-humid environments, nearly complete exercise-heat acclimation occurs after 7 to 10 days of exposure. However, about two-thirds to 75% of the physiological adjustments and improvements in performance are seen in 4 to 6 days. Individuals with high levels of aerobic fitness are partially but not fully acclimated to the heat. Most of the early studies on decay or loss of heat acclimation are flawed by very small samples, incomplete heat acclimation or inappropriate measurements. Nevertheless, these studies are pioneering in a sense because they indicate that the retention of heat acclimation is quite variable between individuals and environments. Retention of the benefits of heat acclimation appears to remain longer for dry compared to humid heat. High levels of aerobic fitness seem associated with greater retention of heat acclimation. Further well-designed and definitive studies on decay or loss of heat acclimation appear necessary.

Acclimatization↗

PubMedDate not supplied

Thermal acclimation effects differ between voluntary, maximum, and critical swimming velocities in two cyprinid fishes.

Temperature acclimation may be a critical component of the locomotor physiology and ecology of ectothermic animals, particularly those living in eurythermal environments. Several studies of fish report striking acclimation of biochemical and kinetic properties in isolated muscle. However, the relatively few studies of whole-animal performance report variable acclimation responses. We test the hypothesis that different types of whole-animal locomotion will respond differently to temperature acclimation, probably due to divergent physiological bases of locomotion. We studied two cyprinid fishes, tinfoil barbs (Puntius schwanenfeldii) and river barbels (Barbus barbus). Study fish were acclimated to either cold or warm temperatures for at least 6 wk and then assayed at four test temperatures for three types of swimming performance. We measured voluntary swimming velocity to estimate routine locomotor behavior, maximum fast start velocity to estimate anaerobic capacity, and critical swimming velocity to estimate primarily aerobic capacity. All three performance measures showed some acute thermal dependence, generally a positive correlation between swimming speed and test temperature. However, each performance measure responded quite differently to acclimation. Critical speeds acclimated strongly, maximum speeds not at all, and voluntary speeds uniquely in each species. Thus we conclude that long-term temperature exposure can have very different consequences for different types of locomotion, consistent with our hypothesis. The data also address previous hypotheses that predict that polyploid and eurythermal fish will have greater acclimation abilities than other fish, due to increased genetic flexibility and ecological selection, respectively. Our results conflict with these predictions. River barbels are eurythermal polyploids and tinfoil barbs stenothermal diploids, yet voluntary swimming acclimated strongly in tinfoil barbs and minimally in river barbels, and acclimation was otherwise comparable.

Acclimatization↗

PubMed2000

Effect of different daytime and night-time temperature regimes on the foliar respiration of Pinus taeda: predicting the effect of variable temperature on acclimation.

The objectives of this study were to determine the acclimation of loblolly pine (Pinus taeda L.) foliar respiration to different night-time low temperatures, daytime high temperatures, and daily mean temperatures, and then to use the responses of temperature acclimation to various temperature regimes to predict acclimation under fluctuating temperatures. Experiments were conducted on two-year-old seedlings in growth chambers using different combinations of day and night-time temperatures. The first experiment exposed trees to 22/22, 29/22, 22/15, and 29/15 degrees C day/night (d/n). When measured at a common temperature (15, 22 or 29 degrees C), respiration rates were lower for trees exposed to higher treatment temperatures and acclimation was influenced by both day and night-time temperature. However, the extent of acclimation did not relate to mean temperature, i.e. respiration rates measured at a common temperature ranked as follows for seedlings exposed to different temperature regimes, 22/15>22/22>29/15 congruent with29/22 degrees C d/n. Rather, acclimation of foliar respiration was linearly related to mean daily respiration rate, where mean daily respiration rate is the average of the respiration rates measured at the day and night-time treatment temperatures. The discrepancy between mean daily respiration rate and mean daily temperature occurred because respiration increased exponentially with increasing temperature. In a second experiment, the same seedlings were exposed to 22/22, 15/15, 25.5/18.5, and 25.5/15 degrees C d/n to test the relationship between mean daily respiration rate and acclimation. As in the first experiment, acclimation was linearly related to mean daily respiration rate. The concept of effective acclimation temperature, which is the temperature at which the mean daily respiration rate occurs, was derived from these results as a means to predict the extent that foliar respiration acclimates to treatment temperature.

Adaptation, Physiological↗

PubMed1978

Environmental and Seasonal Factors Affecting the Frost-induced Stage of Cold Acclimation in Cornus stolonifera Michx.

Stem tissues of red-osier dogwood (Cornus stolonifera Michx.) acclimated from -3 C to -40 or -50 C in 8 to 10 weeks under a short photoperiod (9 hours) and controlled temperature conditions. During the summer months plants did not acclimate as well as at other times. The sequence of day/night temperature regimes which induced maximum acclimation was 20/15 C for 5 to 6 weeks; 15/5 C for 2 to 3 weeks; 15/5 C plus 1 hour of frost per day for 1 week. The duration of exposure to each temperature regime influenced the rate and intensity of frost-induced acclimation. Less than 5 weeks of warm temperature preconditioning at 20/15 C reduced subsequent frost-induced acclimation. The inductive influence of frost on cold acclimation was additive over 5 days of repeated exposure, but its effects after the first exposure(s) were not immediate-requiring 1 to 4 days of 15/5 C following the frost treatments for the expression of the frost-induced acclimation to be manifest. There was a 75% increase in rRNA following 3 days of frost exposure and plants in an O(2)-free atmosphere during frost exposure failed to acclimate. The results suggest that seasonal acclimation behavior was due to endogenous rhythms rather than developmental stage, and that the frost-induced phase of acclimation involves aerobic metabolic processes.

Journal Article↗

PubMed1989

Thermal Acclimation of Photosynthetic Electron Transport Activity by Thylakoids of Saxifraga cernua.

Thermal acclimation by Saxifraga cernua to low temperatures results in a change in the optimum temperature for gross photosynthetic activity and may directly involve the photosynthetic apparatus. In order to test this hypothesis photosynthetic electron transport activity of S. cernua thylakoids acclimated to growth temperatures of 20 degrees C and 10 degrees C was measured in vitro. Both populations exhibited optimum temperatures for whole chain and PSII electron transport activity at temperatures close to those at which the plants were grown. Chlorophyll a fluorescence transients from 10 degrees C-acclimated leaves showed higher rates in the rise and subsequent quenching of variable fluorescence at low measuring temperatures; 20 degrees C-acclimated leaves showed higher rates of fluorescence rise at higher measuring temperatures. At these higher temperatures, fluorescence quenching rates were similar in both populations. The kinetics of State 1-State 2 transitions in 20 degrees C- and 10 degrees C-acclimated leaf discs were measured as changes in the magnitude of the fluorescence emission maxima measured at 77K. Leaves acclimated at 10 degrees C showed a larger F730/F695 ratio at low temperatures, while at higher temperatures, 20 degrees C-acclimated leaves showed a higher F730/F695 ratio after the establishment of State 2. High incubation temperatures also resulted in a decrease in the F695/F685 ratio for 10 degrees C-acclimated leaves, suggesting a reduction in the excitation transfer from the light-harvesting complex of photosystem II to photosystem II reaction centers. The relative amounts of chlorophyll-protein complexes and thylakoid polypeptides separated electro-phoretically were similar for both 20 degrees C- and 10 degrees C-acclimated leaves. Thus, photosynthetic acclimation to low temperatures by S. cernua is correlated with an increase in photosynthetic electron transport activity but does not appear to be accompanied by major structural changes or different relative amounts in thylakoid protein composition.

Journal Article↗

PubMed1988

Role of chemical concentration and second carbon sources in acclimation of microbial communities for biodegradation.

A study was conducted to determine the role of concentration of the test chemical, of a second organic compound, and of mutation in the acclimation period before the mineralization of organic compounds in sewage. The acclimation period for the mineralization in sewage of 2 micrograms of 4-nitrophenol (PNP) per liter increased from 6 to 12 days in the presence of 10 mg of 2,4-dinitrophenol per liter. The extension of the acclimation period was equivalent to the time required for mineralization of 2,4-dinitrophenol. In contrast, the time for acclimation for the degradation of 2 micrograms of PNP per liter was reduced when 10 or 100 mg of phenol per liter was added. Lower phenol levels increased the acclimation period to 8 days. The length of the acclimation period for PNP mineralization decreased as the initial concentration of PNP increased from 2 micrograms to 100 mg/liter. The acclimation period for phenol mineralization was lengthened as the phenol concentration increased from 100 to 1,400 mg/liter. The length of the acclimation period for PNP and phenol biodegradation was reproducible, but it varied among replicates for the biodegradation of other nitro-substituted compounds added to sewage or lake water, suggesting that a mutation was responsible for acclimation to these other compounds. The acclimation period may thus reflect the time required for the destruction of toxins, and it also may be affected by the concentration of the test compound or the presence of other substrates.

2,4-Dinitrophenol↗

PubMed2006

Temperature acclimation modifies sinoatrial pacemaker mechanism of the rainbow trout heart.

The hypothesis of pacemaker level origin of thermal compensation in heart rate was tested by recording action potentials (AP) in intact sinoatrial tissue and enzymatically isolated pacemaker cells of rainbow trout acclimated at 4 degrees C (cold) and 18 degrees C (warm). With electrophysiological recordings, the primary pacemaker was located at the base of the sinoatrial valve, where a morphologically distinct ring of tissue comprising myocytes and neural elements was found by histological examination. Intrinsic beating rate of this pacemaker was higher in cold-acclimated (46 +/- 6 APs/min) than warm-acclimated trout (38 +/- 3 APs/min; P < 0.05), and a similar difference was seen in beating rate of isolated pacemaker cells (44 +/- 6 vs. 38 +/- 6 APs/min; P < 0.05), supporting the hypothesis that thermal acclimation modifies the intrinsic pacemaker mechanism of fish heart. Inhibition of sarcoplasmic reticulum (SR) with 10 microM ryanodine and 1 microM thapsigargin did not affect heart rate in either warm- or cold-acclimated trout at 11 degrees C but reduced heart rate in warm-acclimated trout from 74 +/- 2 to 42 +/- 6 APs/min (P < 0.05) at 18 degrees C. At 11 degrees C, a half-maximal blockade of the delayed rectifier K+ current (I(Kr)) with 0.1 microM E-4031 reduced heart rate more in warm-acclimated (from 45 +/- 1 to 24 +/- 5 APs/min) than cold-acclimated trout (56 +/- 3 vs. 48 +/- 2 APs/min), whereas I(Kr) density was higher and AP duration less in cold-acclimated trout (P > 0.05). Collectively, these findings suggest that a cold-induced increase in AP discharge frequency is at least partly due to higher density of the I(Kr) in the cold-acclimated trout, whereas contribution of SR Ca2+ release to thermal compensation of heart rate is negligible.

Acclimatization↗