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PubMed2004

Changes in gene expression during dehardening of cold-hardened winter rye (Secale cereale L.) leaves and potential role of a peptide methionine sulfoxide reductase in cold-acclimation.

Suppression subtractive hybridization and differential display polymerase chain reactions were used to identify genes that were differentially expressed in cold-hardened and dehardened leaves of winter rye (Secale cereale L.). The transcripts of nine genes declined during dehardening at 22 degrees C of cold-hardened 4 degrees C-grown leaves, indicating some role in cold-acclimation. Among the genes that were strongly expressed in cold-hardened leaves were five genes of photosynthetic metabolism, the gene of the antioxidative enzyme peptide methionine sulfoxide reductase (PMSR) and three genes of RNA and protein metabolism. Four genes were identified that were more strongly expressed during dehardening of cold-hardened leaves at 22 degrees C. A full-length cDNA for a presumed cytosolic PMSR (EC 1.8.4.6) of rye leaves was identified. After heterologous expression in Escherichia coli, an antiserum against the ScPMSR was produced. The content of the ScPMSR protein, visualized by immunoblotting, was much higher in cold-hardened than in non-hardened leaves and declined during dehardening. In non-hardened leaves the mRNA of ScPMSR increased only slowly during exposures to 4 degrees C in light and was not affected by exposure to 4 degrees C in darkness. However, the ScPMSR mRNA was also induced by prolonged exposure (48 h) to high light at 22 degrees C, or by treatment with 2 muM paraquat. Consequently, the induction of cytosolic ScPMSR is a late response to prolonged photooxidative stress conditions, as expected during growth at low temperature in light. In cold-hardened leaves, PMSR may protect proteins from photodamage and thus prevent their degradation and the need for repair.

Acclimatization↗

PubMed2001

A new chloroplast envelope carbonic anhydrase activity is induced during acclimation to low inorganic carbon concentrations in Chlamydomonas reinhardtii.

Using mass-spectrometric measurements of 18O exchange from 13C18O2 we determined the activity of carbonic anhydrase (CA; EC 4.2.1.1) in chloroplast envelope membranes isolated from Chlamydomonas reinhardtii cw-15. Our results show an enrichment of CA activity in these fractions relative to the activity in the crude chloroplast. The envelope CA activity increased about 8-fold during the acclimation to low-CO2 conditions and was completely induced within the first 4 h after the transfer to air levels of CO2. The CA-activity was not dissociated from envelope membranes after salt treatment. In addition, no cross-reactivity with other CA isoenzymes of Chlamydomonas was observed in our chloroplast envelope membranes. All these observations indicated that the protein responsible for this activity was a new CA isoenzyme, which was an integral component of the chloroplast envelopes from Chlamydomonas. The catalytic properties of the envelope CA activity were completely different from those of the thylakoid isoenzyme, showing a high requirement for Mg2+ and a high sensitivity to ethoxyzolamide. Analysis of the integral envelope proteins showed that there were no detectable differences between high- and low-inorganic carbon (Ci) cells, suggesting that the new CA activity was constitutively expressed in both high- and low-Ci cells. Two different high-Ci-requiring mutants of C. reinhardtii, cia-3 and pmp-1, had a reduced envelope CA activity. We propose that this activity could play a role in the uptake of inorganic carbon at the chloroplast envelope membranes.

Adaptation, Physiological↗

PubMed1999

Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide

The effects of elevated CO(2) concentrations on the photochemistry, biochemistry and physiology of C(4) photosynthesis were studied in maize (Zea mays L.). Plants were grown at ambient (350 &mgr;L L(-1)) or ca. 3 times ambient (1100 &mgr;L L(-1)) CO(2) levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO(2) levels, plants grown under elevated CO(2) accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO(2) concentration of growth, mature leaves of high-CO(2)-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use efficiency (225%) and higher dark respiration rates (100%). High-CO(2)-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO(2), and lower leaf protein contents (22%). Activities of a number of C(3) and C(4) cycle enzymes decreased on a leaf-area basis in the high-CO(2)-grown plants by 5-30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose 1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO(2) condition (8% and 36%, respectively). These data show that the C(4) plant maize may benefit from elevated CO(2) through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and starch, and to utilize these end-products of photosynthesis to produce extra energy by respiration, may contribute to the enhanced growth of maize under elevated CO(2).

Journal Article↗

PubMed2001

Acclimation of Arabidopsis thaliana to the light environment: the existence of separate low light and high light responses.

The capacity for photosynthetic acclimation in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta was assessed during growth over a broad range of irradiance. Discontinuities in the response to growth irradiance were revealed for the light- and CO2-saturated rate of photosynthesis (Pmax) and the ratio of chlorophyll a to chlorophyll b (Chl a/b). Three separate phases in the response of Pmax and Chl a/b to growth light were evident, with increases at low and high irradiance ranges and a plateau at intermediate irradiance. By measuring all chlorophyll-containing components of the thylakoid membrane that contribute to Chl a/b we reveal that distinct strategies for growth at low and high irradiance underlie the discontinuous response. These strategies include, in addition to changes in the major light-harvesting complexes of photosystem II (LHCII), large shifts in the amounts of both reaction centres as well as significant changes in the levels of minor LHCII and LHCI components.

Acclimatization↗

PubMed2003

The mode of action of acute and chronic concentrations of waterborne Cd in the digestive gland of the acclimated infested freshwater crab ( Potamonautes warreni).

Cadmium (Cd) uptake, transport and accumulation were investigated in the digestive gland of the freshwater crab, Potamonautes warreni, acclimated in its natural habitat to stresses, such as microbial gill infestations, Cd(2+) and NH(4)(+), and subsequently exposed to increasing concentrations of Cd in the laboratory for up to 21 days. Cd exposure (0.2 mg l(-1)) for 7-14 days led to Cd permeating cell membranes in a particulate form; it was adsorbed intracellularly to endocytotic circulating amoebocytes, lipid droplets and Golgi vesicles in R-cells. Cd also caused dissociation of the fibrillar rough endoplasmic reticulum (RER) and an increase in phagocytotic activity in F- and B-cells. After 21 days, Cd accumulated as crystal deposits on the basal membranes of cells in the haemolymph space and along the microvilli of cells lining the tubular lumen. Elevated Cd concentrations were found in the cytosol, amoebocytes, Golgi vesicles and P/Ca granules in R-cells. Chronic exposure to higher concentrations of Cd (0.5 and 1.0 mg l(-1)) increased crystal deposition, whereas concentrations of Cd, copper and iron decreased in the cell membranes and in amoebocytes and increased in Golgi vesicles. Reduced lipid content, swollen nuclei with vesiculated nucleoli and enhanced activity of RER in R-cells were also noted. Cd was stored in the P/Ca and Ca granules of B-cells. Acute exposure to Cd (2.0 mg l(-1) for 48 h) caused metal granule accumulation along cells lining the tubular lumen and cellular dissociation, with acidosis and necrosis in the cytoplasm and Cd deposits in mitochondria. Cd accumulated in the cells of the digestive gland in a time-, concentration- and cell-type-specific fashion.

Animals↗

PubMed2005

Growth and ecophysiological acclimation of the foliose lichen Lobaria pulmonaria in forests with contrasting light climates.

This study aims to assess biomass and area growth of 600 thalli of the old forest lichen, Lobaria pulmonaria, transplanted to three successional boreal forest stands with (1) natural rainfall regime, (2) additional moistening during dry days, and (3) additional moistening with added nutrients. Mean biomass growth during 100 days varied from 8.3% in the dark young spruce forest to 23.1% in the clear-cut area, with the old forest in between (16.0%). Additional moistening did not enhance lichen growth, probably because the transplantation period was wet. Nutrient additions slightly increased area growth compared to artificial water additions only. Growth was determined by a combination of external (forest stand, site factors) and internal factors (chlorophyll content, biomass per area). Transplants acclimated to high light by increasing thickness and chlorophyll a/b-ratio. Some visible bleaching and a strong positive correlation between chlorophyll content per area and lichen growth in clear-cuts suggest some high light-induced chlorophyll degradation. We believe that biomass growth and natural occurrence of L. pulmonaria is controlled by a delicate balance between light availability and desiccation risk, and that the species is confined to old forests due to a physiological trade-off between growth potential and fatal desiccation damage, both of which increase with increasing light. The discrepancy between potential and realized ecological niches is probably caused by a long-term risk to be killed in open habitats by high light during long periods with no rain.

Ascomycota↗

PubMed1990

Decrease of oxidative activities in brown adipose tissue mitochondria of cold acclimated rats on short term exposure to heat stress.

Exposure of rats to the cold (4-5 degrees C) caused large (2-3-fold) increases in the mass of interscapular brown adipose tissue (BAT), its mitochondrial content and the basal metabolic rate of the animals. The rate of substrate oxidation by BAT mitochondria also increased about 3-fold. When cold-acclimated animals were exposed to heat (37 degrees C), the BMR decreased by half in 3 h, the earliest time interval tested. Mitochondrial substrate oxidation, as well as substrate-dependent H2O2 generation, showed a proportionate decrease in rates. In these mitochondria, activities of cytochrome c reductases, but not dehydrogenases with NADH, alpha-glycerophosphate and succinate as substrates, also showed a significant decrease. The concentration of cytochromes aa3 and b, but not cytochrome c, also decreased in BAT mitochondria from 12-h heat-exposed animals, while the change in concentration of cytochrome b alone was found as early as 3 h of heat exposure. These results identify the change in cytochromes as a mechanism of regulation of oxidative activities in BAT mitochondria under conditions of acute heat stress.

Adaptation, Physiological↗

PubMed1981

Effects of temperature acclimation on Neurospora phospholipids. Fatty acid desaturation appears to be a key element in modifying phospholipid fluid properties.

Experiments were conducted on the effect of growth temperature on phospholipids of Neurospora. Strains grown at high (37 degrees C) and low (15 degrees C) temperatures show large differences in the proportions of phospholipid fatty acid alpha-linolenate (18 : 3) which can vary by 10-fold over this temperature range. Changes in the phospholipid base composition are less dramatic; the most significant is an increase in phosphatidylethanolamines at low temperatures accompanied by a concomitant decrease in phosphatidylcholine. It appears that phospholipid fatty acid desaturation is closely regulated with respect to growth temperature. Over the 37 to 15 degrees C growth temperature range there appear to be at least two desaturase systems in Neurospora which are under different controls. Production of 18 : 1 and 18 : 2 species appears to occur at high levels over the entire temperature range, whereas the production of 18 : 3 seems to be inversely related to growth temperature. Shifting 37 degrees C-acclimated cultures to 15 degrees C produces a growth lag period of approximately 3 h, during which the level of 18 : 3 increases markedly. Differential scanning calorimetry of phospholipids from 37 degrees C cells shows a phase transition at -22 degrees C while lipids from 15 degrees C cultures exhibit a phase transition with reduced enthalpy at about -41 degrees C. The data are consistent with the idea that phospholipid composition in Neurospora is under strict control and suggest that membrane fluidity is regulated with respect to growth temperature through changes in membrane lipid composition.

Acclimatization↗

PubMed1982

The effects of altered levels of phosphatidylcholine and phosphatidylethanolamine on fatty acid desaturase activity and sterol metabolism during temperature acclimation in a choline auxotroph of Neurospora crassa.

Experiments were conducted to determine the effects of choline deprivation on levels of phospholipid fatty acids in a choline auxotroph (chol-1; chol-2) of Neurospora crassa with respect to high (37 degrees C) and low (15 degrees C) growth temperatures and during acclimation following a shift from high to low temperature conditions. Although grossly altered levels of phosphatidylethanolamine and phosphatidylcholine were observed at both temperatures, phospholipid fatty acid levels remained virtually identical to those found in a phenotypically wild-type and maximally supplemented chol-1; chol-2 strains grown under the same conditions. Deprivation of choline from supplemented cultures of the mutant followed by a shift from high to low growth temperatures did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols were reduced, however, and sterol ester levels were elevated in choline-deprived cultures, suggesting that sterol interconversions may be closely tied to aspects of phospholipid biosynthesis. These experiments suggest that although major modifications in membrane fluidity may be brought about by thermally induced changes in fatty acid desaturase activity, it seems probable that additional cellular mechanisms may be involved if fluidity is under precise control.

Acclimatization↗

PubMed1984

Increase in mitochondrial content of long-chain acyl-CoA in brown adipose tissue during cold-acclimation.

The mitochondrial content of long-chain acyl-CoA esters in the brown adipose tissue of guinea pigs increased 3.5-fold from a level of 92 +/- 17 pmol per mg protein (+/- S.E.; n = 7) in the control animals adapted at 22 degrees C to a new steady-state level of 328 +/- 20 pmol per mg protein (+/- S.E.; n = 46) after 10 days of cold-acclimation (5 degrees C). These low values of long-chain acyl-CoA species and the slow adaptive response for their increase do not support the proposal (Cannon, B., Sindin, U. and Romert, L. (1977) FEBS Lett. 4, 43-46) that the fatty acid CoA-esters have a physiological function in the regulation of the H+ (or OH-) permeability of the mitochondrial inner membrane. Experimental evidence is presented supporting the proposal that the long-chain acyl-CoA species are largely confined to the cytosolic side of the inner membrane. The activity of the adenine nucleotide translocase, as estimated at 25 degrees C in the reverse direction, was found to increase 5-fold upon depletion of the mitochondria of fatty acids (free and esterified) by preincubation with bovine serum albumin. The presence of potent inhibitors, i.e., long-chain acyl-CoA species, of adenine nucleotide translocation in brown adipose tissue of thermogenically active animals further supports the conclusion that ATP hydrolyzing mechanisms contribute insignificantly to long-term thermogenesis. The low values of long-chain acyl-CoA hydrolase (EC 3.1.2.1) activity, as measured in intact mitochondria and on a mitochondrial matrix fraction (i.e., 1.6 nmol X min-1 per mg protein), do not support the proposal that the hydrolase activity plays a significant role in the loose-coupling of brown adipose tissue mitochondria, either by a futile cycle mechanism or promoted by free fatty acid-induced uncoupling.

Acyl Coenzyme A↗

PubMed1983

Destabilization of the plasma membrane of isolated plant protoplasts during a freeze-thaw cycle: the influence of cold acclimation.

In conclusion, isolated protoplasts are an excellent arena in which destabilization of the plasma membrane can be directly observed during a freeze-thaw cycle by cryomicroscopy. Destabilization is manifested in various ways--intracellular ice formation, loss of osmotic responsiveness, or expansion-induced lysis. The incidence of any particular form of injury will depend on the freeze-thaw protocol and hardiness of the tissue from which the protoplasts were isolated. In all cases, however, cold acclimation directly increases the stability of the plasma membrane to the multiple stresses that arise during a freeze-thaw cycle. Such observations provide for functional differences in the plasma membrane that may now be used to consider the significance of any compositional changes in the membrane that might be determined.

Acclimatization↗

PubMed1983

Effect of acclimation temperature on the concentration of the mitochondrial 'uncoupling' protein measured by radioimmunoassay in mouse brown adipose tissue.

The effect of acclimation temperature on the concentration of the mitochondrial 'uncoupling' protein (Mr 32000) from brown adipose tissue of mice has been investigated. The uncoupling protein was measured by a specific radioimmunoassay. Between 33 degrees C (thermoneutrality) and -2 degrees C there was a progressive increase with decreasing environmental temperature in the amount of uncoupling protein. For mice at -2 degrees C the mitochondrial concentration of the protein was 9-times higher than at 33 degrees C, while the total amount of the protein in interscapular brown adipose tissue was estimated to be nearly 80-times greater at -2 degrees C compared to 33 degrees C.

Acclimatization↗

PubMed1988

Regulation of fructose 2,6-bisphosphate levels in cold-acclimated brown adipose tissue of rat.

The effects of cold exposure and T4 administration on fructose 2,6-bisphosphate levels, phosphofructokinase-2 and pyruvate kinase activities were examined in rat brown adipose tissue. Cold adaptation (14 days) gave rise to a 2-fold increase in the amount of fructose 2,6-bisphosphate and phosphofructokinase-2 activity, and increased the pyruvate kinase activity 4-fold. If, in addition, the cold-acclimated rats were treated with T4, these parameters were again significantly enhanced. The effect on phosphofructokinase-2 was on the Vmax, without modification of the Km (for both fructose 6-phosphate and ATP) of the enzyme. In the hypothyroid state, however, the activity of pyruvate kinase remains unchanged. These data support previous observations on stimulation of glycolytic flux during cold adaptation in brown adipose tissue, and a permissive role of thyroid hormones in the process.

Adaptation, Physiological↗

PubMed1989

Prolactin cell activity and sodium fluxes in tilapia (Oreochromis mossambicus) after long-term acclimation to acid water.

In tilapia exposed for 3 months to water of pH 4.5, prolactin cell activity, as estimated by ultrastructural morphometry and determination of prolactin synthesis in vitro, was significantly higher than in controls from neutral water. Sodium influx from the water was 50% lower than in the controls, indicating impaired branchial sodium uptake mechanisms. In contrast to predictions based on the results of short-term exposure to acid water--which is known to induce an increase of sodium efflux--the sodium efflux rate was reduced to 70% of the control value. It is concluded that tilapia are able to acclimate to acid water by successful control--probably via prolactin--of diffusional sodium losses across the integument, in particular the gill surface. This compensates for the impaired sodium uptake, and enables the fish to reestablish a positive sodium balance in acid water.

Acclimatization↗

PubMed1990

Effect of gonadal steroid hormones on the metabolic rate of the cold-acclimated gonadectomized male and female Chalcides ocellatus (Forskal).

Male and female Chalcides ocellatus were gonadectomized and cold acclimated at 15 degrees for 1 week. Lizards were injected with testosterone and estradiol, and their oxygen consumption was determined at 15 degrees. Testosterone and estradiol caused a significant increase in the whole body rate of oxygen consumption in male and female lizards, respectively.

Acclimatization↗

PubMed1984

Cold acclimation of obese (ob/ob) mice: effects on skeletal muscle and bone.

Obese (ob/ob) and lean mice at 4 weeks of age were housed at 23 degrees C or 14 degrees C for 4 or 8 weeks to determine effects of acclimation to mild cold on the growth of skeletal muscle, bone, and fat. Body weights at 12 weeks of age averaged 48 +/- 0.6 g and 27 +/- 1.9 g for obese mice housed at 23 degrees C and 14 degrees C and 29 +/- 0.5 g and 26 +/- 0.6 g and 26 +/- 0.6 g for lean mice housed at 23 degrees C and 14 degrees C, respectively. At 23 degrees C, muscle weights of obese mice were approximately 60% of those in lean mice. Muscles of obese mice did not grow during the first 4 weeks at 14 degrees C (4 to 8 weeks of age) but did show a small gain during the second 4 weeks (9 to 12 weeks of age) at 14 degrees C. As a result, by the end of 8 weeks at 14 degrees C, muscles of obese mice weighed only 35% to 45% as much as muscles of lean mice. Growth of the tibia and femur followed the same pattern as the muscles. Obese mice housed at 23 degrees C from 4 to 12 weeks of age contained about six times as much fat as lean mice at this age. Although exposure to 14 degrees C for 8 weeks depressed the accumulation of fat in obese mice, they still contained approximately three times the percentage body fat as lean counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1985

Comparative electrical properties of identified neurons in Elysia chlorotica before and after low salinity acclimation.

Identified neurons in the abdominal ganglion of Elysia chlorotica adapted to 50% seawater (SW) had significantly different electrical properties from the same cells in animals adapted to 100% SW. Resting potential, action potential (AP) overshoot, (AP) duration, threshold and after potential were all different following salinity acclimation. The resting potential of these cells behaves as an ideal potassium electrode above 10 mM [K+]. The action potential has both sodium and calcium components to the rising phase.

Acclimatization↗

PubMed1986

Ionic regulation in fish: the influence of acclimation temperature on plasma composition and apparent set points.

Published data on the influence of acclimation temperature on normal ionic concentrations in fish plasma are summarized. Although osmolality rises near 0 degree C in many marine fish, there is otherwise no general tendency in marine species for osmolality, Na and Cl to fall with increasing temperature. The suggestion that osmolality, Na and Cl in freshwater fish typically fall with decreasing temperature is not supported. K and Ca generally rise with increasing temperature, or stay constant. Mg generally falls with increasing temperature, or stays constant. Evidence on concomitant variations in set points is sparse, but apparent set points for osmolality/Na/Cl, except near 0 degree C, usually vary by less than +/- 2% degrees C-1.

Acclimatization↗