Influence of thermal and nutritional acclimatization on body temperatures and metabolic rate

1. An investigation of the influence of previous thermal and nutritional experience on body temperatures and metabolic rate has been carried out with growing piglets. Littermates were kept, from shortly after birth, at either 10 or 35 degrees C and fed either a high (H) or a low (L) energy intake. At 8 weeks of age the animals were exposed to a series of environmental temperatures of 10, 20, 27 and 35 degrees C for 1.5 hr and their rates of oxygen consumption were determined over the last 45 min. At the end of the session body temperatures were measured. 2. Rectal temperatures measured 24 hr after the start of the last meal were higher at each test temperature in piglets which had been living at 35 degrees C than in those at 10 degrees C. Also, rectal temperatures were higher in those on the H intake for animals which had been living in either the hot or the cold environment. 3. Skin temperature on the back was similar in all groups at any given test temperature although there was a tendency for those on an H intake to have the higher temperatures. Skin temperatures of the legs and ears were higher in the 10H and 10L groups than in the 35H or 35L groups at all the test environmental temperatures; energy intake had little effect. 4. Metabolic rate was greater for the animals on the H than the L intake, for those which had been living at either 10 or 35 degrees C at all the test environmental temperatures. The analysis did not reveal any significant difference related to the overall effect of living temperature, which was independent of energy intake. 5. At thermal neutrality (27 degrees C) there was a significant interaction, between energy intake and normal living temperature, on metabolic rate. Living temperature was found to modify the effect of intake: the difference between the two intakes was greater in those from the cold environment than from the hot.     

Low temperature treatment at the young microspore stage induces protein changes in rice anthers

Male reproductive development in rice is very sensitive to various forms of environmental stresses including low temperature. A few days of cold treatment (<20 degrees C) at the young microspore stage induce severe pollen sterility and thus large grain yield reductions. To investigate this phenomenon, anther proteins at the early stages of microspore development, with or without cold treatment at 12 degrees C, were extracted, separated by two-dimensional gel electrophoresis, and compared. The cold-sensitive cultivar Doongara and the relatively cold-tolerant cultivar HSC55 were used. The abundance of 37 anther proteins was changed more than 2-fold after 1, 2, and 4 days of cold treatment in cv. Doongara. Among them, one protein was newly induced, 32 protein spots were up-regulated, and four protein spots were down-regulated. Of these 37 protein spots, we identified two anther-specific proteins (putative lipid transfer protein and Osg6B) and a calreticulin that were down-regulated and a cystine synthase, a beta-6 subunit of the 20 S proteasome, an H protein of the glycine cleavage system, cytochrome c oxidase subunit VB, an osmotin protein homologue, a putative 6-phosphogluconolactonase, a putative adenylate kinase, a putative cysteine proteinase inhibitor, ribosomal protein S12E, a caffeoyl-CoA O-methyltransferase, and a monodehydroascorbate reductase that were up-regulated. Identification of these proteins is available upon request. Accumulation of these proteins did not vary greatly after cold treatment in panicles of cv. Doongara or in the anthers of the cv. HSC55. The newly induced protein named Oryza sativa cold-induced anther protein (OsCIA) was identified as an unknown protein. The OsCIA protein was detected in panicles, leaves, and seedling tissues under normal growth conditions. Quantitative real time RT-PCR analysis of OsCIA mRNA expression showed no significant change between low temperature-treated and untreated plants. A possible regulatory role for the newly induced protein is proposed.     

Cloning and characterization of a papillomavirus associated with papillomas and carcinomas in the European harvest mouse (Micromys minutus).

Individuals in a colony of European harvest mice (Micromys minutus) were diagnosed with a variety of skin tumors including papillomas, trichoepitheliomas, and sebaceous carcinomas. Papillomavirus group-specific antigens and viruslike particles were detected in the papillomas. A 7.6-kilobase supercoiled circular DNA, which was cleaved once by EcoRI, was visualized in papilloma extracts by low-stringency Southern blot hybridization with a bovine papillomavirus type 2 probe. The molecule was cloned in pUC18, and a restriction map was generated. The molecule was shown to be colinear with the genome of human papillomavirus type 1a by partial sequence analysis. The DNA hybridized to human papillomavirus type 1a, rabbit oral papillomavirus, and the genome of Mastomys natalensis papillomavirus at Tm - 33 degrees C but not to the DNAs of 13 other papillomaviruses. Transformation of NIH 3T3 or C127I cells by tail papilloma extracts or transfected viral DNA was not observed. All 17 tumors examined contained large amounts of viral DNA in a supercoiled, unintegrated form as revealed by Southern blot hybridization. Furthermore, many extracts (25 of 35) from normal organs and skin of individuals with lesions elsewhere on their bodies contained viral DNA. This represents the first reported molecular cloning of a papillomavirus genome from a mouse species.     

Enhancing effect of low culture temperature on specific antibody productivity of recombinant Chinese hamster ovary cells: clonal variation

To understand the different responses of recombinant Chinese hamster ovary (rCHO) cells to low culture temperature regarding specific productivity (q), 12 parental clones and their corresponding amplified clones producing a humanized antibody were cultivated at 32 and 37 degrees C. The specific growth rate of all clones, including both parental and amplified clones, decreased by 30-63% at 32 degrees C, compared to rates at 37 degrees C. In contrast, their specific antibody productivity (qAb) was significantly enhanced at 32 degrees C. Furthermore, the degree of qAb enhancement at 32 degrees C varied a lot from 4- to 25-fold among the parental clones. At 32 degrees C, most of the amplified clones, regardless of methotrexate (MTX) levels, also showed enhanced qAb but to a lesser extent than their parental clones. However, clone 14 amplified at 0.32 microM MTX (clone 14-0.32) and clone 20 amplified at 1 microM MTX (clone 20-1.00), unlike their parental clones, did not show enhanced qAb at 32 degrees C. Thus, it was found that the enhancing effect of low culture temperature on q of rCHO cells depends on clones. Taken together, the results obtained here emphasize the importance of clonal selection for the successful application of low culture temperature to the enhanced foreign protein production in rCHO cells.     

Developmental and environmental regulation of antifreeze proteins in the mealworm beetle Tenebrio molitor.

The yellow mealworm beetle, Tenebrio molitor, contains a family of small Cys-rich and Thr-rich thermal hysteresis proteins that depress the hemolymph freezing point below the melting point by as much as 5. 5 degrees C (DeltaT = thermal hysteresis). Thermal hysteresis protein expression was evaluated throughout development and after exposure to altered environmental conditions. Under favorable growth conditions, small larvae (11-13 mg) had only low levels of thermal hysteresis proteins or thermal hysteresis protein message, but these levels increased 10-fold and 18-fold, respectively, by the final larval instar (> 190 mg), resulting in thermal hysteresis > 3 degrees C. Exposure of small larvae (11-13 mg) to 4 weeks of cold (4 degrees C) caused an approximately 20-fold increase in thermal hysteresis protein concentration, well in excess of the less than threefold developmental increase seen after 4 weeks at 22 degrees C. Exposure of large larvae (100-120 mg) to cold caused 12-fold and sixfold increases in thermal hysteresis protein message and protein levels, respectively, approximately double the maximum levels they would have attained in the final larval instar at 22 degrees C. Thus, thermal hysteresis increased to similar levels (> 4 degrees C) in the cold, irrespective of the size of the larvae (the overwintering stage). At pupation, thermal hysteresis protein message levels decreased > 20-fold and remained low thereafter, but thermal hysteresis activity decreased much more slowly. Exposure to cold did not reverse this decline. Desiccation or starvation of larvae had comparable effects to cold exposure, but surprisingly, short daylength photoperiod or total darkness had no effect on either thermal hysteresis or message levels. As all environmental conditions that caused increased thermal hysteresis also inhibited growth, we postulate that developmental arrest is a primary factor in the regulation of T. molitor thermal hysteresis proteins.     

Regression,proliferation and development of lip papillomas in wild white suckers,Catostomus commersoni,held in the laboratory

Synopsis Epizootics of skin neoplasms in teleost species have been documented within the Great Lakes region over the last decade. The white sucker,Catostomus commersoni, has been proposed as a sentinel species to monitor environmental health in these systems. The prevalence of skin neoplasia is elevated in white suckers and other fish taken from chemically polluted sites or from lake regions adjacent to heavy industry. Lip papillomas regress and proliferate spontaneously in captive wild suckers. It is important to investigate the relevance of these observations to papilloma etiology to determine whether the prevalence of this disease is a suitable biomarker for environmental health. White suckers were captured in the spring of 1992 and 1993 during annual spawning runs (mid to late April) at the Ganaraska River, which discharges into Lake Ontario at Port Hope, Ontario. Under crowded laboratory conditions, there was either proliferation of existing papillomas or development of new papillomas. However, in uncrowded conditions, existing papillomas either regressed completely or there was no development of new papillomas. Protein Kinase C (PKC), a proposed marker enzyme for hyperplasia and neoplasia, was used to determine if regressing and proliferating papillomas could be differentiated on the basis of biochemical activity. PKC activity was lower in proliferating papillomas, but not significantly different from papillomas sampled initially from Ganaraska River suckers. Regressing papillomatous tissue displayed a significantly higher level of enzyme activity than either proliferating or unchanged papillomas, but the PKC activity of regressing papillomas was not significantly different from that of normal lip epidermis.     

Proteomics analysis of major royal jelly protein changes under different storage conditions

Protein changes in fresh royal jelly (RJ) were compared when stored at -20, 4 degrees C, and room temperature (RT) for 12 months. Protein was partially identified using combinations of two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF/MS), gel filtration chromatography, nanoLC MS/MS, and a protein engine identification tool applied to the honeybee genome. Significantly more protein spots were found in fresh (85 spots) and -20 degrees C (81 spots) stored RJ than in samples stored at 4 degrees C (73 spots) and at RT (70 spots) for 1 year. Most identified spots, 56, 57, 51, 46, corresponding to RJ sample of the fresh, -20 degrees C, 4 degrees C, and RT, were assigned to major royal jelly proteins (MRJPs). Marked differences were found in the heterogeneity of the MRJPs, in particular, MRJP3. The quantity of MRJP1 decreased significantly following the temperature trend in all images, but MRJP 2 and -3 did not increase or decrease following the temperature trend, thus, suggesting that MRJP 1-3 are sensitive to temperature. However, MRJP4, 5, glucose oxidase (GOD), peroxiredoxin (PRDX), and glutathione S-transferase (GST) S1 were clearly absent in all images in samples held at RT for 1 year. This indicates that they are the proteins most sensitive to storage temperature and protein markers for freshness of RJ. Combining chromatography and nanoLC MS/MS results, we tentatively conclude that MRJP5 is a reliable freshness marker and that the best way to maintain quality of RJ is under freezing conditions.     

Transgenic overexpression of transforming growth factor alpha bypasses the need for c-Ha-ras mutations in mouse skin tumorigenesis.

The induction of skin papillomas in mice can be divided into two different stages. Chemical initiation frequently elicits mutations in the Ha-ras gene, leading to the constitutive activation of ras. The second step, promotion, involves repetitive topical application of phorbol esters or wounding, leading to epidermal hyperproliferation and papilloma formation. We have found that overexpression of transforming growth factor alpha (TGF-alpha) in the basal epidermal layer of transgenic mice yielded papillomas directly upon wounding or 12-O-tetradecanoylphorbol-13-acetate treatment without the need for an initiator. Moreover, papillomas from TGF-alpha mice did not exhibit mutations in the Ha-ras gene. Interestingly, TGF-alpha acted synergistically with 12-O-tetradecanoylphorbol-13-acetate to enhance epidermal hyperproliferation. Our results demonstrate a central role for TGF-alpha overexpression in tumorigenesis and provide an important animal model for the study of skin tumorigenesis.     

Effects of environmental temperature on life tables of Rhodnius neivai Lent, 1953 (Hemiptera: Reduviidae) under experimental conditions.

Changes in life tables of Rhodnius neivai due to variations of environmental temperature were studied, based on nine cohorts. Three cohorts were kept at 22 degrees C, three at 27 degrees C and three at 32 degrees C. Cohorts were censused daily during nymphal instars and weekly in adults. Nine complete horizontal life tables were built. A high negative correlation between temperature and age at first laying was registered (r=-0,84). Age at maximum reproduction was significantly lower at 32 degrees C. Average number of eggs/female/week and total eggs/female on its life time were significantly lower at 22 degrees C. Total number of egg by cohort and total number of reproductive weeks were significantly higher at 27 degrees C. At 32 degrees C, generational time was significantly lower. At 27 degrees C net reproductive rate and total reproductive value were significantly higher. At 22 degrees C, intrinsic growth, finite growth and finite birth rates were significantly lower. At 22 degrees C, death instantaneous rate was significantly higher.     

Compartmentation and turnover of the low density lipoprotein receptor in skin fibroblasts

The low density lipoprotein receptor (LDLR) was immunoprecipitated from [35S]methionine-labeled skin fibroblasts derivatized at 4 or 18 degrees C with an impermeant biotinylating reagent. Separation of derivatized and underivatized receptor from immunoprecipitates by selective binding to streptavidin-agarose allowed assessment of receptor protein cellular compartmentation and rates of intercompartmental transfer. At both 4 and 18 degrees C the amount of LDLR that is derivatized in cells labeled to near steady state saturates after 1-2 h of reaction at, respectively, 47 and 70% of total immunoprecipitable receptor protein. On the basis of temperature titration experiments, protein exposed only to the cell surface reacts at 4 degrees C; raising the temperature of biotinylation to 18 degrees C provides access to an additional pool of receptor protein. Remaining LDLR is derivatized at 37 degrees C. LDLR unreactive at 18 degrees C largely resides in membrane compartment(s) devoid of plasma membrane on the basis of its fractionation on Percoll gradients. While total cellular LDLR and 4 degrees C-derivatized LDLR labeled to steady state turn over in a first order manner (t1/2 = 12-13 h), the specific activity of pulse-labeled, 4 degrees C-accessible protein peaks after 1-2 h of chase and reaches a reduced level by 3 h of chase. These latter results show that the newly synthesized LDLR is transiently enriched at the cell surface prior to achieving equilibrium distribution between the cell surface and intracellular pools.     

Relationship of critical temperature to macromolecular synthesis and growth yield in Psychrobacter cryopegella

Most microorganisms isolated from low-temperature environments (below 4 degrees C) are eury-, not steno-, psychrophiles. While psychrophiles maximize or maintain growth yield at low temperatures to compensate for low growth rate, the mechanisms involved remain unknown, as does the strategy used by eurypsychrophiles to survive wide ranges of temperatures that include subzero temperatures. Our studies involve the eurypsychrophilic bacterium Psychrobacter cryopegella, which was isolated from a briny water lens within Siberian permafrost, where the temperature is -12 degrees C. P. cryopegella is capable of reproducing from -10 to 28 degrees C, with its maximum growth rate at 22 degrees C. We examined the temperature dependence of growth rate, growth yield, and macromolecular (DNA, RNA, and protein) synthesis rates for P. cryopegella. Below 22 degrees C, the growth of P. cryopegella was separated into two domains at the critical temperature (T(critical) = 4 degrees C). RNA, protein, and DNA synthesis rates decreased exponentially with decreasing temperatures. Only the temperature dependence of the DNA synthesis rate changed at T(critical). When normalized to growth rate, RNA and protein synthesis reached a minimum at T(critical), while DNA synthesis remained constant over the entire temperature range. Growth yield peaked at about T(critical) and declined rapidly as temperature decreased further. Similar to some stenopsychrophiles, P. cryopegella maximized growth yield at low temperatures and did so by streamlining growth processes at T(critical). Identifying the specific processes which result in T(critical) will be vital to understanding both low-temperature growth and growth over a wide range of temperatures.     

Attempts to initiate skin tumours in mice in the 2-stage system using 4-chloromethylbiphenyl (4CMB), 4-hydroxymethylbiphenyl (4HMB), and benzyl chloride (BC). Report of the experiment at 10 months

Groups of T.O. mice (Theiler's Original, derived from Swiss albino mice) were treated topically, with a single dose of 1.0 mg of 4CMB, 4HMB, or BC, or with 0.4 mg benzo[a]pyrene (B[a]P). Twice-weekly promotion of the treated skin area with croton oil was begun 1 week later. At 10 months the skin-tumour incidence in the positive control (B[a]P) was 8/19, with a mean latent period of 20 weeks. Both 4CMB and 4HMB have so far produced 1 papilloma each (1/36 at 40 weeks, and 1/39 at 34 weeks, respectively), while BC has produced none. Further time is required in order to ascertain whether these single papillomas will develop into carcinomas and thereby herald weak initiating activity for 4CMB and 4HMB.     

Perception of foot temperature in young women with cold constitution: analysis of skin temperature and warm and cold sensation thresholds

To examine the disease state of cold constitution, physiological measurements of the foot were conducted by investigating thermal sensations under an environmental condition of 25 degrees C-26 degrees C (neutral temperature) in 29 young women with and without cold constitution. The subjects were classified into 3 groups according to their experiences with cold constitution: cold constitution, intermediate, and normal groups. Foot skin temperature was measured by thermography. Thermal sensations were measured on the dorsum of the left foot using a thermal stimulator. Cold and warm spots on the dorsum of the right foot were ascertained. Thermal stimulation was delivered by a copper probe. No significant differences in foot skin temperature among these 3 groups were identified as measured in a laboratory under neutral temperature conditions. However, the mean warm sensation threshold was +6.3+/-1.09 degrees C (mean+/-SEM) for the cold constitution group (n=14), +3.4+/-2.10 degrees C (mean+/-SEM) for the intermediate group (n=7), and -0.25+/-1.96 degrees C (mean+/-SEM) for the normal group (n=6). The difference was significant between the cold constitution and normal groups. No significant differences among the 3 groups were found in the cold sensation threshold. This may be attributable to the distribution of thermal receptors and to chronically reduced blood flow in subcutaneous tissues, where the skin temperature receptors responsible for temperature sensation are located.     

Temperature-Sensitive Cell Division Mutants of Escherichia coli with Thermolabile Penicillin-Binding Proteins

The thermostability of the penicillin-binding proteins (PBPs) of 31 temperature-sensitive cell division mutants of Escherichia coli has been examined. Two independent cell division mutants have been found that have highly thermolabile PBP3. Binding of [(14)C]benzylpenicillin to PBP3 (measured in envelopes prepared from cells grown at the permissive temperature) was about 30% of the normal level at 30 degrees C, and the ability to bind [(14)C]benzylpenicillin was rapidly lost on incubation at 42 degrees C. The other PBPs were normal in both mutants. At 30 degrees C both mutants were slightly longer than their parents and on shifting to 42 degrees C they ceased dividing, but cell mass and deoxyribonucleic acid synthesis continued and long filaments were formed. At 42 degrees C division slowly recommenced, but at 44 degrees C this did not occur. The inhibition of division at 42 degrees C was suppressed by 0.35 M sucrose, and in one of the mutants it was partially suppressed by 10 mM MgCl(2). PBP3 was not stabilized in vitro at 42 degrees C by these concentrations of sucrose or MgCl(2). Revertants that grew as normal rods at 42 degrees C regained both the normal level and the normal thermostability of PBP3. The results provide extremely strong evidence that the inactivation of PBP3 at 42 degrees C in the mutants is the cause of the inhibition of cell division at this temperature and identify PBP3 as an essential component of the process of cell division in E. coli. It is the inactivation of this protein by penicillins and cephalosporins that results in the inhibition of division characteristic of low concentrations of many of these antibiotics.     

Monitoring of temperature effects on animal cell metabolism in a packed bed process

Animal cell (Chinese Hamster Ovary) concentration was determined on-line in a packed bed process using dielectric spectroscopy. This enabled the evaluation of the effect of temperature on specific metabolic rates during 3 months of continuous culture. The effect of low cultivation temperature on cell growth and metabolism was monitored, and the data were used for process development. At 37 degrees C cells grew exponentially with a specific growth rate of 0.038 d-1 and specific glucose uptake and lactate production rates increased continually. Reduction of the temperature to 33.5 degrees C resulted in a lowering of these metabolic rates while having no effect on cell proliferation. Subsequent reduction of the temperature to 32 degrees C resulted in stabilization of the cell concentration at a high density (3.6 x 10(7) cell per mL of packed bed). In addition, the specific production rate of the protein of interest increased by a factor of 6 compared to the value at 37 degrees C. During the stationary phase at 32 degrees C, all other specific metabolic rates could be controlled to low and constant levels.     

Neem (Azadirachta indica) seed kernel powder retards urease and nitrification activities in different soils at contrasting moisture and temperature regimes

A laboratory experiment was conducted to examine the potentiality of a natural resource neem (Azadirachta indica) seed kernel powder (NSKP) to reduce the urease and nitrification activities in different soils (viz., normal, acid, and sodic) at contrasting moisture (1:1 soil to water and field capacity) and temperature regimes (10 degrees C and 37 degrees C). Results have revealed that application of NSKP with urea did not exhibit any urease inhibitory property in normal and sodic soils, but in acid soil it had maintained higher concentration of urea than the urea alone treated samples for two weeks after application. At 37 degrees C and under field capacity moisture level, urea hydrolysis was more rapid than at 10 degrees C and under waterlogged (1:1) conditions. The NSKP has showed variable effects (4-28%) to inhibit nitrification during 7-21 days after application, depending upon the soil types, temperature and moisture regimes. The nitrification activity was significantly low in acid soil followed by normal and sodic soils. The present study suggests that NSKP has the potential to retard the urease activity in acid soil, and nitrification in all the soils, and thus it may be used along with urea for the better use of applied -N.     

Proline hydroxylation of collagens synthesized at different temperatures in vivo by two poikilothermic species

Extent of prolyl hydroxylation in newly synthesized viper collagen is decreased at 10 degrees C to approximately 23% of normal on skin and to approximately 57% of normal in bone collagen. At 20 degrees C, prolyl hydroxylation is approximately 50% of normal in skin and normal in bone. At 10 degrees C and 20 degrees C, prolyl hydroxylation is decreased approximately 32% in the skin collagen of carp. In contrast, prolyl hydroxylation is unchanged at 10 and 20 degrees C in bone, scale and lepidotrichia. Prolyl hydroxylation of cartilaginous endoskeleton showed an approximately 25% decrease at 20 degrees C.     

Effect of early cold stress on the maturation of rice anthers

Male reproductive development in rice (Oryza sativa Linnaeus is very sensitive to various forms of environmental stresses including low temperature. Here, we present our findings on the proteomic analysis of the later developmental consequences of low temperature treatment on rice anthers. Anther proteins at the trinucleate stage, with or without cold treatment for four days at 12 degrees C at the young microspore stage, were extracted, separated by two-dimensional gel electrophoresis (2-DE) and compared. More than 3000 rice anther proteins of cold-sensitive cultivar Doongara plants at the trinucleate stage were resolved on 2-DE gels over a pH range of 4-7 and detected by silver-staining. Seventy protein spots were differentially displayed after four days of cold treatment at the young microspore stage. Of these, 12 protein spots were newly-induced, 47 were up-regulated, and 11 were down-regulated by cold treatment at the early microspore stage. We identified 18 by matrix-assisted laser desorption/ionization mass spectrometry time of flight (MALDI-TOF) analysis. Of the identified proteins, seven were observed as breakdown (cleavage) products by a combination of 2-DE and MALDI-TOF analysis, thus demonstrating for the first time that cold temperature stress at the young microspore stage enhances and induces partial degradation of proteins in the rice anthers at the trinucleate stage.     

Influence of temperature on growth rate and competition between two psychrotolerant Antarctic bacteria: low temperature diminishes affinity for substrate uptake.

The growth kinetics of two psychrotolerant Antarctic bacteria, Hydrogenophaga pseudoflava CR3/2/10 (2/10) and Brevibacterium sp. strain CR3/1/15 (1/15), were examined over a range of temperatures in both batch culture and glycerol-limited chemostat cultures. The maximum specific growth rate (mu max) and Ks values for both bacteria were functions of temperature, although the cell yields were relatively constant with respect to temperature. The mu max values of both strains increased up to an optimum temperature, 24 degrees C for 2/10 and 20 degrees C for 1/15. Strain 1/15 might therefore be considered to be more psychrophilic than strain 2/10. For both bacteria, the specific affinity (mu max/Ks) for glycerol uptake was lower at 2 than at 16 degrees C, indicating a greater tendency to substrate limitation at low temperature. As the temperature increased from 2 to 16 degrees C, the specific affinity of 1/15 for glycerol increased more rapidly than it did for 2/10. Thus 1/15, on the basis of this criterion, was less psychrophilic than was 2/10. The steady-state growth kinetics of the two strains at 2 and 16 degrees C imply that 1/15 would be able to outgrow 2/10 only at relatively low substrate concentrations (< 0.32 g of glycerol.liter-1) and high temperatures (> 12 degrees C), which suggests that 1/15 has a less psychrotolerant survival strategy than does 2/10. Our data were compared with other data in the literature for bacteria growing at low temperatures. They also showed an increase of substrate-specific affinity with increasing temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Low temperature limits photoperiod control of smolting in atlantic salmon through endocrine mechanisms

We have examined the interaction of photoperiod and temperature in regulating the parr-smolt transformation and its endocrine control. Atlantic salmon juveniles were reared at a constant temperature of 10 degrees C or ambient temperature (2 degrees C from January to April followed by seasonal increase) under simulated natural day length. At 10 degrees C, an increase in day length [16 h of light and 8 h of darkness (LD 16:8)] in February accelerated increases in gill Na(+)-K(+)-ATPase activity, whereas fish at ambient temperature did not respond to increased day length. Increases in gill Na(+)-K(+)-ATPase activity under both photoperiods occurred later at ambient temperature than at 10 degrees C. Plasma growth hormone (GH), insulin-like growth factor, and thyroxine increased within 7 days of increased day length at 10 degrees C and remained elevated for 5-9 wk; the same photoperiod treatment at 2 degrees C resulted in much smaller increases of shorter duration. Plasma cortisol increased transiently 3 and 5 wk after LD 16:8 at 10 degrees C and ambient temperature, respectively. Plasma thyroxine was consistently higher at ambient temperature than at 10 degrees C. Plasma triiodothyronine was initially higher at 10 degrees C than at ambient temperature, and there was no response to LD 16:8 under either temperature regimen. There was a strong correlation between gill Na(+)-K(+)-ATPase activity and plasma GH; correlations were weaker with other hormones. The results provide evidence that low temperature limits the physiological response to increased day length and that GH, insulin-like growth factor I, cortisol, and thyroid hormones mediate the environmental control of the parr-smolt transformation.