Acclimatory Changes Research Articles

Clonal variation in morphological and physiological responses to irradiance and photoperiod for the aquatic angiosperm Potamogeton pectinatus

Summary Widely distributed plants are exposed to contrasting gradients in irradiance and photoperiod across latitude. We investigated the relative contribution of local specialization and phenotypic plasticity to variation in plant growth for three clones of the aquatic angiosperm Potamogeton pectinatus L., originating from 42.5 to 68° N. Plants were grown at a factorial combination of two irradiances (50 and 350 µmol m−2 s−1) and three photoperiods (13, 16 and 22 h) and morphology, gas‐exchange rate and biomass accumulation were recorded. The overall response to variation in irradiance and photoperiod was similar for all three clones. Differences in irradiance resulted in strong acclimative changes in morphological and physiological characteristics. At low irradiance, pronounced vertical shoot extension compensated for the limited plasticity in leaf area production, while photosynthetic capacity, apparent quantum yield and total chlorophyll concentration increased. As a result, biomass yield at the end of the experimental period was similar in both treatments. A decrease in photoperiod also resulted in plastic changes in morphology (increase of leaf biomass per unit plant biomass) and physiology (increase of photosynthetic capacity). However, these acclimative responses did not fully compensate for differences in photoperiod, since biomass was significantly lower under 13 and 16 h photoperiods than at 22 h. P. pectinatus is therefore phenotypically plastic, rather than locally specialized to differences in irradiance and photoperiod.

INTERPRETING REJECTIONS OF THE BENEFICIAL ACCLIMATION HYPOTHESIS: WHEN IS PHYSIOLOGICAL PLASTICITY ADAPTIVE?

Although many studies testing the beneficial acclimation hypothesis have rejected it, what these rejections imply about the adaptive value of physiological change remains unclear. Uncertainty arises because the hypothesis focuses on the relative performance of organisms exposed to one environment versus another, whereas the raw material available to evolution is variation in acclimation responses of individual traits. This mismatch is problematic when organisms are exposed to poor environments. In poor environments, the adaptive or maladaptive value of changes in individual traits may be obscured by long-term decrements in organismal condition. A better match between the evolutionary pressures shaping acclimation and the tests used to examine them can be achieved by focusing on the fitness consequences of acclimation changes in individual traits.

INTERPRETING REJECTIONS OF THE BENEFICIAL ACCLIMATION HYPOTHESIS: WHEN IS PHYSIOLOGICAL PLASTICITY ADAPTIVE?

Although many studies testing the beneficial acclimation hypothesis have rejected it, what these rejections imply about the adaptive value of physiological change remains unclear. Uncertainty arises because the hypothesis focuses on the relative performance of organisms exposed to one environment versus another, whereas the raw material available to evolution is variation in acclimation responses of individual traits. This mismatch is problematic when organisms are exposed to poor environments. In poor environments, the adaptive or maladaptive value of changes in individual traits may be obscured by long-term decrements in organismal condition. A better match between the evolutionary pressures shaping acclimation and the tests used to examine them can be achieved by focusing on the fitness consequences of acclimation changes in individual traits.

Developmental and acclimatory contributions to water loss in a desert rodent: investigating the time course of adaptive change.

Understanding the evolution of physiological traits requires considering three nonexclusive mechanisms that underlie phenotypes and cause their change over different time scales: acclimation, developmental plasticity, and natural selection for genetically fixed traits. Physiological adjustments to changes in the desiccating potential of the environment were investigated with one subspecies of common desert rodent, Dipodomys merriami merriami (Merriam's kangaroo rat). We raised young whose parents originated from environments that differ in both temperature and humidity. These young were raised under either desiccating or water-abundant conditions, and their water loss was measured at a series of temperatures to determine the effect developmental conditions have on resistance to desiccation. We then determined the contribution of acclimation to desiccation resistance by keeping the differentially raised young in conditions opposite to those during their development and again measuring water loss. We found that developmental plasticity and acclimation can completely account for the existing intraspecific variability in desiccation resistance under certain conditions. In fact, developmental and acclimatory changes can equal genetically based differences of the populations. This phenotypic plasticity can operate relatively quickly and therefore may attenuate the actions of natural selection. Understanding the extent and nature of such flexibility is critical to our understanding intraspecific variability and the consequences of changing climate.

Acclimative changes in root epidermal cell fate in response to Fe and P deficiency: a specific role for auxin?

Root hair formation and the development of transfer cells in the rhizodermis was investigated in various existing auxin-related mutants of Arabidopsis thaliana and in the tomato mutant diageotropica. Wild-type Arabidopsis plants showed increased formation of root hairs when the seedlings were cultivated in Fe- or P-free medium. These extranumerary hairs were located in normal positions and in positions normally occupied by nonhair cells, e.g., over periclinal walls of underlying cortical cells. Defects in auxin transport or reduced auxin sensitivity inhibited the formation of root hairs in response to Fe deficiency completely but did only partly affect initiation and elongation of hairs in P-deficient roots. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid or the auxin analog 2,4-dichlorophenoxyacetic acid did not rescue the phenotype of the auxin-resistant axr2 mutant under control and Fe-deficient conditions, indicating that functional AXR2 product is required for translating the Fe deficiency signal into the formation of extra hairs. The development of extra hairs in axr2 roots under P-replete conditions was not affected by auxin antagonists, suggesting that this process is independent of auxin signaling. In roots of tomato, growth under Fe-deficient conditions induced the formation of transfer cells in the root epidermis. Transfer cell frequency was enhanced by application of 2,4-dichlorophenoxyacetic acid but was not inhibited by the auxin transport inhibitor N-1-naphthylphthalamic acid. In the diageotropica mutant, which displays reduced sensitivity to auxin, transfer cells appeared to develop in both Fe-sufficient and Fe-deficient roots. Similar to the wild type, no reduction in transfer cell frequency was observed after application of the above auxin transport inhibitor. These data suggest that auxin has no primary function in inducing transfer cell development; the formation of transfer cells, however, appears to be affected by the hormonal balance of the plants.

Thermal acclimation of locomotor performance in tadpoles of the frog Limnodynastes peronii.

Previous analyses of thermal acclimation of locomotor performance in amphibians have only examined the adult life history stage and indicate that the locomotor system is unable to undergo acclimatory changes to temperature. In this study, we examined the ability of tadpoles of the striped marsh frog (Limnodynastes peronii) to acclimate their locomotor system by exposing them to either 10 degrees C or 24 degrees C for 6 weeks and testing their burst swimming performance at 10, 24, and 34 degrees C. At the test temperature of 10 degrees C, maximum velocity (Umax) of the 10 degrees C-acclimated tadpoles was 47% greater and maximum acceleration (Amax) 53% greater than the 24 degrees C-acclimated animals. At 24 degrees C, Umax was 16% greater in the 10 degrees C-acclimation group, while there was no significant difference in Amax or the time taken to reach Umax (T-Umax). At 34 degrees C, there was no difference between the acclimation groups in either Umax or Amax, however T-Umax was 36% faster in the 24 degrees C-acclimation group. This is the first study to report an amphibian (larva or adult) possessing the capacity to compensate for cool temperatures by thermal acclimation of locomotor performance. To determine whether acclimation period affected the magnitude of the acclimatory response, we also acclimated tadpoles of L. peronii to 10 degrees C for 8 months and compared their swimming performance with tadpoles acclimated to 10 degrees C for 6 weeks. At the test temperatures of 24 degrees C and 34 degrees C, Umax and Amax were significantly slower in the tadpoles acclimated to 10 degrees C for 8 months. At 10 degrees C, T-Umax was 40% faster in the 8-month group, while there were no differences in either Umax or Amax. Although locomotor performance was enhanced at 10 degrees C by a longer acclimation period, this was at the expense of performance at higher temperatures.

Heat acclimation increases the basal HSP72 level and alters its production dynamics during heat stress.

It has been previously shown that heat acclimation leads to an elevated basal level of 72-kDa heat shock protein (HSP72). Augmented expression of HSP72 is considered as a cytoprotective response. This led us to hypothesize that alterations in the heat shock protein (HSP) defense pathway are an integral part of the heat acclimation repertoire. To investigate this, we studied the temporal profile of basal HSP expression upon acclimation and the dynamics of their accumulation subsequent to acute heat stress (HS). In parallel, HSP72 mRNA level before and after HS was measured. For comparison, HSC mRNA [the constitutive member of 70-kDa HSP (HSP70) family] was measured in similar conditions. Heat acclimation was attained by continuous exposure of rats to 34 degrees C for 0, 1, 2, and 30 days. HS was attained by exposure to 41 or 43 degrees C for 2 h. Thermoregulatory capacity of the rats was defined by rectal temperature, heating rate, and the cumulative heat strain invoked during HS. HSP72 and HSP70 gene transcripts were measured in the left ventricle of the heart by means of Western immunoblotting and semiquantitative RT-PCR, respectively. The resultant acclimatory change comprised a higher resting level of the encoded 72-kDa protein (Delta175%, P < 0.0001). After HS, peak HSP72 mRNA level was attained, 40 and 20 min post-HS at 41 and 43 degrees C, respectively, vs. 60 and 40 min in the nonacclimated group. The subsequent HSP synthesis, however, was dependent on the severity of the cumulative heat strain. At the initial phase of heat acclimation, augmented HSP72 transcription unaccompanied by HSP synthesis was observed. It is concluded that upon heat acclimation, the HSP defense pathway is predisposed to a faster response. At the initial phases of heat acclimation, inability to elevate the HSP cytosolic level rules out their direct cytoprotective role.

Light-induced and osmotically-induced changes in chlorophyll a fluorescence in two Synechocystis sp. PCC 6803 strains that differ in membrane lipid unsaturation

Membranes of wild-type (WT) cells of the cyanobacterium Synechocystis sp. PCC 6803 are abundant in polyunsaturated fatty acids in membrane lipids and thus more fluid than membranes of desA-/desD- mutant cells which contain no polyunsaturated fatty acids. Using intact cells we examined the effects of normal and chilling temperatures on membrane fluidity-dependent properties. We probed the thylakoid membranes by inducing light/dark acclimative changes in chlorophyll a (Chl a) fluorescence; and we probed the plasma membranes either by suppressing the Chl a fluorescence of light-acclimated cells under hyper-osmotic conditions, or by measuring the electric conductivity of cell suspensions. Thylakoid membranes of mutant cells undergo reversible thermotropic transition between 19 °C and 22 °C (midpoint at 20.5 °C). No analogous transition was detected in the thylakoid membranes of WT cells in the temperature range from 2 to 34 °C. Plasma me mbranes of both WT and mutant cells did not experience thermotropic transition in the temperature range from 2 °C to 34 °C as detected either fluorimetrically or by means of electric conductivity. Hyper-osmotic conditions caused fast transient fluorescence quenching in WT cells at 34 °C, but not at 14 °C, and not in mutant cells at either 34 °C or 14 °C. This transient quenching sensed probably the higher fluidity of the plasma membranes of WT cells. Hyper-osmotic media and dark acclimation had similar effects on the 77 K fluorescence of Synechocystis cells: they suppressed the ratio of photosystem II fluorescence to photosystem I fluorescence.

Influence of Prenatal and Postnatal Acclimation on Nervous and Peripheral Thermoregulationa

The aim of the present study was to investigate whether prenatal and postnatal adaptation to different ambient temperatures affects the autonomic (heat production, heat loss, rectal or colonic temperature), behavioral (preferred ambient temperature) and nervous mechanisms (neuronal thermosensitivity of the preoptical area of the anterior hypothalamus) of thermoregulation. The experiments were carried out in postnatal, differently acclimated adult rabbits (60 days at 6-7, 20 and 30 degrees C) and adult rats (3 to 6 weeks at 5 and 21 degrees C) and in differently incubated 1- to 10-day-old Muscovy ducklings and turkeys (last week of incubation at 34.5, 37.5 and 38.5 degrees C). The results of the experiments are summarized as follows: (1) Postnatal acclimation changes the threshold ambient temperature of heat loss and heat production. For example, cold-acclimated rabbits have a lower threshold temperature for evaporative heat loss and thermoregulatory heat production than heat-acclimated ones. (2) Prenatal acclimation changes postnatal thermoregulatory behavior as well as autonomic thermoregulatory mechanisms. Birds incubated at higher (38.5 degrees C) or lower (34.5 degrees C) temperatures than the usual 37.5 degrees C for the last week of embryonic development have higher or lower preferred ambient temperatures during the first 10 days post hatching. Besides this, cold-incubated birds have a higher heat/ production and clonic temperature in the first days post hatching than normally/ incubated or heat-incubated ones. (3) Extracellular recordings from hypothalamic neurons in brain slices from differently acclimated rats have shown that adaptation to different ambient temperatures changes firstly the temperature sensitivity of the hypothalamic neurons and secondly the modulatory action of the neuropeptides bombesin and thyrotropin releasing hormone.

Acclimation of leaf carotenoid composition and ascorbate levels to gradients in the light environment within an Australian rainforest

ABSTRACTThe influence of the growth photon flux density (PFD) on the size and composition of the carotenoid pool and the size of the reduced ascorbate pool was determined across a light gradient from the forest floor to the canopy and the forest edge of a sub‐tropical rainforest in New South Wales, Australia. Nineteen plant species (most collected from multiple sites) representing a broad taxonomic range consistently possessed larger total carotenoid pools when found growing in more exposed sites. There was a significant positive correlation between β‐carotene content and growth PFD and a significant negative correlation between α‐carotene content and growth PFD. Neoxanthin content exhibited no significant trend while the trend in lutein content varied with mode of expression. The pigments of the xanthophyll cycle (violaxanthin, antheraxanthin and zeaxanthin) exhibited the most pronounced response to growth PFD; they comprised a much greater portion of the total carotenoid pool in high light‐acclimated plants. The pool of reduced ascorbate was also several‐fold greater in high light‐acclimated plants. These acclimatory changes in carotenoid and ascorbate content are consistent with a need for a greater capacity to dissipate excessive absorbed light energy in high light‐acclimated plants.

Hypoosmotic stimulation of ornithine decarboxylase activity in the brine shrimpArtemia franciscana

In the brine shrimp, long-term (several days) osmotic and ionic regulation is controlled principally by the activity of Na+K+ATPase. However, short-term cell volume regulation in Artemia and most euryhaline crustaceans is not understood. In this study, Artemia stage 1 nauplii reared at 32 ppt salinity and exposed to hypoosmotic conditions (12 or 4 ppt) exhibited an immediate increase in the activity of ornithine decarboxylase, the rate-limiting enzyme in polyamine synthesis. ODC activity increased within 15 min relative to control and reached a peak within 2 hr of hypoosmotic exposure. The level of increased enzyme activity was directly related to the degree of hypoosmotic exposure (a three- and sevenfold increase in activity at 12 and 4 ppt salinity, respectively). This increase in activity was apparently due to the synthesis of a new enzyme, based on cycloheximide administration. Activity decreased significantly by 4 hr but remained above that of the 32 ppt control throughout the 24-hr exposure period. Levels of putrescine increased significantly within 2 hr in organisms exposed to 4 ppt; spermidine and spermine levels were not affected. When nauplii were exposed to altered ion and/or osmotic concentrations it was determined that decreased total osmotic concentration was the proximate factor responsible for ODC induction. However, reduced ion concentration resulted in the induction/activation of DFMO-insensitive ODC activity, suggesting the production of a novel enzyme in polyamine metabolism during hypotonic exposure. Changes in ODC activity and polyamines preceded acclimatory changes normally associated with salinity acclimation, further suggesting that modulation of ODC activity and subsequent polyamines synthesis, degradation, and/or transport are mechanistically related to short-term regulation of osmotic and ionic balance. © 1996 Wiley-Liss, Inc.

Effects of free‐air CO2 enrichment on the development of the photosynthetic apparatus in wheat, as indicated by changes in leaf proteins

ABSTRACTA spring wheat crop was grown at ambient and elevated (550 μmol mol−1) CO2 concentrations under free‐air CO2 enrichment (FACE) in the field. Four experimental blocks, each comprising 21‐m‐diameter FACE and control experimental areas, were used. CO2 elevation was maintained day and night from crop emergence to final grain harvest. This experiment provided a unique opportunity to examine the hypothesis that CO2 elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and lo assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age. Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS‐PAGE. For leaves at completion of emergence of the blade, growth at the elevated CO2 concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined. Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3–4 further leaves formed above with continued development of the crop. By 35 d following completion of blade emergence, leaf 5 was in shade. At this point, the chlorophyll alb ratio had declined by 26% both in plants grown at the control CO2 concentration and in those grown at the elevated CO2 concentration, which is indicative of shade acclimation. The ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO2 concentration. The light‐ harvesting complex of photosystcm II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag‐leaf blade, the elevated‐CO2 treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d. From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated‐CO2 treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%. At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2 concentration treatment relative to the control. By 52 d, all of these proteins showed a significant decline relative to the control. This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated‐CO2 treatment, but that this was preceded by a CO2‐concentration‐dependent decline in Rubisco.

Nutrient-limited growth rates: quantitative benefits of stress responses and some aspects of regulation

Young sunflower plants (Helianthus annuus L.) under stress of low nitrate or phosphate availability exhibited increases in root: shoot ratio and in kinetic parameters for uptake. They showed no significant changes in photosynthetic utilization of either nutrient. Increases in root: shoot ratio were achieved by early and persistent suppression of shoot growth, but not root growth. Affinity for phosphate uptake, 1/K m (P), increased with phosphate stress, as did affinity for nitrate uptake, 1/K m (N), with nitrate stress. Maximal uptake rate, V maX , for phosphate uptake increased with phosphorus stress; V maX for nitrate did not increase with nitrogen stress. Phosphate V maX was related strongly to root nutrient status. Decreases in V maX with plant age were not well explained by changes in age structure of roots. Estimated benefits of acclimatory changes in root: shoot ratio and uptake kinetics ranged up to 2-fold increases in relative growth rate, RGR. The relation of RGR to uptake physiology followed predictions of functional balance moderately well, with some systematic deviations. Analyses of RGR using growth models imply no significant growth benefit from regulating V maX , specifically, not from down-regulating it at high nutrient availability. Quantitative benefits of increases in root:shoot ratio and uptake parameters are predicted to be quite small under common conditions wherein nutrient concentrations are significantly depleted by uptake. The root: shoot response is estimated to confer the smallest benefit under non-depleting conditions and the largest benefit under depleting conditions. Even then, the absolute benefit is predicted to be small, possibly excepting the case of heterogeneous soils. Depleting and non-depleting conditions are addressed with very different experimental techniques. We note that a theoretical framework is lacking that spans both these cases, other than purely numerical formulations that are not readily interpreted.

Changes in smooth muscle contractility of rainbow trout (Oncorhynchus mykiss Walbaum) intestine during acclimation to altered temperature

The effects of altered water temperature in vivo on in vitro smooth muscle contractility of rainbow trout intestine were investigated. Temperature has a significant effect on receptor-mediated intestinal smooth muscle contractility in the rainbow trout. The efficacy of 5-HT, carbachol, and transmural stimulation increased with temperatures above 10°C, with an optimal increase at 15°C. There was also a modest increase in the potency of 5-HT and carbachol within 2 days of establishing trout at 20°C. By day 8, most of these changes had either stabilized or were returning to control values, suggesting that acclimation changes in membranes and enzyme activities were taking effect. However, the contractile responses to carbachol and transmural stimulation were still increasing at this time. This may imply that the muscarinic receptors are more resistant to membrane acclimation changes and may take longer to adapt. Because these experiments were controlled for handling stress and seasonal changes that affect contractility, we have been able to demonstrate some early changes in smooth muscle contractility that occur during acclimation to altered temperature.

Influence of environmental conditions on the ovarian cycle and serum chemistry of Cyprinus carpio in the Dal lake, Kashmir (India)

SUMMARY 1. The study presents adaptive and acclimatory changes observed in Cyprinus carpio communis L with respect to ovarian cycle and serum levels of electrolytes, calcium, total proteins and albumin as a consequence of wide temperature and sunshine variation in the natural environment of Dal lake in Srinagar, Kashmir (India).2. The atmospheric temperatures in Srinagar show well‐defined seasonal and diurnal variations. During the period of study, the mean monthly average temperature in summer (June‐August) was 24°C whereas in winter (December‐February) it fell to 3.6°C. The total hours of sunshine during the winter months were about half of those found in summer.3. Under local thermal and photo conditions the fish was found to spawn once a year compared to biannual spawning in tropical chmates.4. A significant decrease was found in serum sodium, potassium and chloride concentrations during the months of January and February when the mean minimum atmospheric temperatures reached −2.5°C and −l.2°C respectively.5. The serum calcium levels showed a marked increase during the period corresponding to ovarian maturity and spawning of fish.6. A significant rise in total serum protein concentration was induced by decreased environmental temperatures. Serum albumin levels were found to exhibit a sharp fall coinciding with the spawning period.

The effects of acclimation and post-treatment temperature on the toxicity of allethrin to the american cockroach, periplaneta americana

1. The effects of pre- and post-treatment temperatures on the toxicity of allethrin (a synthetic pyrethroid) to the American cockroach were investigated. 2. The toxicity of allethrin was negatively correlated with acclimation (pre-treatment) and posttreatment temperature. 3. The slope of the dose-response curve for allethrin increased with acclimation temperature, but not with post-treatment temperature. 4. Possible acclimative changes that could account for the differences in toxicity are discussed, including degree of saturation of the lipids at or near the target site of allethrin.

Plasma opioid peptide responses during heat acclimation in humans

Plasma β-endorphin, Met-enkephalin and Peptide F immunoreactivity (ir) were measured at rest and following exercise on three days (days 1, 4, 8) of an eight day heat acclimation regime. Fourteen male subjects demonstrated physiological heat acclimation adaptations. Our data demonstrated a differential response of peripheral plasma levels of endogenous opioid peptides (EOP) to exercise in the heat. In addition, EOP did not follow the same time-course of other physiological adaptations as no differences (day 1 vs. 4 vs. 8) in resting or exercise levels were observed over the eight day heat acclimation regime. Significant increases in β-endorphin ir (pre- to post-exercise) appear to reflect concomitant exercise-heat related changes. The increased peripheral levels of β-endorphin were correlated to plasma levels of cortisol. Heat and exercise stress may result in a reduction of Met-enkephalin ir observed in peripheral plasma and might be due to degradation or a decrease in processing from the larger precursors. The differential responses of EOP suggest the possibility of separate physiological roles for these peptides during exercise in the heat but peripheral plasma levels of EOP do not appear to reflect acute heat acclimation changes.

Salinity Acclimation and Intestinal Salt Transport in the Flounder: the Role of the Basolateral Cell Membrane

ABSTRACT Intestinal absorption of Na+ and Cl−, measured using bidirectional tracer fluxes, is higher in saltwater (SW)-acclimated flounders than in freshwater (FW)-acclimated ones. Removal of the selective permeability of the apical cell membrane by application of amphotericin B to the mucosal solution enhances the difference in Na+ transport, whilst the difference in Cl− absorption is lost. Transepithelial resistance and were similar between the two groups of fish, whilst , was always greatest in SW-acclimated tissues, even after mucosal application of amphotericin. Analysis of the present results and previous work suggests that the principal acclimatory changes following salt adaptation occur in the basolateral cell membrane, and that both the Na+,K+-ATPase activity and the basolateral cell membrane permeability to Cl− are increased in the SW-acclimated tissues.

Muscle Protein Synthesis Rates During Temperature Acclimation in a Eurythermal (Cyprinus Carpio) and a Stenothermal (Salmo Gairdneri) Species of Teleost

ABSTRACT Rates of protein synthesis were measured in the white myotomal muscle of carp (Cyprinus carpio) and rainbow trout (Salmo gairdneri) at a number of environmental temperatures before and after they had spent an acclimatory period at these temperatures. For carp previously kept at a mid-range temperature of 15 °C the rates of muscle protein synthesis showed a Q10 of 3·07 over the range of 10–25 °C. Acclimation to low temperatures resulted in the rate of protein synthesis being elevated whilst acclimation to high temperatures resulted in the depression of protein synthesis rate. Rainbow trout also initially maintained at 15 °C showed an initial Q10 of 3·57 between 5 and 20 °C. In this species, however, there was no significant difference in protein synthesis rates after being kept for 1 month at any given temperature within this temperature range. In the carp where acclimatory changes were recorded, it was found that these changes occurred at a faster rate at 25 °C than at 10°C. The ability of the carp to modify its protein metabolism in this way is discussed as a strategy for reducing temperature effects upon growth and muscle function.

Thermal Acclimation of Oxygen Consumption and Cardiorespiratory Frequencies in Frog Larvae

Tadpoles of the frog Xenopus laevis underwent significant thermal acclimation of the rate of oxygen consumption. Acclimation to cool temperatures increased the rate of oxygen consumption at cool temperatures; the Q10 of oxygen consumption between 16 C and 33 C was 1.36. Acclimatory changes in the lung ventilatory frequency, buccopharyngeal ventilatory frequency, and the heart rate were evident at some (but not all) experimental temperatures and corresponded poorly to acclimatory changes in rates of oxygen consumption. Tadpoles of Rana berlandieri showed similar changes in oxygen consumption after thermal acclimation. According to an earlier study, tadpoles of Rana pipiens also exhibit metabolic acclimation at certain temperatures. These results suggest that lack of acclimatory ability in some frog larvae is associated neither with the aquatic habits of tadpoles nor with immaturity of the tadpole stage.