Temperature-dependent impact of 24-epibrassinolide on the fatty acid composition and sugar content in winter oilseed rape callus

The aim of this experiment was to study the effect of 24-epibrassinolide (BR₂₇) on fatty acids composition and sugar content in winter oilseed rape callus cultured at 20 and 5°C. Studies have showed that BR₂₇ action is highly temperature-dependent. The increase in sugar content (sucrose, glucose and fructose) by BR₂₇ in concentration 100 nM was observed only in calli cultured at 20°C. At 5°C, quite the opposite effect of BR₂₇ action was observed; where cold increased the sugar content, BR₂₇ decreased it. BR₂₇ at 20°C had a similar effect on the fatty acid composition of phospholipids (PL) as the cold in the process of frost hardening of oilseed rape calli. BR₂₇ decreased the 16:0, 18:1 and 18:2 and increased the 18:3 fatty acid content. At 5°C, BR₂₇ (100 nM) generally did not influence the fatty acid composition of PL. In case of digalactosyl diacylglycerols and monogalactosyl diacylglycerols, the influence of BR₂₇ on the fatty acid composition is ambiguous but still depends on temperature.     

Effects of low temperature on growth and non-structural carbohydrates of the imperial bromeliad <Emphasis Type="Italic">Alcantarea imperialis</Emphasis> cultured in vitro

The imperial bromeliad Alcantarea imperialis grows naturally on rocky outcrops (‘inselbergs’) in regions where daily temperatures vary from 5 to 40°C. As carbohydrate metabolism is altered in response to cold, it could lead to reprogramming of the metabolic machinery including the increase in levels of metabolites that function as osmolytes, compatible solutes, or energy sources in order to maintain plant homeostasis. The aim of this study was to evaluate the effects of different temperatures on plant growth and non-structural carbohydrates in plants of A. imperialis adapted to low temperature. Seedlings of A. imperialis were grown in vitro under a 12-h photoperiod with four different day/night temperature cycles: 5/5°C, 15/15°C, 15/30°C (dark/light) and 30/30°C. Plants were also cultivated at 26°C in ex vitro conditions for comparison. The results showed an inverse relationship between temperature and germination time and no differences in the percentage of germination. Plants maintained for 9 months at 15°C presented a reduced number of leaves and roots, and a dry mass four times lower than plants grown at 30°C. Sugar content was higher in plants grown at 15°C than at 30°C. However, the highest amount of total sugar was found in plants growing under warm day/cold night conditions. Myo-inositol, glucose, fructose and sucrose were found predominantly under high temperatures, while under low temperatures, sucrose was apparently replaced by trehalose, raffinose and stachyose. Starch content was highest in plants grown under high temperatures. The lowest starch content was detected under low temperatures, suggesting its conversion into soluble carbohydrates to protect the plants against cold. These results indicated that low temperature retarded growth of A. imperialis and increased sugar levels, mainly trehalose, thus suggesting that these sugar compounds could be involved in cold tolerance.     

Interaction of Growth Retardants and Temperature in Growth, Flowering, Regeneration, and Auxin Activity of Begonia × cheimantha Everett

Soil application of CCC reduced stem and leaf growth in Begonia plants. This effect was evident with all concentrations tested at 18°C, whereas at 21 and 24°C no growth–retarding effect was observed with 2 × 10^?2 M CCC, and with 5 × 10^?3 M growth was even stimulated. Flowering was promoted by CCC in long day and neur–critical temperature, particularly under low light intensity in the winter. The formation of adventitious buds in leaves of plants grown at 21 and 24°C was stimulated when the plants received 5 × 10^?2 and 2 × 10^?2 M CCC, while 8 7times; 10^?2 M was inhibitory. In plants grown at 18°C bud formation was inhibited by all CCC concentrations. Root formation in the the leaves was usually stimulated by high CCC concentrations, while root elongation was reduced. The level of ether–extractable. acidic auxin (presumably IAA) in the leaves was lowered by CCC treatment of the plants, hut this required higher CCC concentrations at higt than at low temperature. When applied to detached leaves CCC stimulated bud formation at concentrations ranging from 10^?4 to 10^?2 M in leaves planted at 18 and 21°C. At 24°C budding was inhibited by 10^?2 M CCC, the lower concentrations being stimulatory also at this temperature. Root formation and growth were not much affected by CCC treatment of the leaves, but increased with the temperature. Soil application of Phosfon (4 × 10^?4 M) had no effect on growth and flowering, nov did it affect the subsequent regeneration of buds and roots in the leaves. In detached leaves Phosfon stimulated bud formation with au optimum at 10^?6 M. Root formation was stimulated by Phosfon at all temperatures, the optimal concentration being 10^?5 M, whereas root length was conversely affected. Foliar application of B-995 to intact plants and treatment of detached leaves greatly inhibited the formation of buds and had little effect on root formation. B-99D reduced the growth and delayed flowering in the plants.     

Relationship between respiratory depletion of sugars and loss of cold hardiness in coniferous seedlings over-wintering at raised temperatures: indications of different sensitivities of spruce and pine

Long-term effects of elevated winter temperatures on cold hardiness were investigated for Norway spruce (Picea abies L. Karst.), lodgepole pine (Pinus contorta Dougl.) and Scots pine (Pinus sylvestris L.). Two-year-old seedlings with the same pre-history of growth and cold hardening in the field were maintained from early December to late March at two field sites in northern Sweden and in a cold room. The temperatures at these locations averaged –13·5, –8·9 and 5·5°C, respectively. Following treatments, carbohydrate contents and cold tolerances were assessed. Needle respiration was also analysed during the 5·5°C treatment. Cold tolerance of lodgepole pine and Scots pine was much reduced following the 5·5°C treatment. Cold tolerance was somewhat reduced in lodgepole pine following the –8·9 °C treatment, but was essentially maintained in spruce throughout all treatments. The cold tolerance of needles was strongly correlated with their soluble sugar contents. Spruce maintained cold hardiness by having larger reserves of sugars and lower rates of respiration which decreased more rapidly as sugars were depleted. Tolerance of lodgepole pine to frost desiccation was also much reduced following the 5·5°C treatment.     

The after-effects of temperature and irradiance during early growth of winter oilseed rape (Brassica napus L. var. oleifera, cv. Górczański) seedlings on the progress of their cold acclimation

Experiments performed under controlled conditions showed that level of PPFD (photosynthetic photon flux density) during early seedlings growth (preceding cold acclimation at +2 °C) was not the key factor for the development of frost resistance. It did not modify the beneficial effects of prehardening (Rapacz 1997, in this issue) at moderately low (+12 °C) day temperature. Now I have shown that the increase of PPFD may replace to some extent prehardening in the development of frost resistance. It was particularly seen in non-prehardened plants, which had been grown under warm-day (+20 °C) conditions. Prehardening performed under controlled conditions, as well as seedlings growth under natural autumn conditions in the field, allowed to maintain a high net-photosynthesis rate at chilling temperatures. A net-photosynthesis rate during cold acclimation at +2 °C corresponded well with higher frost resistance. As a result, seedlings non subjected to prehardening and grown before cold acclimation under low PPFD acclimated better, if the cold treatment was applied only at nights (+20/2 °C day/night). Only under such conditions the photosynthetic rate was sufficiently high to allow plants to reach a higher level of frost resistance. All other plants acclimated better when they were exposed to the hardening temperature continuously during days and nights (+2/2 °C day/night).     

Induction of Frost Hardiness in Stem Cortical Tissues of Cornus stolonifera Michx. by Water Stress: I. Unfrozen Water in Cortical Tissues and Water Status in Plants and Soil

Water supply and day length were varied in cold hardiness studies of red osier dogwood plants (Cornus stolonifera Michx.). The frost killing temperature, the content and freezing of stem cortical tissue water along with soil moisture content and tension were evaluated. Seven days of water stress in long and short day photoperiod regimes caused a rapid decrease in soil moisture content and plant water potential. During the same period, the frost hardiness increased from −3 to −11 C. Further water stress treatment had little effect. Control plants in short days showed only a gradual decrease in plant water potential and only gradually increased in frost hardiness while control plants in long days were unchanged. Freezing studies using nuclear magnetic resonance showed that increased hardiness in water-stressed plants resulted from both an increased tolerance of freezing and an increased avoidance of freezing, the latter resulting from higher solute concentration in the tissue solutions. The short day controls also showed similar changes; however, the changes were smaller over the 21 days of the study.     

Morphophysiological monitoring of winter wheat in spring in the context of global climate warming

Data on morphophysiological monitoring of winter wheat (Triticum aestivum L.) cultivar Mironovskaya 808 grown in Hoagland and Arnon solution in a greenhouse and transferred to natural conditions in March–April 2004 with the mean daily temperature of 0.6 ± 0.7°C within the exposure period of 42 days are presented. Water content, dry weight of plants and their organs, frost hardiness of plants, degree of tissue damage by frost, CO₂ metabolism (photosynthesis and respiration), concentrations of sugars in tissues and proportions between different sugar forms, and activities of soluble and insoluble acid and alkaline phosphatases were monitored. Monitoring was carried out for three experimental variants simulating different microclimatic conditions in spring: after snow melting (experiment I), under ice crust (experiment II), and under snow cover (experiment III). Plants in experiments III and II demonstrated a higher water content in tissues, lower frost hardiness, higher rates of biomass loss, lower concentration of sugars and lower di-to monosaccharide ratio in tissues, and higher total invertase activity, particularly, cell wall-associated acid invertase activity. The dark respiration rates at 0°C did not significantly differ between experimental variants. The photosynthetic capacity at this measurement temperature was maintained in all experimental variants being most pronounced in experiment II with the most intense photoinhibition under natural conditions. Comparison of experiments III and II with experiment I is used to discuss the negative effect of changes in certain microclimatic indices associated with global warming and leading to plant exhaustion and death from frost in spring.     

Suppression of the source activity affects carbon distribution and frost hardiness of vegetating winter wheat plants

Effect of suppression of the source activity on some physiological characteristics of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) was studied on plants grown in water culture. The plants were examined at the mixotrophic stage of growth period, during their transition from vegetative state to relative dormancy in autumn. The average temperature over 10 days of the experiment was 6°C at 9-h photoperiod and illuminance of 8–20 klx. The source strength was suppressed successively with a series of treatments: intact control plants (V1); plants with the seed endosperm removed (V2); plants with photosynthesis inhibited (V3); plants with the seed endosperm removed and photosynthesis inhibited (V4); plants with the seed endosperm removed, photosynthesis inhibited, and the root nutrient medium replaced with distilled water (V5). On the 6th–10th day of the experiment, the relative growth rate (RGR) was determined from dry weight increments. At the same time, the distribution of biomass among organs, the CO₂ exchange rates (photosynthesis and dark respiration), the content and proportions of sugars (sucrose, glucose, and fructose), the total content of phenolic compounds and flavonoids, the index of membrane stability (IMS) in leaves, and frost hardiness of plants were measured. Frost hardiness of vegetating plants was shown to be inversely related to RGR (R = ?0.906), dark respiration rate (R = ?0.789), the percentage of sucrose in total sugar content (R = ?0.737), leaf IMS (R = ?0.390), and the rate of apparent photosynthesis (R = ?0.288); it was directly proportional to the content of flavonoids (R =0.973), total phenols (R = 0.743), and sugars (R = 0.385). The role of modified source-sink relations in frost hardiness of vegetating plants at the stage of their transition to cold hardening is discussed. The differences between plants undergoing this transition and cold-hardened plants are considered, as well as the importance of phenolic compounds for the development of frost hardiness.     

Effect of frost nights and day and night temperature during dormancy induction on frost hardiness, tolerance to cold storage and bud burst in seedlings of Norway spruce

For trees, the ability to obtain and maintain sufficient levels of frost hardiness in late autumn, winter and spring is crucial. We report that temperatures during dormancy induction influence bud set, frost hardiness, tolerance to cold storage, timing of bud burst and spring frost hardiness in seedlings of Norway spruce (Picea abies (L.) Karst.). Bud set occurred later in 12°C than in 21°C, and later in cool nights (7°C) than in constant temperature. One weekly frost night (−2.5°C) improved frost hardiness. Cool nights reduced frost hardiness early, but improved hardiness later during cold acclimation. Buds and stems were slightly hardier in 21°C than in 12°C, while needles were clearly hardier in 12°C. Cold daytime temperature, cool nights and one weekly frost night improved cold storability (0.7°C). Seedlings receiving high daytime temperatures burst buds later, and were less injured by light frost some days after bud burst.     

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 O₂-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.     

The timing of leaf fall affects cold acclimation by interactions with air temperature through water and carbohydrate contents

Three parameters (i.e. the water content, soluble sugar content and minimal air temperature) can be used to predict the cold acclimation process of walnut trees. In order to test this assumption, two-year-old walnuts were defoliated at two different dates, i.e. mechanical defoliation in early October (early leaf fall, EF) or natural defoliation in early November (natural leaf fall, NF) and conditioned in either outdoor freeze-deprived or cold-deprived (T_min > 13 °C) greenhouses over winter. Even if early defoliation date could have affected short day signal perception (SDSP), water balance and carbohydrate metabolism were more altered. EF treatment, by stopping transpiration, significantly increased tree's water content and at warm temperature high root activity stopped normal winter dehydration. Starch content decreased in all treatments, but there was only a significant increase in soluble sugar content when water content had sufficiently decreased. Thus, depending on date of defoliation, cold-deprived trees were or were not able to acclimate to frost (minimal frost hardiness = −21.8 °C vs. −22.1 °C in controls (freeze-deprived) for NF and −13.7 °C vs. −25.3 °C in controls for EF). Different treatments showed the relationship between minimal water content observed during winter and maximal soluble sugars synthesized. Thus, the cold acclimation process appeared dependent on these physiological parameters (water and soluble sugar contents) through the interaction between air temperature and timing of leaf fall.     

N uptake and growth responses to sub-lethal freezing in the grass Poa pratensis L.

Background and aims

Climate warming has the potential to increase both the exposure and vulnerability of grass roots to frost in temperate regions by reducing snow cover and altering the timing of cold acclimation. Despite a strong research focus on the direct effects of freezing on grass mortality, the direct sub-lethal effects of freezing on grass performance have not been well-characterized. We examined sub-lethal responses of the grass Poa pratensis to variation in the timing, severity, rate and length of freezing.

Methods

We assessed short term root functional responses (¹⁵N uptake) and longer term plant growth responses to freezing administered both under controlled conditions in a refrigerated incubator, and in the field by manipulating snow and litter cover.

Results

In fall and spring, ¹⁵N uptake declined in response to 1?day of freezing down to ?10?°C or to 3?days of freezing at ?5?°C, whereas in winter, ¹⁵N uptake was insensitive to freezing. Long term growth responses were similar, with reduced growth only occurring for grasses frozen for 3?days at ?5?°C in spring, but not for grasses frozen in fall or winter. Snow and litter removal intensified soil freezing over winter, but did not significantly affect plant growth.

Conclusions

Our results demonstrate that while P. pratensis is relatively tolerant to frost damage over winter, it may be vulnerable to sub-lethal frost effects in fall, and particularly in spring. These sub-lethal effects occur at temperatures approximately 15–20?°C warmer than the published LT₅₀ values for this species.     

Plant resistance to cold stress: Mechanisms and environmental signals triggering frost hardening and dehardening

This introductory overview shows that cold, in particular frost, stresses a plant in manifold ways and that the plant’s response, being injurious or adaptive, must be considered a syndrome rather than a single reaction. In the course of the year perennial plants of the temperate climate zones undergo frost hardening in autumn and dehardening in spring. Using Scots pine (Pinus sylvestris L.) as a model plant the environmental signals inducing frost hardening and dehardening, respectively, were investigated. Over 2 years the changes in frost resistance of Scots pine needles were recorded together with the annual courses of day-length and ambient temperature. Both act as environmental signals for frost hardening and dehardening. Climate chamber experiments showed that short day-length as a signal triggering frost hardening could be replaced by irradiation with far red light, while red light inhibited hardening. The involvement of phytochrome as a signal receptor could be corroborated by respective night-break experiments. More rapid frost hardening than by short day or far red treatment was achieved by applying a short period (6 h) of mild frost which did not exceed the plant’s cold resistance. Both types of signals were independently effective but the rates of frost hardening were not additive. The maximal rate of hardening was − 0.93°C per day and frost tolerance of < − 72°C was achieved. For dehardening, temperature was an even more effective signal than day-length.     

Comparison of cold hardiness and sugar content between diapausing and nondiapausing pupae of the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract. To understand overwintering of the cotton boll worm Helicoverpa armigera, cold hardiness and sugar content are compared between diapausing and nondiapausing pupae. Diapausing and nondiapausing pupae reared at 20 °C under short and long photoperiods are acclimatized with a reduction of 5 °C per 5 days to 0 °C. When the acclimation temperature reaches 0 °C, the survival of diapausing pupae is assessed. The survival gradually decreases as the period of treatment progresses and approximately half survive for 112 days. However, nondiapausing pupae survive only 14 days after exposure to 0 °C. The surpercooling points of nondiapausing, diapausing and acclimatized pupae are approximately −17 °C. The major sugars contained in pupae are trehalose and glucose. Even though trehalose contents in diapausing pupae (initial level: 0.6 mg 100 mg⁻¹ fresh weight) increase significantly during cold acclimation and continue increasing until 58 days after exposure to 0 °C (maximum level: 1.8 mg 100 mg⁻¹), glucose is maintained at low levels (0.02 mg 100 mg⁻¹) for 56 days at 0 °C. However, glucose contents increase (maximum level: 0.8 mg 100 mg⁻¹) with decreasing contents of trehalose 84 days after exposure to 0 °C. Glycogen content gradually decreases during cold acclimation. When nondiapausing pupae are acclimatized with a reduction of 5 °C per 5 days to 5 °C from the beginning of pupation until the eyespots move, trehalose content increases (maximum level: 1.0 mg 100 mg⁻¹). Glucose contents in nondiapausing pupae increase before eclosion (0.09 mg 100 mg⁻¹). From these results, diapausing pupae of H. armigera can overwinter in regions where average winter temperatures are higher than 0 °C, but nondiapausing pupae cannot.     

Cold-acclimation of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. in natural and controlled environments

Abstract Seasonal cold-acclimation patterns and the effects of photoperiod and temperature on cold-hardiness of Hibiscus rosa-sinensis L. and Hibiscus syriacus L. were determined. Field-grown H. rosasinensis consistently failed to survive freezing at - 2°C. Two genotypes of field- and container-grown H. syriacus initiated cold-acclimation in mid September, in response to decreasing daylength, and continued to an ultimate midwinter hardiness level of - 27°C in early February. Controlled environment experiments using combinations of short days (SD) and cool day/night temperatures were unable to induce even minimal cold acclimation of H. rosasinensis. In controlled environments, H. syriacus attained a moderate amount of cold tolerance at warm temperatures and long days (LD). Low night temperature combined with LD, warm day produced the same degree of cold-acclimation as the SD treatments. While not essential, SD enhanced H. syriacus cold-acclimation in controlled environments. A - 5°C frost treatment of intact plants did not enhance cold-hardiness of H. syriacus.     

Is survival after ice encasement related with sugar distribution in organs of the Antarctic plants <Emphasis Type="Italic">Deschampsia antarctica</Emphasis> Desv. (Poaceae) and <Emphasis Type="Italic">Colobanthus quitensis</Emphasis> (Kunth) Bartl. (Caryophyllaceae)?

Deschampsia antarctica and Colobanthus quitensis are usually covered by snow from April to November. It is unknown whether the leaves survive ice encasement. This study proposes that day length influences sugar distribution in C. quitensis and that sugar accumulation favors re-growths after an ice encasement period. The objectives of this work were: (1) to study the effect of day length and low temperature on sugar distribution in organs of C. quitensis and (2) to study the survival and recovery of D. antarctica and C. quitensis after a period of ice encasement. Extremely short day length (SD) (8/16 h) and long day length (LD) (21/3 h) was used, medium (MD) (16/8 h) corresponding at control day length. Also two temperatures: 4°C (cold acclimated) and 15°C (control) were evaluated. Both factors: day length and cold acclimation significantly affected sugar distribution in C. quitensis. Both species presented a high rate of survival after ice encasement. D. antarctica conserved most of their leaves green, while C. quitensis presented dead leaves and new shoots in plants from cold acclimated under SD. Only in D. antarctica the number of green leaves after ice encasement was positively correlated with sugar content in underground organs. The high sugar content in green leaves of both species suggested fast activity recovery after snow melting.     

A chamber for the simulation of radiation freezing of plants

Frost injury to plants can occur following episodic radiation frosts. In the UK this is particularly important to spring sown crops such as potatoes. Most laboratory based frost studies simulate freezing using either conductive or convective freezing chambers. Such frost tests do not simulate overnight freezing events adequately. A freezing chamber based on radiative cooling is described which mimics overnight radiative freezing. The chamber is rectangular in design (1 m × lm × 2 m high) with a radiative cooling plate at the top of the chamber cooled to -40°C to -45°C using HFC coolants, which acts as a cold black body. The sides of the chamber are also cooled to variable temperatures down to -5°C in order to prevent the chamber walls radiating to the plant material during testing. Using thermocouples to measure air temperature and plant temperature the chamber has been characterised to simulate the radiative cooling conditions found in the UK during autumn and spring. Exotherm detection upon plant freezing is simplified by virtue of the reduction in temperature fluctuation normally experienced at the plant surface during natural freezing. Radiation frosts and subsequent frost damage to potatoes have been recorded in the temperature range -4°C to –5°C. The equipment is recommended for studies of frost damage to plants normally caused by episodic radiation frost events.     

Frost tolerance in winter wheat cultivars: different effects of chromosome 5A and association with microsatellite alleles

Frost tolerance of ten Bulgarian winter wheat (Triticum aestivum L.) cultivars (Milena, Pobeda, Sadovo-1, Enola, Kristal, Laska, Svilena, Russalka, No301 and Lozen) and five foreign cultivars (Mironovskaya 808, Bezostaya-1, Rannaya-12, Skorospelka-35 and Chinese Spring) was studied in two experimental seasons following natural cold acclimation and in one experiment carried out in controlled acclimation conditions. Considerable intercultivar variability in plant survival was observed after freezing at ?21 °C following sufficient cold acclimation, or at ?18 °C following insufficient or controlled acclimation. In seven cultivars, the effects of chromosome 5A on frost tolerance were investigated in their F₂ hybrids with chromosome 5A monosomic lines of cultivars with high, intermediate and low frost tolerance. The effects of chromosome 5A depended on the stress severity and the genetic background of the hybrids and varied even in cultivars of similar frost tolerance and vernalization requirements. Effects of other chromosomes besides 5A on frost tolerance were assumed. The analysis of six microsatellite loci located in the interval from centromere to Vrn-1 on of chromosomes 5AL, 5BL and 5DL showed that the major loci determining frost tolerance in Bulgarian winter wheats were Fr-A2 on chromosome 5AL, and, to a lesser extent, Fr-B1 on chromosome 5BL. A strong association of the 176 bp allele at locus wmc327 tightly linked to Fr-A2 with the elevated frost tolerance of cvs. Milena, Pobeda, Sadovo-1, Mironovskaya-808 and Bezostaya-1 was revealed. Relatively weaker association between frost tolerance and the presence of the 172 bp allele at locus Xgwm639 tightly linked to Fr-B1 was also observed.     

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus)

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day – warm temperature (16L:8D, 23 °C), (2) Long day – cold temperature (16L:8D, 5 °C), (3) short day – warm temperature (8L:16D, 23 °C), and (4) short day – cold temperature (8L:16D, 5 °C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat. Accepted: 10 November 1998     

Shivering and non-shivering thermogenesis in a marsupial,the eastern barred bandicoot (Perameles gunnii)

We investigated the metabolic rate of the Tasmanian marsupial, the eastern barred bandicoot, Perameles gunnii, before and after acclimation to cold temperature (5 °C) for a 2-week period. Although body temperature did not change significantly, we observed a significant increase in the metabolic rate (MR) when measured at 5 °C before and after cold acclimation. Nor-epinephrine had a significant effect on the metabolic rate when measured in the thermoneutral zone and when measured at 5 °C after cold acclimation; however, there was no significant increase when measured at 5 °C before cold acclimation. Nor-epinephrine also resulted in a small but significant decrease in body temperature. Electromyography (EMG) measurements were obtained before and after cold acclimation during shivering. Shivering decreased after two weeks of cold exposure indicating that the bandicoot had acclimated to that temperature. Nor-epinephrine (NE) significantly reduced shivering before but not after cold acclimation. The metabolic rate and shivering decreased in the adult eastern barred bandicoot after acclimation at 5 °C and nor-epinephrine had similar effects to cold acclimation. Our findings of minor changes in thermal conductance suggest that insulation differences were unlikely explanations for our results. These experiments indicate that this marsupial is able to increase its heat production by non-shivering thermogenesis.