Changes in the composition of xylem sap during development of the spadix of skunk cabbage (Symplocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is thermogenic and maintains an internal temperature of around 20 degrees C even when the ambient air temperature drops below freezing. This homeothermic heat production is observed only during the stigma stage, and thereafter ceases at the male stage when pollen is shed. To clarify the regulatory mechanism by which the stigma stage-specific heat production occurs in the spadix, sugars, organic acids, and amino acids in xylem sap were analyzed and compared with those of post-thermogenic plants. Interestingly, no significant difference was observed in the total volume of xylem sap per fresh weight of the spadix between thermogenic (31.2+/-24.7 microl h(-1) g(-1)) and post-thermogenic (50.5+/-30.4 microl h(-1) g(-1)) plants. However, concentrations of sugars (sucrose, glucose, and fructose), organic acids (malate and succinate), and amino acids (Asp, Asn, Glu, Gln, Gly, and Ala) in xylem sap decreased remarkably in post-thermogenic plants. Our results indicate that the composition of the xylem sap differs during the development of the spadix of S. foetidus.     

Structural requirements for the perception of ambient temperature signals in homeothermic heat production of skunk cabbage (Symlocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is capable of maintaining an internal temperature of around 20 degrees C even when the ambient temperature drops to around 0 degrees C. To determine the crucial structure that is required for detection of ambient temperature signals, detailed measurements of the temperatures of the spadix were made under field conditions. The spadix temperature was well regulated even when the spathe or the leaf of the plant was removed. Furthermore, maintenance of the temperature of the central stalk at either 10 or 20 degrees C had no effect on the thermoregulation when the ambient temperature increased from 10 to 25 degrees C or decreased from 20 to 8 degrees C. Therefore, it seemed that the heat production in the spadix required neither the spathe, the leaf, nor the central stalk for perception of the external temperature signals. Finally, analysis of sugar composition in xylem exudates showed that the concentrations of sucrose, glucose, and fructose, all of which are potential energy sources of thermogenesis, did not change significantly at different ambient temperatures. It is concluded that the spadix is a unique organ in which the perception of ambient temperature signals and heat production occurs in S. foetidus.     

Zonal thermogenetic dynamics of two species of Philodendron from two different subgenera (Araceae)

Spadix temperature was measured in two species of Philodendron : P. melinonii (subgenus Philodendron ) and P. solimoesense (subgenus Meconostigma ). For each species, the temperature of the male zone, the sterile male zone and the female zone of the spadix were recorded. In both species, the temperature of the male zone warmed up at the beginning of each of the two flowering nights. In P. melinonii , the temperature of the male sterile zone increased the first day but remained not significantly different from that of the ambient air during the second day. The temperature of the male zone warmed up slightly on the second day. In P. melinonii , the temperature of the three zones was not significantly different from that of the ambient air between the two peaks. In P. solimoesense , the temperature of the male zone and sterile zone rose to above that of the ambient air during the first night and then progressively cooled down but remained 3–6°C above the ambient air temperature until the second peak. In both species the temperature of the female zones remained more or less constant during the entire flowering cycle, very close to the temperature of the ambient air. We suggest that the heat production and the spadix temperature patterns observed may reflect a general physiological process common to all species of Philodendron . The biphasic pattern present in the subgenus Meconostigma can be seen as a variant of the 'two peaks' pattern, occurring in the subgenus Philodendron , with a 'plateau' phase between them. The comparison of the different thermogenic cycles occurring in Philodendron , Arum and Dracunculus seems to indicate some clear evolutionary trends. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 79–86.     

Heat Production in the Voodoo Lily (Sauromatum guttatum) as Monitored by Infrared Thermography

The pattern of surface temperatures of the inflorescence of Sauromatum guttatum was investigated by using an infrared camera. The male flowers are weakly thermogenic on the first day of inflorescence opening (D-day) as well as on the next day (D + 1), reaching 0.5 to 1°C above ambient temperature. The appendix (the upper sterile part of the inflorescence) is highly thermogenic on D-day, reaching 32°C, and is faintly thermogenic on D + 1, reaching 1°C above ambient temperature. The lower part of the spadix, close to the female flowers, is also thermogenic on D-day and D + 1, reaching a temperature similar to that of the appendix only on D + 1. Salicylic acid does not induce heat production in the lower part of the spadix, as it does in the appendix. Respiration of tissue slices obtained from the appendix shows that the capacity for cyanide-insensitive respiration is present in young and mature appendices. This alternative respiratory pathway is not, however, utilized in young appendix tissue, but is engaged during the maturation of that tissue.     

Changes in the Composition of Xylem Sap during Development of the Spadix of Skunk Cabbage (Symplocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is thermogenic and maintains an internal temperature of around 20 °C even when the ambient air temperature drops below freezing. This homeothermic heat production is observed only during the stigma stage, and thereafter ceases at the male stage when pollen is shed. To clarify the regulatory mechanism by which the stigma stage-specific heat production occurs in the spadix, sugars, organic acids, and amino acids in xylem sap were analyzed and compared with those of post-thermogenic plants. Interestingly, no significant difference was observed in the total volume of xylem sap per fresh weight of the spadix between thermogenic (31.2±24.7 μl h^?1g^?1) and post-thermogenic (50.5±30.4 μl h^?1g^?1) plants. However, concentrations of sugars (sucrose, glucose, and fructose), organic acids (malate and succinate), and amino acids (Asp, Asn, Glu, Gln, Gly, and Ala) in xylem sap decreased remarkably in post-thermogenic plants. Our results indicate that the composition of the xylem sap differs during the development of the spadix of S. foetidus.     

Dynamics and precision of thermoregulatory responses of eastern skunk cabbage Symplocarpus foetidus

Inflorescences of the arum lily Symplocarpus foetidus are thermogenic and thermoregulatory. The spadix increases respiratory heat production rate as ambient temperature decreases. This study examined the relationships between spadix temperature (T_s), respiration rate () and ambient temperature (T_a) at equilibrium and during transient responses to step changes in T_a. Intact inflorescences inside a miniature constant temperature cabinet in the field showed the most precise temperature regulation yet recorded; over a 37.4 °C range in T_a (?10.3 to 27.1 °C), T_s changed only 3.5 °C (22.7 to 26.2 °C). Regulated temperatures were not related to spadix size (1.9–7.3 g) or circadian cycle. Dynamic responses to step changes in T_a involved a phasic change in T_s, first in the same direction as T_a, then reversing at 38.3 min, and finally approaching equilibrium at 87.6 min, on average. Meanwhile changed in a monotonic curve toward equilibrium. Models revealed that the dynamics of temperature change were inconsistent with simply a physical lag in the system, but involved some form of biochemical regulation, possibly by changes in activity of a rate‐limiting functional protein.     

Functional analysis of skunk cabbage SfUCPB, a unique uncoupling protein lacking the fifth transmembrane domain, in yeast cells

Skunk cabbage, Symplocarpus foetidus, expresses two uncoupling proteins (UCPs), termed SfUCPA and SfUCPB, in the thermogenic organ spadix. SfUCPB exhibits unique structural features characterized by the absence of the putative fifth transmembrane domain (TM5) observed in SfUCPA, which is structurally similar to UCP1, and is abundantly expressed in the thermogenic spadix. Here, we conducted a series of comparative analyses of UCPs with six transmembrane domains, SfUCPA and rat UCP1, and TM5-deficient SfUCPB, using a heterologous yeast expression system. All UCPs were successfully expressed and targeted to the mitochondria, although the expression level of SfUCPB protein was approximately 10% of rat UCP1. The growth rate, mitochondrial membrane potential, and ATP content were significantly lower in cells expressing SfUCPB than in those expressing rat UCP1 and SfUCPA. These results suggest that SfUCPB, a novel TM5-deficient UCP, acts as an uncoupling protein in yeast cells.     

Physical constraints on temperature difference in some thermogenic aroid inflorescences

* BACKGROUNDS AND AIMS: Thermogenesis in reproductive organs is known from several plant families, including the Araceae. A study was made of the relationship between temperature increase and spadix size in the subfamily Aroideae in order to determine whether the quantitative variation of heat production among species and inflorescences of different sizes follows a physical law of heat transfer. * METHODS: Spadix temperature was measured in 18 species from eight genera of tropical Araceae from the basal clade of Aroideae, both in French Guiana and in the glasshouses of the Montreal Botanical Garden. * KEY RESULTS: A significant logarithmic relationship was found between the volume of the thermogenic spadix zone and the maximum temperature difference between the spadix and ambient air. Four heat transfer models were applied to the data (conductive heat transfer alone, convective heat transfer alone, radiative heat transfer alone, and convective and radiative heat transfers) to test if physical (geometric and thermic) constraints apply. Which heat transfer model was the most probable was determined by using the criterion of a classical minimization process represented by the least-squares method. Two heat transfer models appeared to fit the data well and were equivalent: conductive heat transfer alone, and convective plus radiative heat transfers. * CONCLUSIONS: The increase in the temperature difference between the spadix and ambient air appears to be physically constrained and corresponds to the value of a thermal model of heat conduction in an insulated cylinder with an internal heat source. In the models, a heat metabolic rate of 29.5 mW g(-1) was used, which was an acceptable value for an overall metabolic heat rate in aroid inflorescences.     

The cryptoendolithic microbial environment in the Antarctic cold desert: Temperature variations in nature

Summary In the Antarctic cold desert, cryptoendolithic microorganisms live under the surface of porous sandstone rocks. During the austral summer, the environment of the near-surface rock layers colonized by organisms is characterized by two kinds of temperature oscillations, both occurring across the freezing point. Low-frequency (diurnal) and large-amplitude (up to about 20°C) oscillations on the sunlit surface of rocks result in a daily freeze-thaw cycle. This is a result of the diurnal changes in the sun altitude and angle with respect to the rock surface. The biological effect of this oscillation is the regulation of the onset and cessation of metabolic activity. The high-frequency (few minutes) oscillations occur only under certain weather conditions (sunny days with light winds) and are superimposed on the low-frequency oscillations. They are caused by the cooling effect of wind gusts on rock surfaces that are much warmer than ambient air temperatures. High-frequency oscillations result in a rapid freeze-thaw cycle on the surface, which, however, does not reach the microbial zone. These high-frequency freeze-thaw oscillations are probably the cause of the abiotic nature of the rock surface. Both oscillations seem to have an effect on rock weathering.     

Flowering and Pollination of Philodendron melinonii (Araceae) in French Guiana

Abstract: The pollination ecology of Philodendron melinonii was studied at two locations in French Guiana. Inflorescences of P. melinonii were regularly visited by Cyclocephala colasi, a scarab beetle also found in inflorescences of P. solimoesense in the same area. The flowering cycle lasted two days and the inflorescence exhibited features typical for beetle pollination (e.g., floral chamber, food rewards, flower heating). The flowering process is well synchronized with the night activity of Cyclocephala visitors. The spadix temperature was measured during the entire flowering cycle in the field in French Guiana and in greenhouse conditions at the Montreal Botanical Garden. Both measurements gave a similar temperature pattern with a two hour delay at the Botanical Garden. The spadix warmed up twice during the flowering period and its temperature was not significantly different from that of ambient air between the two peaks. These two temperature peaks are also well synchronized with the arrival and departure of the beetles on two consecutive nights.     

Unstable, self-limiting thermochemical temperature oscillations in Macrozamia cycads

Field measurements and laboratory experiments on the Australian cycads Macrozamia lucida and Macrozamia macleayi demonstrate that their cones' diel peak thermogenic temperature increase varies systematically with cone stage, with single thermogenic temperature peaks occurring daily for up to 2 weeks and reaching 12 degrees C above ambient at midstage. The initiation, magnitude and timing of those peaks are strongly modulated by ambient temperature; the period between successive thermogenic temperature peaks is not circadian, and light is neither necessary nor sufficient to initiate a thermogenic event. A mathematical analysis is developed that provides a unified explanation of the experimental results. It describes these unstable, self-limiting thermogenic events in terms of conservation of energy and a first-order chemical reaction rate model that includes an Arrhenius equation dependence of the cone's metabolic heating rate on the cone temperature.     

Respiration and heat production by the inflorescence of Philodendron selloum Koch

During a 2-d sequence of anthesis, the spadices of the thermogenic arum lily, Philodendron selloum, regulated maximum temperature within a small range (37–44°C) by reversible thermal inhibition of respiratory heat production. This response protects the inflorescence and the attracted insects from thermal damage. Heat production by whole spadices, measured by O₂ respirometry, equalled heat loss, measured by gradient layer calorimetry, which confirmed the heat equivalence of O₂ consumption (20.4 J ml^-1). This also indicated that there was no net phosphorylation during thermogenesis, heat production being the primary function of high rates of respiration. The sterile male florets consumed about 30 ml g^-1 h^-1 and the average 124-g spadix produced about 7 W to maintain a 30°C difference between spadix and ambient temperature. Most of the energy for thermogenesis is present in the florets before anthesis. Despite high respiratory rates, thermogenesis is an energetically inexpensive component of the reproductive process.     

Physical fitness and thermoregulatory reactions in a cold environment in men

The relationship between the physical fitness level (maximal O2 consumption, VO2max) and thermoregulatory reactions was studied in 17 adult males submitted to an acute cold exposure. Standard cold tests were performed in nude subjects, lying for 2 h in a climatic chamber at three ambient air temperatures (10, 5, and 1 degrees C). The level of physical fitness conditioned the intensity of thermoregulatory reactions to cold. For all subjects, there was a direct relationship between physical fitness and 1) metabolic heat production, 2) level of mean skin temperature (Tsk), 3) level of skin conductance, and 4) level of Tsk at the onset of shivering. The predominance of thermogenic or insulative reactions depended on the intensity of the cold stress: insulative reactions were preferential at 10 degrees C, or even at 5 degrees C, whereas colder ambient temperature (1 degree C) triggered metabolic heat production abilities, which were closely related to the subject's physical fitness level. Fit subjects have more efficient thermoregulatory abilities against cold stress than unfit subjects, certainly because of an improved sensitivity of the thermoregulatory system.     

Bronchial reactivity of healthy subjects: 18-20 h postexposure to ozone.

Exposure of humans to ambient levels of ozone (O(3)) causes inflammatory changes within lung tissues. These changes have been reported for the "initial" (1- to 3-h) and "late" (18- to 20-h) postexposure periods. We hypothesized that at the late period, when protein and cellular markers of inflammation at the airway surface remain abnormal and the integrity of the epithelial barrier is compromised, bronchial reactivity would be increased. To test this, we measured airway responsiveness to cumulative doses of methacholine (MCh) aerosol in healthy subjects 19+/-1 h after a single exposure to O(3) (130 min at ambient levels between 120 and 240 parts/billion and alternate periods of rest and moderate exercise) or filtered air. Exposures were conducted at two temperatures: mild (22 degrees C) and moderate (30 degrees C). At the late period, bronchial reactivity to MCh increased, i.e., interpolated dose of MCh leading to a 50% fall in specific airway conductance (PC(50)) was less after O(3) than after filtered air. PC(50) for O(3) at 22 degrees C was 27 mg/ml (20% less than the PC(50) after filtered air), and for O(3) at 30 degrees C it was 19 mg/ml (70% less than the PC(50) after filtered air). The forced expiratory volume in 1 s (FEV(1)) at the late time point after O(3) was slightly but significantly reduced (2.3%) from the preexposure level. There was no relationship found between the functional changes observed early after exposure to O(3) and subsequent changes in bronchial reactivity or FEV(1) at the late time point. These results suggest that bronchial reactivity is significantly altered approximately 1 day after O(3); this injury may contribute to the respiratory morbidity that is observed 1-2 days after an episode of ambient air pollution.     

Evaluation of a new tail-cuff method for blood pressure measurements in rats with special reference to the effects of ambient temperature

We evaluated a recently developed tail-cuff apparatus for the indirect blood pressure measurement in rats with special reference to the effects of ambient temperature. For this purpose, we designed two preparations 1) an intact preparation to determine the effect of ambient temperature on blood pressure measurements and 2) an anesthetized and catheterized preparation for comparison of the values of blood pressure obtained by the indirect and by the direct method. This apparatus also required enough pulse volume oscillations to measure the accurate value of blood pressure. Sufficient pulse volume oscillations were obtained within 20 min at 30 and 40 degrees C. At 40 degrees C, the values of blood pressure, pulse rate and rectal temperature were significantly higher than those at 30 degrees C. Correlation between blood pressure and rectal temperature was significant, and blood pressure increased with rectal temperature dependently. The values of the indirect measurement were close to the values measured directly, and these correlations were highly significant. Thus, we showed the effects of temperature for indirect blood pressure measurement. This tail-cuff apparatus could measure the accurate value of indirect blood pressure without thermal stress at 30 degrees C.     

Thermal balance and survival time prediction of man in cold water.

Metabolic rates and rectal temperatures were continuously monitored for humans immersed in cold ocean water (4.6--18.2 degrees C) under stimulated accident conditions. The subjects wore only light clothing and a kapok lifejacket while either holding-still or swimming. While holding-still, metabolic heat production (Hm,kcal-min--1) was inversely related to water temperature (Tw, degrees C) according to the equation Hm equals 4.19 minus-0.117 Tw. This temperature response pattern is shown to be similar to that for exposure to air of the same temperature when air velocity is just over 5 m.p.h. (2.24 m/s). The thermogenic response was one-third efficient in balancing the calculated heat loss in cold water, resulting in hypothermia at a rectal temperature cooling rate (C, degrees C-min--1) dependent on water temperature (Tw, degrees C) according to the relation C equal 0.0785 - 0.0034Tw. Although swimming increased heat production to 2.5 times that of holding-still at 10.5 degrees C water temperature, cooling rate was 35% greater while swimming. A prediction equation for survival time (ts, min) of persons accidentally immersed in cold water (Tw, degrees C) has the form ts equal 15 + 7.2/(0.0785-0.0034Tw), based on the findings of this study, and it is compared to pre-existing models.     

Effect of ambient temperature on cardiovascular parameters in rats and mice: a comparative approach

Ambient air temperatures (T(a)) of <6 degrees C or >29 degrees C have been shown to induce large changes in arterial blood pressure and heart rate in homeotherms. The present study was designed to investigate whether small incremental changes in T(a), such as those found in typical laboratory settings, would have an impact on blood pressure and other cardiovascular parameters in mice and rats. We predicted that small decreases in T(a) would impact the cardiovascular parameters of mice more than rats due to the increased thermogenic demands resulting from a greater surface area-to-volume ratio in mice relative to rats. Cardiovascular parameters were measured with radiotelemetry in mice and rats that were housed in temperature-controlled environments. The animals were exposed to different T(a) every 72 h, beginning at 30 degrees C and incrementally decreasing by 4 degrees C at each time interval to 18 degrees C and then incrementally increasing back up to 30 degrees C. As T(a) decreased, mean blood pressure, heart rate, and pulse pressure increased significantly for both mice (1.6 mmHg/ degrees C, 14.4 beats.min(-1). degrees C(-1), and 0.8 mmHg/ degrees C, respectively) and rats (1.2 mmHg/ degrees C, 8.1 beats.min(-1). degrees C(-1), and 0.8 mmHg/ degrees C, respectively). Thus small changes in T(a) significantly impact the cardiovascular parameters of both rats and mice, with mice demonstrating a greater sensitivity to these T(a) changes.     

Effect of cold air inhalation on core temperature in exercising subjects under heat stress

Whether increasing respiratory heat loss (RHL) during exercise under heat stress can contain elevation of rectal temperature (Tre) was examined. Eight men cycled twice at 45-50% their maximum work rate until exhaustion at ambient temperature and relative humidity of 38 degrees C and 90-95%, respectively. They inspired either cold (3.6 degrees C) or ambient air in random sequence. When subjects breathed cold air during 23 min of exercise, a ninefold increase in RHL was observed vs. similar work during hot air inhalation (32.81 vs. 3.46 W). Respiratory frequency (f) and rate of rise in Tre decreased significantly (P less than or equal to 0.004 and P less than or equal to 0.002, respectively). The rise in skin temperature in each inhalant gas condition was accompanied by a parallel almost equal increase in core temperature above basal (delta Tre) for equivalent gains in skin temperature. The increase in tidal volume and decreased f in the cold condition allowed more effective physical conditioning of cold inspirate gas in the upper airways and aided RHL. Cold air inhalation also produced a significant (P less than or equal to 0.05) decrease in heart rate vs. hot air inhalation in the final stages of exercise. Insignificant changes in O2 consumption and total body fluid loss were found. These data show that cold air inhalation during exercise diminishes elevation of Tre and suggest that both the intensity and duration of work can thus be extended. The importance of the physical exchange of heat energy and any physiological mechanisms induced by the cold inspirate in producing the changes is undetermined.