LOW THERMAL LIMIT OF GROWTH RATE OF SYMBIODINIUM CALIFORNIUM (DINOPHYTA) IN CULTURE MAY RESTRICT THE SYMBIONT TO SOUTHERN POPULATIONS OF ITS HOST ANEMONES (ANTHOPLEURA SPP.; ANTHOZOA,CNIDARIA)1

Symbiodinium californium (#383, Banaszak et al. 1993 ) is one of two known dinoflagellate symbionts of the intertidal sea anemones Anthopleura elegantissima, A. xanthogrammica, and A. sola and occurs only in hosts at southern latitudes of the North Pacific. To investigate if temperature restricts the latitudinal distribution of S. californium, growth and photosynthesis at a range of temperatures (5°C–30°C) were determined for cultured symbionts. Mean specific growth rates were the highest between 15°C and 28°C (μ 0.21–0.26 · d^?1) and extremely low at 5, 10, and 30°C (0.02–0.03 · d^?1). Average doubling times ranged from 2.7 d (20°C) to 33 d (5, 10, and 30°C). Cells cultured at 10°C had the greatest cell volume (821 μm³) and the highest percentage of motile cells (64.5%). Growth and photosynthesis were uncoupled; light‐saturated maximum photosynthesis (P_max) increased from 2.9 pg C · cell^?1 · h^?1 at 20°C to 13.2 pg C · cell^?1 · h^?1 at 30°C, a 4.5‐fold increase. Less than 11% of daily photosynthetically fixed carbon was utilized for growth at 5, 10, and 30°C, indicating the potential for high carbon translocation at these temperatures. Low temperature effects on growth rate, and not on photosynthesis and cell morphology, may restrict the distribution of S. californium to southern populations of its host anemones.     

INTERACTIVE EFFECTS OF IRRADIANCE AND TEMPERATURE ON THE PHOTOSYNTHETIC PHYSIOLOGY OF THE PENNATE DIATOM PSEUDO‐NITZSCHIA GRANII (BACILLARIOPHYCEAE) FROM THE NORTHEAST SUBARCTIC PACIFIC1

This study examined how light and temperature interact to influence growth rates, chl a, and photosynthetic efficiency of the oceanic pennate diatom Pseudo‐nitzschia granii Hasle, isolated from the northeast subarctic Pacific. Growth rates were modulated by both light and temperature, although for each irradiance tested, the growth rate was always the greatest at ～14°C. Chl a per cell was affected primarily by temperature, except at the maximum chl a per cell (at 10°C) where the effects of light were noticeable. At both ends of the temperature gradient, cells displayed evidence of chlorosis even at low light intensities. Chl fluorescence data suggested that cells at 8°C were significantly more efficient in their photosynthetic processes than cells at 20°C, despite having comparable concentrations of chl. Cells at low temperature showed photosynthetic characteristics similar to high‐irradiance‐adapted cells. The decline of growth rates beyond the optimum growth temperature coincided with the cell's inability to accumulate chl in response to increasing temperature. The decline in photosynthetic ability at 20°C was likely due to a combination of high‐temperature stress on cellular membranes and a decline in chl. Our results highlight the important interactions between light and temperature and the need to incorporate these interactions into the development of phytoplankton models for the subarctic Pacific.     

INORGANIC CARBON REPLETION DISRUPTS PHOTOSYNTHETIC ACCLIMATION TO LOW TEMPERATURE IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS1

Acclimation of cyanobacteria to ambient fluctuations in inorganic carbon (Ci) and temperature requires reorganization of the major protein complexes involved in photosynthesis. We grew cultures of the picoplanktonic cyanobacterium Synechococcus elongatus Naegeli across most of its range of tolerable temperatures from 23 to 35°C at both low (<0.1 mM) and high Ci (approximately 4 mM). Over that range of temperatures, the chl‐based doubling time did not differ between low and high Ci grown cells but did increase with decreasing temperature. Cells grown at 23°C high Ci showed an elongated morphology, which was not present in 23°C low Ci cells nor at 35°C high and low Ci. Furthermore, 23°C high Ci cells showed premature senescence and death compared with all other treatments. Phycocyanin per cell was greater in high Ci grown cells at all temperatures but showed a characteristic decrease with decreasing temperature. Functional PSII determination showed that 23°C high Ci cells had 1.5 × 10⁵ PSII·cell^–1 compared with only 6.9 × 10⁴ PSII·cell^–1 for 23°C low Ci. The 35°C high and low Ci cells had 7.7 × 10⁴ and 6.4 × 10⁴ PSII·cell^–1, respectively. These data were supported by immunoblot determinations of PsbA content·cell^–1. As a result of their high PSII·cell^–1, 23°C high Ci cells generated more reductant from PSII than could be accommodated by downstream assimilative metabolism, resulting in early senescence and death of 23°C high Ci cells, probably as a result of the generation of reactive byproducts of electron transport.     

INFLUENCE OF SALINITY AND TEMPERATURE ON GROWTH AND PHOTOSYNTHESIS IN THE EXTREMOPHILIC CHLOROPHYTE,NANNOCHLORIS SP.

Major, K. M. & Henley, W. J. Department of Botany, Oklahoma State University, Stillwater, OK 74078-3013 USA Preliminary data suggest Nannochloris sp., isolated from the Great Salt Plains National Wildlife Refuge, is a true extremophile. This alga is able to withstand salinities ranging from 0 to 150 ç and temperatures up to 45°C. To test the hypothesis that acclimation to high salinity confers tolerance to high temperature, experimental cultures were acclimated to salinities of 25 and 100 ç and/or temperatures of 23 and 38°C; irradiance (500 mol photons m^-2 s^-1) was saturating for both growth and photosynthesis. Cells acclimated to low salt and low temperature exhibited high photosynthetic performance in terms of both light-saturated photosynthesis (P_max; 45.0 fmol O₂ cell^-1 h^-1) and light-harvesting efficiency (0.103 fmol O₂ cell^-1 h^-1/mol photons m^-2 s^-1). However, high-salinity cells exhibited values for net P_max (18.1 fmol O₂ cell^-1 h^-1), (0.107 fmol O₂ cell^-1 h^-1/mol photons m^-2 s^-1) and growth rates (ca. 0.4 d^-1) that were equal to, or higher than, those of low-salinity cells when acclimated to high temperature. Both the amount of light required to achieve net photosynthesis (I_c) and that required to achieve light-saturated photosynthesis (I_k) were lower in high-salinity cells than those exhibited by low-salinity cells grown at high temperature; reductions in I_c and I_k were primarily due to increases in light-harvesting efficiency. We propose that an increase in growth temperature might release Nannochloris sp. from energy constraints associated with osmolyte production and low-temperature effects on enzyme activity. These data are consistent with effects of short-term temperature stress on Chl a fluorescence kinetics in this alga.     

RESPONSE OF TRACHYDISCUS MINUTUS (XANTHOPHYCEAE) TO TEMPERATURE AND LIGHT1

The effects of different temperatures and light intensities on growth, pigments, sugars, lipids, and proteins, as well as on some antioxidant and proteolytic enzymes of Trachydiscus minutus (Bourr.) H. Ettl, were investigated. The optimum growth temperature and light intensity were 25°C and 2 × 132 μmol photons · m^?2 · s^?1, respectively. Under these conditions, proteins were the main biomass components (33.45% dry weight [dwt]), with high levels of carbohydrates (29% dwt) and lipids (21.77% dwt). T. minutus tolerated temperatures between 20°C and 32°C, with only moderate changes in cell growth and biochemical composition. Extremely low (15°C) and high (40°C) temperatures decreased chl and RUBISCO contents and inhibited cell growth. The biochemical response of the alga to both unfavorable conditions was an increase in lipid content (up to 35.19% dwt) and a decrease in carbohydrates (down to 13.64% dwt) with much less of a change in total protein content (in the range of 30.51%–38.13% dwt). At the same time, the defense system of T. minutus was regulated differently in response to heat or cold treatments. Generally, at 40°C, the activities of superoxide dismutase (SOD), catalase (CAT), and proteases were drastically elevated, and three polypeptides were overexpressed, whereas the glutathione reductase (GR) and peroxidase (POD) activities were reduced. In contrast, at 15°C, all these enzymes except GR were suppressed. The effect of light was to enhance or decrease the temperature stress responses, depending on intensity. Our studies demonstrate the broad temperature adaptability of T. minutus as well as the potential for the production of valuable algal biomass.     

RESPONSE TO SALINITY AND HEAT STRESS IN TWO HALOTOLERANT CHLOROPHYTE ALGAE1

Two new isolates of halotolerant chlorophyte algae from the Salt Plains National Wildlife Refuge in Oklahoma, USA, tentatively identified as Dunaliella sp. Teodoresco and Nannochloris sp. Naumann, were characterized with respect to interaction between growth salinity and short‐term heat tolerance. Cells were cultured at 23–25° C over a wide range of salinity. In both species, salinity alone had little effect on maximum photochemical yield (measured by pulse modulated fluorescence) and integrity of the light harvesting system (77 K fluorescence emission spectra). In contrast, Nannochloris exhibited decreasing growth rate (μ), light‐saturated photosynthetic capacity (P^cell_max), respiration (R_d), light‐harvesting efficiency (α^cell), and chl content with increasing salinity. Cultures were heated for 2 h near their upper temperature limits (41.5° C for Dunaliella and 45° C for Nannochloris grown at 50 psu). Dunaliella was progressively more heat‐tolerant with increasing salinity. Photochemical yield of cells at 100 and 50 psu was inhibited by about 15% and 40%, respectively, and largely recovered within 30 min after return to 23° C. Thermal inhibition of photochemical yield in Nannochloris was about 45% at both 50 and 100 psu, but recovery was slower at 100 psu. At 20 psu, both species were almost 90% inhibited by high temperature and required more than a day to recover. In both species, 2 h of heating increased the PSI:PSII fluorescence emission ratio (714:690 nm) at all salinities. This ratio largely recovered within 24 h in Dunaliella at 50 and 100 psu and partially recovered in Nannochloris at 100 psu, but cells of both species heated at 20 psu were chlorotic the next day.     

The effect of temperature on photosynthetic and respiratory electron transport system activity in the shallow and deep-living phytoplankton of a subalpine lake

SUMMARY. 1. The influence of temperature on in vivo photosynthetic and in vitro respiratory electron transport system (ETS) activity was determined over the season for the 3 m (warm-water) and a 20m (cold-water) phytoplankton communities in Castle Lake. The optimum temperature of photosynthesis at 3 m (X?=20.8°C) was significantly higher than the average optimum at 20 m (X?=14.8°C). 2. Seasonally, the photosynthetic temperature optimum increased when the blue-green alga Chroococcus limneticus Lemm. was present. The temperature characteristics of this organism were maintained even after it had settled into the cold water of the hypolimnion. 3. Temperature optima were not significantly different in experiments conducted under limiting or saturating photosynthetic photon flux densities (PPFD). 4. Short-term (1 h) preincubations with dissolved inorganic nitrogen (DIN) (?80 μg NH₄NO₃-N l^?1) had little effect on the temperature characteristics of photosynthesis while the longer (>24 h) incubations provided by a whole-lake epilimnetic DIN addition (?75 μg NH₄NO₃- N l^?1) significantly lowered the photosynthetic temperature optimum to 12.5°C. Once this epilimnetic DIN was depleted the optimum roseto25°C, a value higher than that present before the enrichment, which coincided with the growth of C limneticus. 5. Respiratory ETS activity usually began to inactivate between 19 and 20°C. However, when C. limneticus was abundant the inactivation temperature was often greater ihan 25°C. 6. The average energy of activation (E) and Q₁₀ value for the 3 m community (15.9 kcal mol^?1 and 2.6 respectively) were significantly higher than those at 20 m (14.2 kcal mol^?1 and 2.4 respectively). Seasonally, the highest E and Q₁₀ values of ETS activity occurred during the late-summer bloom of C. limneticus. 7. These results demonstrate that the epilimnetic and hypolimnetic phytoplankton communities in Castle Lake are physiologically distinct with regards to their temperature characteristics.     

THE EFFECTS OF TEMPERATURE ON THE PHOTOSYNTHETIC PARAMETERS AND RECOVERY OF TWO TEMPERATE BENTHIC MICROALGAE,AMPHORA CF. COFFEAEFORMIS AND COCCONEIS CF. SUBLITTORALIS (BACILLARIOPHYCEAE)1

Temperature and irradiance are the most important factors affecting marine benthic microalgal photosynthetic rates in temperate intertidal areas. Two temperate benthic diatoms species, Amphora cf. coffeaeformis (C. Agardh) Kütz. and Cocconeis cf. sublittoralis Hendey, were investigated to determine how their photosynthesis responded to temperatures ranging from 5°C to 50°C after short‐term exposure (1 h) to a range of irradiance levels (0, 500, and 1,100 μmol photons · m^?2 · s^?1). Significant differences were observed between the temperature responses of maximum relative electron transport rate (rETRmax), photoacclimation index (E_k), photosynthetic efficiency (α), and effective quantum yield (ΔF/F_m’) in both species. A. coffeaeformis had a greater tolerance to higher temperatures than C. sublittoralis, with nonphotochemical quenching (NPQ) activated at temperatures of 45°C and 50°C. C. sublittoralis, however, demonstrated a more rapid rate of recovery at ambient temperatures. Temperatures between 10°C and 20°C were determined to be optimal for photosynthesis for both species. High temperatures and irradiances caused a greater decrease in ΔF/F_m’ values. These results suggest that the effects of temperature are species specific and that short‐term exposure to adverse temperature slows the recovery process, which subsequently leads to photoinhibition.     

THE INABILITY OF THE TEXAS “BROWN TIDE” ALGA TO USE NITRATE AND THE ROLE OF NITROGEN IN THE INITIATION OF A PERSISTENT BLOOM OF THIS ORGANISM1

A planktonic alga similar in general morphology and pigments to Aureococcus anophagefferens Hargraves and Sieburth has caused persistent and ecologically damaging blooms along the south Texas coast. Experiments using 100 μM NO₃^?, NO₂^?, and NH₄⁺ demonstrated that the alga could not use NO₃^? for growth but could use NO₂^? and NH₄⁺. Doubling iron or trace metal concentrations did not permit growth on NO₃^?. Chemical composition data for cultures grown in excess NO₃^? or NH₄⁺, respectively, were as follows: N·cell^?1 (0.88 vs. 1.3 pg), C:N ratio (25:1 vs. 6.4:1), C:chlorophyll a (chl a) (560:1 vs. 44:1), and chl a·cell^?1 (0.033 vs. 0.16 pg). These data imply that cells supplied with NO₃^? were N-starved. Culture addition of 10 mM final concentration chlorate (a nitrate analog) did not affect the Texas isolate while NO₃^? utilizing A. anophagefferens was lysed, suggesting that the NO₃^? reductase of the Texas isolate is nonfunctional. Rates of primary productivity determined during a dense bloom indicated that light-saturated growth rates were ca. 0.45 d^?1, which is similar to maximum rates determined in laboratory experiments (0.58 d^?1± 0.16). However, chemical composition data were consistent with the growth rate of these cells being limited by N availability (C:N 28, C:chl a 176, chl a·cell^?1 0.019). Calculations based on a mass balance for nitrogen suggest that the bloom was triggered by an input of ca. 69 μM NH₄⁺ that resulted from an extensive die-off of benthos and fish.     

Applicability of the fluorescein diacetate assay for metabolic activity measurement of Microcystis aeruginosa (Chroococcales,Cyanobacteria)

The fluorescein diacetate (FDA) assay has been widely used to measure metabolic activity in phytoplankton. It was found that FDA fluorescence values did not decrease in some stressed cells, demonstrating that the applicability of the method needs to be assessed further in the context of growth‐influencing conditions. In the present study, changes of FDA fluorescence values were studied in bloom‐forming cyanobacterial Microcystis aeruginosa Kütz cells under stress conditions such as nitrogen (N) or phosphorus (P) deficiency, or darkness and low temperature (10°C), respectively. The results demonstrated that esterase activity decreased immediately in dark‐stressed cells, which correlated with the decline of biomass and photosynthetic activity. Under the other three stress conditions, however, especially at low temperature, the cells lost photosynthetic activity but had the highest esterase activity, which was five times higher than the control group. These findings contrast with the assay criteria that the expression of a stain should reflect the change of photosynthetic activity and that stressed cells should have a lower staining intensity than the control cells. According to these results, the esterase activity response was dependent on environmental factors. Furthermore, higher fluorescence intensity did not mean higher metabolic activity, but a discrepant value indicated a severe stress.     

PHYSIOLOGICAL RESPONSES OF ECKLONIA RADIATA (LAMINARIALES) TO A LATITUDINAL GRADIENT IN OCEAN TEMPERATURE1

We tested the ability of sporophytes of a small kelp, Ecklonia radiata (C. Agardh) J. Agardh, to adjust their photosynthesis, respiration, and cellular processes to increasingly warm ocean climates along a latitudinal gradient in ocean temperature (～4°C). Tissue concentrations of pigment and nutrients decreased with increasing ocean temperature. Concurrently, a number of gradual changes in the metabolic balance of E. radiata took place along the latitudinal gradient. Warm‐acclimatized kelps had 50% lower photosynthetic rates and 90% lower respiration rates at the optimum temperature than did cool‐acclimatized kelps. A reduction in temperature sensitivity was also observed as a reduction in Q₁₀‐values from cool‐ to warm‐acclimatized kelps for gross photosynthesis (Q₁₀: 3.35 to 1.45) and respiration (Q₁₀: 3.82 to 1.65). Respiration rates were more sensitive to increasing experimental temperatures (10% higher Q₁₀‐values) than photosynthesis and had a higher optimum temperature, irrespective of sampling location. To maintain a positive carbon balance, E. radiata increased the critical light demand (E_c) exponentially with increasing experimental temperature. The temperature dependency of E_c was, however, weakened with increasing ocean temperature, such that the critical light demand was relaxed in kelp acclimated to higher ocean temperatures. Nevertheless, calculations of critical depth limits suggested that direct effects of future temperature increases are unlikely to be as strong as effects of reduced water clarity, another globally increasing problem in coastal areas.     

EFFECTS OF LIGHT AND TEMPERATURE ON GROWTH,NITRATE UPTAKE,AND TOXIN PRODUCTION OF TWO TROPICAL DINOFLAGELLATES: ALEXANDRIUM TAMIYAVANICHII AND ALEXANDRIUM MINUTUM (DINOPHYCEAE)1

The two tropical estuarine dinoflagellates, Alexandrium tamiyavanichii Balech and A. minutum Halim, were used to determine the ecophysiological adaptations in relation to their temperate counterparts. These species are the two main causative organisms responsible for the incidence of paralytic shellfish poisoning (PSP) in Southeast Asia. The effects of light (10, 40, 60, and 100 μmol photons·m^?2·s^?1) and temperature (15, 20, and 25°C) on the growth, nitrate assimilation, and PST production of these species were investigated in clonal batch cultures over the growth cycle. The growth rates of A. tamiyavanichii and A. minutum increased with increasing temperature and irradiance. The growth of A. tamiyavanichii was depressed at lower temperature (20°C) and irradiance (40 μmol photons·m^?2·s^?1). Both species showed no net growth at 10 μmol photons·m^?2·s^?1 and a temperature of 15°C, although cells remained alive. Cellular toxin quotas (Q_t) of A. tamiyavanichii and A. minutum varied in the range of 60–180 and 10–42 fmol PST·cell^?1, respectively. Toxin production rate, R_tox, increased with elevated light at both 20 and 25°C, with a pronounced effect observed at exponential phase in both species (A. tamiyavanichii, r²=0.95; A. minutum, r²=0.96). Toxin production rate also increased significantly with elevated temperature (P<0.05) for both species examined. We suggest that the ecotypic variations in growth adaptations and toxin production of these Malaysian strains may reveal a unique physiological adaptation of tropical Alexandrium species.     

EFFECT OF TEMPERATURE,LIGHT AND pH ON GROWTH,PHOTOSYNTHESIS AND RESPIRATION OF THE DINOFLAGELLATE PERIDINIUM CINCTUM FA. WESTII IN LABORATORY CULTURES1

Optimum light, temperature, and pH conditions for growth, photosynthetic, and respiratory activities of Peridinium cinctum fa. westii (Lemm.) Lef were investigated by using axenic clones in batch cultures. The results are discussed and compared with data from Lake Kinneret (Israel) where it produces heavy blooms in spring. Highest biomass development and growth rates occurred at ca. 23° C and ≥50 μE· m^?2·s¹ of fluorescent light with energy peaks at 440–575 and 665 nm. Photosynthetic oxygen release was more efficient in filtered light of blue (BG 12) and red (RG 2) than in green (VG 9) qualities. Photosynthetic oxygen production occurred at temperatures ranging from 5° to 32° C in white fluorescent light from 10 to 105 μE·m^?2·s^?1 with a gross maximum value of 1500 × 10^?12 g·cell^?1·h^?1 at the highest irradiance. The average respiration amounted to ca. 12% of the gross production and reached a maximum value of ca. 270·10^?12 g·cell^?1·h^?1 at 31° C. A comparison of photosynthetic and respiratory Q₁₀-values showed that in the upper temperature range the increase in gross production was only a third of the corresponding increase in respiration, although the gross production was at maximum. Short intermittent periods of dark (>7 min) before high light exposures from a halogen lamp greatly increased oxygen production. Depending on the physiological status of the alga, light saturation values were reached at 500–1000 μE·m^?2·s^?1 of halogen light with compensation points at 20–40 μE·m^?2·s^?1 and I_k-values at 100–200 μE·m^?2·s^?1. The corresponding values in fluorescent light in which it was cultured and adapted, were 25 to 75% lower indicating the ability of the alga to efficiently utilize varying light conditions, if the adaptation time is sufficient. Carbon fixation was most efficient at ca. pH 7, but the growth rates and biomass development were highest at pH 8.3.     

EFFECT OF ELEVATED TEMPERATURE,DARKNESS, AND HYDROGEN PEROXIDE TREATMENT ON OXIDATIVE STRESS AND CELL DEATH IN THE BLOOM‐FORMING TOXIC CYANOBACTERIUM MICROCYSTIS AERUGINOSA1

This study assessed the implication of oxidative stress in the mortality of cells of Microcystis aeruginosa Kütz. Cultures grown at 25°C were exposed to 32°C, darkness, and hydrogen peroxide (0.5 mM) for 96 h. The cellular abundance, chl a concentration and content, maximum photochemical efficiency of PSII (F_v/F_m ratio), intracellular oxidative stress (determined with dihydrorhodamine 123 [DHR]), cell mortality (revealed by SYTOX‐labeling of DNA), and activation of caspase 3–like proteins were assessed every 24 h. The presence of DNA degradation in cells of M. aeruginosa was also assessed using a terminal deoxynucletidyl transferase‐mediated dUTP nick end labeling (TUNEL) assay at 96 h. Transferring cultures from 25°C to 32°C was generally beneficial to the cells. The cellular abundance and chl a concentration increased, and the mortality remained low (except for a transient burst at 72 h) as did the oxidative stress. In darkness, cells did not divide, and the F_v/F_m continuously decreased with time. The slow increase in intracellular oxidative stress coincided with the activation of caspase 3–like proteins and a 15% and 17% increase in mortality and TUNEL‐positive cells, respectively. Exposure to hydrogen peroxide had the most detrimental effect on cells as growth ceased and the F_v/F_m declined to near zero in less than 24 h. The 2‐fold increase in oxidative stress matched the activation of caspase 3–like proteins and a 40% and 37% increase in mortality and TUNEL‐positive cells, respectively. These results demonstrate the implication of oxidative stress in the stress response and mortality of M. aeruginosa.     

Gene or Size: Metabolic Rate and Body Temperature in Obese Growth Hormone‐Deficient Dwarf Mice

Objective: SMA1 mice carry a missense mutation in the growth hormone gene that leads to semidominant dwarfism and obesity. In this study, the basic thermal and metabolic properties of SMA1 mice were examined to detect metabolic alterations that can support the accretion of excess fat. Research Methods and Procedures: Basal and resting metabolic rates (RMRs) in wild‐type and SMA1 (sma1/+ and sma1/sma1) mice were determined by indirect calorimetry. Body temperature (T_b) was recorded using intraperitoneally implanted temperature‐sensitive transmitters, and body composition was determined by DXA. Results: SMA1 mice have proportionally lower basal and resting metabolic rates, higher body mass (BM)‐specific RMRs, and a higher lower critical temperature, and display a decrease in T_b by 0.4 °C in sma1/+ and 0.9 °C in sma1/sma1. Discussion: The analysis of gene effects on BM and energy expenditure in mouse mutants must consider the appropriate allometric relationship between BM and metabolic rate. With the exception of T_b, all metabolic alterations observed in SMA1 reflect reduced size.     

A COMPARISON OF THE IMMEDIATE EFFECTS OF MODERATE EXERCISE IN THE EARLY MORNING AND LATE AFTERNOON ON CORE TEMPERATURE AND CUTANEOUS THERMOREGULATORY MECHANISMS

Twelve healthy male subjects each undertook two bouts of moderate exercise (70% VO₂max for 30 minutes) in the morning (08:00) and late afternoon (18:00) at least 4 days apart. Measurements were made of heart rate, core (rectal) temperature, sternum skin temperature, and forearm skin blood flow during baseline conditions, during the bout of exercise, and throughout a 30-minute recovery period. Comparisons were made of the changes of heart rate, temperature, and skin blood flow produced by the exercise at the two times of day. Student t tests indicated that baseline values for core temperature (37.15°C ±. 06°C vs. 36.77°C ± 0.06°C) and sternum temperature (33.60°C ± 0.29°C vs. 32.70°C ± 0.38°C) were significantly (p <. 05) higher in the late afternoon than the early morning. Two-way analysis of variance (ANOVA) indicated that the increases in core and sternum temperatures during exercise were significantly less (p =. 0039 and. 0421, respectively) during the afternoon bout of exercise compared with the morning, even though the work loads, as determined by changes in heart rate, were not significantly different (p =. 798) at the two times of testing. There were also tendencies for resting forearm skin blood flow to be higher in the afternoon than in the morning and for exercise to produce a more rapid rise in this variable in the afternoon. The possible mechanisms producing these responses to exercise are discussed in terms of those that are responsible for the normal circadian rhythm of core temperature. It is concluded that the body's ability to remove a heat load is less in the early morning, when the circadian system is in a “heat gain” mode, than in the late afternoon, when heat gain and “heat loss” modes are balanced more evenly. (Chronobiology International, 17(2), 197–207, 2000)     

THE EFFECT OF CONSTANT TEMPERATURES ON THE HATCHING OF EGGS AND SURVIVAL OF THE FRESHWATER SNAIL BIOMPHALARIA GLABRATA (SAY)

SUMMARY

The incubation period and percentage hatching of eggs of pigmented and unpigmented Biomphalaria glabrata at constant temperatures were investigated in the range 14 °C to 34 °C. In order to determine the influence of extreme temperatures on adult snails, specimens of the same species were exposed to 0 °C and 40 °C for selected time periods. The results indicate that sustained temperatures below 16 °C and above 32 °C are detrimental to the development and hatching of B. glabrata embryos. The optimum temperatures for incubation period and hatching differ from each other. As far as temperature is concerned, this foreign snail species should be capable of successfully colonizing the warmer parts of southern Africa.     

COMPARATIVE STUDY ON THE PHOTOSYNTHETIC PROPERTIES OF PRASIOLA (CHLOROPHYCEAE) AND NOSTOC (CYANOPHYCEAE) FROM ANTARCTIC AND NON‐ANTARCTIC SITES1

The terrestrial cyanobacterium Nostoc commune Vaucher ex Bornet et Flahault occurs worldwide, including in Japan and on the Antarctic continent. The terrestrial green alga Prasiola crispa (Lightf.) Kütz. is also distributed in Antarctica. These two species need to acclimate to the severe Antarctic climate including low ambient temperature and desiccation under strong light conditions. To clarify this acclimation process, the physiological characteristics of the photosynthetic systems of these two Antarctic terrestrial organisms were assessed. The relative rate of photosynthetic electron flow in N. commune collected in Japan and in Antarctica reached maxima at 900 and 1,100 μmol photons · m^?2 · s^?1, respectively. The difference seemed to reflect the presence of high amounts of UV‐absorbing substances within the Antarctic cyanobacterium. On the other hand, the optimal temperatures for photosynthesis at the two locations were 30°C–35°C and 20°C–25°C, respectively. This finding suggested a decreased photosynthetic thermotolerance in the Antarctic strain. P. crispa exhibited desiccation tolerance and dehydration‐induced quenching of PSII fluorescence. Re‐reduction of the photooxidized PSI reaction center, P700, was also inhibited at fully dry states. Photosynthetic electron flow in P. crispa reached a maximum at 20°C–25°C and at a light intensity of 700 μmol photons ? m^?2 ? s^?1. Interestingly, the osmolarity of P. crispa cells suggested that photosynthesis is performed using water absorbed in a liquid form rather than water absorbed from the air. Overall, these data suggest that these two species have acclimated to optimally photosynthesize under conditions of the highest light intensity and the highest temperature for their habitat in Antarctica.     

PHYSIOLOGICAL AND ENVIRONMENTAL CONTROL OF GERMINATION IN SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE) RESTING CYSTS1

The effects of aging, temperature, and growth medium on germination in culture-produced resting cysts of the marine dinoflagellate Scrippsiella trochoidea (Stein) Loeblich ore examined. Cysts undergo a mandatory period of dormancy lasting approximately 25 days, during which germination does not occur. The duration of this period is not affected by temperature. Once the dormancy period is completed, germination is regulated by external factors. Cysts germinate optimally in nutrient replete medium at temperatures greater than approximately 14° C. At lower temperatures or in nutrient-depleted media germination rate is dramatically slowed, although the final germination frequency appears unchanged. The large Q₁₀ of this temperature effect (ca. 11) suggests that the reduction in germination rate at lower temperatures is not merely the reflection of generally reduced metabolic rates, but rather the result of a temperature response specific to germination. At the highest temperatures tested (22–25° C), germination rate remains maximal although vegetative growth is greatly reduced. A shift in temperature or nutrient conditions, per se, is not necessary for germination. The relatively short dormancy period combined with the absence of a requirement for a dramatic shift in environmental conditions could facilitate rapid cycling between resting and vegetative stages in natural S. trochoidea populations. At the same time, the dramatic reduction in germination rate at low temperatures would permit cysts of this species to serve as overwintering cells as well.