Triacylglycerol phase and ‘intermediate’ seed storage physiology: a study of Cuphea carthagenensis

Seeds with ‘intermediate’ storage physiology store poorly under cold and dry conditions. We tested whether the poor shelf life can be attributed to triacylglycerol phase changes using Cuphea carthagenensis (Jacq.) seeds. Viability remained high when seeds were stored at 25°C, but was lost quickly when seeds were stored at 5°C. Deterioration was fastest in seeds with high (≥0.10 g g⁻¹) and low (0.01 g g⁻¹) water contents (g H₂O g dry mass⁻¹), and slowest in seeds containing 0.04 g g⁻¹. A 45°C treatment before imbibition restored germination of dry seeds by melting crystallized triacylglycerols. Here, we show that the rate of deterioration in C. carthagenensis seeds stored at 5°C correlated with the rate that triacylglycerols crystallized within the seeds. Lipid crystallization, measured using differential scanning calorimetry, occurred at 6°C for this species and was fastest for seeds stored at 5°C that had high and very low water contents, and slowest for seeds containing 0.04 g g⁻¹. Germination decreased to 50% (P50) when between 16 and 38% of the triacylglycerols crystallized; complete crystallization took from 10 to over 200 days depending on water content. Our results demonstrate interactions between water and triacylglycerols in seeds: (1) water content affects the propensity of triacylglycerols to crystallize and (2) hydration of seed containing crystallized triacylglycerols is lethal. We suggest that these interactions form the basis of the syndrome of damage experienced when seeds with intermediate storage physiologies are placed in long-term storage.     

An examination of the moisture sorption characteristics of commercial magnesium stearate

The objective of this study was to characterize the moisture sorption of magnesium stearate and the morphological changes, if any, resulting from moisture sorption. Six samples of commercial magnesium stearate USP were examined. Moisture sorption isotherms were obtained at 25°C and 5% to 98% relative humidity (RH) using a moisture balance. Changes in crystal form resulting from moisture sorption were determined by x-ray diffraction. There were differences in the shape of the isotherm, reversibility of moisture uptake, and shape of the hysteresis loop in the isotherms of crystalline and amorphous magnesium stearates. The isotherm of crystalline magnesium stearate was almost parallel to the pressure axis until and RH of ∼80%. The isotherm of the amorphous sample was characterized by continuous uptake of water over the entire range of RH. Exposure of amorphous magnesium stearate to RH greater than 70% resulted in the formation of the trihydrate. The trihydrate was converted into the anhydrous form when heated to a temperature of 100°C to 105°C. The trihydrate could be generated by exposing the anhydrate to RH higher than 70%.     

Effects of brassinosteroid infiltration prior to cold treatment on ion leakage and pigment contents in rape leaves

The effect of 24-epibrassinolide (BR₂₇) on cold resistance of rape seedlings was studied by ion leakage and photosynthetic pigment degradation measurements. Aqueous solutions of BR₂₇ were injected into cotyledons or primary leaves of rape plants and these plants were incubated at 2 °C or 20 °C. Cold treatment (2 °C) without BR₂₇ injection elevated the membrane permeability in both primary leaves and cotyledons significantly. Surprisingly, injection of leaves with water or 0.467 % aqueous ethanol solution led to a massive increase in membrane permeability after cold stress at 2 °C. The synergistic effect of leaf infiltration and cold on permeability was abolished by 0.05 and 1.00 μM of BR₂₇ in primary leaves and by 1.00 μM of BR₂₇ in cotyledons. On the other hand, BR₂₇ solutions strongly elevated the membrane permeability at 20 °C, while water and ethanol solutions brought about only negligible increases. Water or ethanol infiltrations strongly reduced the leaf contents of chlorophyll (Chl) a, Chl b and carotenoids at 2 °C but less markedly at 20 °C. However, in seedlings exposed to 2 °C pigments content was significantly higher in BR₂₇-treated leaves as compared to water/ethanol control. There were no differences between pigment contents of leaves injected with BR₂₇ solutions or only water/ethanol at 20 °C. The above data strongly support the stress protecting effect of BR₂₇.     

Physiological responses of Opuntia ficus-indica to growth temperature

The influences of various day/night air temperatures on net CO₂ uptake and nocturnal acid accumulation were determined for Opuntia ficus-indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO₂ uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO₂ residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO₂ uptake at all growth temperatures. Nocturnal CO₂ uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO₂ uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non-optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO₂ uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus-indica and presumably for other CAM plants.     

Effects of ambient temperature and of temperature acclimation on nitrogen excretion and differential catabolism of protein and nonprotein resources in the intertidal snails,Littorina saxatilis (Olivi) and L. obtusata (L.)

Nitrogenous excretion in two snails, Littorina saxatilis (high intertidal) and L. obtusata (low intertidal) was studied in relation to temperature acclimation (at 4° and 21°C), including total N excretion rates, the fraction of urea in N excretion, corresponding O:N ratios and the partitioning of deaminated protein between catabolic and anabolic processes at 4°, 11° and 21°C. Aggregate N excretion rates in both species showed no significant compensatory adjustments following acclimation. Total weight specific N excretion rates at 21°C were higher in standard 3 mg L. saxatilis (739 ng N mg⁻¹ h⁻¹) than standard 5 mg L. obtusata (257 ng N mg⁻¹ h⁻¹) for snails acclimated to 21°C. Comparisons of Q₁₀ values of total weight specific N excretion to Q₁₀ values for weight specific oxygen consumption ({xxV}O₂) between 4° to 11 °C and 11° to 21°C indicated that, while total rates of catabolic metabolism ({xxV}O₂) and protein deamination in L. obtusata were essentially parallel, the relationship between N excretion and {xxV}O₂ in L. saxatilis revealed the partitioning of a larger share of deaminated protein carbon into anabolism at 4° and 21°C than at 11°C. Urea N accounted for a larger share of aggregate N excreted in L. saxatilis than in L. obtusata, but in both species urea N is a greater proportion of total N excreted when acclimated at 4°C (urea N: ammonia N ratio range: 1 to 2.15) than in snails acclimated to 21°C (urea N: ammonia N ratio range: 0.46 to 1.39). Molar O:N ratios indicate that the proportion of metabolism supported by protein catabolism is greater in L. saxatilis (O:N range: 2.5–8.4) than in L. obtusata (O:N range: 7.3–13.0). In both species, regardless of acclimation temperature, the O:N ratios are generally lowest (high protein catabolism) at 4°C and highest at 21°C.     

Preformulation Studies of a Prodrug of Δ9-Tetrahydrocannabinol

Preformulation studies were performed on a hemiglutarate ester prodrug of Δ⁹-tetrahydrocannabinol (THC-HG), to facilitate the development of stable formulations by hot-melt methods. The various studies performed included solid-state thermal characterization, pKa, logP, aqueous and pH dependent solubility, pH stability and effect of moisture, temperature and oxygen on solid-state stability. A hot-melt method was utilized to fabricate THC-HG incorporated poly (ethylene oxide) (PEO) matrices and the bioadhesive properties, release profiles and post-processing stability of these matrices were assessed as a function of the polymer molecular weight. The prodrug exhibited a T _g close to 0°C, indicating its amorphous nature. Thermogravimetric analysis revealed a rapid weight loss after 170°C. The prodrug exhibited a seven-fold higher aqueous solubility as compared to the parent drug (THC). Also, the solubility of the compound increased with increasing pH, being maximum at pH 8. The prodrug exhibited a v-shaped pH-rate profile, with the degradation rate minimum between pH 3 and 4. The moisture uptake and drug degradation increased with an increase in relative humidity. Solid-state stability indicated that the prodrug was stable at −18°C but demonstrated higher degradation at 4°C, 25°C and 40°C (51.6%, 74.5% and 90.1%, respectively) at the end of 3-months. THC-HG was found to be sensitive to the presence of oxygen. The release of the active from the polymeric matrices decreased, while bioadhesion increased, with an increase in molecular weight of PEO.     

The Effect of Tripalmitin Crystallization on the Thermomechanical Properties of Candelilla Wax Organogels

The effect of tripalmitin (TP) crystallization on the thermomechanical properties of organogels developed with candelilla wax (CW) was investigated using safflower oil high in triolein (HOSFO) as the liquid phase. Factorial combinations of CW (i.e., 0–3%) and TP (i.e., 0–1%) in the HOSFO were used to develop organogels at three different temperatures (T _set). The onset of crystallization (T _g) during the cooling stage (10 °C/min), the melting temperature (T _M), and the corresponding heat of melting (ΔH _M) of the organogels were determined by differential scanning calorimetry. Results showed that, without CW, the crystallization of TP in the HOSFO at the concentrations and T _set investigated (i.e., −10 °C to 25 °C) did not develop a three-dimensional network that provided significant viscoelasticity (i.e., solid-like behavior) to the HOSFO. The CW developed organogels in the HOSFO with T _M’s that increased from ≈30.5 °C up to ≈42.5 °C as a function of CW concentration. In contrast, in the CW–1% TP system, the co-crystallization of TP and CW resulted in organogels with T_M’s that varied just between 36 °C and 38 °C, independent of the CW concentration. Higher elastic modulus (G′) and yield stress (σ*) were obtained with 3% CW–1.0% TP organogels than with organogels developed just by CW, particularly at T _set’s of −5 °C and 15 °C. This research showed that co-crystallization of TP and CW, occurring at different extent as a function of T _set, resulted in organogels with thermomechanical properties different from the ones showed by CW organogels. The results showed that co-crystallization of triacylglycerides with CW might be a useful alternative to tailor particular physicochemical properties associated to a specific functionality (i.e., melting profile and texture). Organogelation of vegetable oil might be used to develop trans-free vegetable-oil-based spreads and coatings and also novel food products with new textural perceptions for the consumers.     

Relationships of microclimatic variables to colonization of rose debris by Botrytis cinerea and the biocontrol agent Clonostachys rosea

Biological control of Botrytis cinerea by Clonostachys rosea is an alternative to chemical control of rose Botrytis blight in greenhouses. Environmental conditions affect the colonization of senescing and dead tissues by both fungi. The contribution of microclimatic variables to debris colonization/sporulation by both fungi was estimated by path coefficient analysis. We monitored daily values of: maximum, average, and minimum temperatures (T _max, T _ave, and T _min), and relative humidity (RH_max, RH_ave, and RH_min); accumulated rainfall; vapour pressure deficit average; hours with RH?>?90% (RH₉₀); and average temperature during RH₉₀ (T _ave90). Association of variables accumulated between the first and seventh day before sampling explained colonization/sporulation variation: R ²=0.81–0.86 for B. cinerea and 0.91–0.96 for C. rosea. RH_max and RH₉₀ were the main factors that directly favoured colonization/sporulation of both fungi. Colonization/sporulation negatively correlated with RH_min, T _min, and T _ave for B. cinerea and T _min, T _ave, and T _ave90 for C. rosea. The antagonist can suppress B. cinerea colonization/sporulation on rose debris under a wide range of environmental conditions.     

Effect of Bacterial Cell Moisture on the Sporicidal Activity of β-Propiolactone Vapor

The activity of a vapor-phase disinfectant is usually expressed in terms of the atmospheric relative humidity (RH). This study shows that, in β-propiolactone (BPL) vapor disinfection, the important factor is really the moisture content and location of water in the cell, and not necessarily the atmospheric RH. Previous studies revealed that only about 50% of the bacterial spores equilibrated to 45% RH were killed when exposed to the same RH to BPL vapor. On the other hand, all the spores equilibrated to and then exposed at 75% RH to BPL were readily killed. The present study shows that spores equilibrated to 98% RH are readily killed by BPL at 45% RH, but only 99% of the spores equilibrated to 75% RH are killed by BPL at 45% RH. Also, in order to be killed, desiccated spores must be exposed to BPL at higher humidities than would be required if the spores had not been previously desiccated.     

Effect of Bacterial Cell Moisture on the Sporicidal Activity of β-Propiolactone Vapor

The activity of a vapor-phase disinfectant is usually expressed in terms of the atmospheric relative humidity (RH). This study shows that, in β-propiolactone (BPL) vapor disinfection, the important factor is really the moisture content and location of water in the cell, and not necessarily the atmospheric RH. Previous studies revealed that only about 50% of the bacterial spores equilibrated to 45% RH were killed when exposed to the same RH to BPL vapor. On the other hand, all the spores equilibrated to and then exposed at 75% RH to BPL were readily killed. The present study shows that spores equilibrated to 98% RH are readily killed by BPL at 45% RH, but only 99% of the spores equilibrated to 75% RH are killed by BPL at 45% RH. Also, in order to be killed, desiccated spores must be exposed to BPL at higher humidities than would be required if the spores had not been previously desiccated.     

Transformation of water clusters in wet starch under changing environmental conditions

Transformation of the water cluster distribution in wet potato starch (with a water content of 27 to 45%) at temperatures that ranged from–50 to +80°C was studied by differential scanning calorimetry. A significant difference was observed between the transformations in the temperature ranges below and above 0°C. Both cooling and heating at T < 0°C enabled a reorganization of the initial size distribution of water clusters characteristic for room temperature. These changes could lead to an increase of the average cluster size during both crystallization and melting. The transformation intensity depended on the water content and scanning rate and differed between the native and amorphous states of starch. In this case, the cluster-size distribution remained unimodal. However, heating of wet native starch to temperatures close to the point of transition into the amorphous state (75–80°C) induced a bimodal distribution due to the emergence of large water clusters; thus, the heterogeneity of the water distribution within the native granules increased.     

Stoichiometry and temperature sensitivity of methanogenesis and CO2 production from saturated polygonal tundra in Barrow,Alaska

Arctic permafrost ecosystems store ~50% of global belowground carbon (C) that is vulnerable to increased microbial degradation with warmer active layer temperatures and thawing of the near surface permafrost. We used anoxic laboratory incubations to estimate anaerobic CO₂ production and methanogenesis in active layer (organic and mineral soil horizons) and permafrost samples from center, ridge and trough positions of water‐saturated low‐centered polygon in Barrow Environmental Observatory, Barrow AK, USA. Methane (CH₄) and CO₂ production rates and concentrations were determined at ?2, +4, or +8 °C for 60 day incubation period. Temporal dynamics of CO₂ production and methanogenesis at ?2 °C showed evidence of fundamentally different mechanisms of substrate limitation and inhibited microbial growth at soil water freezing points compared to warmer temperatures. Nonlinear regression better modeled the initial rates and estimates of Q₁₀ values for CO₂ that showed higher sensitivity in the organic‐rich soils of polygon center and trough than the relatively drier ridge soils. Methanogenesis generally exhibited a lag phase in the mineral soils that was significantly longer at ?2 °C in all horizons. Such discontinuity in CH₄ production between ?2 °C and the elevated temperatures (+4 and +8 °C) indicated the insufficient representation of methanogenesis on the basis of Q₁₀ values estimated from both linear and nonlinear models. Production rates for both CH₄ and CO₂ were substantially higher in organic horizons (20% to 40% wt. C) at all temperatures relative to mineral horizons (<20% wt. C). Permafrost horizon (~12% wt. C) produced ~5‐fold less CO₂ than the active layer and negligible CH₄. High concentrations of initial exchangeable Fe(II) and increasing accumulation rates signified the role of iron as terminal electron acceptors for anaerobic C degradation in the mineral horizons.     

High precision measurements of atmospheric concentrations and plant exchange rates of carbonyl sulfide using mid‐IR quantum cascade laser

Linking measurements of carbonyl sulfide (COS) with those of carbon dioxide (CO₂) has a potential in providing a powerful tracer of gross CO₂ fluxes between the atmosphere and land plants, a critical element in understanding the response of the land biosphere to global change. A new application of online COS, CO₂ and water vapor measurements based on newly designed mid‐infrared (IR) dual quantum cascade laser (QCL) spectrometer measures COS and CO₂ (at 2056 cm^?1) and water vapor (at 2190 cm^?1), with detectors cooled thermoelectrically (at ?43 °C) or with liquid nitrogen (?197 °C) for improved precision. Using the cryogenic detectors with averaging time of 1 s, precision was 50 pmol mol^?1, 0.4 μmol mol^?1 and 0.01 mmol mol^?1 for COS, CO₂ and water vapor, respectively (14, 0.2 and 0.003, respectively, for 60 s averaging time). We measured COS concentrations in ambient air, and changes in the rates of COS, CO₂ and water vapor exchange of attached leaves in response to changes in light intensity and ambient COS concentrations. The results were consistent with those of nononline gas chromatography–mass spectrometry for COS and IR gas analyzer for CO₂ and water vapor, with a high linear correlation for a broad range of concentrations (R²= 0.85 for COS and R²= 1.00 for CO₂ and water vapor). The new methodology opens the way for lab and field explorations of COS fluxes as a powerful new tracer for CO₂ exchange in the land biosphere.     

Effects of spray-drying and storage on astaxanthin content of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis> biomass

The main objective of this study was to evaluate the stability of astaxanthin after drying and storage at different conditions during a 9-week period. Recovery of astaxanthin was evaluated by extracting pigments from the dried powders and analysing extracts by HPLC. The powders obtained were stored under different conditions of temperature and oxygen level and the effects on the degradation of astaxanthin were examined. Under the experimental conditions conducted in this study, the drying temperature that yielded the highest content of astaxanthin was 220°C, as the inlet, and 120°C, as the outlet temperature of the drying chamber. The best results were obtained for biomass dried at 180/110°C and stored at −21°C under nitrogen, with astaxanthin degradation lower than 10% after 9 weeks of storage. A reasonable preservation of astaxanthin can be achieved by conditions 180/80°C, −21°C nitrogen, 180/110°C, 21°C nitrogen, and 220/80°C, 21°C vacuum: the ratio of astaxanthin degradation is equal or inferior to 40%. In order to prevent astaxanthin degradation of Haematococcus pluvialis biomass, it is recommended the storage of the spray dried carotenized cells (180/110oC) under nitrogen and −21°C.     

Reproduction and population parameters of the Nearctic predator Geocoris punctipes at constant and varying temperature regimes

The heteropteran predator Geocoris punctipes (Say) has been used in augmentative biological control since 2000 to control Lepidoptera. However, surprisingly, few data are available about the influence of temperature on its population development, which is of key importance to plan the number and moment of releases to obtain sufficient pest reduction. The objective of this study was to evaluate daily and total fecundity, longevity and life table parameters (m_x, l_x, r_m, R, λ, T and TD) of G. punctipes at constant (16.8°C, 21.5°C, 24.5°C and 28.3°C) and corresponding varying (day/night) (21/11°C, 24/18°C, 27/21°C and 30/26°C) temperatures. Pairs of adult predators aged 24 h and originating from nymphs exposed to the same temperature regimes were kept at the above‐mentioned temperature regimes in Petri dishes containing Anagasta kuehniella (Zeller) eggs and an oviposition substrate. Tests were conducted in climatic chambers at the different temperature regimes and a RH 70 ± 10% and a 14L: 10D photoperiod. Reproduction, longevity and life table parameters were significantly affected by temperature, with clear differences between treatments at low (16.8°C, 21/11°C, 21.5°C, 24/18°C) or a high (24.5°C, 27/21°C, 28.3°C, 30/26°C) temperature regimes. Highest reproduction and fastest population growth of G. punctipes took place at average temperatures ranging from 24.5°C to 30°C, and neither reproduction nor population growth was negatively influenced by varying temperatures at any of the temperature regimes.     

Gibberellins and the photoperiodic control of leaf growth in Poa pratensis

The role of gibberellins (GAs) in photoperiodic control of leaf elongation in Poa pratensis was studied by both application of exogenous GAs and analysis of endogenous GAs. Leaf elongation was strongly increased under long day (LD, 24 h) conditions at both 9 and 21°C, leaf length at 9°C LD being similar to that in plants grown in short days (SD, 8 h) at 21°C. However, even at 21°C leaf elongation was enhanced by LD. Exogenous GA₁ could completely compensate for LD at both 9 and 21°C. Gibberellins A₂₀, A₁₉ and A₄₄ could also partly replace LD, but they were significantly less active than GA₁, GA₅₃ was inactive when applied to plants grown at 9°C in SD and exhibited only marginal activity at 9°C LD and 21°C SD. The total level of GAs of the early 13-hydroxylation pathway (A₅₃, A₄₄, A₁₉, A₂₀ and A₁) increased rapidly when plants were transferred from SD to LD at 9°C. After transfer from 9 to 21°C, there was an increase in GA levels at both LD and SD, followed by a decrease under LD conditions. In all cases, GA₁₉ was the predominant GA, accounting for 60 to 80% of the analysed GAs. Levels of the bioactive GA₁ were low and increased transiently by LD four days after transfer from SD to LD. At both temperatures, the ratio GA₁₉ to GA₂₀ and GA₂₀ to GA₁ at 9°C was enhanced by LD compared with SD. Taken together, these results support the hypothesis that photoperiodic regulation of leaf elongation in Poa pratensis is GA-mediated, and they indicate a photoperiodic control of oxidation of GA₅₃ to GA₄₄ and GA₁₉ to GA₂₀, and perhaps also of 3β-hydroxylation of GA₂₀ to GA₁.     

Fermentability of the hemicellulose‐derived sugars from steam‐exploded softwood (douglas fir)

Steam explosion ofDouglas fir wood chips under low‐severity conditions (log Ro = 3.08 corresponding to 175°C, 7.5 min, and 4.5% SO₂) resulted in the recovery of around 87% of the original hemicellulose component in the water‐soluble stream. More than 80% of the recovered hemicellulose was in a monomeric form. As the pretreatment severity increased from 3.08 to 3.76, hemicellulose recovery dropped to 43% of the original hemicellulose found in Douglas fir chips while the concentration of glucose originating from cellulose hydrolysis increased along with the concentration of sugar degradation products such as furfural and hydroxymethylfurfural. Despite containing a higher concentration of hexose monomers (mainly glucose originating from cellulose degradation), the water‐soluble fraction prepared under high‐severity conditions (log Ro = 3.73 corresponding to 215°C, 2.38 min, and 2.38% SO₂) was not readily fermented. Only the two hydrolyzates obtained at low and medium (195°C, 4.5 min, and 4.5% SO₂) severities were fermented to ethanol using a spent sulfur liquor adapted strain of Saccharomyces cerevisiae. High ethanol yields were obtained for these two hydrolyzates with 0.44 g of ethanol produced per gram of hexose utilized (86% of theoretical). However, the best results of hemicellulose recovery and fermentability were obtained for the low‐severity water‐soluble fraction which was fermented significantly faster than the fraction obtained after medium‐severity treatment probably because it contained higher amounts of fermentation inhibitors. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 284–289, 1999.     

Freeze fitness in alpine Tiger moth caterpillars and their parasitoids

The adaptive fitness of a freeze-tolerant insect may be mediated by both endogenous and exogenous interactions. The aim of the study presented here was to characterize the freeze tolerance of alpine Tiger moth caterpillars (Metacrias huttoni) and highlight two poorly explored indices of the potential attrition of fitness: (1) downstream development and reproduction; (2) parasitism. Caterpillars survived temperatures as low as −16°C and demonstrated >90% 72-h survival after exposures to −10°C. Two-week acclimations at 5, 10, and 20°C had no effect on body water content, haemolymph osmolality or survival of equilibrium freezing, but there was a significant elevation of the temperature of crystallization (T _c) in those caterpillars acclimated to 5°C. Cell viability of fat body tissue was resilient to freezing (−10 to −16°C), but midgut and tracheal cells showed significant degradation. Pupation and eclosion were unaffected by freezing at −5 or −10°C. Likewise, there were no significant differences in egg production or the proportion of eggs that hatched between control and frozen insects. By contrast, the ability of tachinid larvae to survive freezing within their hosts means that parasitism plays an important role in regulating population size. Mean parasitism of caterpillars by tachinids was 33.3 ± 7.2%. Pupation and imago emergence of tachinids after host ‘endo-nucleation’ was >75%. Eclosed adult tachinids showed a non-significant increase in the incidence of wing abnormalities in relation to low temperature exposure.     

Temperature dependence of embryonic cardiac gap junction conductance and channel kinetics

We have investigated the effects of temperature on the conductance and voltage-dependent kinetics of cardiac gap junction channels between pairs of seven-day embryonic chick ventricle myocytes over the range of 14–26°C. Records of junctional conductance (G _j ) and steady-state unit junctional channel activity were made using the whole-cell double patch-clamp technique while the bath temperature was steadily changed at a rate of about 4°C/min. The decrease inG _j upon cooling was biphasic with a distinct break at 21°C. In 12 cell pairs,Q ₁₀ was 2.2 from 26 to 21°C, while between 21 and 14°C it was 6.5. The meanG _j at 22°C (G _j22 ) was 3.0±2.1 nS, ranging in different preparations from 0.24 to 6.4 nS. At room temperature, embryonic cardiac gap junctions contain channels with conductance states near 240, 200, 160, 120, 80 and 40 pS. In the present study, we demonstrate that cooling decreases the frequency of channel openings at all conductance levels, and at temperatures below 20°C shifts the prevalence of openings from higher to lower conductance states: all 240 pS openings disappear below 20°C; 200 pS openings are suppressed at 17°C; below 16°C 160 and 120 pS events disappear and only 80 and 40 pS states are seen. Temperature also affected the voltage-dependent kinetics of the channels. Application of a 6 sec, 80 mV voltage step across the junction (V _j80 ) caused a biexponential decay in junctional conductance. Decay was faster at lower temperatures, whereas the rate of recovery ofG _j after returning toV _j0 was slowed. Cooling reduced the fast decay time constant, increased both recovery time constants, and decreased the magnitude of GitG_j decay, thus leaving a 10–16% larger residual conductance (G _ss/G _init,±80 mVV _j ) at 18 than at 22°C. From these results we propose that embryonic chick cardiac gap junctions contain at least two classes of channels with different conductances and temperature sensitivities.     

Components of natural gas resulting from thermal degradation of the blue-green alga (cyanobacterium)Oscillatoria tenuis

Cultures of the blue-green alga (cyanobacterium)Oscillatoria tenuis were used to simulate thermal degradation and gas formation by heating without oxygen at 250° and 350 °C for 100 h. Analysis through gas chromatography showed that the gases were mainly CH₄, C₂H₆, C₃H₈, iC₄ (isobutane), nC₄ (normal butane), iC₅ (isopentane), nC₅ (normal pentane), H₂, C0₂ and N₂. The volume of gases per g dry weight of alga was 44 ml at 250 °C and 100 ml at 350 °C. Alkane gas comprised only 2.04% of the total at 250 °C and rising to 40.0% at 350 °C. The fraction of C0₂ decreased from 83.3% at 250 °C to 40.0% at 350 °C. The quantity of alkane in the soluble organic matter doubled with rising temperature but the H/C atomic ratio in the ‘kerogen’, insoluble organic matter, decreased sharply. Infrared spectra of the ‘kerogen’ showed that the peak of adipose radical at 2900 cm⁻¹ disappeared gradually with rising temperature, which reflects the gradual break of CH₄ or C₂H₆ from ‘kerogen’. This demonstrates that insoluble organic matter rather than soluble organic matter in blue-green algae are the main sources of the gas alkanes in the process of simulated thermal degradation.