Freezing pattern in apple seeds as affected by the temperature of fruit storage

Storage of apple fruits ( Pyrus malus L. cv. Golden Delicious) at different temperatures (0, 12 and 35°C) markedly altered the pattern of water freezing in the seeds. Higher temperatures of storage brought about a shift from the sequential to the discontinuous type of freezing in seeds, the low temperature exotherm (LTE) being much more pronounced than the high temperature one (HTE). The occurrence of LTE was highly correlated with embryo death. Fruit storage at higher temperatures also caused a decrease in the threshold super cooling temperature of seeds and of naked embryos, removed from the seed coat and endosperm. The decrease was less pronounced in naked embryos than in intact seeds. The results presented show that the frost resistance of apple seeds relies mainly on the supercooling ability of the embryos and is increased by the presence of seed coat and endosperm. The broad peak of the LTE indicates that, in contrast with other seeds and many super cooling organs, massive ice nucleation in apple seeds occurs within the embryo tissues and that extra organ freezing seems to be of less importance. Therefore, the increased super cooling ability of apple seeds, isolated from fruits stored at higher temperatures, seems to rely on those seed properties that protect embryo cells against heterogeneous ice nucleation.     

A new microcomputer-controlled neutron activation and analysis system

A microcomputer-controlled irradiation and measurement system and a microprocessor-controlled sample changer have been installed at the SLOWPOKE-2 Facility at the Royal Military College of Canada (RMC). These systems can provide the gamut of instrumental neutron activation analysis (INAA) techniques for the analyst. Custom software has been created for system control, data acquisition, and off-line spectral analysis using programs that incorporate Gaussian peak-fitting methods of analysis. The design and use of the equipment is discussed, and the performance is illustrated with results obtained from the analysis of marine sediment and biological reference materials.     

Direct analysis of root zone data in a microculture system

Disks were isolated from young leaves of winter rape plants and grown in vitro at ambient (15°C) or low (2°C) temperatures for two weeks. In the control disks the growth cessation and beginning of chlorophyll degradation were observed after 1 week of culture. In the low-temperature treated disks the expansion of cells was slower than that in the control material but it continued for two weeks and was accompanied by a marked accumulation of dry matter. Practically, no chlorophyll degradation was observed. The low temperature treatment brought about the decrease in the frost killing temperature of the tissue which was associated with its increased capacity to subcool water. A short (18 h) exposure of the cold-grown leaf disks to slight frost (–5°C) increased further their resistance to freezing, despite the fact that the subcooling capacity of disks decreased in result of the treatment. Therefore, the two stages of hardening, observed previously for the whole plants, can also be detected in the isolated material. In the cold-grown disks, a transient accumulation of reducing sugars but a steady decrease in ATP and water-soluble protein contents were observed. These observations indicate that tissue isolation might affect processes involved in the functional adaptation of cells to cold.Abbreviations DTA differential thermal analysis - T_k50 frost killing temperature - T_in ice nucleation temperature     

Subjective experiences associated with thermal biofeedback treatment of hypertension

Reports of subjective experiences of 73 hypertensive patients who were treated with thermal biofeedback for hand warming were obtained over 16 treatment sessions. Most of the differential responding in subjective report occurred in the first 5 sessions. Differences in reports of throbbing were associated with medication status during treatment (presence of sympatholytic antihypertensive agent). From 4 to 9% of patients report negative subjective experiences at any one session. When short-term clinical successes (either elimination of medication or reduction of BP) were compared with short-term failures, it was found that successes reported more warmth, more likelihood of falling asleep, and more dreamlike experiences. The latter were more likely to occur suddenly for the successes. Correlational analyses revealed consistent positive associations between reports of warmth and relaxation with highest temperature achieved in the session and consistent negative associations between experiencing physical sensations and degree of temperature change within the session.This research was supported in part by grants from NHLBI, HL-27622 and HL-31189.     

Effect of temperature on the optimal substrate for β-oxidation

The enzyme carnitine palmitoyl tranferase (CPT) is able to use a range of fatty acids as substrates, with some variation in catalytic rate among tissue. The substrate giving maximal activity of the enzyme under optimal conditions (C16: 1) is similar in trout, salmon, goldfish, eel and tilapia. There is no evidence that thermal acclimation affects substrate preference for β-oxidation.     

THERMAL EVOLUTION OF EGG SIZE IN DROSOPHILA MELANOGASTER

We measured the size of eggs produced by populations of Drosophila melanogaster that had been collected along latitudinal gradients in different continents or that had undergone several years of culture at different temperatures in the laboratory. Australian and South American populations from higher latitudes produced larger eggs when all were compared at a standard temperature. Laboratory populations that had been evolving at 16.5°C produced larger eggs than populations that had evolved at 25°C or 29°C, suggesting that temperature may be an important selective agent in producing the latitudinal clines. Flies from laboratory populations produced larger eggs at an experimental temperature of 16.5°C than at 25°C, and there was no indication of genotype-environment interaction for egg size. Evolution of egg size in response to temperature cannot be accounted for by differences in adult body size between populations. It is not clear which life-history traits are direct targets of thermal selection and which are showing correlated responses, and disentangling these is a task for the future.     

Effects of temperature, multiple allelochemicals and larval age on the performance of a specialist caterpillar

To understand the mechanisms underlying plant-insect herbivore interactions, it is necessary to examine the simultaneous effects of temperature, food quality and larval age. We examined the simultaneous effects of three allelochemicals (tomatine, rutin and chlorogenic acid) on the performance of first and second instar Manduca sexta larvae under two representative thermal regimes 21 : 10°C and 26 : 15°C for spring and summer, respectively. Thermal regime and allelochemicals interacted to influence the time from egg hatch to ecdysis to the third instar. On average, it took about half as much time to reach the third instar at 26 : 15°C as it did at 21 : 10°C. Separately, tomatine and rutin had a negative effect on developmental time from egg hatch to the third instar, but their simutaneous effects were not additive. Chlorogenic acid significantly reduced the negative effect of tomatine. The magnitude of the allelochemical effect was larger at the cooler thermal regime compared to the warmer regime. For instance, chlorogenic acid by itself had no effect at the 26 : 15°C regime, but at the 21 : 10°C regime it significantly shortened total developmental time. The effect of chlorogenic acid on stadium duration was distinctly different for the two instars. Chlorogenic acid shortened stadium duration of first instar larvae. However, depending on thermal regime and the presence of tomatine, chlorogenic acid had a negative, positive or neutral effect on stadium duration of second instar larvae. Molting duration of second instar larvae was shortened by a half day at the warmer thermal regime but was not affected by the allelochemicals. Final larval weight was influenced by rutin and chlorogenic acid. Caterpillars fed diets containing 20 moles of rutin were on average 10% lighter than those fed plain diet, whereas those fed diets containing 20 moles of chlorogenic adic were on average 7% heavier. However, the effect of chlorogenic acid depended on thermal regime. Overall, our results indicated that: 1) temperature and food quality can interact to influence insect performance and 2) these effects are influenced by larval age.     

Thermal stratification, nutrient dynamics, and phytoplankton productivity during the onset of spring phytoplankton growth in Lake Baikal, Russia

Lake Baikal, Russian Siberia, was sampled in July 1990 during the period of spring mixing and initiation of thermal stratification. Vertical profiles of temperature, dissolved nutrients (nitrate and soluble reactive phosphorus), phytoplankton biomass, and primary productivity were determined in an eleven-station transect encompassing the entire 636 km length of the lake. Pronounced horizontal variability in hydrodynamic conditions was observed, with the southern region of the lake being strongly thermally stratified while the middle and north basins were largely isothermal through July. The extent of depletion of surface water nutrients, and the magnitude of phytoplankton biomass and productivity, were found to be strongly correlated with the degree of thermal stratification. Horizontal differences likely reflected the contribution of two important factors: variation in the timing of ice-out in different parts of the lake (driving large-scale patterns of thermal stratification and other limnological properties) and localized effects of river inflows that may contribute to the preliminary stabilization of the water column in the face of intense turbulent spring mixing (driving meso-scale patterns). Examination of the relationships between surface water inorganic N and P depletion suggested that during the spring and early summer, phytoplankton growth in unstratified portions of the lake was largely unconstrained by nutrient supplies. As summer progressed, the importance of co-limitation by both N and P became more apparent. Uptake and regeneration rates, measured directly using the stable isotope ¹⁵N, revealed that phytoplankton in stratified portions of the lake relied primarily on NH₄ as their N source. Rates of NH₄ regeneration were in approximate equilibrium with uptake; both processes were dominated by organisms <2 µm. This pattern is similar to that observed for oligotrophic marine systems. Our study underscores the importance of hydrodynamic conditions in influencing patterns of biological productivity and nutrient dynamics that occur in Lake Baikal during its brief growing season.     

Behavioral responses of Colorado potato beetle larvae to combinations of temperature and insolation, under field conditions

In short-term field trials at combinations of ambient temperature (°C) and insolation (W·m⁻²), larval Colorado potato beetles (Leptinotarsa decemlineata [Say] [Coleoptera: Chrysomelidae]) were observed after their release on the adaxial surface of leaflets on potato plants (Solanum tuberosum L. Solanaceae). The larvae either began feeding or moved under the leaflet; mean interval from release to expression of these behaviors (2.9±0.05 min [n =358]) was independent of air temperature and insolation. Proportion of larvae moving under the leaflet increased logistically with both air temperature and insolation. A 1 W·m⁻² change in insolation (P) evoked the same effect on this proportion as a 0.0838 °C change in air temperature (T _a ), so the two quantities were combined as T^*=T _a +P·0.0838 °C/(W·m⁻²), which has units of °C. The proportion of larvae moving under the leaflet increased logistically with T^*. In 1-day field trials we monitored air temperature, insolation and proportion of larvae under the leaflet, and compared the latter to predictions from the logistic regression derived from the short-term trials. Consistently more larvae occurred under leaflets than predicted from the logistic regression; this bias diminished as T^* increased until at T^*≥40 °C, observed and predicted proportions were equal. This pattern of deviation from the predictions of the logistic regression is consistent with a thermoregulatory strategy in which larvae move away from hostile conditions, rather than seek optimal conditions.     

Variable thermal dissipation in a Photosystem I submembrane fraction

Photoacoustic spectroscopy was used to study the thermal deactivation processes in a Photosystem I submembrane fraction isolated from spinach. A large part of the thermal dissipation was variable. The yield of this variable thermal emission depended on the redox state of the Photosystem. It increased with the measuring modulated light intensity coinciding with the gradual closure of the reaction centers. Thermal deactivation was maximal when the reaction centers were closed by a saturating illumination. Extrapolation of the data at zero light intensity indicated that the yield of non-variable thermal emission represented about 37% of the maximal emission. The presence of methylviologen as artificial electron acceptor decreased the yield of variable thermal emission whereas inhibition following heat stress treatments increased it. The significance of the variable and non-variable components of thermal dissipation is discussed and the measured energy storage is suggested to originate from the reduction of the plastoquinone pool during cyclic electron transport around Photosystem I.Abbreviations Chl chlorophyll - DCIP 2,6-dichlorophenolindophenol - MV methylviologen - Pheo pheophytin - PA photoacoustic - PS I Photosystem I - PS II Photosystem II - Tes [N-tris (hydroxymethyl)] methyl-2-aminoethanesulfonic acid