Germination and mitochondrial damage in spores of Dictyostelium discoideum following supraoptimal heating.

Spores of Dictyostelium discoideum may be quantitatively activated with a heat treatment of 45 degrees C for 30 min. Heat activation at either higher temperatures of for longer duration at 45 degrees C resulted in damaged spores. The spores showed an increased postactivation lag time at 23 degrees C and an increased inability to respond to deactivation with 0.2 M sucrose. As the severity of supraoptimal heating increased, a greater percentage of the spores appeared to contain phase dark lesions and to lose viability. Oxygen uptake began to decrease during and after the appearance of the lesions. Using electron microscopy, the phase dark lesions were found to be mitochondria with disrupted cristae.     

Relationships between circadian rhythm of chilling resistance and acclimation to chilling in cotton seedlings

Cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 12:12h at 35°C showed rhythmic daily changes in chilling resistance. Chilling treatment (5°C, 48h) started at the beginning or middle of the daily light period resulted in a substantial growth inhibition of the seedlings upon return to 35°C whereas when chilling was started at the beginning or middle of the dark period the subsequent growth of the seedlings was much less inhibited. This rhythm in chilling resistance persisted under continuous light for three 24-h periods, indicating that it is of an endogenous nature. Seedlings grown under continuous light from germination showed no daily changes in resistance, but a rhythm was initiated by introduction of a dark period of 6h or longer. In 24-h cycles with different light and dark periods, maximal resistance was reached just before the start of dark period. Seedlings grown at 35°C could be acclimated to chilling by exposure to low, non-damaging temperatures (25–15°C). A short-term (6h) exposure to 25°C started at the resistant phase resulted in a large increase in resistance during the following otherwise sensitive phase. The resistance induced by the low temperature matched or slightly exceeded the maximal resistance reached during the resistant phase of the daily rhythm of chilling. The low-temperature-induced resistance and the daily rhythmic increase in resistance were not additive, indicating a common mechanism for the two kinds of resistances. An adaptive advantage of a combination of a rapid temperature-induced acclimation and the daily rhythmic increase in resistance is suggested.     

Cold-induced changes affect survival after exposure to vitrification solution during cryopreservation in the south-west Australian Mediterranean climate species Lomandra sonderi (Asparagaceae)

There is limited knowledge of the effects of exposure to low temperatures in the unique Mediterranean climate plant species of Western Australia. We have thus investigated the effect of low temperature on cryogenic tolerance in Lomandra sonderi, an endemic perennial species of southwest Western Australia. Lomandra sonderi plants were preconditioned in tissue culture at constant 23 °C (12 h light/dark cycle) or alternating 20/?1 °C (16 h light and 8 h dark cycle). Shoot tips from both conditions were analysed for their phospholipid, sterol and soluble sugar compositions. Shoot tips were also cryoexposed via a droplet-vitrification protocol. Survival in both preconditioning regimes for cryoexposed and non-cryoexposed samples was the same, but plants from the 20/?1 °C regime displayed an improved tolerance to the overall cryopreservation process in both cryoexposed and non-cryoexposed samples, thereby eliminating exposure to liquid nitrogen as a primary cause of reduced post-cryogenic viability. Preconditioning of in vitro shoots of L. sonderi at 20/?1 °C induced significant increases in phosphatidylcholine (from 7.30 ± 3.46 to 22.2 ± 7.80 ng mg^?1 FW) and increases in several soluble sugars (fructose, galactose, glucose, sucrose) compared to shoots incubated at 23 °C—changes consistent with known cold acclimation responses in plant species generally—but sterol content remained largely unchanged. Analysis of electrolyte leakage in shoot tips from both preconditioning regimes generated a significantly lower LT₅₀ value in the 20/?1 °C samples (?5.45 ± 0.53 °C) over the 23 °C samples (?2.5 ± 0.08 °C). Increased tolerance to cryoexposure in L. sonderi appears to lie mainly with acclimation-induced changes in membrane composition and promotion of membrane stability and hence increased resistance to freeze damage.     

Fatty acids profile and temperature in the cultured marine diatom Odontella aurita

The diatom Odontella aurita has now been industrially cultured and commercialized as a dietary supplement rich in omega-3 fatty acids for several years. In this study, we investigated the effect of three temperatures (8, 16, and 24 °C) on the growth and fatty acid composition of cells harvested during the exponential and stationary growth phases. These temperatures were selected on the basis of photosynthesis responses previously obtained at different temperatures using a modulated fluorometer. Our results confirm that both growth and lipid composition were sensitive to culture temperature. Growth was reduced when O. aurita was cultured at low temperature (8 °C) compared to when it was cultured at high temperatures (16 and 24 °C), but the proportion of polyunsaturated fatty acids (PUFAs, 20:5 n-3 and 22:6 n-3) increased while the level of saturated fatty acids (SFAs, 14:0 and 16:0) decreased in the cells harvested during both the exponential and stationary growth phases. On the other hand, the cells grown at 24 °C displayed a marked decrease in PUFA and an increase in SFA levels. Harvesting time is also a critical parameter in achieving optimum n-3 PUFA productivity during batch cultivation. Indeed, changes in fatty acid composition with growth phase seem to be dependent on the culture temperature, with the most marked effects being observed at 24 °C. PUFA levels (i.e., levels of 20:5 n-3 and 22:6 n-3) increased during the stationary growth phase, while the proportion of SFAs and monounsaturated fatty acids (MUFAs) fell with time. As this species is currently grown in outdoor ponds with seasonal temperature variations (minimal and maximal average temperatures in winter and summer, from 3 to 9 °C and from 13 to 26 °C, respectively), this factor can be expected to have a strong influence on the fatty acid content and composition of the algal biomass harvested and commercialized.     

Reorganization of chloroplast ultrastructure associated with low-temperature hardening of Arabidopsis plants

When following low-temperature acclimation (5 days at 2°C) of cold-resistant plants of Arabidopsis (Arabidopsis thaliana Heynh. (L.), ecotype Columbia) in relation to the changes in chloroplast ultrastructure, we registered the high efficiency of hardening and the ability of hardened plants to lower a threshold of frost damage by about 3°C. During hardening, the area of grana in the chloroplasts more than doubled, with considerably increased numbers of thylakoids per granum and thylakoids per chloroplast. The rate of apparent photosynthesis decreased to lesser extent than the rate of dark respiration, as a result the content of soluble sugars increased fourfold, ensuring an adaptive reorganization of metabolism, which enabled the hardened plants to survive even at below-zero temperatures (up to ?7°C). The authors conclude that a considerable increase in the number of thylakoids in the chloroplasts helps maintain photosynthesis at low above-zero temperatures and is a prerequisite for the accumulation of soluble sugars in Arabidopsis leaves.     

Effects of Mild and Moderate Hypothemia Therapy on Expression of Cerebral Neuron Apoptosis Related Proteins and Glial Fiber Acidic Protein After Rat Cardio-pulmonary Resuscitation

To explore the effects of different degrees of hypothermia on brain tissue apoptosis after cardio-pulmonary resuscitation (CPR). Cardiac arrest for 5 min induced by asphyxia method was used to create CPR model. 30 SD rats were randomly divided into control group (normothermia), 33 °C hypothermia group and 30 °C hypothermia group with ten rats in each. Rats in control group received routine treatment at 25 °C room temperature after CPR; Rats in mild hypothermia and moderate hypothermia groups were given hypothermia treatment 0.5 h after CPR. Brain tissue in all groups was taken 24 h after CPR, and immunohistochemistry was used to detect the caspase-3 in cerebral cortex and glial fiber acidic protein (GFAP) expression in astrocyte. Western blotting was used to detect Bcl-2 and Bax protein expression, and histopathological change was observed in brain tissue. Compare to the control group, caspase-3 expression in cerebral neurons in hypothermia group was significantly decreased (p<0.01), which was significantly lower in 30 °C group than that in 33 °C group (p > 0.05); GFAP level in hypothermia groups was significantly increased (p < 0.01), which was higher in 30 °C hypothermia group than that in 33 °C hypothermia group (p < 0.05); Bcl-2 expression level in hypothermia group was significantly increased (p < 0.01), which was higher in 30 °C hypothermia group than that in 33 °C hypothermia group (p < 0.05); The level of Bax had no significant difference among the three groups. Hypothermia-regulated GFAP expression by decreasing caspase-3 expression and increasing Bcl-2 expression to promote brain cell signaling transduction, and further inhibited cell apoptosis and reduced brain injury. Moderate hypothermia therapy is more effective than mild hypothermia in preventing brain injure.     

Pacemakers in aggregation fields of Dictyostelium discoideum: does a single cell suffice?

In this paper we address the following question: can a single cell of the cellular slime mold Dictyostelium discoideum serve as a pacemaker for the aggregation phase? Whether or not this is possible is determined by the relative importance of cyclic AMP production due to self-stimulation as compared to diffusion of cyclic AMP away from the cell and extracellular degradation. We determine the conditions under which a single cell on an infinite place can emit periodic signals of cyclic AMP using a model developed previously for signal relay and adaptation in Dictyostelium. Elsewhere it has been shown that this model provides an accurate representation of the stimulus-response behavior of Dictyostelium for a variety of experimental conditions.     

Drosophila lactate dehydrogenase: Molecular and genetic aspects

(LDH) obtained from larvae of Drosophila melanogaster was purified to homogeneity by affinity chromatography on oxamate-Sepharose. The purification procedure is simple to operate and gives a homogeneous preparation in a good yield (34.86%) after only two steps. Utilizing the homogeneous LDH preparation, an attempt was made to characterize the LDH molecule. Thus, it was found that the N-terminal amino acid is isoleucine, and the enzyme is tetrameric and composed of four identical subunits of apparent molecular weight 38,000, suggesting that it is controlled by a single gene. Homogeneous LDH preparations exhibit one band on neutral acrylamide gels when the substrate is either dl-lactic acid or l-(+)-lactate. The optimum temperature is 45°C for the purified enzyme and 40°C for the crude homogenate. The K _m values for pyruvate and NADH are 0.154 and 0.027mm, respectively, while the K _m values for lactate and NAD are 29.4 and 1.33mm, respectively. A discontinuity in the E _a slope was observed at a transition temperature of 30°C. The E _a value between 20 and 30°C was calculated as 12.06 kcal/mol, while between 30 and 45°C the E _a value was 4.01 kcal/mol. This evidence, together with other observations reported in the literature, suggests that the LDHs of invertebrates and vertebrates have arisen by divergent evolution from a common ancestral gene.     

The HPLC profile of proteins of thermoprotection-acquired wheat (Triticum aestivum L.) seedlings

A pre-treatment of 40 °Cprovided thermoprotection to wheat seedlings against 43 °C, which was otherwise a lethal temperature. Due to temperature pretreatment, the rate of protein synthesis at 45 °C increased in both plumules and radicles. The HPLC profile of plumule and radicle proteins of thermoprotection-acquired seedlings was different from the plumules and radicles of non-treated seedlings.     

The effect of temperature on the development,reproduction, and longevity of two common cyclopoid copepods — Eucyclops serrulatus (Fischer) and Cyclops strenuus (Fischer)

The embryonic and postembryonic development times, time interval between clutches, and longevity of two common cyclopoid copepods — Eucyclops serrulatus and Cyclops strenuus — were studied at constant temperatures (5°, 10°, 15°, 20° and 25 °C), using algae and protozoans as food. Both, E. serrulatus and C. strenuus showed a considerable temperature tolerance and adaptability. Embryonic development times were similar in both species but postembryonic development times were shorter in E. serrulatus. Time intervals between successive clutches were relatively variable at all temperatures in both species. Longevity was shorter in E. serrulatus than in C. strenuus. The embryonic and postembryonic development of E. serrulatus was short relative to that of littoral copepods; the development of C. strenuus was similar or shorter than that of other species of the genus Cyclops.     

Effect of temperature on development and reproduction of Proprioseiopsis asetus (Acari: Phytoseiidae) fed on asparagus thrips,Thrips tabaci

Thrips tabaci Lindeman (Thysanoptera: Thripidae) is one of the most important pests of asparagus in China. In this study the effects of five constant temperatures (15, 20, 25, 30 and 35 °C) on the growth, survivorship and reproduction of Proprioseiopsis asetus (Chant) (Acari: Phytoseiidae) fed on T. tabaci was examined under laboratory conditions. Development time of immatures decreased with increasing temperature. The lower egg-to-adult developmental threshold (T ₀) and thermal constant (K) of P. asetus were estimated at 15.2 °C and 75.8 degree days by means of a linear model. Fertilized females fed on T. tabaci produced offspring of both sexes, whereas the offspring sex ratio [♀/(♀ + ♂)] of P. asetus at 20–35 °C was female-biased (0.68–0.78) and not significantly influenced by temperature. Survivorship during immature development was significantly influenced by temperature, and was especially low at 15 °C. Pre- and post-oviposition periods of fertilized females shortened with the increase in temperature. The longest oviposition period was 20.4 days, at 25 °C, whereas at 15 °C the mites did not reproduce. Maximum average life time fecundity and mean daily fecundity was recorded at 25 and 35 °C, respectively; the intrinsic rate of increase ranged from 0.05 (20 °C) to 0.17 (35 °C). The results indicate the capability of P. asetus to develop and reproduce at a broad range of temperatures, especially above 25 °C, which can be used for better management of T. tabaci in asparagus.     

Nitrate reductase of Dunaliella parva

Nitrate reductase of the salt tolerant alga Dunaliella parva, in contrast to that of most green algae, can use NADPH as well as NADH as electron donor. Extracts of cells contained various amounts of latent nitrate reductase. The latent enzyme could be activated at 45°C but only in the presence of flavine adenine dinucleotide. The heat activated enzyme did not require flavine adenine dinucleotide for activity and was fully active with NADH, NADPH or reduced flavine mononucleotide as electron donors.     

Effect of temperature on growth and macromolecular biosynthesis in cryptococcus species

Cryptococcus neoformans, a pathogenic yeast, grows at temperatures between 25 and 37°C. However, the closely related non-pathogen C. albidus exhibits restricted growth at temperatures above ambient with little or no growth at 37°C. The inhibition of growth of the non-pathogen, as measured by turbidity, cell number, and per cent budding, is reversible after 48 hr at the non-permissive temperature (37°C). Growth cessation at 37°C is accompanied by a corresponding decrease in DNA synthesis, which is not observed in C. neoformans. RNA and protein synthesis in C. albidus and C. neoformans are only slightly affected at the elevated temperature. Degradation by nucleases does not seem to account for the differences found in this cumulative DNA synthesis in C. albidus at 25 and 37°C. These facts suggest that C. albidus may possess a thermo-sensitive defect in the machinery responsible for the initiation of DNA replication.     

<Emphasis Type="Italic">Polytrichum commune</Emphasis> spores nucleate ice and associated microorganisms increase the temperature of ice nucleation activity onset

Moss spores disperse via wind and have been found previously in precipitation and air samples. Their presence in the atmosphere led to this study’s examining the potential of moss spores to contribute to ice nucleation, a process necessary for ice formation in clouds prior to precipitation. Ice nucleation assays were conducted using Polytrichum commune spores that were either associated with natural assemblages of microbes or extracted aseptically from capsules and subsequently confirmed to be free of culturable microbes. Liquid suspensions of capsule spores and non-sterile spores nucleated ice at temperatures as high as ?12 and ?7 °C, respectively. When capsule and non-sterile spores were heated at 95 °C for 10 min, which killed all culturable microbes on non-sterile spores, both nucleated ice from ?10 to ?13 °C. An additional non-sterile spore sample collected from partially opened capsules in a forested ecosystem (ID, USA) nucleated ice at temperatures as high as ?7 °C, similar to non-sterile P. commune spores. This is the first set of results to indicate that P. commune spores themselves are capable of nucleating ice at temperatures higher than many abiological particles such as mineral dust (≤?15 °C) and that natural assemblages of microbes can increase their ice nucleation efficiency. Future studies aimed at determining the abundance of moss spores in the atmosphere and the identity of ice-nucleating microbes associated with them will provide further insights into the ability of moss spores to impact precipitation patterns.