The Relationship between Chiasmata and Crossing over in TRITICUM AESTIVUM

Telocentrics for the β arm of chromosome 4A and the long arm of 6B were used as cytological markers for the determination of chiasma frequency. In concomitant studies of recombination, terminal segments of rye and T. umbellulatum chromatin carrying Hp (Hairy peduncle) and Lr9 (Leaf-rust resistance), respectively, marked 4A and 6B. Two temperatures, 21° and 32°, were used for both the 4A and 6B experiments.—Only one chiasma was observed in each heteromorphic bivalent. Because there was a substantial reduction in pairing between diakinesis and metaphase I, all determinations of chiasma frequency were made at diakinesis. In the 21° experiments, agreement was good between genetic recombination and cytological prediction on the basis of the partial chiasmatypy hypothesis that each chiasma represents a crossover. At 32° both chiasma frequency and crossing over, but particularly the latter, were strongly reduced. The fewer crossovers than expected are explained in part by stickiness of chromosomes at the high temperature, sometimes resulting in adjacent chromosomes being wrongly scored as having a chiasma, and in part by premetaphase disjunction of some recombined bivalents and subsequent independent behavior of the two resulting univalents.—Male transmission of the 4A telocentric from the heteromorphic bivalent was unusually high: 51% at 21° and 31% at 32°.     

Domain-specific regulation of recombination in Caenorhabditis elegans in response to temperature, age and sex

It is generally considered that meiotic recombination rates increase with temperature, decrease with age, and differ between the sexes. We have reexamined the effects of these factors on meiotic recombination in the nematode Caenorhabditis elegans using physical markers that encompass >96% of chromosome III. The only difference in overall crossover frequency between oocytes and male sperm was observed at 16°. In addition, crossover interference (CI) differs between the germ lines, with oocytes displaying higher CI than male sperm. Unexpectedly, our analyses reveal significant changes in crossover distribution in the hermaphrodite oocyte in response to temperature. This feature appears to be a general feature of C. elegans chromosomes as similar changes in response to temperature are seen for the X chromosome. We also find that the distribution of crossovers changes with age in both hermaphrodites and females. Our observations indicate that it is the oocytes from the youngest mothers—and not the oldest—that showed a different pattern of crossovers. Our data enhance the emerging hypothesis that recombination in C. elegans, as in humans, is regulated in large chromosomal domains.     

On the Temperature Behavior of Pulse Propagation and Relaxation in Worms,Nerves and Gels

The effect of temperature on pulse propagation in biological systems has been an important field of research. Environmental temperature not only affects a host of physiological processes e.g. in poikilotherms but also provides an experimental means to investigate the thermodynamic phenomenology of nerves and muscle. In the present work, the temperature dependence of blood vessel pulsation velocity and frequency was studied in the annelid Lumbriculus variegatus. The pulse velocity was found to vary linearily between 0°C and 30°C. In contrast, the pulse frequency increased non-linearly in the same temperature range. A heat block ultimately resulted in complete cessation of vessel pulsations at 37.2±2.7°C (lowest: 33°C, highest: 43°C). However, quick cooling of the animal led to restoration of regularly propagating pulses. This experimentally observed phenomenology of pulse propagation and frequency is interpreted without any assumptions about molecules in the excitable membrane (e.g. ion channels) or their temperature-dependent behaviour. By following Einstein’s approach to thermodynamics and diffusion, a relation between relaxation time τ and compressibility κ of the excitable medium is derived that can be tested experimentally (for κ_T ∼ κ_S). Without fitting parameters this theory predicts the temperature dependence of the limiting (i.e. highest) pulse frequency in good agreement with experimental data. The thermodynamic approach presented herein is neither limited to temperature nor to worms nor to living systems. It describes the coupling between pulse propagation and relaxation equally well in nerves and gels. The inherent consistency and universality of the concept underline its potential to explain the dependence of pulse propagation and relaxation on any thermodynamic observable.     

Genetic Linkage in the Horse. II. Distribution of Male Recombination Estimates and the Influence of Age, Breed and Sex on Recombination Frequency

In the present study an extensive amount of data, comprising more than 30,000 offspring in total, was analyzed to evaluate the influence of age and sex on the recombination frequency in the K-PGD segment of the equine linkage group (LG) I and the influence of age, breed and sex on recombination in the Al-Es segment of LG II. A highly significant sex difference is reported for both segments. Male and female recombination values in the K-PGD segment were estimated at 25.8 ± 0.8 and 33.3 ± 2.5%, respectively. Similarly, recombination was less frequent in the male (36.6 ± 0.7%) than in the female (46.6 ± 1.2%) in the Al-Es segment. Comparison of data from two Swedish horse breeds revealed no significant breed differences in either sex for recombination in the Al-Es segment. No evidence of an age effect was found in any segment or sex. The distribution of individual male recombination estimates was also investigated, and a significant heterogeneity among stallions was revealed in the K-PGD segment. The results are discussed in relation to previous studies on factors affecting recombination in mammals.     

Nitrate Transport and Not Photoinhibition Limits Growth of the Freshwater Cyanobacterium Synechococcus Species PCC 6301 at Low Temperature

The effect of low temperature on cell growth, photosynthesis, photoinhibition, and nitrate assimilation was examined in the cyanobacterium Synechococcus sp. PCC 6301 to determine the factor that limits growth. Synechococcus sp. PCC 6301 grew exponentially between 20°C and 38°C, the growth rate decreased with decreasing temperature, and growth ceased at 15°C. The rate of photosynthetic oxygen evolution decreased more slowly with temperature than the growth rate, and more than 20% of the activity at 38°C remained at 15°C. Oxygen evolution was rapidly inactivated at high light intensity (3 mE m⁻² s⁻¹) at 15°C. Little or no loss of oxygen evolution was observed under the normal light intensity (250 μE m⁻² s⁻¹) for growth at 15°C. The decrease in the rate of nitrate consumption by cells as a function of temperature was similar to the decrease in the growth rate. Cells could not actively take up nitrate or nitrite at 15°C, although nitrate reductase and nitrite reductase were still active. These data demonstrate that growth at low temperature is not limited by a decrease in the rate of photosynthetic electron transport or by photoinhibition, but that inactivation of the nitrate/nitrite transporter limits growth at low temperature.     

DNA intermediates of meiotic recombination in synchronous S. pombe at optimal temperature

Crossovers formed by recombination between homologous chromosomes are important for proper homolog segregation during meiosis and for generation of genetic diversity. Optimal molecular analysis of DNA intermediates of recombination requires synchronous cultures. We previously described a mutant, pat1-as2, of the fission yeast Schizosaccharomyces pombe that undergoes synchronous meiosis at 25°C when an ATP analog is added to the culture. Here, we compare recombination intermediates in pat1-as2 at 25°C with those in the widely used pat1-114 temperature-sensitive mutant at 34°C, a temperature higher than optimal. DNA double-strand breaks at most hotspots are similarly abundant in the two conditions but, remarkably, a few hotspots are distinctly deficient at 25°C. In both conditions, Holliday junctions at DNA break hotspots form more frequently between sister chromatids than between homologs, but a novel species, perhaps arising from invasion by only one end of broken DNA, is more readily observed at 25°C. Our results confirm the validity of previous assays of recombination intermediates in S. pombe and provide new information on the mechanism of meiotic recombination.     

Temperature Effects on Bacterial Phytochrome

Bacteriophytochromes (BphPs) are light-sensing regulatory proteins encoded in photosynthetic and non-photosynthetic bacteria. This protein class incorporate bilin as their chromophore, with majority of them bearing a light- regulated His kinase or His kinase related module in the C-terminal. We studied the His kinase actives in the temperature range of 5°C to 40°C on two BphPs, Agp1 from Agrobacterium tumefaciens and Cph1 from cyanobacterium Synechocystis PCC 6803. As reported, the phosphorylation activities of the far red (FR) irradiated form of the holoprotein is stronger than that of the red (R) irradiated form in both phytochromes. We observed for the apoprotein and FR irradiated holoprotein of Agp1 an increase in the phosphorylation activities from 5°C to 25°C and a decrease from 25°C to 40°C. At 5°C the activities of the apoprotein were significantly lower than those of the FR irradiated holoprotein, which was opposite at 40°C. A similar temperature pattern was observed for Cph1, but the maximum of the apoprotein was at 20°C while the maximum of the FR irradiated holoprotein was at 10°C. At 40°C, prolonged R irradiation leads to an irreversible bleaching of Cph1, an effect which depends on the C-terminal His kinase module. A more prominent and reversible temperature effect on spectral properties of Agp1, mediated by the His kinase, has been reported before. His kinases in phytochromes could therefore share similar temperature characteristics. We also found that phytochrome B mutants of Arabidopsis have reduced hypocotyl growth at 37°C in darkness, suggesting that this phytochrome senses the temperature or mediates signal transduction of temperature effects.     

Nuclear Magnetic Resonance Studies of Sodium Ions in Isolated Frog Muscle and Liver

Nuclear magnetic resonance (NMR) was used to determine Na⁺ complexing in muscle and liver (at 23°C) from bullfrogs (Rana catesbeiana) and to study the influence of temperature on Na⁺ complexing in muscle from leopard frogs (Rana pipiens). The Na⁺ complexed in muscle and liver was found to be 36.6 ± 4.6% and 66.1 ± 3.5% respectively. A temperature decrease from +34°C to -2°C results in a 20% decrease in the mobility of the free Na⁺ in the fresh muscle. This 20% decrease in mobility results in about 50% of the free Na⁺ at 34°C being complexed at the lower temperature.     

Modeling the Recovery of Heat-Treated Bacillus licheniformis Ad978 and Bacillus weihenstephanensis KBAB4 Spores at Suboptimal Temperature and pH Using Growth Limits

The apparent heat resistance of spores of Bacillus weihenstephanensis and Bacillus licheniformis was measured and expressed as the time to first decimal reduction (δ value) at a given recovery temperature and pH. Spores of B. weihenstephanensis were produced at 30°C and 12°C, and spores of B. licheniformis were produced at 45°C and 20°C. B. weihenstephanensis spores were then heat treated at 85°C, 90°C, and 95°C, and B. licheniformis spores were heat treated at 95°C, 100°C, and 105°C. Heat-treated spores were grown on nutrient agar at a range of temperatures (4°C to 40°C for B. weihenstephanensis and 15°C to 60°C for B. licheniformis) or a range of pHs (between pH 4.5 and pH 9.5 for both strains). The recovery temperature had a slight effect on the apparent heat resistance, except very near recovery boundaries. In contrast, a decrease in the recovery pH had a progressive impact on apparent heat resistance. A model describing the heat resistance and the ability to recover according to the sporulation temperature, temperature of treatment, and recovery temperature and pH was proposed. This model derived from secondary mathematical models for growth prediction. Previously published cardinal temperature and pH values were used as input parameters. The fitting of the model with apparent heat resistance data obtained for a wide range of spore treatment and recovery conditions was highly satisfactory.     

Isolation, Complementation, and Initial Characterization of Temperature-Sensitive Mutants of the Baculovirus Autographa californica Nuclear Polyhedrosis Virus

Sixteen temperature-sensitive mutants of Autographa californica nuclear polyhedrosis virus were isolated. Several interesting phenotypes were observed. A large proportion of the mutants were unable to form polyhedral occlusion bodies (polyhedra) at the nonpermissive temperature (32.5°C). At 32.5°C, one mutant formed plaques in which the cells lacked polyhedra. Another mutant type was defective in the production of progeny extracellular nonoccluded virus and produced a “plaque” consisting of only a single cell containing polyhedra at 32.5°C. One mutant was defective in plaque formation, progeny nonoccluded virus formation, and polyhedra formation at 32.5°C. Several mutants produced nonoccluded virus but failed to produce plaques or polyhedra at 32.5°C. Other phenotypes were also distinguished. Complementation analyses, performed by either measuring the increase in extracellular nonoccluded virus formation or by observing polyhedra formation in mixed infections at 32.5°C, indicated the presence of 15 complementation groups. A high frequency of recombination was observed. Four of the mutants were found to be host dependent in their temperature sensitivity for polyhedra formation.     

Temperature characteristics and adaptive potential of wheat ribosomes

The translational efficiency of wheat ribosomes was studied as a function of an in vivo temperature pretreatment of wheat seedlings (Triticum aestivum L.). Ribosomes were isolated from heat-pretreated (36°C) and reference (4°C, 20°C) wheat seedlings. The efficiency of the ribosomes in translating polyuridylic acid was assayed. Ribosomes from heat-pretreated seedlings exhibit a threefold enhanced incorporation rate of phenylalanine as compared to ribosomes from wheat seedlings adapted to 20 or 4°C. This difference develops within 24 hours after onset of the heat treatment of seedlings following a 3 hour lag phase. The temperature induced changes can be traced back to the cytoplasmic ribosomes, since cycloheximide inhibits translation almost completely. Thermal inactivation of ribosomes occurs at 45°C, irrespective of the temperature pretreatment of the wheat seedlings. Specific differences in the yield of ribosomes, in the polyribosomal profiles, and in the apparent Arrhenius' activation energy of protein synthesis were observed depending on the age and the temperature pretreatments. The results presented here are considered an important molecular correlation to phenotypical temperature adaptation of in vivo protein synthesis in wheat (M Weidner, C Mathée, FK Schmitz 1982 Plant Physiol 69: 1281-1288).     

Heat stress reveals a specialized variant of the pachytene checkpoint in meiosis of Arabidopsis thaliana

Plant growth and fertility strongly depend on environmental conditions such as temperature. Remarkably, temperature also influences meiotic recombination and thus, the current climate change will affect the genetic make-up of plants. To better understand the effects of temperature on meiosis, we followed male meiocytes in Arabidopsis thaliana by live cell imaging under three temperature regimes: at 21°C; at heat shock conditions of 30°C and 34°C; after an acclimatization phase of 1 week at 30°C. This work led to a cytological framework of meiotic progression at elevated temperature. We determined that an increase from 21°C to 30°C speeds up meiosis with specific phases being more amenable to heat than others. An acclimatization phase often moderated this effect. A sudden increase to 34°C promoted a faster progression of early prophase compared to 21°C. However, the phase in which cross-overs mature was prolonged at 34°C. Since mutants involved in the recombination pathway largely did not show the extension of this phase at 34°C, we conclude that the delay is recombination-dependent. Further analysis also revealed the involvement of the ATAXIA TELANGIECTASIA MUTATED kinase in this prolongation, indicating the existence of a pachytene checkpoint in plants, yet in a specialized form.

Live cell imaging of plants exposed to different heat stresses provides a temporal framework of meiosis at high temperatures in wild-type and mutants for several meiotic recombination factors.     

THE TEMPERATURE CHARACTERISTIC OF RESPIRATION OF AZOTOBACTER

The temperature characteristic of respiration of Azotobacter vinelandii possesses a constant value of 19,330 ± 165 over the temperature range 20–30°C. This value is independent of pH, oxygen tension, age of culture, and other factors within the limits studied. The optimum temperature of respiration is 34–35°C., with limits at about 10° and 50°C.     

Effects of Temperature on Resistance in Phaseolus vulgaris Genotypes and on Development of Meloidogyne Species

Phaseolus vulgaris lines with heat-stable resistance to Meloidogyne spp. may be needed to manage root-knot nematodes in tropical regions. Resistance expression before and during the process of nematode penetration and development in resistant genotypes were studied at pre- and postinoculation temperatures of 24 °C and 24 °C, 24 °C and 28 °C, 28 °C and 24 °C, and 28 °C and 28 °C. Resistance was effective at all temperature regimes examined, with fewer nematodes in roots of a resistant line compared with a susceptible line. Preinoculation temperature did not modify resistance expression to later infections by root-knot nematodes. However, postinoculation temperatures affected development of Meloidogyne spp. in both the resistant and susceptible bean lines tested. The more rapid development of nematodes to adults at the higher postinoculation temperature of 28 °C in both bean lines suggests direct temperature effects on nematode development instead of on resistance expression of either of two gene systems. Also, resistance was stable at 30 °C and 32 °C.     

Differential Sensitivities and the Target of Heat-Induced Recombination at the Base of the X Chromosome of DROSOPHILA MELANOGASTER

The effect of heat on two small adjacent segments at the base of the X chromosome was examined. Recombination in the two segments delimited by recessive lethals was measured after treatment with 30° and 34°.Both segments were sensitive at 30°, while only the proximal one responded to 34° treatment. When the same segments were studied in structural heterozygotes (for deletions) the relative increase in recombination was greater, suggesting that heat exerts its effect on the "pairing" rather than the "exchange" components of crossing over. The effect of c (3) G/+ on the same segments in both homozygous and heterozygous structurals was studied. The results indicate that this meiotic mutant mediates its effect on a step different than that affected by heat.     

TEMPERATURE CHARACTERISTICS FOR THE OXYGEN CONSUMPTION OF GERMINATING SEEDS OF LUPINUS ALBUS AND ZEA MAYS

The rate of oxygen consumption by germinating seeds of Lupinus albus and of Zea mays was studied as a function of temperature (7–26°C.). The Warburg manometer technique was used, with slight modifications. Above and below a critical temperature at 19.5°C. the temperature characteristic for oxygen consumption by Lupinus albus was found to be µ = 11,700± and 16,600 respectively. The same critical temperature was encountered in the case of Zea mays, with temperature characteristics µ = 13,100± above and µ = 21,050 below that temperature.     

Temperature-Dependent Fecundity and Life Table of the Fennel Aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae)

Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) is a cosmopolitan species and the main pest of fennel in northeastern Brazil. Understanding the relationship between temperature variations and the population growth rates of H. foeniculi is essential to predict the population dynamics of this aphid in the fennel crop. The aim of this study was to measure the effect of constant temperature on the adult prereproductive period and the life table fertility parameters (infinitesimal increase ratio (r_m), gross reproduction rate (GRR), net reproduction rate (R₀), finite increase ratio (λ), generation time (GT), the time required for the population to double in the number of individuals (DT), and the reproduction value (RV_x)) of the fennel pest H. foeniculi. The values of lx (survival of nymphs at age x) increased as the temperature rose from 15 to 28°C and fell at 30°C, whereas mx (number of nymphs produced by each nymph of age x) increased from 15 to 25°C and fell at 28 and 30°C. The net reproduction rates (R₀) of populations of H. foeniculi increased with temperature and ranged from 1.9 at 15°C to 12.23 at 28°C for each generation. The highest population increase occurred with the apterous aphids at 28°C. The rate of population increase per unit time (r_m) (day) ranged from 0.0033 (15°C) to 0.1995 (28°C). The highest values of r_m were recorded at temperatures of 28°C and 30°C. The r_m values were a good fit to the models tested, with R² > 0.91 and R² _adj > 0.88. The models tested (Davidson, Sharpe and DeMichele modified by Schoolfield et al., Logan et al., Lamb, and Briere et al.) were very good fits for the r_m values observed, with R² > 0.91 and R² _adj > 0.88. The only exception was the Davidson model. Of the parameters studied, the reproductive capacity was higher in the apterous aphids, with the unique exception of daily fecundity at 28°C, which was higher in the alate aphids of H. foeniculi. Parameters relating to the age-specific fertility table for H. foeniculi were heavily influenced by temperature, with the highest biotic potential and population growth capacity found at 34°C. Therefore, the results obtained in this study could be of practical significance for predicting outbreaks of fennel aphids and improving the management of this aphid in fennel crops.     

Cold Shock and Its Effect on Ribosomes and Thermal Tolerance in Listeria monocytogenes

Differential scanning calorimetry (DSC) and fatty acid analysis were used to determine how cold shocking reduces the thermal stability of Listeria monocytogenes. Additionally, antibiotics that can elicit production of cold or heat shock proteins were used to determine the effect of translation blockage on ribosome thermal stability. Fatty acid profiles showed no significant variations as a result of cold shock, indicating that changes in membrane fatty acids were not responsible for the cold shock-induced reduction in thermal tolerance. Following a 3-h cold shock from 37 to 0°C, the maximum denaturation temperature of the 50S ribosomal subunit and 70S ribosomal particle peak was reduced from 73.4 ± 0.1°C (mean ± standard deviation) to 72.1 ± 0.5°C (P ≤ 0.05), indicating that cold shock induced instability in the associated ribosome structure. The maximum denaturation temperature of the 30S ribosomal subunit peak did not show a significant shift in temperature (from 67.5 ± 0.4°C to 66.8 ± 0.5°C) as a result of cold shock, suggesting that either 50S subunit or 70S particle sensitivity was responsible for the intact ribosome fragility. Antibiotics that elicited changes in maximum denaturation temperature in ribosomal components also elicited reductions in thermotolerance. Together, these data suggest that ribosomal changes resulting from cold shock may be responsible for the decrease in D value observed when L. monocytogenes is cold shocked.     

The Biology and Thermal Requirements of the Fennel Aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae)

The relationship between the insect development rate and temperature was established very early and represents an important ecological variable for modeling the population dynamics of insects. The accurate determination of thermal constant values and the lower and upper developmental thresholds of Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) on fennel (Foeniculum vulgare Miller (Apiales: Apiaceae)) crops would obviously benefit the effective application of control measures. This paper is a study of the biology and thermal requirements of H. foeniculi. Winged insects were collected from fennel crops at the Embrapa Algodão in Campina Grande, Paraíba. Nymphs (age ≤24 h) produced by winged insects were subjected to constant temperatures of 15, 20, 25, 28, 30 or 33°C, a photophase of 12 h and a relative humidity of 70±10%. The results of the study showed that at temperatures between 15 and 30°C, H. foeniculi nymphs were able to develop normally. The four instars were found at all temperatures tested. However, temperatures of 3 and 33°C were lethal to the nymphs. The nymph stage development time varied from 5 (30°C) to 19 (15°C) days. The influence of temperature on the development time is dependent on the instar. The base temperature (Tb) and the thermal constant (K) for the nymph stage were estimated at 11.2°C and 107.5 degree-days, respectively. The shortest nymph development stage was observed at 30°C, and the highest nymph viability (85.0%) was observed at 28°C. This information can be used for developing phenological models based on the temperature and development rate relationships so that outbreaks of H. foeniculi in the fennel crop can be predicted, therefore improving the application of control programs targeting this fennel pest.     

Temperature response of photosynthesis in different drug and fiber varieties of Cannabis sativa L.

The temperature response on gas and water vapour exchange characteristics of three medicinal drug type (HP Mexican, MX and W1) and four industrial fiber type (Felinq 34, Kompolty, Zolo 11 and Zolo 15) varieties of Cannabis sativa, originally from different agro-climatic zones worldwide, were studied. Among the drug type varieties, optimum temperature for photosynthesis (T_opt) was observed in the range of 30–35 °C in high potency Mexican HPM whereas, it was in the range of 25–30 °C in W1. A comparatively lower value (25 °C) for T_opt was observed in MX. Among fiber type varieties, T_opt was around 30 °C in Zolo 11 and Zolo 15 whereas, it was near 25 °C in Felinq 34 and Kompolty. Varieties having higher maximum photosynthesis (P_{N max}) had higher chlorophyll content as compared to those having lower P_{N max}. Differences in water use efficiency (WUE) were also observed within and among the drug and fiber type plants. However, differences became less pronounced at higher temperatures. Both stomatal and mesophyll components seem to be responsible for the temperature dependence of photosynthesis (P_N) in this species, however, their magnitude varied with the variety. In general, a two fold increase in dark respiration with increase in temperature (from 20 °C to 40 °C) was observed in all the varieties. However, a greater increase was associated with the variety having higher rate of photosynthesis, indicating a strong association between photosynthetic and respiratory rates. The results provide a valuable indication regarding variations in temperature dependence of P_N in different varieties of Cannabis sativa L.