Recessive lethals induced by ethyl methanesulfonate and diethyl sulfate in Drosophila melanogaster post-meiotic male cells pre-treated with butylated hydroxytoluene

The response of Drosophila melanogaster male germ cells to the induction of mutation by ethyl methanesulfonate (EMS) and diethyl sulfate (DES) and the influence of pre-treatments with butylated hydroxytoluene (BHT) were studied. Careful sampling of cell stages revealed that fully mature motile sperm were less sensitive to the induction of sex-linked recessive lethals by EMS than late spermatids, and that the remaining cell stages presented a fairly homogeneous response to the mutagen. The frequency of lethals induced by DES could be grouped into two plateaus: the first one, with a higher mutation rate, comprised motile and immotile sperm and late spermatids, the second one, medium and early spermatids. No sparing action of BHT was detected in any of the developing germ cells treated with EMS or DES, whereas an increase in sex-linked recessive lethal frequency was observed in some experiments in early spermatids. The enhancement of damage is attributed to impairment of repair achieved through the ability of BHT to modify enzymic activity.     

Different cellular fatty acid pattern behaviours of two strains of Listeria monocytogenes Scott A and CNL 895807 under different temperature and salinity conditions

Cells of two strains of Listeria monocytogenes CNL 895807 and Scott A were grown to late exponential phase at different growth temperatures (37, 20 and 4 degrees C) with or without NaCl (7%), and their fatty acid compositions were analysed. The results showed that low thermal adaptation response of L. monocytogenes CNL was different than that of the Scott A strain, and it was based on both an increase of anteiso-branched-chain fatty acids and a significant decrease of straight-chain fatty acids. However, the main modifications observed in the Scott A strain when grown at a low temperature were a decrease of the proportion of ai17:0 and an increase of ai15:0. In hyperosmotic medium and over the entire temperature range (4 degrees C, 20 degrees C and 37 degrees C) the two L. monocytogenes strains showed a cellular fatty acid profile dominated by ai15:0. In addition, a decrease of the two major straight-chain fatty acids (14:0 and 16:0) was observed in the CNL strain. These results demonstrated that the CNL strain showed different behaviours of low thermal and salt adaptation to maintain membrane fluidity, which are based both on an increase of anteiso-branched-chain fatty acids, and a significant decrease of straight-chain fatty acids.     

beta-Amylase induction and the protective role of maltose during temperature shock

A number of studies have demonstrated beta-amylase induction in response to abiotic stress. In the present work, a temperature response profile in 5 degrees C increments from 45 degrees C to 0 degrees C showed that induction at temperature extremes was specific for two members of the gene family (BMY7 and BMY8). Both members encode proteins that possess apparent transit peptides for chloroplast stromal localization. However, induction was not observed for other key starch degrading enzymes demonstrating a rather specific response to temperature stress for BMY7 and BMY8. Time course experiments for heat shock at 40 degrees C and cold shock at 5 degrees C showed that beta-amylase induction correlated with maltose accumulation. Maltose has the ability, as demonstrated by in vitro assays, to protect proteins, membranes, and the photosynthetic electron transport chain at physiologically relevant concentrations. Therefore, beta-amylase induction and the resultant maltose accumulation may function as a compatible-solute stabilizing factor in the chloroplast stroma in response to acute temperature stress.     

Teratogenicity of 27.12-MHz radiation in rats is related to duration of hyperthermic exposure

Five groups of pregnant Sprague-Dawley rats were either sham exposed or were irradiated in a 27.12-MHz radiofrequency (RF) field at 55 A/m and 300 V/m on gestation day 9. The absorbed power (approximately 11 W/kg) caused a relatively rapid increase in the rat's colonic temperature. Rats in group I were sham irradiated for 2.5 h at 0 A/m, 0 V/m. In group II RF irradiation was terminated after the rat's colonic temperature reached 41.0 degrees C. In group III the 41.0- degrees C temperature was maintained an additional 2 h by manually varying the incident field strength. In group IV irradiation was terminated after the rat's colonic temperature reached 42.0 degrees C. In group V the 42.0- degrees C temperature was maintained an additional 15 min by varying the field strength. At both temperatures the teratogenic and embryotoxic effects of the RF-induced hyperthermia increased as the exposure duration increased, but the increase was especially noticeable at 42.0 degrees C. The results indicate that the teratogenic and embryotoxic effects of RF-induced hyperthermia are related to both the temperature of the dam during exposure and the length of time the dam's temperature remains elevated.     

Low temperature limits photoperiod control of smolting in atlantic salmon through endocrine mechanisms

We have examined the interaction of photoperiod and temperature in regulating the parr-smolt transformation and its endocrine control. Atlantic salmon juveniles were reared at a constant temperature of 10 degrees C or ambient temperature (2 degrees C from January to April followed by seasonal increase) under simulated natural day length. At 10 degrees C, an increase in day length [16 h of light and 8 h of darkness (LD 16:8)] in February accelerated increases in gill Na(+)-K(+)-ATPase activity, whereas fish at ambient temperature did not respond to increased day length. Increases in gill Na(+)-K(+)-ATPase activity under both photoperiods occurred later at ambient temperature than at 10 degrees C. Plasma growth hormone (GH), insulin-like growth factor, and thyroxine increased within 7 days of increased day length at 10 degrees C and remained elevated for 5-9 wk; the same photoperiod treatment at 2 degrees C resulted in much smaller increases of shorter duration. Plasma cortisol increased transiently 3 and 5 wk after LD 16:8 at 10 degrees C and ambient temperature, respectively. Plasma thyroxine was consistently higher at ambient temperature than at 10 degrees C. Plasma triiodothyronine was initially higher at 10 degrees C than at ambient temperature, and there was no response to LD 16:8 under either temperature regimen. There was a strong correlation between gill Na(+)-K(+)-ATPase activity and plasma GH; correlations were weaker with other hormones. The results provide evidence that low temperature limits the physiological response to increased day length and that GH, insulin-like growth factor I, cortisol, and thyroid hormones mediate the environmental control of the parr-smolt transformation.     

Effects of photoperiod and temperature on testicular function in amphibians

Most amphibians present an annual testicular cycle characterized by a quiescent period (late autumn-winter) and a spermatogenic period (spring and summer). At the end of the period of spermatogenesis undifferentiated interstitial cells transform into steroid-secreting Leydig cells which regress in spring at the beginning of the new spermatogenetic cycle. The testicular cycle is controlled by the pituitary gonadotropin levels which are high in autumn and winter, low in spring and increase temporarily in the middle of summer. Photoperiod and temperature seem to be the most important external factors involved in the regulation of this cycle in many amphibian species since the colder the geographic area, the longer the quiescent period and the shorter the spermatogenic period. This suggests the occurrence of a potentially continuous cycle in these species, in contrast with that which occurs in other species having an endogenous rhythm of testicular function which is much less sensitive to environmental factors. Although the specific response to temperature can vary widely between species, the most frequent observation in amphibians with a potentially continuous cycle is that exposure to mild temperatures (15-20 degrees C, according to the spring temperatures of the different geographic areas) stimulates spermatogenesis even during the period of testicular quiescence. If this mild temperature is combined with a long photoperiod, complete spermatogenesis is attained. Experiments performed during the period of germ-cell proliferation (development from spermatogonia to round spermatids) indicated that low temperatures (below 11 degrees C) as well as short photoperiods (less than 8 h of light) hinder germ-cell proliferation. Moderately high temperatures (about 30 degrees C) do not impair this proliferation. In the newt Triturus marmoratus, it has been shown that an excessively long photoperiod (over 16 h) has the same effect as a short photoperiod. In this species eyes are not required for the testicular photoperiodic response. Photoperiod appears to have no effect on spermiogenesis (differentiation of round spermatids into spermatozoa), because once round spermatids are formed, spermiogenesis will occur even in total darkness. Mild temperatures seem to be necessary for spermiogenesis as well as for androgen biosynthesis because neither process will take place at extreme temperatures. Results on the effect of photoperiod in steroidogenesis differ between species.     

Effect of heat shock on function of frozen/thawed bull spermatozoa

Deposition of spermatozoa in the reproductive tract of hyperthermic cows could conceivably result in sperm damage. Accordingly, a series of experiments tested the effects of heat shock on functional characteristics and free radical production of bull spermatozoa. Viability was reduced slightly by short-term (1 to 3 h) culture at 42 and 43 degrees C as compared with culture at 39 degrees C. There was no effect of culture at 42 degrees C on the ability of spermatozoa to undergo swim-up or of 42 degrees C on the percentage of motile spermatozoa. However, exposure to 41 degrees C for 3 h reduced percentage of motile sperm, 41 and 42 degrees C reduced sperm velocity and 43 degrees C decreased the proportion of spermatozoa undergoing swim-up. In other experiments, there was no effect of heat shock (41 or 42 degrees C for 1 to 3 h) on DNA integrity, presence of intact acrosomes, or fertilizing ability of the spermatozoa. Superoxide production by spermatozoa was higher at 42 degrees C than at 39 or 41 degrees C, but there was no detectable hydrogen peroxide production at any temperature. The antioxidant, glutathione, tended to improve the ability of spermatozoa to undergo swim-up at 39 degrees C but not at 43 degrees C. Taken together, these results suggest that heat shock of a magnitude similar to that seen in vivo (41 to 42 degrees C) has little effect on sperm functions that affect fertilizing capability.     

Studies on cephalopod rhodopsin: photoisomerization of the chromophore.

Photoisomerization of the chromophore of squid rhodopsin is dependent upon the irradiation temperature. Above 0 degrees C, only 11-cis in equilibrium all-trans reaction proceeds and the all-trans leads to 9-cis reaction is limited to extremely low efficiency. At liquid nitrogen temperature, 11 cis in equilibrium all-trans in equilibrium 9-cis reaction takes place. At intermediary low temperatures (-80 degrees C to -15 degrees C) another isomer of retinal may be produced by the irradiation, which forms a pigment having an absorbance maximum at 465 nm (P-465). The formation of P-465 decreases remarkably in the narrow temperature range from -30 degrees C to 0 degrees C where mesorhodopsin converts to metarhodopsin. Medsorhodopsin is quite different from metarhodopsin in the photoisomerization of the chromophore because P-465 is produced from the former but not from the latter. No P-465 is produced both at liquid nitrogen temperature and above 0 degrees C. P-465 is more labile than any of the other photoproducts so far known, that is isorhodopsin, alkaline and acid metarhodopsins. P-465 is converted to metarhodopsin by irradiation.     

Effects of glucose and fructose on motility patterns of dog spermatozoa from fresh ejaculates

This study was performed to gain insight about how fructose and glucose modulate dog spermatozoa motility in the absence of other motility-modulating factors. Incubation of dog spermatozoa from fresh ejaculates in a basal medium without sugars for 60 min at 37 degrees C induced a progressive decrease in the percentage of motile spermatozoa and in some mean motility parameters, such as mean velocity (VAP), linear coefficient (LIN) and dance (DNC), and an increase in the mean frequency of head displacement (BCF). This indicates a progressive loss of linearity and an increase in oscillatory movement. Addition of 10 mM fructose prevented these effects. Incubation in a basal medium with 10 mM glucose for 60 min at 37 degrees C provoked a fast and intense decrease of LIN and a slight increase of DNC, inducing a less linear and more oscillatory mean movement. Neither fructose nor glucose modified the percentage of motile spermatozoa. The response to both sugars was dose-dependent, with differences appearing at concentrations as low as 1 mM. An analysis of the spermatozoa subpopulation placed above the 95th percentile of the whole population and a factorial analysis of the data indicated that the changes in the mean values of the motility parameters were mainly due to a specific motile subpopulation that had a strong reaction to the two sugars. Our results indicate that fructose, at concentrations from 1 to 10 mM, induced a more linear and less oscillatory motility pattern than glucose. Moreover, from our results we suggest the presence of motile dog sperm subpopulations with an increased sensitivity to fructose and glucose.     

Inhalation exposure-rate of ethylene oxide affects the level of DNA breakage and unscheduled DNA synthesis in spermiogenic stages of the mouse

The effect of ethylene oxide (EtO) inhalation-exposure rate on the induction of DNA breakage in late spermatids and on unscheduled DNA synthesis (UDS) in early spermatids was studied. The exposures were 450 parts per million (ppm) for 4 h, 900 ppm for 2 h, and 1800 ppm for 1 h. Thus, the total exposure was always 1800 ppm-h. Both DNA breakage and UDS were found to increase by a factor of approximately 3 in going from the low to high EtO concentration, suggesting that the molecular dose of EtO to the testis had increased by a similar factor. Our results are consistent with the EtO exposure-rate effect found by Generoso et al. (1986) for induction of dominant-lethal mutations in late spermatids and early spermatozoa.     

Protective effects of catalase overexpression on UVB-induced apoptosis in normal human keratinocytes

UV-induced apoptosis in keratinocytes is a highly complex process in which various molecular pathways are involved. These include the extrinsic pathway via triggering of death receptors and the intrinsic pathway via DNA damage and reactive oxygen species (ROS) formation. In this study we investigated the effect of catalase and CuZn-superoxide dismutase (SOD) overexpression on apoptosis induced by UVB exposure at room temperature or 4 degrees C on normal human keratinocytes. Irradiation at low temperature reduced UV-induced apoptosis by 40% in normal keratinocytes independently of any change in p53 and with a decrease in caspase-8 activation. Catalase overexpression decreased apoptosis by 40% with a reduction of caspase-9 activation accompanied by a decrease in p53. Keeping cells at low temperature and catalase overexpression had additive effects. CuZn-SOD overexpression had no significant effect on UVB-induced apoptosis. UVB induced an increase in ROS levels at two distinct stages: immediately following irradiation and around 3 h after irradiation. Catalase overexpression inhibited only the late increase in ROS levels. We conclude that catalase overexpression has a protective role against UVB irradiation by preventing DNA damage mediated by the late ROS increase.     

Studies on mutagen-sensitive strains of Drosophila melanogaster. IV. Modification of genetic damage induced by X-irradiation of spermatozoa and spermatids in N2 or O2 by mei-9a, mei-41D5 and mus(1)101D1

The influence of defects in DNA repair processes on X-ray-induced genetic damage in post-meiotic male germ cell stages of Drosophila melanogaster was studied using the 'maternal effects approach'. Basc males were irradiated in N2, air or O2 either as 48-h-old pupae (to sample spermatids) or as 3-4-day-old adults (to sample mature spermatozoa) and mated to females of 3 repair-deficient strains (mei-9a: excision-repair-deficient; mei-41D5: post-replication-repair-deficient; mus(1)101D1: post-replication-repair-deficient and impaired in DNA synthesis). Simultaneous controls involving mating of males to repair-proficient females (mei+) were run. The frequencies of sex-linked recessive lethals and of autosomal translocations were determined following standard genetic procedures. The responses elicited in the different crosses with repair-deficient females were compared with those in mei+ crosses. The main findings are the following: with mei-9 females, the frequencies of recessive lethals are higher after irradiation of spermatids in N2, but not after irradiation in air of O2 (relative to those in the mei+ crosses); this result is different from that obtained in earlier work with spermatozoa, in which cell stage, higher yields of recessive lethals were obtained after irradiation of males in either N2 or air; in the mei-9 crosses, there are no significant differences in response (relative to mei+) after irradiation of either spermatozoa or spermatids in O2; the translocation frequencies in the mei-9 crosses are similar to those in the mei+ crosses, irrespective of the treated germ cell stage or the irradiation atmosphere; irradiation of either spermatozoa or spermatids in N2, air or O2 does not result in any differential recovery of recessive lethals in the mei-41 relative to mei+ crosses; irradiation of spermatids in N2 and of spermatozoa in air leads to a higher recovery of translocations in the mei-41 crosses; and after irradiation of spermatids or spermatozoa in any of the gaseous atmospheres, the frequencies of recessive lethals and of translocations are lower in the mus-101 crosses. The differences in responses (between cell stages, in different gaseous atmospheres and with different repair-deficient females) are explained on the basis of both qualitative and quantitative differences in the composition of the initial lesions and the extent to which their repair may be affected by the defects present in the different repair-deficient females. Several discrepancies between expectations based on biochemical results and the genetic results are pointed out.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hyperthermic potentiation of unrejoined DNA strand breaks following irradiation

Previous reports have suggested that the potentiation of cellular radiation sensitivity by hyperthermia may be due to its inhibition of the repair of single-strand breaks in DNA. Such inhibition could result in increased numbers of unrejoined breaks at long times following irradiation, lesions that are presumed to be lethal to the cell. As a test of this hypothesis, the amounts of residual strand-break damage in cells following combined hyperthermia and ionizing radiation were measured. The results show that hyperthermia does significantly enhance the relative number of unrejoined strand breaks as measured by the technique of alkaline elution and that the degree of enhancement is dependent on both the temperature and duration of the hyperthermia treatment. For example, compared to unheated cells, the proportion of unrejoined breaks measured 8 hr after irradiation was increased by a factor of 1.5 in cells that were treated for 30 min at 43 degrees C, by a factor of 6 for cells treated for 30 min at 45 degrees C, and by a factor of 4 for cells treated at 43 degrees C for 2 hr. In experiments in which the sequence of heat and irradiation were varied, a high degree of correlation was observed between the resulting level of cell killing and the relative numbers of unrejoined strand breaks. The greatest effects on both of these parameters were observed in those protocols in which the irradiation was delivered either during, just before, or just after the heat treatment.     

In vivo enzyme control through a strong stationary magnetic field--the case of thymidine kinase in mouse bone marrow cells

The influence of a strong homogeneous and stationary magnetic field (SMF) on the activity of the enzyme thymidine kinase (TdR-K) in bone marrow cells, and as a consequence of this on the incorporation of 125I-labelled 5-iodo-2-deoxyuridine (125IUdR) into DNA of mice and into isolated bone marrow cells in vitro, was assayed after exposure of immobilized mice. No effect could be elicited in moving mice, in cells in suspension or in enzyme in solution. The response depended on the body temperature during exposure: at 27 degrees C and 29 degrees C there was an increase and at 37 degrees C and a depression of enzyme activity. The TdR-K activity at low temperature increased with the field strength ranging from 0.2 to 1.4T. Thirty minutes were required for full expression of the effect at 1.4T; 5-10 min were needed after exposure for a return to base-line levels. Mice were given total-body irradiation at a dose of 0.1 Gy 137Cs gamma rays and then exposed immediately to a magnetic field at 1.4T for 30 min at a body temperature of 27 degrees C; gamma irradiation no longer inhibited the enzyme. Exposure to the magnetic field further removed from the time of gamma irradiation, did not negate the inhibitory effect of gamma irradiation. The observed responses to given challenges in this complex system support the hypothesis that the magnetic field affects TdR-K activity by way of a mediating structure, such as a membrane.     

Effect of freezing temperature,at which straws were plunged into liquid nitrogen,on the post-thaw motility and acrosomal status of ram spermatozoa

The present study was conducted to observe the effect of initial freezing temperature on subsequent survival and acrosomal integrity of Malpura and Bharat Merino ram spermatozoa during post-thawing incubation. Semen samples were diluted in TEST-yolk-glycerol extender, loaded in 0.25 ml straws and cooled down to -25, -75 or -125 degrees C freezing temperature using a programmable cell freezer. Computer assisted sperm analysis and acrosomal integrity of thawed samples were assessed after thawing and at hourly intervals during incubation at 37 degrees C for 4 h. The percentage of motile cells in samples frozen at -125 degrees C were 80.3 and 63.7 after post-thawing and -thawing incubation, compared to 75.9 and 39.7 at -25 degrees C or 73.9 and 51.8 at -75 degrees C temperatures, respectively. The spermatozoa with normal acrosome were also significantly, respectively, higher in samples frozen at -125 degrees C, compared to -25 and -75 degrees C temperatures. There were no significant breed variations on percentage of motile, percentage of rapidly motile cells, percentage of normal acrosomes, curvilinear velocity and lateral head displacement except straight line velocity and average path velocity of spermatozoa. The results indicated that -125 degrees C initial freezing temperature conferred the best cryopreserving ability to ram spermatozoa for post-thawing thermoresistance test compared to -25 or -75 degrees C freezing temperature.     

Motility and fertility of equine spermatozoa in a milk extender after 12 or 24 hours at 20 degrees C

The effects of extender and storage at 20 degrees C on equine spermatozoa were evaluated in two experiments using embryo recovery as the end point. In both experiments, inseminations were every other day, starting on Day 2 or 3 of estrus or after a 35-mm follicle was detected, with 250 x 10(6) progressively motile cells (based on initial evaluation). In Experiment 1, semen from two stallions was used to compare the motility and fertility of spermatozoa maintained in a) heated skim milk extender at 37 degrees C with insemination in <1 h; b) E-Z Mixin extender at 37 degrees C with insemination in <1 h; and c) E-Z Mixin extender at 37 degrees C with cooling to 20 degrees C and insemination after storage for 12 h at 20 degrees C. The percentage of motile spermatozoa was 34% after 12 h compared to 55% at 0 h (P < 0.05). However, the percentage of mares from which an embryo was recovered 6.5 d after ovulation was 62, 56, and 50% for Treatments A, B, and C (P > 0.05). In Experiment 2, semen from three stallions was used to compare the motility and fertility of spermatozoa in a) E-Z Mixin extender at 37 degrees C with insemination in <1 h or b) E-Z Mixin extender at 37 degrees C with cooling to 20 degrees C and insemination after storage for 24 h at 20 degrees C. The percentage of motile spermatozoa was 17% after 24 h compared to 54% at 0 h (P < 0.05). There was no difference between treatments (P > 0.05) in the percentage of mares from which an embryo was recovered 6.0 d after ovulation (68 vs 62%) or among stallions. Thus, stallion semen extended in E-Z Mixin was held at 20 degrees C for 24 h without a marked decline in fertility.     

Hyperthermic killing and hyperthermic radiosensitization in Chinese hamster ovary cells: effects of pH and thermal tolerance

To quantitatively relate heat killing and heat radiosensitization, asynchronous or G1 Chinese hamster ovary (CHO) cells at pH 7.1 or 6.75 were heated and/or X-irradiated 10 min later. Since no progression of G1 cells into S phase occurred during the heat and radiation treatments, cell cycle artifacts were minimized. However, results obtained for asynchronous and G1 cells were similar. Hyperthermic radiosensitization was expressed as the thermal enhancement factor (TEF), defined as the ratio of the D0 of the radiation survival curve to that of the D0 of the radiation survival curve for heat plus radiation. The TEF increased continuously with increased heat killing at 45.5 degrees C, and for a given amount of heat killing, the amount of heat radiosensitization was the same for both pH's. When cells were heated chronically at 42.4 degrees C at pH 7.4, the TEF increased initially to 2.0-2.5 and then returned to near 1.0 during continued heating as thermal tolerance developed for both heat killing and heat radiosensitization. However, the shoulder (Dq) of the radiation survival curve for heat plus radiation did not manifest thermal tolerance; i.e., it decreased continuously with increased heat killing, independent of temperature, pH, or the development of thermotolerance. These results suggest that heat killing and heat radiosensitization have a target(s) in common (TEF results), along with either a different target(s) or a difference in the manifestation of heat damage (Dq results). For clinical considerations, the interaction between heat and radiation was expressed as (1) the thermal enhancement ratio (TER), which is the dose of X rays alone divided by the dose of X rays combined with heat to obtain an isosurvival, e.g., 10(-4), and (2) the thermal gain factor (TGF), the ratio of the TER at pH 6.75 to the TER at pH 7.4. Since low pH reduced the rate of development of thermal tolerance during heating at low temperatures, low pH enhanced heat killing more at 42-42.5 degrees C than at 45.5 degrees C where thermal tolerance did not develop. Therefore, the increase in the TGF after chronic heating at 42-42.5 degrees C was greater than after acute heating at 45.5 degrees C, due primarily to the increase in heat killing causing an even greater increase in heat radiosensitization. These findings agree with animal experiments suggesting that in the clinic, a therapeutic gain for tumor cells at low pH may be greater for temperatures of 42-42.5 degrees C than of 45.5 degrees C.     

Temperature and the formation of radiation-induced chromosome aberrations. I. The effect of irradiation temperature

Irradiation temperature, changed from 37 degrees C to 4 degrees C, acts as a dose-modifying factor with regard to the dose-yield relationship for dicentric chromosome aberrations in human lymphocytes irradiated with 150 kV X-rays. The temperature dependence of the aberration yield observed at constant dose is S-shaped, with a sharp rise near 15 degrees C from a lower plateau below 12 degrees C to a higher plateau beyond 17 degrees C. The aberration yield is determined by the irradiation temperature, irrespective of fast temperature changes from 4 degrees C to 37 degrees C or from 37 degrees C to 4 degrees C, applied at various delay times before and after irradiation. It is concluded that irradiation temperature influences the formation of chromatin lesions rather than their interaction.     

Evidence for two domains of growth temperature for the psychrotrophic bacterium Pseudomonas fluorescens MF0.

The variations in the maximal specific growth rate of the psychrotrophic bacterium Pseudomonas fluorescens MF0 with respect to temperature were studied between 0 and 30 degrees C (optimal for growth). The Arrhenius plot showed a drastic change in slope at the intermediate temperature of 17 degrees C. Over the cold domain from 0 to 17 degrees C, the temperature characteristic was twofold higher than over the suboptimal domain from 17 to 30 degrees C. The macromolecular composition of exponentially growing cells was invariant over the entire range from 0 to 30 degrees C. Variations of temperature and growth rate were independently investigated through chemostat experiments in order to characterize their respective effects on cell macromolecular composition and size. The effect of growth rate in this psychrotrophic strain is identical to that of all other bacteria assayed so far. In contrast, an original biphasic variation of total protein concentration was demonstrated in strain MF0 with respect to temperature, with a maximum at 17 to 20 degrees C. Indeed, increasing the temperature in the chemostat resulted in a biphasic decrease in the net protein production rate: a very slight decrease below 17 degrees C and a much larger decrease from 17 to 28 degrees C. These results could signify an increase in the cellular protein degradation rate with increasing temperature, especially above 17 degrees C.     

The effects of temperature and glucose on protein biosynthesis by immature (round) spermatids from rat testes

A method is described for the preparation of highly purified fractions (greater than 80% pure) of immature spermatids (round, steps 1--8) from rat testes by centrifugal elutriation in sufficient yields for biochemical studies when four rat testes are used. Electron microscopy established the identity of the cells and demonstrated that the cell membrane is intact. Some cells develop nuclear and cytoplasmic vacuoles during the 2 h required for preparation. Immature spermatids prepared by this method use glucose with an increase in oxygen consumption, lactate production, and protein synthesis over control levels (no glucose). The testicular cell suspension from which spermatids are separated, like whole testis and spermatids themselves, show higher incorporation of amino acids into TCA-precipitable material at 34 degrees C than at 38 degrees C and in the presence of glucose. A subcellular system prepared from immature spermatids with excess ATP shows greater incorporation of amino acids into TCA-precipitable material at 34 degrees C than at 38 degrees C. This difference does not result from increased breakdown of protein. It is concluded that body temperature (38 degrees C) inhibits some aspect(s) of protein synthesis in addition to previously reported effects on amino acid transport and production of ATP (Means and Hall. 1969. Endocrinology. 84:285--297.).