Periods Of Different Durations Research Articles

Chlamydomonas reinhardtii: duration of its cell cycle and phases at growth rates affected by temperature

Synchronized cultures of the green alga Chlamydomonas reinhardtii were grown photoautotrophically under a wide range of environmental conditions including temperature (15-37 °C), different mean light intensities (132, 150, 264 μmol m⁻² s⁻¹), different illumination regimes (continuous illumination or alternation of light/dark periods of different durations), and culture methods (batch or continuous culture regimes). These variable experimental approaches were chosen in order to assess the role of temperature in the timing of cell division, the length of the cell cycle and its pre- and post-commitment phases. Analysis of the effect of temperature, from 15 to 37 °C, on synchronized cultures showed that the length of the cell cycle varied markedly from times as short as 14 h to as long as 36 h. We have shown that the length of the cell cycle was proportional to growth rate under any given combination of growth conditions. These findings were supported by the determination of the temperature coefficient (Q₁₀), whose values were above the level expected for temperature-compensated processes. The data presented here show that cell cycle duration in C. reinhardtii is a function of growth rate and is not controlled by a temperature independent endogenous timer or oscillator, including a circadian one.

Anoxic survival of the Pacific hagfish (Eptatretus stoutii)

It is not known how the Pacific hagfish (Eptatretus stoutii) can survive extended periods of anoxia. The present study used two experimental approaches to examine energy use during and following anoxic exposure periods of different durations (6, 24 and 36h). By measuring oxygen consumption prior to anoxic exposure, we detected a circadian rhythm, with hagfish being active during night and showing a minimum routine oxygen consumption (RMR) during the daytime. By measuring the excess post-anoxic oxygen consumption (EPAOC) after 6 and 24h it was possible to mathematically account for RMR being maintained even though heme stores of oxygen would have been depleted by the animal's metabolism during the first hours of anoxia. However, EPAOC after 36h of anoxia could not account for RMR being maintained. Measurements of tissue glycogen disappearance and lactate appearance during anoxia showed that the degree of glycolysis and the timing of its activation varied among tissues. Yet, neither measurement could account for the RMR being maintained during even the 6-h anoxic period. Therefore, two independent analyses of the metabolic responses of hagfish to anoxia exposure suggest that hagfish utilize metabolic rate suppression as part of the strategy for longer-term anoxia survival.

The characterisation of rainfall in the arid and semi-arid regions of Ethiopia

In order to plan effective agricultural and water resource projects, it is necessary to understand the spatial and temporal variability of rainfall. Although it is one of the most drought-hit countries in the world, almost no study has ever been conducted in characterising the rainfall pattern of the arid and semi-arid regions of Ethiopia. In this study, rainfall data of the past 50 years was used to study the basic statistical characteristics of the rainfall of this region. Annual and monthly rainfall was fitted to the theoretical probability distributions and the best distributions describing the data at respective stations were determined. Probability of wet days and dry periods of different durations was determined. It has been found that both annual and monthly rainfall at different stations was described by different probability distributions. There is high variation of rainfall pattern among the stations. Heavier rainfall events are infrequent but they make up a significant percentage of the total rainfall. In arid and semi-arid regions where both the amount and frequency of rainfall occurrence is low, it is essential to take into account the unique rainfall characteristics in such regions. Water SA Vol.32 (3) 2006: pp.429-436

Effect of two fasting periods of different duration on ghrelin response to a mixed meal

Background and aim The inhibitory effect of food on ghrelin secretion is reduced in several eating disorders such as restricting type anorexia nervosa, bulimia and obesity. These conditions are frequently characterised by irregular distribution of meals during the day. It is unknown whether two short fasting periods different duration affect ghrelin response to a mixed meal. Aim of the present study was to examine, in healthy volunteers, the effects of two fasting periods of different duration on pre- and post-prandial ghrelin concentrations after a standard mixed meal. Methods and results Nine healthy men (mean age ± S.E.M., 25.1 ± 0.2 years; mean body mass index ± S.E.M., 22.6 ± 0.3 kg/m 2) were studied in 2 days after 12 h of fasting (12F) and 17 h of fasting (17F) with a within-subject repeated measure design. On both days they ate a standardized mixed meal. Before each meal hunger rating was evaluated with a visual analogue score. Blood samples for ghrelin, insulin, and glucose were collected at 0, 45, 60, 90, 120, 150 and 180 min after meal. Comparing fasting values of 17F with 12F there was a significant increase in plasma ghrelin (160 ± 20 vs. 146 ± 18 fmol/mL, P = 0.015) and hunger rating (evaluated with a visual analogue scores) (7.0 ± 0.3 vs. 5.1 ± 0.4, P < 0.003). A positive correlation between fasting ghrelin and hunger rating ( r = 0.52, P < 0.01) was found. Circulating ghrelin decreased after both meals without any significant difference in relation with the previous length of fasting. Also postmeal ghrelin AUC as well as fasting and postmeal concentrations of insulin and glucose were similar after 12F and 17F. Conclusions In healthy subjects a longer fasting period increases ghrelin concentration but did not affect post-prandial ghrelin response to a mixed meal.

Out-of-season recollection of drug use for seasonal IgE-mediated rhinitis: Useful but an overestimation

The history of seasonal, IgE-mediated (allergic) rhinitis is often obtained postseasonally as a retrospective assessment. It is not known whether recollected drug use is representative for the in-seasonal medication history. To investigate the agreement between in-seasonal and out-seasonal reports on drugs and drug doses, and to investigate whether retrospective assessment was sufficiently sensitive to detect the effect of intervention. Thirty-five patients allergic to birch pollen were allocated to allergen-specific immunotherapy (SIT) or placebo in a double-blind study. Drug use was recorded daily during the season 2000 and out-seasonally 6 months after the seasons 1999 and 2000. The mean daily drug use was transformed into a 4-point categorical scale for simplicity and was calculated for the out-seasonal rating and for 6 in-seasonal periods of different durations. In-seasonal and postseasonal ratings were compared with the Cohen weighted kappa (kappa w). We observed a high level of agreement between in-seasonal and retrospective reports of drugs used (kappa w > 0.60) and drug doses (kappa w > 0.50). The highest agreement was observed for the in-seasonal day, week, or 2 weeks with the highest drug intake. Out-seasonal ratings significantly overestimated the daily oral and nasal antihistamine use compared with in-seasonal periods >2 weeks. Despite being comparable pretreatment, only the SIT group had a significant decrease in recollected total drug use during SIT. Out-seasonal recollection of hay fever drugs represented a period of a maximum 14 days. It appeared sufficiently sensitive to detect the effect of intervention.

Reproductive performance of beef cow herds in New Zealand

AIM: To describe the reproductive performance of beef cow herds in New Zealand and to develop reference ranges for assessing the reproductive performance of individual herds from in-calf rates, that take into account variation in the length of mating periods. METHODS: Veterinary practices throughout New Zealand involved in beef cattle work were asked to collect reproductive data from seasonally calving beef cow herds mated in the spring of 2001 through to the end of summer of 2002. An estimate of conception rate (termed calculated conception rate: CCR) was determined for each herd, assuming that the conception rate was constant for each 21-day interval of the mating period. The algebraic relationship between CCR and in-calf rate at pregnancy testing was defined for mating periods of different durations and, therefore, given the in-calf rate and the duration of the mating period, a CCR could be determined for each herd. Expected pregnancy rates were recalculated from CCR data for a range of mating period durations to produce a look-up table for assessing herd reproductive performance. Reproductive data describing regional differences in in-calf rates and CCRs, bull:cow ratios, breed characteristics, start dates of mating and durations of mating periods were summarised. The effect of study variables in explaining CCRs was examined using a general linear model (GLM). RESULTS: Data were collected from 1,005 beef cow herds distributed throughout New Zealand. The median in-calf rate for all herds was 91%, the lower quartile was ≤88% and the upper quartile ≥94%. The mean CCR for herds with complete reproductive data (862) was 55% (SD 11), the lower quartile was ≤48% and upper quartile ≥61%. Median in-calf rates for 2-year-old heifers (mated at approximately 15 months of age), 3-year-old heifers (mated at approximately 27 months of age), and mixed-age cows were 90%, 91% and 92%, respectively. The study variables that accounted for significant variation in breeding group CCR in a multivariate GLM were ‘region’ (p<0.01) and ‘date mating commenced’ (<0.01). The adjusted R2 for the model was 0.055. CONCLUSIONS: The reproductive reference range produced provides veterinarians and herd managers with a quantitative method for assessing reproductive performance of beef cow herds compared with industry averages, from in-calf rates at the time of pregnancy testing and durations of mating periods.

Cell Cycle Plasticity in Response of Low Temperature in Root Tips of Tetraploid Medicago

ABSTRACTFlow-cytometric analysis was carried out to determine the effect of low temperature on the changes in proportion of 2C:4C complement of DNA in root cells from three different zones (meristem apex, elongation and differentiation) in seedlings of Medicago sativa cv. Sitel. 2C:4C complement of DNA in cells were estimated after the treatments of the roots at control temperature of24°C, elevated temperatures of26°C, 30°C, 37°C and low temperatures—10°C and 5°C (in three different periods of duration 15, 38, 45 days). The observed results showed that at control temperature percentage of nuclei 2C:4C in meristem apex is 65:35, in elongation zone 50:50 and in differentiation zone is 40:60. The elevated temperatures (26°C, 30°C, 37°C) influenced this proportion very slightly while treatments of roots with low temperature especially in a period of 45 days changed 2C:4C complement of DNA drastically. It was found that root treated for 45 days at temperature of 10°C the 2C:4C in meristem apex is 78:22, elongation zone 74:26 and in differentiation zone is 70:30. In the case of temperature of 5°C it was 85:15 in meristem apex, 80:20 in elongation zone and 71:29 in differentiation zone.In order to visualize the impact of low temperature on cell cycle plasticity with decrease of dividing cells, roots of transgenic Medicago falcata plants were exposed at control (24°C) and low (5°C) temperatures for the period of 15 and 45 days. These plants carried gus gene under the promoters (cycl, cyc3a)from cell cycle genes After this temperature treatment roots cells were activated for division with different treatments for 1hour. GUS assay were performed for control and pre-treated root tips. The expression of marker gene was observed in highly divided cells of pre-treated root at control temperature. GUS gene was not expressed in pre-treated roots exposed to low temperature for 45 days.

Rotating-frame spin–lattice relaxation time imaging by radio-frequency field gradients: visualization of strained crosslinked natural rubbers

NMR imaging by radio-frequency field gradients ( B 1 gradients) is especially convenient for heterogeneous samples and/or in the case of relatively short transverse relaxation times. The method has been combined with the application of two spin-lock periods of different duration so as to produce rotating-frame spin–lattice relaxation time ( T 1 ρ ) images. In the case of natural rubber samples with different crosslink densities, such images are not only characteristic of the crosslink density but also reveal the way in which the material has been stressed. The strained parts can be visualized either directly or through histograms showing the T 1 ρ distribution over the whole sample.

The effects of fasting duration on the metabolic response to feeding in Python molurus: an evaluation of the energetic costs associated with gastrointestinal growth and upregulation.

The oxygen uptake of Python molurus increases enormously following feeding, and the elevated metabolism coincides with rapid growth of the gastrointestinal organs. There are opposing views regarding the energetic costs of the gastrointestinal hypertrophy, and this study concerns the metabolic response to feeding after fasting periods of different duration. Since mass and function of the gastrointestinal organs remain elevated for several days after feeding, the metabolic increment following a second meal given soon after the first can reveal whether the metabolic costs relate to the upregulation of gastrointestinal organs or merely the metabolic cost of processing a meal. Eight juvenile pythons were kept on a regular feeding regime for 6 mo after hatching. At the beginning of the metabolic measurements, they were fed mice (20% of body mass), and the metabolic response to similarly sized meals was determined following 3, 5, 7, 14, 21, 30, and 60 d of fasting. Our data show that the metabolic response following feeding was large, ranging from 21% to 35% of ingested energy (mean=27%), but the metabolic response seems independent of fasting duration. Hence, the extraordinarily large cost of digestion in P. molurus does not appear to correlate with increased function and growth of gastrointestinal organs but must be associated with other physiological processes.

Roles of aorta, ostia and tracheae in heartbeat and respiratory gas exchange in pupae of Troides rhadamantus Staudinger 1888 and Ornithoptera priamus L. 1758 (Lepidoptera, Papilionidae)

In non-diapausing pupae of the two birdwing butterfly species Troides rhadamantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO 2 release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three different types of activity: Continuous forward-pulse periods of different duration with a frequency range of about 0.25–0.52 s −1, continuous backward-pulse periods with lower frequencies (0.15–0.29 s −1) and intermittent backward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12–0.35 s −1 alternated with heart pauses of 2–10 min. CO 2 release was discontinuous (CFO-type) from about four to 12 days after pupation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO 2 release rates were very low in both species (10–30 nmol g −1 min −1). After this period, heart pauses occurred more frequently, probably indicating the onset of metamorphosis and the beginning partial histolysis of the heart. Infrared-optical and thermometrical measurements of heartbeat indicated that haemolymph transport within the dorsal vessel in forward direction is more effective than in backward direction. This is deduced from the higher heartbeat frequency and heartbeat amplitude of the forward pulsations. Results from ultrasonic doppler velocimetry suggest that haemolymph flow velocity is highest during the relatively long diastasis of 2–3 s (30–40 mm s −1), while minimum particle speed (about 20 mm s −1) is at the end of systole and the beginning of diastole. This would mean that haemolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave measured with the infrared transmission technique was lower (about 8.4–22 mm s −1 in Troides, 10–23 mm s −1 in Ornithoptera) and remained constant during forward pulse periods. During backward beating the speed was lower (8–20 mm s −1 in Troides, 9–17 mm s −1 in Ornithoptera) and decreased during backward pulse periods. During day two to seven in Troides and day three to nine in Ornithoptera, spiracular opening periods coincided with changes in heartbeat direction from backward to forward pulsations. A possible influence is the more efficient convective haemolymph mixing in the haemocoel during forward heartbeat. The mixing allows to bring the haemolymph in close contact with the tracheal system where the discharge of CO 2 takes place. Heartbeat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles.

Evaluación neurofisiológica en pacientes afectados por ataxia espinocerebelosa tipo 2

Type 2 spinocerebellar ataxia (SCA2) is the condition most often described (to date) in patients with hereditary ataxia, its prevalence being 52 per 100,000 persons. In patients with SCA2 neurogenic patterns are identified by means of electrophysiological techniques. A transverse study was made of 70 persons with SCA2 of different periods of duration and from different regions of the country. The control group was made up of 108 volunteers. Electrophysiological recordings made were: conventional and quantitative electromyography, late F wave and H reflex responses. Multivariate methods with a confidence interval of 95% (alpha = 0.05) were used for statistical analysis. Conventional electromyography showed a pattern of isolated contractions, predominantly in patients who had had the disorder < or = 5 years, classified as Grade I by the authors; in those with a history of > 5 years there was a pattern of very isolated contractions with motor potentials of amplitudes > 10 microV, without denervation, classified as Grade II. The patients with worse clinical condition were concentrated in this latter group. Significant differences were observed between Groups I, II and control and also regarding the late responses of the F wave and H reflex. For the first time two types of neurogenic patterns of SCA2 have been established to describe alterations which denote participation of the first and second motor neurones.

Velocity Criteria for ???Foveation Periods??? Determined from Image Motions Simulating Congenital Nystagmus

Foveation periods are brief intervals in the congenital nystagmus (CN) waveform when the image is on or near the fovea and eye velocity is relatively slow. The purpose of this study was to determine how visual acuity depends on image velocity for foveation periods of different durations. Visual acuity was measured using high-contrast, single Landolt Cs in four normal observers during image motion simulating that in jerk nystagmus. The "simulated foveation periods" ranged from 20 to 100 ms in duration and 0 to 16 degrees approximately in velocity. The "critical velocity" was defined as the velocity during simulated foveation periods that produced a just-noticeable worsening of acuity (0.05 and 0.1 logMAR) from that in the zero-velocity condition. Critical velocity increased from approximately 3 degrees approximately for simulated foveation durations between 100 and 40 ms to approximately 5 degrees approximately for a simulated foveation duration of 20 ms. Critical velocities increased further when the targets were presented peripherally or with optical blur, to introduce an additional acuity loss. A consequence of these findings is that less recovery of acuity should be expected when retinal image motion is reduced in individuals with CN if a sensory acuity deficit coexists.

Immunocytochemistry, autoradiography, in situ hybridization, selective stains: complementary tools for ultrastructural study of structure-function relationships in the nucleus. Applications to adenovirus-infected cells.

A significant amount of new information on structure-function relationships in nuclei of adenovirus-infected cells has accumulated during the last decade as a result of the combined use of several new cytochemical techniques. Localization of viral DNA on ultrathin sections of infected cells has been investigated at the ultrastructural level by using specific DNA staining and immunocytochemistry with monoclonal anti-DNA antibodies. Both techniques, however, concomitantly visualize cellular and viral DNA. The specific stain for DNA reveals the configuration of the DNA molecules in the different nuclear substructures, whatever their synthetic activities. The immunodetection of DNA reveals that specific antibodies strongly bind to DNA of condensed host chromatin and to both encapsidated and nonencapsidated inactive viral genomes. However, the observation of an abnormally low level of labeling over the substructures in which synthetic activities of viral genomes are known to be intense demonstrates a serious limitation of this technique for the detection of active DNA. Postembedding in situ hybridization is the most useful method for identifying with certainty the structures containing defined nucleic acid sequences. By using a biotinylated viral DNA probe, in situ hybridization provides specific identification of structures containing either viral DNA or viral RNA molecules. In addition, with appropriate pretreatment of the sections, it is possible to reveal either all the viral DNA--that is, both double- and single-stranded DNA molecules (dsDNA, ssDNA)--or more specific species such as only ssDNA or only dsDNA molecules. The replicative and transcriptional activities of viral genomes are determined by high-resolution autoradiography. Autoradiography after a short pulse incorporation of appropriate radioactive precursors by infected cells reveals the sites of cellular and viral DNA replication or transcription. A short pulse followed by chase periods of different durations reveals the progressive migration of the cellular and viral synthesized products. The in situ distribution of the viral 72 kDa DNA-binding protein, a highly phosphorylated protein which protects the viral ssDNA, is revealed either by immunocytochemistry with specific antibodies or by the bismuth staining method which stains all highly phosphorylated proteins, including both cellular and viral proteins. The combined results of all these cytochemical procedures reveal the composition and functions of some of the structures induced by adenovirus infection. They demonstrate that viral genomes engaged in replication lead to the formation of the replicative foci in which two compartments rapidly develop, one of which results from the aggregation of single strands of viral DNA and their accompanying 72 kDa protein.(ABSTRACT TRUNCATED AT 400 WORDS)

Fatigue and recovery of voluntary and electrically elicited dynamic force in humans.

1. Percutaneous electrical stimulation of the human quadriceps muscle has been used to assess the loss of central activation immediately after a bout of fatiguing exercise and during the recovery period. 2. Fatigue was induced in eight healthy males by a maximal effort lasting 25 s performed on an isokinetic cycle ergometer at a constant pedal frequency of 60 revolutions per minute. The cranks of the ergometer were driven by an electric motor. Before and after the sprint, subjects allowed their legs to be passively taken round by the motor. During the passive movement the knee extensors were stimulated (4 pulses; 100 Hz). Peak voluntary force (PVF) during the sprint and peak stimulated forces (PSF) before and in recovery were recorded via strain gauges in the pedals. Recovery of voluntary force was assessed in a series of separate experiments in which subjects performed a second maximal effort after recovery periods of different durations. 3. Peak stimulated forces were reduced to 69.8 +/- 9.3% immediately after the maximal effort, (P < 0.05), but had returned to pre-exercise values after 3 min. The maximum rate of force development (MRFD) was also reduced following fatigue to 68.8 +/- 11.0% (P < 0.05) of control and was fully recovered after 2 min. PVF was reduced to 72.0 +/- 9.4% (P < 0.05) of the control value following the maximal effort. After 3 min voluntary force had fully recovered. 4. The effect of changing the duration of the fatiguing exercise (10, 25 and 45 s maximal effort) resulted in an increased degree of voluntary force loss as the duration of the maximal effort increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Development in wheat as affected by timing and length of exposure to long photoperiod

Seeds of a spring wheat (Triticum aestivum L. cv. 'Condor') were vernalized and then grown at 19°C in two naturally-lit environments, one with a moderate (12 h) and the other with long (18 h) photoperiod. Treatments consisted of transfers of plants from the moderate to the long photoperiod chamber on different occasions, or for periods of different durations. The main objectives were to determine whether wheat development responds to current and previous photoperiodic environments and whether there is a juvenile phase when the plants are insensitive to photoperiod. Plants under constant 18 h photoperiod had fewer leaves which appeared faster than those under constant 12 h photoperiod (i.e. phyllochron was increased from 4.4 to 5.1 d leaf -1 ). Plants transferred from 12 h to 18 h photoperiod at terminal spikelet appearance (TSA) reached anthesis 4 d earlier than plants retained at 12 h, while plants under continuous long photoperiod (18 h) completed this phase most rapidly. Thus, there was some evidence for a historic effect of photoperiod on development. Exposure to long photoperiod during the first 5 d after plant emergence accelerated the rate of development towards anthesis, suggesting that there was no juvenile period of photoperiodic insensitivity. There were, however, changes during ontogeny in the degree of sensitivity to long photoperiod, increasing from seedling emergence to a maximum c. 15 d later, and then decreasing again. Although all treatments were imposed before TSA, the response was not limited to the pre-TSA phase, suggesting that well before the terminal spikelet appeared, the plant was already committed to the initiation of this spikelet. Spikelet number decreased with delayed transfer to long photoperiod with a minimum for plants transferred to long days from 16-20 d after seedling emergence. Additionally, there was a trend for an increase in the rate of leaf appearance (decrease in phyllochron) when the plants were exposed to long days between 10 and 35 d after seedling emergence. Although the differences were small, when considered in conjunction with the effects on final leaf number they become important in explaining differences in time to anthesis.

The role of enzyme activation state in limiting carbon assimilation under variable light conditions

The mechanisms regulating transient photosynthesis by soybean (Glycine max) leaves were examined by comparing photosynthetic rates and carbon reduction cycle enzyme activities under flashing (saturating 1 s lightflecks separated by low photon flux density (PFD) periods of different durations) and continuous PFD. At the same mean PFD, the mean photosynthetic rates were reduced under flashing as compared to continuous light. However, as the duration of the low PFD period lengthened, the CO2 assimilation attributable to a lightfleck increased. This enhanced lightfleck CO2 assimilation was accounted for by a greater postillumination CO2 fixation occurring after the lightfleck. The induction state of photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), fructose 1,6-bisphosphatase (FBPase) and ribulose 5-phosphate kinase (Ru5P kinase) activities all responded similarly and were all lower under flashing as compared to constant PFD of the same integrated mean value. However, the fast phase of induction and FBPase and Ru5P kinase activities were reduced more than were the slow phase of induction and rubisco activity. This was consistent with the role of the former enzymes in the fast induction component that limited RuBP regeneration. Competition for reducing power between carbon metabolism and thioredoxin-mediated enzyme activation may have resulted in lower enzyme activation states and hence lower induction states under flashing than continuous PFD, especially at low lightfleck frequencies (low mean PFD).

Modelling of British rainfall using a random parameter Bartlett-Lewis Rectangular Pulse Model

The performance of a stochastic model, in which Poisson cluster processes represent the arrival of rain cells within a rainstorm, is assessed for hourly point rainfall data from Birmingham, UK. The Bartlett-Lewis Rectangular Pulse Model is extended to include random cell duration, and its performance is compared with that of the basic model analysed previously. Both models perform well in reproducing statistics of the rainfall depth distribution at different time-scales for individual months, but the randomised model also enables a good reproduction of the proportions of dry periods of different durations. Performance is improved by an optimisation method which addresses issues of parameter identification. However, some deficiencies remain with respect to extreme values. Finally, the seasonal variability of parameters is represented on a daily, rather than monthly basis, with comparable results.

The Dark-Light-Transient of the C02 Fixation Influenced by Light Intensity and Predarkening Period of Attached Leaves of Phaseolus vulgaris var. nanus L.

Summary The induction phase of C02 fixation of intact attached bean leaves was examined at 25°C under two different photon flux densities (242 and 833 μmol photons m−2 s−1) and after dark periods of different durations (0. 5, 1, 3, 6, 12, and 24 h). During a 50 minute time period following the dark/light change, the transient of the C02 fixation was analysed. The values used were IVmax (= the maximal induction velocity) and Γt (= the time compensation point). Γt rose with the duration of the dark period from about 98 s to about 360 s. IVmax decreased under the same conditions from 0.034 to 0.003 μmol C02 m−2 s−2 under strong light, and from 0.002 to 0.006 μmol C02 m−2 s−2 under moderate light. These results suggest that Γt and IV-max are related to different metabolic patways. Γt seems to be correlated to the activation of the Calvin cycle. IVmax is basically determined by the supply of assimilatory power created by the given light conditions and is modified by the adaptation velocity of the pool sizes of appropriate Calvin cycle intermediates. A second result of these examinations is that plants start C02 fixation faster than expected if the duration of the dark period equals the duration of the cultivation period. A very long dark period of 24 h leads to an injury of the photosynthetic apparatus. A very slow increase of the C02 fixation can be noticed.

Shift sequences, duration of rest periods, and accident risk of bus drivers.

This paper presents a portion of the results of a comprehensive analysis of the etiology of bus driver accidents. This portion of the analysis concentrates on two questions. First, does the sequence of various shifts influence accident risk on a given day? Various analyses led us to conclude that there was no interaction between the type of shift (either stand-by shift or day off) on preceding days, the actual shift, and the bus drivers' accident risk. This leads to the supposition that the actual situation on the working day is an important factor in determining accident risk. Second, is there any interaction between accident risk and the duration of total (added) rest periods during the shift up to the moment of the accident? No such association could be detected. Our analysis and conclusions are restricted to possible effects of total resting time and cannot be extended to possible effects on accident risk of particular rest periods of different duration and at a different stage within a shift.

Estrogen-induced weight gain cannot be predicted in individuals.

The effect of high estrogen doses on weight was studied in 36 adolescent girls with familial tall stature treated to reduce adult height. Mean weight gain during the first year was 9.0 +/- 3.6 kg. Thereafter, there was no or minimal gain on continued treatment. The largest weight velocity occurred during the first 6 months. Within that period, it was most marked during the first 5 weeks, probably due to early water retention. The gain (total, in different groups of patients and in treatment periods of different duration) did not correlate with height and weight before treatment expressed in absolute values or standard deviation scores. It is concluded that the weight gain induced by long-term estrogen treatment cannot be predicted quantitatively before treatment in individuals, and that heavy or fat girls do not necessarily gain more weight than light and lean girls.