The molecular basis of temperature compensation in the Arabidopsis circadian clock

Circadian clocks maintain robust and accurate timing over a broad range of physiological temperatures, a characteristic termed temperature compensation. In Arabidopsis thaliana, ambient temperature affects the rhythmic accumulation of transcripts encoding the clock components TIMING OF CAB EXPRESSION1 (TOC1), GIGANTEA (GI), and the partially redundant genes CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY). The amplitude and peak levels increase for TOC1 and GI RNA rhythms as the temperature increases (from 17 to 27 degrees C), whereas they decrease for LHY. However, as temperatures decrease ( from 17 to 12 degrees C), CCA1 and LHY RNA rhythms increase in amplitude and peak expression level. At 27 degrees C, a dynamic balance between GI and LHY allows temperature compensation in wild-type plants, but circadian function is impaired in Ihy and gi mutant plants. However, at 12 degrees C, CCA1 has more effect on the buffering mechanism than LHY, as the cca1 and gi mutations impair circadian rhythms more than Ihy at the lower temperature. At 17 degrees C, GI is apparently dispensable for free-running circadian rhythms, although partial GI function can affect circadian period. Numerical simulations using the interlocking-loop model show that balancing LHY/CCA1 function against GI and other evening-expressed genes can largely account for temperature compensation in wild-type plants and the temperature-specific phenotypes of gi mutants.

Circadian blood pressure variation after acute stroke

We aimed to characterise the patterns of circadian blood pressure (BP) variation after acute stroke and determine whether any relationship exists between these patterns and stroke outcome. BP was recorded manually every 4 h for 48 h following acute stroke. Patients were classified according to the percentage fall in mean systolic BP (SBP) at night compared to during the day as: dippers (fall >= 10-= 20%); non-dippers (>= 0-

The relationship between diurnal type and time duration estimation at morning and evening times of day

This study investigates whether different diurnal types (morning versus evening) differ in their estimation of time duration at different times of the day. Given that the performance of morning and evening types is typically best at their preferred times of day, and assuming different diurnal trends in subjective alertness (arousal?) for morning and evening types, and adopting the attentional gate model of time duration estimation, it was predicted that morning types would tend to underestimate and be more accurate in the morning compared to evening types where the opposite pattern was expected. Nineteen morning types, 18 evening types and 18 intermediate types were drawn from a large sample (N=1175) of undergraduates administered the Early/Late Preference Scale. Groups performed a time duration estimation task using the production method for estimating 20-s unfilled intervals at two times of day: 0800/1830. The median absolute error, median directional error and frequency of under- and overestimation were analysed using repeated-measures ANOVA. While all differences were statistically non-significant, the following trends were observed: morning types performed better than evening types; participants overestimated in the morning and underestimated in the evening; and participants were more accurate later in the day. It was concluded that the trends are inconsistent with a relationship between subjective alertness and time duration estimation but consistent with a possible relationship between time duration estimation and diurnal body temperature fluctuations. (C) 2002 Elsevier Ltd. All rights reserved.

Additional signalling compounds are required to orchestrate plant development

Plants are necessarily complex systems that require monitoring of multiple environmental signals and, in response to those signals, coordination of differentiation and development of an extensive array of cell types at multiple locations. This coordination must rely on integration of long-distance signals that provide a means of communication among different plant parts. We propose that the relatively well-characterized classical phytohormones must act with several other long-distance signals to achieve this level of organization with dynamic yet measured responses. This is supported by observations that classical phytohormones: (i) operate in complex yet experimentally unresolved networks involving cross-talk and feedback, (ii) are generally multifunctional and nonspecific and hence must rely on other long-distance cues or pre-set conditions to achieve specificity and (iii) are likely to mask roles of other long-distance signals in several experimental contexts. We present evidence for involvement of novel long-distance signals in three developmental processes-branching, flowering and nodulation, and discuss the possible identities of novel signalling molecules.

Subjective and predicted sleepiness while driving in young adults

Sleepiness is a significant contributor to car crashes and sleepiness related crashes have higher mortality and morbidity than other crashes. Young adult drivers are at particular risk for sleepiness related car crashes. It has been suggested that this is because young adults are typically sleepier than older adults because of chronic sleep loss, and more often drive at times of increased risk of acute sleepiness. This prospective study aimed to determine the relationship between predicted and perceived sleepiness while driving in 47 young-adult drivers over a 4-week period. Sleepiness levels were predicted by a model incorporating known circadian and sleep factors influencing alertness, and compared to subjective ratings of sleepiness during 25 18 driving episodes. Results suggested that young drivers frequently drive while at risk of crashing, at times of predicted sleepiness (>7% of episodes) and at times they felt themselves to be sleepy (>23% of episodes). A significant relationship was found between perceived and predicted estimates of sleepiness. However, the participants nonetheless drove at these times. The results of this study may help preventative programs to specifically target factors leading to increased sleepiness when driving (particularly time of day), and to focus interventions to stop young adults from driving when they feel sleepy. (c) 2005 Elsevier Ltd. All rights reserved.

Transcultural properties of the Composite Scale of Morningness: The relevance of the "morning affect" factor

Morningness scales have been translated into several languages, but it lack of normative data and methodological differences make cross-cultural comparisons difficult. This study examines the psychometric properties and factor structure of the Composite Scale of Morningness (CSM) in samples from five countries: France (n = 627), Italy (n, = 702), Spain (n = 391), Thailand (n. = 503), and Australia (17 = 654). Strong national differences are identified. A quadratic relationship between age and CSM total score was apparent in the Australian data with a downward trend after age 35 yrs. There was no age effect in air), sample in the range from 18 to 29 yrs. Factor analysis identified a three-factor solution in all groups for both men and women. Tucker's congruence coefficients indicate that: (1) this solution is highly congruent between sexes in each culture, and (2) a morning affect factor is highly congruent between cultures. These results indicate there are national differences in factorial structure and that cut-off scores used to categorize participants as morning- and evening-types should be established for different cultural and age groups.

Evaluation of random plasma cortisol and the low dose corticotropin test as indicators of adrenal secretory capacity in critically ill patients: A prospective study

It is unclear whether a random plasma cortisol measurement and the corticotropin (ACTH) test adequately reflect glucocorticoid secretory capacity in critical illness. This study aimed to determine whether these tests provide information representative of the 24 hour period. Plasma cortisol was measured hourly for 24 hours in 21 critically ill septic patients followed by a corticotropin test with 1 μ g dose administered intravenously. Serum and urine were analysed for ACTH and free cortisol respectively. Marked hourly variability in plasma cortisol was evident (coefficient of variation 8-30%) with no demonstrable circadian rhythm. The individual mean plasma cortisol concentrations ranged from 286 59 nmol/l to 796 &PLUSMN; 83 nmol/l. The 24 hour mean plasma cortisol was strongly correlated with both random plasma cortisol (r(2) 0.9, P< 0.0001) and the cortisol response to corticotropin (r(2) 0.72, P< 0.001). Only nine percent of patients increased their plasma cortisol by 250 nmol/l after corticotropin (euadrenal response). However, 35% of non-responders had spontaneous hourly rises > 250 nmol/l thus highlighting the limitations of a single point corticotropin test. Urinary free cortisol was elevated (865&PLUSMN; 937 nmol) in both corticotropin responders and non-responders suggesting elevated plasma free cortisol. No significant relationship was demonstrable between plasma cortisol and ACTH. We conclude that although random cortisol measurements and the low dose corticotropin tests reliably reflect the 24 hour mean cortisol in critical illness, they do not take into account the pulsatile nature of cortisol secretion. Consequently, there is the potential for erroneous conclusions about adrenal function based on a single measurement. We suggest that caution be exercised when drawing conclusions on the adequacy of adrenal function based on a single random plasma cortisol or the corticotropin test.

Digenean trematodes infecting the tropical abalone Haliotis asinina have species-specific cercarial emergence patterns that follow daily or semilunar spawning cycles

Approximately 1-2% of the tropical abalone Haliotis asinina inhabiting Heron Island Reef are infected with opecoelid digeneans. These largely inhabit the haemocoel surrounding the cerebral ganglia and digestive gland-gonad complex, and infected abalone typically have significantly reduced or ablated gonads. Observations of infected abalone reveal two distinct cercarial emergence patterns, one which correlates tightly with the abalone's highly regular and synchronous fortnightly spawning cycle, and the other which occurs in a circadian pattern. The former appears to be a novel emergence strategy not previously observed in digeneans. While the cercariae in all abalone are morphologically indistinguishable, comparison of sequences from the internal transcribed spacer 2 (ITS 2) region of the ribosomal DNA reveals a 5.7% difference between cercariae displaying different emergence patterns, indicating these are two distinct species that probably belong to the same genus. The ITS 2 sequences of the species with the daily emergence pattern are identical to that of an undescribed adult opecoelid from the gut of the barramundi cod, Cromileptes altivelis. Combined molecular, morphological and emergence data suggest that while these opecoelid cercariae use the same first intermediate host and are closely related species-members of the genus Allopodocotyle-they fill different ecological niches that are likely to include different definitive hosts.