Rhythmic activity of uptake hydrogenase in the prokaryote Rhodospirillum rubrum.

Growth of Rhodospirillum rubrum was followed in cultures kept under anoxic conditions at constant temperature in either continuous light (LL, 32 degrees C) or continuous darkness (DD, 32 degrees C and 16 degrees C). In DD, only small modifications of the turbidity were detected; linear regression analysis nevertheless gives a very significant slope (t(34) = 13.07, p < 10(-14), with R2 of 0.834). Mean generation times reflected these differences of growth with 11.9+/-0.5 h in LL and 43.2+/-1.1 h in DD at 32 degrees C and 37.4+/-1.0 h at 16 degrees C cultures. The uptake hydrogenase (Hup) activity has been followed in situ in whole cells of R. rubrum grown in the same conditions, and a clear ultradian rhythm of activity has been observed. Indeed, after about 12 h in the new media, a rapid rise of hydrogenase activity was observed in both LL and DD cultures after which it decreased again to very low values. The activity of Hup continued to show such fluctuations during the rest of the experiment, both in DD and in LL, during the growth and stationary phases. The Lomb-Scargle power periodogram method demonstrates the presence of a clear rhythmic Hup activity both in LL and DD. In the LL-grown cultures, the oscillating activity is faster and continues throughout the growth and the stationary phases, with an ultradian period of 12.1+/-0.5 h. In DD, the slow-growing bacteria showed an ultradian oscillatory pattern of Hup activity with periods of 15.2+/-0.5 h at 32 degrees C and 23.4+/-2.0 h at 16 degrees C. The different periods obtained for LL- and DD-grown bacteria are significantly different.

Involvement of indole-3-acetic acid in the circadian growth of the first internode of Arabidopsis.

The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity. Decapitation induced a strong inhibition of stem extension. Subsequent application of IAA restored growth and the associated extension-rate oscillations. In addition, IAA treatments, after decapitation, re-established the circadian rhythmicity visible in the intact plants during free run. This indicates that the upper zone of the inflorescence has a major influence on the extension rate of floral stems and implies a role for auxin. Application of N-(1-naphthyl)phthalamic acid, an IAA transport inhibitor, to an intact floral stem inhibited growth and the rhythmicity in the extension rate oscillations, indicating that IAA polar transport may play a role in the dynamics of stem elongation. Furthermore, IAA-aspartate application, after decapitation, did not restore growth and rhythmicity. Nevertheless, biochemical analysis of IAA and IAA-aspartate demonstrated circadian fluctuations of the endogenous levels of both compounds. These observations suggest that IAA metabolism is an essential factor in the regulation of the circadian growth rhythm of Arabidopsis floral stems.

Parallel nocturnal secretion of melatonin and testosterone in the plasma of normal men.

Differences and similarities in the temporal organization of hormone secretion in plasma reflect the activity of CNS pacemakers. One aspect of this activity, the temporal synchronization of the secretion of different hormones is still poorly understood. We report the analysis of melatonin and testosterone plasma concentrations during two nights in 6 normal healthy young men. Blood was collected every 20 min between 2040 and 0640. Plasma testosterone concentrations increased by 1.5- to 2-fold during the second part of the night, and melatonin by 2.5- to 4-fold. In each subject, the individual temporal pattern of melatonin was quite stable over the two nights of sampling, while testosterone profiles showed fluctuations. There was a high degree of parallelism in these two hormones nocturnal secretion. These results, together with previous studies, suggest that melatonin might entrain the nocturnal secretion of testosterone.

Plasma concentration of nine hormones and neurotransmitters during usual activities or constant bed rest for 34 H.

Thyroid-stimulating hormone (TSH), cortisol, melatonin, prolactin, luteinizing hormone (LH), delta-sleep-inducing peptide (DSIP), its phosphorylated form (P-DSIP), heart rate, and body temperature were measured every half hour during two 24-h periods in five normal men. tau-Amino-butyric acid (GABA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured less frequently. The first period, the "activity" condition, included usual daily activities. The second period, or "rest" condition, consisted of fasting, constant bed rest during 34 h, and partial light deprivation. Compared with the "rest" condition, the "activity" condition increased heart rate, temperature, LH, and TSH in most subjects, and cortisol in two of five subjects. It retarded the onset of nocturnal cortisol and melatonin secretion. The temporal pattern and the absolute values of the concentrations of DSIP, P-DSIP, MHPG, GABA, and prolactin showed no or minimal changes during the two conditions. In spite of the influence of the "activity" versus "rest" condition on several hormones, the mean concentrations as well as the temporal organization of their secretion into plasma were quite stable within each subject, whereas they varied much more between individuals. TSH, cortisol, and melatonin values were also stable within an 8-month period in one subject who was studied on four occasions. The results illustrate that the patterns of hormones rhythms and their reactivity to changes in the environment are, to a large extent, specific to each subject.

Effect of chloride ions on the kinetic parameters of the potato tuber and mung bean pyrophosphate-dependent phosphofructokinase.

The affinity constant Ka of PPi-PFK for Fru 2,6-P2 is equal to 1.56 nM for the potato enzyme and to 6.67 nM for that of the mung bean in the absence of chloride ions. These results are notably lower than the currently reported 5.5 nM and 30, 50 nM respectively. It is shown that the chloride ion is a competitive inhibitor of Fru 2,6-P2 for both enzymes. The inhibition constant Ki is equal to 15.6 mM for potato PPi-PFK up to 40 mM chloride. For the mung bean enzyme, the Ki is 19.0 mM up to 30 mM chloride. No effects are detected on the Michaelis-Menten constants Km of the substrates Fru-6-P and PPi up to 40 mM chloride. Other halide ions are also found to inhibit the potato PPi-PFK: bromide is competitive like chloride, whereas fluoride and iodide have a mixed inhibition towards Fru 2,6-P2.