Distinct Diurnal Rhythm Research Articles

Salivary Profiles of 11-oxygenated Androgens Follow a Diurnal Rhythm in Patients With Congenital Adrenal Hyperplasia.

ContextSeveral studies have highlighted the importance of the 11-oxygenated 19-carbon (11oxC19) adrenal-derived steroids as potential biomarkers for monitoring patients with 21-hydroxylase deficiency (21OHD).ObjectiveTo analyze circadian rhythmicity of 11oxC19 steroids in saliva profiles and evaluate their relevance as potential monitoring parameters in 21OHD.Design, Setting, and ParticipantsCross-sectional single-center study including 59 patients with classic 21OHD (men = 30; women = 29) and 49 body mass index- and age-matched controls (men = 19; women = 30).Outcome MeasuresSalivary concentrations of the following steroids were analyzed by liquid chromatography-tandem mass spectrometry: 17-hydroxyprogesterone (17OHP), androstenedione (A4), testosterone (T), 11β-hydroxyandrostenedione (11OHA4), and 11-ketotestosterone (11KT).ResultsSimilar to the previously described rhythmicity of 17OHP, 11OHA4 and 11KT concentrations followed a distinct diurnal rhythm in both patients and controls with highest concentrations in the early morning and declining throughout the day (11-OHA4: mean reduction of hormone concentrations between timepoint 1 and 5 (Δ mean) in male patients = 66%; male controls Δ mean = 83%; female patients Δ mean = 47%; female controls Δ mean = 86%; 11KT: male patients Δ mean = 57%; male controls Δ mean = 63%; female patients Δ mean = 50%; female controls Δ mean = 76%). Significant correlations between the area under the curve for 17OHP and 11KT (rpmale = 0.773<0.0001; rpfemale = 0.737<0.0001), and 11OHA4 (rpmale = 0.6330.0002; rpfemale = 0.5640.0014) were observed in patients but not present or reduced in controls.ConclusionsAdrenal 11oxC19 androgens are secreted following a diurnal pattern. This should be considered when evaluating their utility for monitoring treatment control.

Salivary profiles of 11-oxygenated androgens follow a diurnal rhythm in patients with congenital adrenal hyperplasia

CONTEXT Several studies have highlighted the importance of the 11-oxygenated 19-carbon (11oxC19) adrenal-derived steroids as potential biomarkers for monitoring patients with 21-hydroxylase deficiency (21OHD). OBJECTIVE To analyze circadian rhythmicity of 11oxC19 steroids in saliva profiles and evaluate their relevance as potential monitoring parameters in 21OHD. DESIGN, SETTING, AND PARTICIPANTS Cross-sectional single-center study including 59 patients with classic 21OHD (men = 30; women = 29) and 49 body mass index- and age-matched controls (men = 19; women = 30). OUTCOME MEASURES Salivary concentrations of the following steroids were analyzed by liquid chromatography-tandem mass spectrometry: 17-hydroxyprogesterone (17OHP), androstenedione (A4), testosterone (T), 11β-hydroxyandrostenedione (11OHA4), and 11-ketotestosterone (11KT). RESULTS Similar to the previously described rhythmicity of 17OHP, 11OHA4 and 11KT concentrations followed a distinct diurnal rhythm in both patients and controls with highest concentrations in the early morning and declining throughout the day (11-OHA4: mean reduction of hormone concentrations between timepoint 1 and 5 (Δ mean) in male patients = 66%; male controls Δ mean = 83%; female patients Δ mean = 47%; female controls Δ mean = 86%; 11KT: male patients Δ mean = 57%; male controls Δ mean = 63%; female patients Δ mean = 50%; female controls Δ mean = 76%). Significant correlations between the area under the curve for 17OHP and 11KT (rpmale = 0.773<0.0001; rpfemale = 0.737<0.0001), and 11OHA4 (rpmale = 0.6330.0002; rpfemale = 0.5640.0014) were observed in patients but not present or reduced in controls. CONCLUSIONS Adrenal 11oxC19 androgens are secreted following a diurnal pattern. This should be considered when evaluating their utility for monitoring treatment control.

Seasonal effects on fertility in gilts and sows

The ancestral wild pig is a short day length seasonal breeder. The domestic pig appears to have retained some of this seasonality as evidenced by a reduction in fertility during the summer—autumn period. The most important aspect of this seasonality is a reduction in the number of mated sows that farrow. Many of these sows conceive and embryos develop normally for 20 - 25 days before pregnancy is terminated and the sow returns to oestrus (25 - 35 days after mating). In other species, transduction of photoperiodic information is achieved by release of melatonin during the dark period. In the pig, the pattern of melatonin secretion and the subsequent hypothalamo—pituitary—gonadal responses appear to be more complex. A relatively high light intensity is required for pigs to generate a distinct diurnal melatonin rhythm and they appear unable to respond appropriately to abrupt changes in photoperiod. Pigs on restricted feeding and maintained under long photoperiods (but not under short photoperiods) have higher concentrations of melatonin than do similarly maintained pigs fed ad libitum. Continuous release melatonin implants have a deleterious effect on farrowing rate, suggesting that the abnormally high melatonin concentrations observed in sows in summer—autumn play a role in the pathogenesis of seasonal infertility. Ad libitum feeding of sows during the first few weeks of pregnancy may prevent the increase in melatonin concentrations and so remove the seasonal influence on fertility. The pituitary response to different photoperiods is also somewhat confusing. Although there is some evidence of increased sensitivity to the negative feedback of ovarian steroids in the prepubertal gilts and weaned sows during summer—autumn, LH concentrations are increased in early pregnant sows. It is proposed that the failure of sows to maintain pregnancy in summer—autumn results from disruption of maternal recognition of pregnancy causing regression of the corpora lutea, loss of pregnancy and return of the sow to oestrus.

Diurnal Patterns for Cortisol, Cortisone and Agouti-Related Protein in Human Cerebrospinal Fluid and Blood.

Cortisol in blood has a robust circadian rhythm and exerts potent effects on energy balance that are mediated in part by central mechanisms. These interactions involve orexigenic agouti-related protein (AgRP) neurons that are stimulated by glucocorticoids. However, diurnal changes in brain or cerebrospinal fluid (CSF) cortisol and cortisone, which are interconverted by 11ß-HSD1, have not been characterized in humans. To conduct a secondary analysis of existing samples to characterize diurnal changes in cortisol and cortisone in CSF and examine their relationships to changes in AgRP. Stored CSF and plasma samples were obtained from 8 healthy subjects who served as controls for a sleep study. CSF was collected every 2h for 36h via indwelling lumbar catheter; plasma was collected every 2h. There was a diurnal rhythm for cortisol and cortisone in CSF that closely followed the plasma rhythm by 2 h with peak and nadir levels at 0900h and 0100h. The ratio of cortisol (active) to cortisone (inactive) in CSF was 48% higher at the peak versus nadir. There was a diurnal rhythm for AgRP in plasma that was out of phase with the cortisol rhythm. There was a less distinct diurnal rhythm for AgRP in CSF that oscillated with a similar phase as cortisol. There is a robust diurnal rhythm for cortisol and cortisone in CSF. Diurnal changes were noted for AgRP that are related to the cortisol changes. It remains to be determined if AgRP mediates adverse metabolic effects associated with disruption of the cortisol circadian rhythm.

MON-163 Lowering of Circulating FGF21 by Modulation of Bile Acid Metabolism in Healthy Males

FGF21 is a circulating protein of hepatic origin proposed to be involved in the regulation of lipid and glucose metabolism. Increased levels have been reported in conditions of metabolic overload. Recent animal studies have also suggested that FGF21 levels may be influenced by modulation of bile acid metabolism, but knowledge about the human situation is sparse. In this study we aimed to evaluate the response of circulating FGF21 to perturbations of bile acid metabolism in healthy humans. We studied samples obtained from two clinical studies characterizing bile acid metabolism: (i) Eight healthy males underwent repeated blood sampling during 32 hr in three experiments: under basal conditions, following initiation of treatment with cholestyramine (CME), and following initiation of CME when under treatment with atorvastatin (CME+STAT). (ii) 54 healthy males were randomized into 8 groups that were treated orally with a single dose of placebo or the nonsteroidal FXR agonist, Px-102 (0.15mg/kg, 0.3mg/kg, 0.6mg/kg, 1.12mg/kg, 2.25mg/kg, 3.38mg/kg, or 4.5mg/kg) and monitored for 24 hr. Serum levels of FGF21 were related to previously reported levels of markers of cholesterol and bile acid metabolism. (iii) In a third previously conducted study based on a survival training program for healthy volunteers, FGF21 serum levels were investigated during 50 hrs of sleep and 66 hrs of food deprivations. In the untreated normal subjects, serum FGF21 levels displayed a distinct diurnal rhythm, characterized by an early morning peak. Following CME and CME+STAT treatment, circulating FGF21 was lowered and the early morning peak was abolished. Intake of Px-102 strongly and rapidly reduced FGF21 levels which remained lowered for the 24 hr-period. There was no obvious correlation of FGF21 levels to the diurnal variation patterns of the enterohepatic circulation of BAs, nor to those of cholesterol and bile acid syntheses or serum FGF19. Our data also failed to show any clear effects of sleep deprivation or 66 hrs of starvation on circulating FGF21. Both during marked stimulation and pronounced reduction of bile acid synthesis, serum FGF21 levels were reduced. The results do not support the proposal that FXR activation is an important regulator of hepatic FGF21 secretion in humans, which has been suggested from animal experiments. Instead, we would propose that our findings reflect the response to depletion of intracellular bile acid levels, both when caused by interruption of their normal enterohepatic circulation and by suppression of their de novo synthesis from cholesterol.

Peripheral regulation of stress and fear responses in pigs from tail-biting pens

This study focused on stress physiology by characterizing cortisol responses to stressors in tail biters (n = 10), victims (n = 10), and control pigs (n = 10) of two different breeds (Landrace × Yorkshire, LY; Landrace/Yorkshire × Landrace/Duroc; LYLD) and sexes (females and castrated males). We exposed pigs to 10 min of isolation with a human at the farm and transported them to a controlled environment. There, the behaviour was registered for 10 min during sessions when subjected to a novel object test and to a novel arena test. Sampling times of salivary cortisol were in all the fear tests before testing and 60 min thereafter, while for transportation as well 120 min after the beginning of transportation. We additionally measured cortisol at 7:00 and 16:00 h during three days following transportation. The basal stress axis activity followed a distinct diurnal rhythm between sexes and breeds, with castrated males having higher cortisol level than females and LY pigs higher than LYLD pigs. Following isolation at the farm and transportation, the concentration of salivary cortisol was higher in LY than in LYLD pigs. Pigs considered the exposure to a novel arena, but not to a novel object, stressful by showing a cortisol level after testing higher than before testing. The results suggest a genotypic effect on sensitivity to stress in pigs that have performed tail biting, have been victimized, or have not been involved in tail biting.

Corticosterone metabolites in laying hen droppings—Effects of fiber enrichment, genotype, and daily variations

There is growing interest and concern for animal welfare in commercial poultry production. To evaluate stress and welfare in an objective and noninvasive way, fecal corticosterone metabolites (FCM) in droppings can be analyzed. However, the influence of diet, genotype, and daily variations in FCM and production of droppings in laying hens has been poorly investigated. This study examined the effect of insoluble fiber by adding 3% ground straw pellets to the feed to Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) hens housed in furnished cages between 20 and 40 wk of age. In total, 960 hens were included in the study. Droppings were collected 4 times per day for 3 consecutive days and analyzed by corticosterone immunoassay. Biological validation confirmed the ability of the assay to detect changes in FCM levels. Inclusion of straw pellets in the feed increased FCM concentration in both hen genotypes and increased excretion rate of FCM in LB hens. The LB hens also produced greater amounts of droppings than LSL hens. Both FCM levels and production of droppings varied during the day, although no distinct diurnal rhythm was found. These findings demonstrate that when using FCM to evaluate stress and welfare in laying hens, many factors (e.g., diet, genotype used, and so on) need to be taken into account to allow accurate interpretation of the results. In addition, under certain conditions, excretion rate of FCM might be more appropriate to use compared with FCM concentration.

Root exudation of phytosiderophores from soil-grown wheat.

For the first time, phytosiderophore (PS) release of wheat (Triticum aestivum cv Tamaro) grown on a calcareous soil was repeatedly and nondestructively sampled using rhizoboxes combined with a recently developed root exudate collecting tool. As in nutrient solution culture, we observed a distinct diurnal release rhythm; however, the measured PS efflux was c. 50 times lower than PS exudation from the same cultivar grown in zero iron (Fe)-hydroponic culture.Phytosiderophore rhizosphere soil solution concentrations and PS release of the Tamaro cultivar were soil-dependent, suggesting complex interactions of soil characteristics (salinity, trace metal availability) and the physiological status of the plant and the related regulation (amount and timing) of PS release.Our results demonstrate that carbon and energy investment into Fe acquisition under natural growth conditions is significantly smaller than previously derived from zero Fe-hydroponic studies. Based on experimental data, we calculated that during the investigated period (21–47 d after germination), PS release initially exceeded Fe plant uptake 10-fold, but significantly declined after c. 5 wk after germination.Phytosiderophore exudation observed under natural growth conditions is a prerequisite for a more accurate and realistic assessment of Fe mobilization processes in the rhizosphere using both experimental and modeling approaches.

Differential Modulation of Excitatory and Inhibitory Striatal Synaptic Transmission by Histamine

Information processing in the striatum is critical for basal ganglia function and strongly influenced by neuromodulators (e.g., dopamine). The striatum also receives modulatory afferents from the histaminergic neurons in the hypothalamus which exhibit a distinct diurnal rhythm with high activity during wakefulness, and little or no activity during sleep. In view of the fact that the striatum also expresses a high density of histamine receptors, we hypothesized that released histamine will affect striatal function. We studied the role of histamine on striatal microcircuit function by performing whole-cell patch-clamp recordings of neurochemically identified striatal neurons combined with electrical and optogenetic stimulation of striatal afferents in mouse brain slices. Bath applied histamine had many effects on striatal microcircuits. Histamine, acting at H(2) receptors, depolarized both the direct and indirect pathway medium spiny projection neurons (MSNs). Excitatory, glutamatergic input to both classes of MSNs from both the cortex and thalamus was negatively modulated by histamine acting at presynaptic H(3) receptors. The dynamics of thalamostriatal, but not corticostriatal, synapses were modulated by histamine leading to a facilitation of thalamic input. Furthermore, local inhibitory input to both classes of MSNs was negatively modulated by histamine. Subsequent dual whole-cell patch-clamp recordings of connected pairs of striatal neurons revealed that only lateral inhibition between MSNs is negatively modulated, whereas feedforward inhibition from fast-spiking GABAergic interneurons onto MSNs is unaffected by histamine. These findings suggest that the diurnal rhythm of histamine release entrains striatal function which, during wakefulness, is dominated by feedforward inhibition and a suppression of excitatory drive.

Examining the daily feeding rhythms of amago Oncorhynchus masou masou using self-feeding systems

Knowledge of circadian feeding rhythms in farmed fish species can help farmers determine the optimal feeding times to maximise feed consumption and minimise feed wastage. This study examined i) the circadian feeding rhythms, ii) the inter-day variability in feed demanded and iii) feed wastage of amago, Oncorhynchus masou masou, fed using self-feeding systems. Three replicate groups of 16 fish were held under a 12:12 light:dark cycle at 16 °C for 56 days. After a 28-day self-feeder acclimation period all three groups had become competent self-feeders and the treatment period ran from day 28 to day 56. Under the experimental light and temperature regime utilised amago appear to be visual self-feeders, actuating self-feeders almost exclusively during the light phase (99.9% of actuations). All three groups exhibited a distinct diurnal feeding rhythm within the light phase and demonstrated significant ( P < 0.05) crepuscular peaks in feed demand. In addition, one group also displayed a significant peak at midday. Daily ration varied both within and between groups but no clear rhythmicity was observed in these variations. Feed waste was very low (always < 2%) for each group. The results of this study suggest that farmers can optimise daily feed consumption by feeding amago exclusively during the light phase, specifically at dawn and dusk, with a possible extra meal at midday.

Further characterization of ferric--phytosiderophore transporters ZmYS1 and HvYS1 in maize and barley

Roots of some gramineous plants secrete phytosiderophores in response to iron deficiency and take up Fe as a ferric–phytosiderophore complex through the transporter YS1 (Yellow Stripe 1). Here, this transporter in maize (ZmYS1) and barley (HvYS1) was further characterized and compared in terms of expression pattern, diurnal change, and tissue-type specificity of localization. The expression of HvYS1 was specifically induced by Fe deficiency only in barley roots, and increased with the progress of Fe deficiency, whereas ZmYS1 was expressed in maize in the leaf blades and sheaths, crown, and seminal roots, but not in the hypocotyl. HvYS1 expression was not induced by any other metal deficiency. Furthermore, in maize leaf blades, the expression was higher in the young leaf blades showing severe chlorosis than in the old leaf blades showing no chlorosis. The expression of HvYS1 showed a distinct diurnal rhythm, reaching a maximum before the onset of phytosiderophore secretion. In contrast, ZmYS1 did not show such a rhythm in expression. Immunostaining showed that ZmYS1 was localized in the epidermal cells of both crown and lateral roots, with a polar localization at the distal side of the epidermal cells. In maize leaves, ZmYS1 was localized in mesophyll cells, but not epidermal cells. These differences in gene expression pattern and tissue-type specificity of localization suggest that HvYS1 is only involved in primary Fe acquisition by barley roots, whereas ZmYS1 is involved in both primary Fe acquisition and intracellular transport of iron and other metals in maize.

PRECLINICAL STUDY: Circadian regulation of central ethanol sensitivity by the mPer2 gene

The effect of alcohol is known to vary with the time of the day. Although initially it was suggested that this phenomenon may be due to diurnal differences in ethanol metabolism, more recent studies were contradicting. In the present study, we therefore first set out in assessing the diurnal variations in ethanol sensitivity in mice analysing, concurrently, ethanol elimination rates. Ethanol-induced (3.5 g/kg; intraperitoneal) loss of righting reflex (LORR) duration was thus determined at several Zeitgeber time (ZT) points (ZT5, 11, 17 and 23) in C57BL/6N mice. In parallel, the corresponding ethanol elimination rates were also assessed. The results display the existence of a distinct diurnal rhythm in LORR duration peaking at ZT11, whereas no differences could be observed regarding the elimination rates of alcohol. Successively, we checked the involvement of the clock genes mPer1 and mPer2 in conveying this rhythm in sensitivity, testing LORR and hypothermia at the peak and trough previously observed (ZT5 and ZT11). Per1(Brdm1) mice demonstrate a similar diurnal pattern as control mice, with enhanced LORR durations at ZT11. In contrast, Per2(Brdm1) mice did not exhibit a temporal variation to the depressant effects of ethanol with respect to LORR, revealing a constant high sensitivity to ethanol. The present study reveals a central role of the mPer2 gene in inhibiting alcohol sensitivity at the beginning of the inactive phase.

Secretion time of phytosiderophore differs in two perennial grasses and is controlled by temperature

Some perennial grasses secrete phytosiderophores from the roots in response to Fe-deficiency. Here, we characterized the pattern of phytosiderophore secretion by Lolium perenne (cv. ‘Tove’) and Poa pratensis (cv. ‘Baron’), which are used to correct iron-deficiency induced chlorosis in fruit trees grown on calcareous soils. Both species showed a distinct diurnal rhythm in phytosiderophore secretion, but the secretion time differed between species; the secretion peak time was about 2 h earlier in L. perenne than in P. pratensis under the same growth conditions. The secretion time was shifted by changing temperature during the collection of phytosiderophores in both L. perenne and P. pratensis. Increasing root-zone temperature resulted in earlier secretion, while lowering the temperature resulted in delayed secretion. Furthermore, this shift of secretion time was achieved by changing the temperature around the root-zone. Shading treatment during the secretion period did not affect the secretion time in either species. These results indicate that the secretion of phytosiderophore is triggered by the temperature around the roots, but not light, in these two perennial grasses.

Steroid hormones control circadian ELOVL3 expression in mouse liver

The Elovl3 gene belongs to the Elovl gene family, which encodes for enzymes involved in the elongation of very long chain fatty acids. The recognized role for the enzyme is to control the elongation of saturated and monounsaturated fatty acids up to 24 carbons in length. Elovl3 was originally identified as a highly expressed gene in brown adipose tissue on cold exposure. Here we show that hepatic Elovl3 mRNA expression follows a distinct diurnal rhythm exclusively in mature male mice, with a sharp increase early in the morning Zeitgeber time (ZT) 20, peaks around ZT2, and is back to basal level at the end of the light period at ZT10. In female mice and sexually immature male mice, the Elovl3 expression was constantly low. Fasting and refeeding mice with chow or high-fat diet did not alter the Elovl3 mRNA levels. However, animals that were exclusively fed during the day for 9 d displayed an inverted expression profile. In addition, we show that Elovl3 expression is transcriptionally controlled and significantly induced by the exposure of the synthetic glucocorticoid dexamethasone. Taken together, these data suggest that Elovl3 expression in mouse liver is under strict diurnal control by circulating steroid hormones such as glucocorticoids and androgens. Finally, Elovl3 expression was found to be elevated in peroxisomal transporter ATP-binding cassette, subfamily D(ALD), member 2 ablated mice and suppressed in ATP-binding cassette subfamily D(ALD) member 2 overexpressing mice, implying a tight cross talk between very long chain fatty acid synthesis and peroxisomal fatty acid oxidation.

Steroid Hormones Control Circadian Elovl3 Expression in Mouse Liver

The Elovl3 gene belongs to the Elovl gene family, which encodes for enzymes involved in the elongation of very long chain fatty acids. The recognized role for the enzyme is to control the elongation of saturated and monounsaturated fatty acids up to 24 carbons in length. Elovl3 was originally identified as a highly expressed gene in brown adipose tissue on cold exposure. Here we show that hepatic Elovl3 mRNA expression follows a distinct diurnal rhythm exclusively in mature male mice, with a sharp increase early in the morning Zeitgeber time (ZT) 20, peaks around ZT2, and is back to basal level at the end of the light period at ZT10. In female mice and sexually immature male mice, the Elovl3 expression was constantly low. Fasting and refeeding mice with chow or high-fat diet did not alter the Elovl3 mRNA levels. However, animals that were exclusively fed during the day for 9 d displayed an inverted expression profile. In addition, we show that Elovl3 expression is transcriptionally controlled and significantly induced by the exposure of the synthetic glucocorticoid dexamethasone. Taken together, these data suggest that Elovl3 expression in mouse liver is under strict diurnal control by circulating steroid hormones such as glucocorticoids and androgens. Finally, Elovl3 expression was found to be elevated in peroxisomal transporter ATP-binding cassette, subfamily D(ALD), member 2 ablated mice and suppressed in ATP-binding cassette subfamily D(ALD) member 2 overexpressing mice, implying a tight cross talk between very long chain fatty acid synthesis and peroxisomal fatty acid oxidation.

Postpubertal feeding experience affects sex-specific spatial ability in rats

We previously reported that feeding with powdered diet after weaning (3 weeks of age) enhanced spatial ability, and increased the amount of acetylcholine (ACh) released in the dorsal hippocampus in female rats. In the present study, to specify the time when feeding conditions caused these effects, a radial 8-arm maze task and an in vivo microdialysis study were performed in both sexes of rats. In rats fed standard laboratory diet (i.e., pelleted diet), males learned the radial 8-arm maze faster than females. Moreover, the ACh release showed a distinct diurnal rhythm which was high during the dark phase and low during the light phase, but males showed a greater amount of ACh released in the dorsal hippocampus than females. However, in rats fed powdered diet after 6 weeks of age, no significant sex differences were observed in the radial 8-arm maze task or in the amount of ACh released, since feeding with powdered diet enhanced spatial ability, and increased the amount of ACh released only in females. These results suggest that feeding conditions after 6 weeks of age may contribute to the sex difference in the spatial ability associated with the changes in the amount of ACh released in the dorsal hippocampus in rats.

Treatment of Male Hypogonadism

Physiology Androgens are responsible for the development and maintenance of secondary sexual characteristics, fertility, and anabolic effects of somatic tissues (lean body mass) in men. The primary androgen in circulation is testosterone. Production and secretion of testosterone is under the tonic control of leutinizing hormone (LH). LH and follicle-stimulating hormone (FSH) are secreted by the anterior pituitary and regulated by the pulsatile action of gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus. FSH, with the effects of testosterone, is responsible for spermatogenesis. Testosterone secretion is episodic and follows a distinct diurnal rhythm, with testosterone levels maximal in the morning and minimal in the evening.

Settling abalone veliger larvae in a free-swimming microalgal culture

In the current abalone hatchery in China, insufficient diatoms on vertically placed corrugated pvc plates at later stage often could not support the growth of postlarvae up to the stage that they can feed on live macroalgae. As a result, stripping the spats (3–5 mm) off by anaesthetization and switching the diet from live diatoms to artificial powdered diet in combination has to be performed in most of the abalone farms. This manipulation normally leads to more than 50% mortality. Here we report the direct use of the unicellular green alga Platymonas helgolandica Kylin var. tsingtaoensis as a potential alga to be used to settle the veliger larvae of the Pacific abalone Haliotis discus hannai and to feed the postlarvae. Settlement rate of 2-day-old veliger larvae in mono culture of P. helgolandica could be as high as 92% (± 4.2%) on day 10 in small scale trials, higher than that in the selected benthic diatom strain (53.6% ± 12.7%) when settled in the water in which bacteria propagation was controlled by treatment of 2 ppm of benzylpenicillinum calcium and streptomycin sulfate. Postlarvae fed solely on P. helgolandica or the selected benthic diatom Navicula-2005-A grew at rates of 40.1 (± 1.9) and 45.8 (± 3.4) μm day − 1 , respectively, when raised at 22 °C until day 50 postfertilization. P. helgolandica was shown to have distinct diurnal settling rhythm characterized with a peak of settled cells in the middle of the night for cell division and a peak of free-swimming cells in the middle of the day. High density of attached P. helgolandica cells on the inner surface of the culture facility in the night fits the nocturnal feeding behavior of the abalone spats. Judged by the promising larvae settling rate, growth and survival rates of the postlarvae fed with this alga, the free-swimming micro-green alga P. helgolandica constitutes a potential species for settling the veliger larvae and for supporting the growth of postlarvae as well.

A MOVING MAT: PHOTOTAXIS IN THE FILAMENTOUS GREEN ALGAE SPIROGYRA (CHLOROPHYTA, ZYGNEMATACEAE)1

A blue light– (peak at 470 nm) induced photomovement was observed in the filamentous eukaryotic algae, Spirogyra spp. When Spirogyra filaments were scattered in a water chamber under a unilateral light source, they rapidly aligned toward the light source in 1 h and bound with neighboring filaments to form thicker parallel bundles of filaments. The filaments in the anterior of the bundles curved toward the light first and then those in the posterior began to roll up toward the light, forming an open‐hoop shape. The bundle of filaments then moved toward the light source by repeated rolling and stretching of filaments. When the moving bundle met other filaments, they joined and formed a bigger mat. The coordination of filaments was essential for the photomovement. The average speed of movement ranged between 7.8 and 13.2 μm·s−1. The movement was induced in irradiance level from 1 to 50 μmol photons·m−2·s−1. The filaments of Spirogyra showed random bending and stretching movement under red or far‐red light, but the bundles did not move toward the light source. There was no distinct diurnal rhythm in the photomovement of Spirogyra spp.

Diurnal changes in the expression of genes that participate im phytosiderophore synthesis in rice

The roots of graminaceous plants secrete mugineic acid family phytosiderophores (MAs), allowing the acquisition of sparingly soluble iron (Fe) from the soil. In barley, the secretion of MAs occurs in a distinct diurnal rhythm. Rice also secretes deoxymugineic acid (DMA) in response to Fe deficiency, but it is unclear whether the secretion also occurs in a diurnal rhythm. A time course analysis with Northern blots was used to examine the expression of genes encoding enzymes in the MA biosynthetic pathway. The transcriptional levels of the NAS and NAAT genes fluctuated diurnally in Fe-deficient rice roots. These results suggest that, as in barley, the secretion of DMA in rice changes in a diurnal rhythm. Furthermore, the transcriptional levels of genes encoding translation initiation factor 4A2 (elF4A2), ras-related small GTP-binding protein (GTPase), and ADP-ribosylation factor 1 (ARF1), which fluctuate diurnally in barley and are thought to be involved in the diurnal changes in MA secretion, also changed diurnally. As these genes are involved in intracellular vesicular transport, it is possible that secretion of DMA in rice is under the control of vesicular transport, as in barley root cells.