CIRCADIAN GROWTH IN PORPHYRA UMBILICALIS (RHODOPHYTA): SPECTRAL SENSITIVITY OF THE CIRCADIAN SYSTEM

The circadian rhythm in growth of the red macroalga Porphyra umbilicalis (Linnaeus) J. Agardh was investigated under different spectral light conditions in laboratory-grown thalli. A free-running rhythm was observed in constant green or red light at irradiances of 2.5 to 20 μmol photons·m⁻²·s⁻¹, whereas arhythmicity occurred in constant blue light at 6–20 μmol photons·m⁻²·s⁻¹. The circadian oscillator controlling growth rhythmicity in Porphyra uses most of the visible sunlight spectrum and possibly multiple photoreceptors with a high sensitivity for blue light and a lower sensitivity for red light. This was inferred from three experimental results: (1) The free-running period, τ, of the growth rhythm decreased with increasing irradiance, from approximately 25 h at 2.5 μmol photons·m⁻²·s⁻¹ to 22 h at 20 μmol photons·m⁻²·s⁻¹ in red or green light, (2) Dark pulses of 3 h duration, interrupting otherwise continuous green or red light, caused advances during the subjective day and delays during the subjective night; the circadian oscillator in Porphyra can discriminate darkness from green or red light, and (3) Low-irradiance blue light pulses (2.5 μmol photons·m⁻²·s⁻¹) shifted the growth rhythm in red light of higher irradiance (e.g. 10 μmol photons·m⁻²·s⁻¹), and a strong, high amplitude, type 0 phase response curve was obtained that is usually observed with light pulses shifting a circadian rhythm in otherwise continuous darkness.     

Photoperiod and light quality effects on rate of dark respiration and on photosynthetic capacity in developing seedlings of Chenopodium rubrum

Development and acclimation of energy transduction were studied in seedlings of Chenopodium rubrum L. ecotype selection 184 (50° 10' N; 105° 35' W) in response to photomorphogenic and photoperiodic treatments. Dark respiration and photosynthetic capacity [nmol O₂ (pair of cotyledons)⁻¹ h⁻¹] were measured with an oxygen electrode. Changes in chloroplast ultrastructure were analyzed concomitantly. After germination, seedlings were grown at constant temperature either in darkness or in continuous light (white, red, far-red and blue) or were subjected to diurnal cycles of light/dark or changes in light quality. Dark respiration was low in far-red light treated seedlings. In red light treated seedlings dark respiration was high and the mean value did not depend on fluence rate or photoperiod. Blue light stimulated transitorily and modulated dark respiration in photoperiodic cycles. Photosynthetic capacity was reduced by far-red light and increased by red light. In response to blue light photosynthetic capacity increased, with indications of a requirement for continuous energy input. Phytochrome and a separate blue light receptor seemed to be involved. In continuous red light a clear cut circadian rhythm of dark respiration was observed. Blue light had a specific effect on chloroplast structure.     

Influence of blue light on the activity of phosphofructokinase in Chlorella kessleri

In crude extracts of Chlorella kessleri Fott and Novákóva cells grown autotrophically in white light the activity of phosphofructokinase (PFK, EC 2.7.1.11) is 62.9 ± 1.5 nmol (mg protein)⁻¹ min⁻¹ under optimized test conditions. It is greatly increased in red [88.3 ± 1.8 nmol (mg protein)⁻¹ min⁻¹], but somewhat decreased [57.0 ± 0.5 nmol (mg protein)⁻¹ min⁻¹] in blue light of equal productivity. Mixtures of blue and red light yield the low activity as long as blue light represents at least 35% of the total quantum fluence rate. The rough wavelength dependence of the counteracting effect of short wavelength light on the increasing effect of red light exhibits a broad peak at 460 nm, reminiscent of action spectra of the blue/UV photoreceptors(s). Upon transfer of red light-grown cells to blue light, the decrease develops slowly within 72 h; it cannot be prevented by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU). Since there is less carbohydrate in blue than in red light-exposed cells, correlations between biosynthesis of PFK and level of carbohydrate are discussed, based on the assumption that red light decreases and/or blue light increases the transport of metabolites across the chloroplast envelope.     

PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme , after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na ⁺ -free and Na ⁺ + Li ⁺ media but were not affected by the absence of Cl ⁻ , implying that the bicarbonate uptake was associated with Na ⁺ / HCO₃ ⁻ symport rather than Cl ⁻ /HCO₃ ⁻ exchange system.     

Photosynthesis and photoassimilation of glucose during photomixotrophic growth of Marchantia polymorpha cells in suspension culture

Even in the presence of glucose the growth of Marchantia polymorpha L. (cell line HYH-2F) requires light, and growth is more sensitive to 10⁻⁶ M 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea than to 10⁻⁴ Antimycin A. The inability of the cells to grow in the dark is due to the low level of respiration. The respiration rate under light increased to four times the dark value. The values of the compensation ratio (the photosyntehtic rate/the respiration rate) for the oxygen exchange were below 1.0 daring the growth period, although oxygen evolution was found. At the early exponential phase, oxygen evolution was 0.373 μmol (mg cell dry weight)⁻¹ h⁻¹ [61.7 μmol (mg chlorophyll)⁻¹ h⁻¹]. M. polymorpha cells are unable to grow anaerobically in the light without a supply of carbon dioxide. When 1% carbon dioxide in nitrogen is supplied, photochemically produced oxygen and energy are sufficient for sustained growth although at significantly reduced yields in both cell dry weight and chlorophyll. Photosyntehtic CO₂ assimilation rate was 0.13 μmol (mg cell dry weight)⁻¹ h⁻¹[11.3 μmol (mg chlorophyll)⁻¹ h⁻¹]. At least one-third of the carbon atoms in cellular constituents seem to be derived from atmospheric carbon dioxide, which indicates that M. polymorpha cells grow photomixotrophicaily.     

Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina

Light effects on in vitro adventitious root formation in axillary shoots of a 95-year-old black cherry ( Prunus serotina Ehrh.) were examined using microcuttings derived from cultured vegetative buds. Three studies were performed: 1) complete darkness and 4 levels of continuous white light irradiance were tested at 70, 278, 555 and 833 μmol m⁻² s⁻¹; 2) white, red, yellow and blue light were tested to assess the importance of spectral quality; and 3) the effect of blue light at intensities of 7,15, 22 and 30 μmol m⁻² s⁻¹ was also studied, Measurements included rooting percentage, total number of roots per shoot, and shoot and root dry weight. There was a strong negative effect of white light intensity upon root formation. Blue light between 15 and 22 μmol m⁻²: s⁻¹ significantly retarded root formation and completely inhibited it at 36 μmol m⁻² s⁻¹. Shoots treated with yellow light exhibited the highest rooting percentage, mean number of roots per shoot, and root dry weight.     

Light-quality effects on Arabidopsis development. Red, blue and far-red regulation of flowering and morphology

Arabidopsis thaliana (L.) Heynh. race Columbia plants were grown in red. blue, red + far-red, blue + far-red and various light mixtures of red + blue + far-red light under 14 h light/10 h dark photoperiods. Each single light source and light mixture maintained a constant irradiance (50 μmol m⁻² s⁻¹) and the mixtures of red + blue + far-red maintained a constant ratio of red/far-red light, but varied in the ratio of blue to red + far-red light. Depending on the method used for calculation, values of the fraction of phytochrome in the far-red absorbing form (P_fr/P_tot) for these light mixtures were either constant or decreased slightly with increasing percentage of blue light in the mixtures. Arabidopsis flowered early (20 days) in blue, blue + far-red and red + far-red light and late (55 days) in red light. In mixtures of red + blue + far-red light, each of which established a nearly constant P_fr/P_tot flowering was in direct relation to time and irradiance level of blue light. Leaf area and petiole length were also correlated with blue light irradiance levels.     

The composition and function of thylakoid membranes from pea plants grown under white or green light with or without far-red light

Pea plants ( Pisum sativum L. ev. Greenfeast) were grown for 2 to 3 weeks in while (˜ 50 μmol photons m⁻² s⁻¹; 400–700 nm) or green (˜ 30 μmol photons m⁻² s ⁻¹ 400–700 nm) light (16 h day/8 h night), with or without far-red light. Supplementary far-red light decreased leaf area and increased internodal length in both white and green light, demonstrating that phytochrome influenced leaf size and plant growth. However, there was no effect of far-red light on chlorophyll a /chlorophyll b ratios, chlorophyll-protein composition, the stoichiometry of electron transport complexes or photosynthetic function of isolated thylakoids. These results suggest that phytochrome is ineffective in modulating the composition and function of thylakoids in pea plants grown at low irradiance. One possible explanation of the ineffectiveness of phytochrome on thylakoids is discussed in terms of the drastic attenuation of red relative to far-red light in green tissue.     

Blue, red and blue plus red light control of chloroplast pigment and pigment-proteins in corn mesophyll cells: Irradiance level-quality interaction

Corn ( Zea mays L. cv. OP Golden Bantum) was grown under low irradiance blue, red or blue plus red light. Red was more effective than blue light for synthesis of Chl a, b and light-harvesting proteins (LHC-2) associated with photosystem 2(PS2). Blue light was slightly more effective for synthesis of light-harvesting proteins (LHC-1) associated with photosystem 1 (PS1), but below a fluence rate of 1 μmol m⁻² s⁻¹ the response to blue vs that to red depended on irradiance level. Blue light containing a small amount of red light was as effective as red light for Chl a and b synthesis, but no more effective than blue light for LHC-2 synthesis. Adding small amounts of blue light to red repressed the effect of red light on LHC-2 synthesis and produced irradiance response curves similar to those produced by blue alone for LHC-2 synthesis. This repression by blue light depended on the ratio of red to blue and the level of the blue light.     

Limited acclimation of photosynthesis to blue light in the seaweed Gracilaria tenuistipitata

Changes in photosynthetic capacity of the seaweed Gracilaria tenuistipitata Zhang et Xia acclimated to monochromatic blue light were studied. For this purpose, affinity for external inorganic carbon, light use efficiency, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli acclimated to 45 µmol m⁻² s⁻¹ of blue light. Thalli cultured in white light of the same photon fluence rate were used as a control. Lower maximal photosynthetic rates (i.e. at light and carbon saturation) were obtained in the thalli cultured in blue light. Apparently, this lower photosynthetic capacity was not due to differences in affinity and/or capacity for use of external dissolved inorganic carbon (DIC) since (1) CA activity did not change significantly and (2) similar values of photosynthetic conductance for DIC at alkaline pH were obtained (0.95 × 10⁻⁶ m s⁻¹). In addition, the pool size of Rubisco was not modified by the blue light treatment since there were no significant differences in Rubisco content between white (12.14% of soluble proteins) and blue light (12.13% of soluble proteins) treatments. In contrast, F _v/ F _m was increased by 11% and photosynthetic efficiency for oxygen production was reduced by 50% in blue light. This absence of correlation between quantum yields for maximum stable charge separation of photosystem II and oxygen evolution suggests that blue light promote changes in rates of photosynthetic electron flow.     

Cytoskeletal Changes in the Brains of Mice Lacking Calcineurin Aα

Abstract: Hyperphosphorylated τ, the major component of the paired helical filaments of Alzheimer's disease, was found to accumulate in the brains of mice in which the calcineurin Aα gene was disrupted [calcineurin Aα knockout (CNAα^−/−)]. The hyperphosphorylation involved several sites on τ, especially the Ser³⁹⁶ and/or Ser⁴⁰⁴ recognized by the PHF-1 monoclonal antibody. The increase in phosphorylated τ content occurred primarily in the mossy fibers of the CNAα^−/− hippocampus, which contained the highest level of calcineurin in brains of wild-type mice. The CNAα^−/− mossy fibers also contained less neurofilament protein than normal, although the overall level of neurofilament phosphorylation was unchanged. In the electron microscope, the mossy fibers of CNAα^−/− mice exhibited abnormalities in their cytoskeleton and a lower neurofilament/microtubule ratio than those of wild-type animals. These findings indicate that hyperphosphorylated τ can accumulate in vivo as a result of reduced calcineurin activity and is accompanied by cytoskeletal changes that are likely to have functional consequences on the affected neurons. The CNAα^−/− mice were found in a separate study to have deficits in learning and memory that may result in part from the cytoskeletal changes in the hippocampus.     

Attraction of zebrafish, Brachydanio rerio, to alanine and its suppression by copper

Preference responses of zebrafish to 10⁻³, 10⁻⁴ and 10⁻⁵M alanine (Ala) were concentration- dependent. Behavioural responses to copper (Cu) and Cu + Ala mixtures were also assessed. Zebrafish avoided 100 and 10 μg Cu l⁻¹, but not 1 μg l⁻¹. Mixtures of 10⁻³ m Ala+ 100 μg Cu l⁻¹ and 10 ⁴ M Ala + 10 μg Cu 1⁻¹ were avoided as intensely as was Cu alone. Responses to 10⁻³ M Ala + 10 or 1 μg Cu l⁻¹ and 10 ⁴ M Ala +1 μg Cu l⁻¹ did not differ statistically from controls (no detectable preference or avoidance). These results demonstrate, firstly, that a concentration of a pollutant avoided by itself (10 μg Cu l⁻¹) may not be avoided when encountered with an attractant chemical stimulus (Ala) and may suppress the preference for an attractant stimulus, and secondly, that a concentration of a pollutant not avoided by itself and not considered deleterious (1 μg Cu l⁻¹) suppresses attraction to Ala (an important constituent of prey odours for many fishes).     

ABSORPTION AND UTILIZATION OF IRRADIANCE BY CYANOBACTERIAL MATS IN TWO ICE-COVERED ANTARCTIC LAKES WITH CONTRASTING LIGHT CLIMATES

We investigated the under-ice light climate and the efficiency with which light was absorbed and utilized by benthic algal mats in Lakes Hoare and Vanda, two perennially ice-covered lakes in the McMurdo Dry Valleys area of Southern Victoria Land, Antarctica. The ice cover and water column of Lake Vanda were much more transparent than those of Lake Hoare (18% vs. 2% transmission though ice and attenuation coefficients for downwelling irradiance of 0.05 vs. 0.12 m ^{− 1}, respectively). In both lakes the under-ice spectra were dominated by blue-green wavelengths. The benthic flora under perennial ice covers of both lakes comprised thick mucilaginous mats, dominated by cyanobacteria. The mats were well suited to absorb the dominant blue-green wavelengths of the under-ice light, with phycoerythrin being present at high concentrations. The pigment systems of the benthic mats absorbed 30%–50% of the light that reached them, varying with depth and lake. There was a tendency for the percentage of absorption to increase as ambient irradiance decreased. The efficiency of utilization of absorbed irradiance was examined by constructing absorbed irradiance/oxygen evolution curves to estimate community quantum yield. Mats from 13 m in Lake Hoare showed the highest quantum yields, approaching 1 mol of carbon fixed for every 8 mol quanta absorbed under light-limiting conditions. Lake Vanda mats had lower quantum yields, but these increased with depth. Calculated in situ irradiance occasionally exceeded the measured saturating irradiance for oxygen evolution in both lakes, thus efficiency in situ was below the maximum at times. As in other environments, optimization strategies allowed efficient capture and utilization of the lower and middle ranges of experienced irradiance but led to a compromised capacity to use the highest irradiances encountered at each depth.     

MIXOTROPHIC GROWTH MODIFIES THE RESPONSE OF SPIRULINA (ARTHROSPIRA) PLATENSIS (CYANOBACTERIA) CELLS TO LIGHT

Spirulina (Arthrospira) platensis (Nordstedt) Geitler cells grown under mixotrophic conditions exhibit a modified response to light. The maximal photosynthetic rate and the light saturation value of mixotrophic cultures were higher than those of the photoautotrophic cultures. Dark respiration and light compensation point were also significantly higher in the mixotrophically grown cells. As expected, the mixotrophic cultures grew faster and achieved a higher biomass concentration than the photoautotrophic cultures. In contrast, the growth rate of the photoautotrophic cultures was more sensitive to light. The differences between the two cultures were also apparent in their responses to exposure to high photon flux density of 3000 μmol·m ^{− 2}·s ^{− 1}. The light-dependent O₂ evolution rate and the maximal efficiency of photosystem II photochemistry declined more rapidly in photoautotrophically grown than in mixotrophically grown cells as a result of exposure to high photon flux density. Although both cultures recovered from the high photon flux density stress, the mixotrophic culture recovered faster and to a higher extent. Based on the above results, growth of S. platensis with a fixed carbon source has a significant effect on photosynthetic activity.     

Scaling of oxygen consumption of Lake Magadi tilapia, a fish living at 37°C

Rates of oxygen consumption were measured in the geothermal, hot spring fish, Oreochromis alcalicus grahami by stopped flow respirometry. At 37° C, routine oxygen consumption followed the allometric relationship: V o₂=0.738 M ^0.75, where V o₂ is ml O₂ h ⁻¹ and M is body mass (g). This represents a routine metabolic rate for a 10 g fish at 37° C of 0.415 ml O₂ g⁻¹ h ⁻¹ (16.4 μmol O₂ g ⁻¹ h ⁻¹). Acutely increasing the temperature from 37 to 42° C significantly elevated the rate of O₂ consumption from 0.739 to 0.970 ml O₂ g ⁻¹ h ⁻¹ ( Q ₁₀=l.72). In the field, O. a. grahami was observed to be 'gulping' air from the surface of the water especially in hot springs that exceeded 40° C. O. a. grahami may utilize aerial respiration when O₂ requirements are high.     

Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response

Baumgartner, N. and Fondeville, J. C. 1989. Photocontrol of the hypocotyl hook opening of Sinapis alba seedlings. Involvement of phytochrome and a high irradiance response.
A statistical evaluation of the hypocotyl hook opening (hook opening index) was used for measurement of the hook angle in lots of etiolated Sinapis alba L. cv. Albatros seedlings. Studies of the kinetics for hook opening were carried out in continuous fluorescent white, blue and red light (6, 15 and 40 μmol m^-2s^-1) with 2-day-old dark-grown seedlings. At the beginning of the irradiation period the photoresponse in red light was the opposite to that in blue (low photon fluences). Blue rapidly induced the hook opening (in less than 20 min), while red produced hook tightening (photon fluences up to 70 mmol m^-2), which precedes the normal progressive hook opening. For low fluences, the data were consistent with the involvement of phytochrome and a specific blue light photoreceptor. A phytochrome effect was observed in the hook opening, dependent upon a high irradiance response (HIR). This HIR (like that for the inhibition of the hypocotyl elongation) was characterized by a wavelength response curve with maxima in the blue and far-red regions of the spectrum.     

Direct and indirect effects of light on stomata. I. In Scots pine and Sitka spruce

Abstract. The response of stomatal conductance to broadband blue and red light was measured in whole shoots of Scots pine and Sitka spruce, two species which have low stomatal sensitivity to CO². In Scots pine, blue light was more than three times more effective than red light (on an incident quantum basis) in opening stomata, particularly at low quantum flux densities (<100μmiol m⁻² s⁻¹). However, the apparent quantum yield of net CO² assimilation rate in blue light was only half that in red light. The contrasting effects of red and blue light on conductance and assimilation led to higher intercellular CO² concentrations (C_i) in blue light (up to 100 μmol mol⁻¹ higher) than in red light. Similar results were obtained with Sitka spruce shoots, though differences in the effectiveness of red and blue light were less marked. In both species, both red and blue light increased conductance in normal and CO²-free air, indicating that neither red nor blue light exert effects through changes in C_i or mesophyll assimilation. However, decreases in C_i caused increases in conductance in both red and blue light, suggesting that these direct effects of light are not wholly independent of CO².     

Kinetics of photoautotrophic growth of Marchantia polymorpha cells in suspension culture

Chlorophyllous, cultured cells of Marchantia polymorpha L. (HYA-2 cell line) grow actively under photoautotrophic (lithotrophic) conditions. The maximum specific growth rate (μ_cell) was 0.64 day⁻¹ and the doubling time was 1.08 days under optimum conditions (165 μmol m⁻² s⁻¹, 1% carbon dioxide enriched atmosphere, 25^°C). The photosynthetic activity was 1.30 μmol CO₂-fixed (10⁶ cells)⁻¹ h⁻¹ [66 μmol (mg chlorophyll)⁻¹ h⁻¹] in the exponential phase. The growth course has two distinct phases, an exponential and a linear one. The exponential phase is observed as long as the population density is sufficiently low (less than 7.9 × 10⁶ cells ml⁻¹), so that practically all individual cells directly receive the full incident light. The effect of light on the specific growth rate is a linear function of photon flux density. Linear growth occurs after the population density is so high that the incident light is almost completely absorbed by the cell suspension. The growth rate is a logarithmic function of photon flux density, in contrast to the specific growth rate, and saturates at high photon flux densities. The conditions of maximum growth, however, are not wellbalanced between cell mass production and cell division. Therefore, the maximum growth does not continue for a long time.     

Effects of constant light on the rhythm of adult locomotor activity in the blowfly, Calliphora vicina

Abstract. Females of the blowfly, Calliphora vicina , showed an increase in the free-running period (γ) of their locomotor activity rhythm when transferred from continuous darkness (DD) to continuous 'dim' light (LL) at an irradiance below about 0.03 Wm^-2. Transfer to LL of this intensity also caused a reduction in the duration of the active phase (α) of the cycle. Transfer to 'bright' light (>0.03 Wm²), however, lead to arrhythmicity. Data suggest that constant light of this intensity does not 'stop' the circadian pacemaker but imposes behavioural arrhythmicity at a more superficial level.     

Light-quality and irradiance-level control of light-harvesting complex of photosystem 2 in maize mesophyll cells. Evidence for a low fluence-rate threshold in blue-light reduction of mRNA and protein

Levels of pigment-proteins and mRNA coding for proteins associated with the light-harvesting complex of photosystem 2 (LHCP2) were reduced in maize ( Zea mays L. cv. OP Golden Bantum) plants grown for 14 days in 8.0 nmol m^-2s^-1 of blue light compared to those in plants grown under an equal irradiance of red light. At the same time, there was a small increase in steady state levels of mRNA for the Dl protein of PS2 (psbA) in blue-grown plants. The reduction of LHCP2 mRNA and the increase in psbA mRNA were observed in both 5- and 10-day-old blue-light-grown leaves, but the degree of reduction or increase was much greater in 10-day-old leaves. Maize grown under 6 different mixtures of blue and red light, each with a total irradiance level of 8.0 μmol m^-2 s^-1, showed the same degree of LHCP2 mRNA reduction relative to red light. This is different from the behavior of psbA which increased in a linear manner with increasing amounts of blue light. The amounts of Chi a and Chi b in these mixed-light samples were not significantly different froi those found in pure red light. This indicates that a low fluence level of blue light, even when combined with red light, is sufficient to reduce equilibrium levels of proteins and mRNA of LHCP2, and this reduction is independent of pigment formation. It also suggests that the mechanisms of blue-light regulation of mRNA may operate differently at the nuclear and chloroplast levels.