Twofold effect of blue light on a circadian rhythm in Acetabularia

Abstract

The circadian chloroplast migration in Acetabularia mediterranea was monitored by continuously measuring the transmission of the cells near the apex. Under continuous red light the amplitude of the rhythm decreased rapidly within a few days. However, circadian changes of chloroplast density were still detectable even after 28 days of red light, indicating the persistence of the rhythm. When blue light was added after red light preirradiation of several days phase shifts were observed which were expressed as advances as well as delays. The period of the rhythm proved to be strongly dependent on the intensity of the continuous blue light which was given in addition to red light. Different red light intensities did not change the period. The occurrence of both effects indicates that the sensory transduction of blue light photoreception in Acetabularia works in two different ways: quanta counting processes and processes of light intensity measurement.     

Chloroplast fine structure in the japonica-2 maize mutant exposed to continuous illumination. 1. The green tissues.

Exposure to continuous illumination causes the appearance of numerous plastoglobuli in the stroma of both the mesophyll and bundle sheath chloroplasts of the green tissues of the leaves of the japonica-2 mutant of maize. In the pale green tissues the thylakoids have markedly swollen membranes. Another feature of the plastids exposed to continuous illumination is the heavy accumulation of starch. The japonica-2 chloroplasts show a different sensitivity to light, the chloroplasts of the pale green tissues being affected more markedly than the ones of the dark green tissues, and the bundle sheath chloroplasts more than those of the mesophyll. The effects of continuous illumination may be interpreted as an acceleration of chloroplast ontogenesis.     

Evidence for an endogenous circadian rhythm of feeding in the trout (Oncorhynchus mykiss)

Abstract

The possible endogenous circadian rhythm in the feeding activity of rainbow trout (Oncorhynchus mykiss) was investigated using individual fish previously trained for self‐feeding. Under LD 12:12 conditions, the fish showed a diurnal behaviour, in many cases with a feeding rhythm with two main peaks of food demand at dawn and dusk, with an 8h interval of low feeding activity, and the actograms showed an expected 24 h rhythm. Fish kept under constant conditions (L : L, 15°±0.5°C), showed free‐running feeding activity for about 12 days. Food demands were concentrated at dawn, with a periodogram of 25.3 hour, under continuous environmental conditions. Results showed evidence for the endogenous origin of the circadian rhythm of feeding in this species.     

Circadian rhythm of autophagy and light responses of autophagy and disk-shedding in the rat retina

Summary The rhythm of autophagic degradation (AV) in visual cell inner segments shows circadian characteristics: it persists under constant conditions of continuous darkness (DD) and continuous light (LL) and can be reentrained to phase-shifts of the light-dark (LD) cycle. However, unlike the rhythm of disk-shedding and many other circadian rhythms, the rhythm of AV persists with a distinct peak even after 3 days of LL and is rapidly abolished to almost baseline levels after 1.5 days of DD, confirming our previous observations of a strong light-dependence of AV. Since the rhythms of disk-shedding and AV reveal this inverse pattern in DD and LL, different regulative mechanisms may be involved.Light stimulation with increasing intensities at day-time and night-time evoked AV responses that increased and disk-shedding responses that decreased at higher intensities. Furthermore, both the AV and phagosome response was different according to day-time or night-time stimulation, pointing towards the possibility of a circadian phase of sensitivity to light.Abbreviations AV autophagic degradation, autophagic vacuole, autophay - LD light dark cycle - DD constant darkness - LL constant light - CNS central nervous system - SCN suprachiasmatic nucleus - DA dopamine - ftc footcandle - ANOVA analysis of variance     

Chloroplast suppressors that act on a mitochondrial mutation in Chlamydomonas reinhardtii

We report genetic evidence supporting the existence of suppressor genes in the chloroplast that act on a mitochondrial mutation that impairs heterotrophic growth in the green alga Chlamydomonas reinhardtii. One of these suppressors also acts on a point mutation in the rbcL gene in the chloroplast. These results are consistent with previous data showing that mitochondrial protein synthesis depends on chloroplast protein synthesis in C. reinhardtii. The nature of the interaction between chloroplasts and mitochondria is discussed in light of the requirement for import of tRNAs by plant mitochondria. Received: 28 January 1999 / Accepted: 29 April 1999     

Rapid mass movement of chloroplasts during segment formation of the calcifying siphonalean green alga, Halimeda macroloba

Background

The calcifying siphonalean green alga, Halimeda macroloba is abundant on coral reefs and is important in the production of calcium carbonate sediments. The process by which new green segments are formed over-night is revealed here for the first time.

Methodology/Principal Findings

Growth of new segments was visualised by epifluorescence and confocal microscopy and by pulse amplitude modulation (PAM) fluorimetry. Apical colourless proto-segments were initiated on day 1, and formed a loose network of non-calcified, non-septate filaments, containing no chloroplasts. Rapid greening was initiated at dusk by i) the mass movement of chloroplasts into these filaments from the parent segment and ii) the growth of new filaments containing chloroplasts. Greening was usually complete in 3–5 h and certainly before dawn on day 2 when the first signs of calcification were apparent. Mass chloroplast movement took place at a rate of ∼0.65 µm/s. Photosynthetic yield and rate remained low for a period of 1 to several hours, indicating that the chloroplasts were made de novo. Use of the inhibitors colchicine and cytochalasin d indicated that the movement process is dependent on both microtubules and microfilaments.

Significance

This unusual process involves the mass movement of chloroplasts at a high rate into new segments during the night and rapid calcification on the following day and may be an adaptation to minimise the impact of herbivorous activity.     

Varying competence for protein import into chloroplasts during the cell cycle in Chlamydomonas.

By studying the import of radioactively labelled small subunit of ribulose-1,5-bisphosphate carboxylase (pSS) into chloroplasts of the green alga C. reinhardtii cw-15 protein delivery to chloroplasts was found to vary during the cell cycle. Chloroplasts were isolated from highly synchronous cultures at different time points during the cell cycle. When pSS was imported into 'young' chloroplasts isolated early in the light period about three times less pSS was processed to small subunit SS than in 'mature' chloroplasts from the middle of the light period. In 'young' chloroplasts also, less pSS was bound to the envelope surface. During the second half of the light period the import competence of isolated chloroplasts decreased again when based on chlorophyll content or cell volume, but did not change significantly when related to chloroplast number. Measurements of pSS binding to the surface of chloroplasts of different age indicated that the adaptation of protein import competence during the cell cycle is due to a variation of the number of binding sites per chloroplast surface area, rather than to modulation of the binding constant.     

A comparison of plants regenerated from a variegated <Emphasis Type="Italic">Epipremnum aureum</Emphasis>

In order to study chloroplast biogenesis, we chose natural variegated Epipremnum aureum (golden pothos) and regenerated pale yellow, variegated and green plants from all three types of tissue explants. The percentage of three types of regenerated shoots from three different explants was very close. Regenerated plants have been maintained for a year and show no sign of a colour switch. By comparing their protein profiles, two major differences between pale yellow and green plants were observed at the 15 and 40 to 50 kDa proteins. Moreover, pale yellow plants had unexpected high molecular mass proteins (greater than 60 kDa). Both variegated and green plants had more chlorophyll (Chl) a than Chl b, the ratios were about 1.46 and 1.93, respectively. In contrast, the pale yellow plants not only had less total Chl, but also the reduction of Chl a was much greater than Chl b, resulting in a higher content of Chl b than Chl a. Microscopic analysis revealed that pale yellow plants contained predominantly undeveloped chloroplasts with low Chl contents, even though their mesophyll cells were similar to green and variegated plants. PCR amplification of chloroplast DNA with 14 universal chloroplast primers did not reveal any difference among these regenerated plants.     

Chlamydomonas reinhardtii as a unicellular model for circadian rhythm analysis

Chlamydomonas reinhardtii has been used as an experimental model organism for circadian rhythm research for more than 30 yr. Some of the physiological rhythms of this alga are well established, and several clock mutants have been isolated. The cloning of clock genes from these mutant strains by positional cloning is under way and should give new insights into the mechanism of the circadian clock. In a spectacular space experiment, the question of the existence of an endogenous clock vs. an exogenous mechanism has been studied in this organism. With the emergence of molecular analysis of circadian rhythms in plants in 1985, a circadian gene expression pattern of several nuclear and chloroplast genes was detected. Evidence is now accumulating that shows circadian control at the translational level. In addition, the gating of the cell cycle by the circadian clock has been analyzed. This review focuses on the different aspects of circadian rhythm research in C. reinhardtii over the past 30 yr. The suitability of Chlamydomonas as a model system in chronobiology research and the adaptive significance of the observed rhythms will be discussed.     

Circadian rhythms of feeding with microalgae of Ceriodaphnia quadrangula in laboratory culture

The circadian rhythm of grazing of microalgae by a laboratory culture of Ceriodaphnia quadrangula under continuous illumination was studied by continuous registration of chlorophyll fluorescence at the outlet of a flow-through cultivator. A culture of green alga Chlorella vulgaris was used as a feed. The data obtained were treated by the statistical spectral analysis. It was found that animals preliminarily grown under a 12 h light: 12 h dark regime and transferred to constant light showed two maxima in the circadian rhythm of grazing with periods of 0.7 and 1.1 h. Animals preliminarily grown under constant light showed no circadian rhythm of grazing. It was concluded that the circadian rhythm of grazing of C. quadrangula has endogenous nature and can change according to light conditions.     

CIRCADIAN GROWTH RHYTHM IN JUVENILE SPOROPHYTES OF LAMINARIALES (PHAEOPHYTA)1

A circadian rhythm in growth was detected by computer-aided image analysis in 3–4-cm-long, juvenile sporophytes of the kelp species Pterygophora California Rupr. and in seven Laminaria spp. In P. californica, the free-running rhythm occurred in continuous white fluorescent light, had a period of 26 h at 10°or 15°C, and persisted for at least 2 weeks in white or blue light. The rhythm became insignificant in continuous green or red light after 3 cycles. Synchronization by white light-dark regimes, e.g. by 16 h light per day, resulted in an entrained period of 24 h and in a shift of the circadian growth minimum into the middle of the light phase. A morning growth peak represented the decreasing portion of the circadian growth curve, and an evening peak the increasing portion. The circadian growth peak was not visible during the dark phase, because growth rate decreased immediately after the onset of darkness. At night, some growth still occurred at 16 or 12 h light per day, whereas growth stopped completely at 8 h light per day, as in continuous darkness. During 11 days of darkness, the thallus area became reduced by 3.5%, but growth rate recovered in subsequent light–dark cycles, and the circadian growth rhythm reappeared in subsequent continuous light.     

Locomotor activity rhythm of two sympatric species Talitrus saltator (Amphipoda) and Tylos europaeus (Oniscidea) from Tunisian beaches under continuous light

Locomotor activity rhythm of the supralittoral species Talitrus saltator and Tylos europaeus was studied under continuous light in populations of Korba and Barkoukech beaches in summer. Results showed that these two species were characterized by a nocturnal behaviour. Under the subjective night, the activity was continuous for T. saltator and interrupted in T. europaeus with the presence of a clear drift towards the right more accentuated for the second species. Whatever the site, using actograms and the waveforms, results showed the absence of bimodal profile in T. europaeus and the plurimodal one in T. saltator. Moreover, the most important activity peaks were observed around the dawn and the dusk, respectively. Furthermore, periodogram and MESA analyzes highlighted the presence of ultradian and circadian components. Whatever the component and the site, the inter-individual variability was more pronounced in T. europaeus. Moreover, whatever the site, individuals of T. europaeus were more active and the locomotor rhythm was more defined in T. saltator. With reference to environmental stability and variability, the differences of locomotor activity characteristics observed between these two species are explained as a need for plasticity to adapt to environmental changes.     

The effects of continuous illumination on the function and structure of Micrasterias torreyi Bail. (Conjugatophyceae)

Abstract. The division rate of Micrasterias torreyi cells grown under continuous illumination first accelerated but soon slowed down, and the cells lost their ability to divide after about 1 month. During the treatment the cells became pale green, the pyrenoids became fewer in number and defects appeared in the chloroplasts. After 1 month, the cells also soon died, even when subjected to intermittent illumination. The most striking structural alterations were found in the chloroplasts: the starch granules lost their typical structure, the lamellae were damaged and numerous electron dense precipitates appeared in the chloroplasts. The precipitates were similar to those formed in cells treated with supraoptimal external calcium concentrations and X-ray microanalysis showed that the precipitates were rich in calcium in both cases. The results suggest that light controls and activates the Ca²⁺ uptake in the plasma membrane as well as in the chloroplast envelope, that the large sized chloroplasts of Micrasterias are effective in regulation of cytoplasmic Ca²⁺ concentration, and that the injuries caused by continuous illumination may be largely due to the accumulation of Ca²⁺ in the chloroplasts.     

BPG3 is a novel chloroplast protein that involves the greening of leaves and related to brassinosteroid signaling

Brassinosteroids are plant steroid hormones that regulate plant organs and chloroplast development. The detailed molecular mechanism for plant development by BR signaling is yet to be revealed, and many points regarding the relationship between BR signaling and chloroplast development remain unknown. We identify here the dominant mutant Brz-insensitive-pale green3-1D (bpg3-1D) from the Arabidopsis FOX lines that show reduced sensitivity to the chlorophyll accumulation promoted by the BR biosynthesis inhibitor, Brassinazole (Brz), in the light. BPG3 encodes a novel chloroplast protein that is evolutionally conserved in bacteria, algae, and higher plants. The expression of BPG3 was induced by light and Brz. The inhibition of electron transport in photosystem II of the chloroplasts was detected in bpg3-1D. These results suggest that BPG3 played an important role in regulating photosynthesis in the chloroplast under BR signaling.     

Vertical-migration patterns of flagellates in a community of freshwater benthic algae

The population densities of sediment-inhabiting flagellates sampled from a shallow eutrophic lake in April 1986 were investigated at intervals of 1 or 1.5 h over a twenty hour period in the laboratory under natural irradiance and in controlled conditions. In natural irradiance the flagellates exhibited a vertical migration rhythm up onto the sediment surface after dawn and down into the sediment during the afternoon. Details of the timing of the migration movements and period of time flagellates were present on the sediment surface differed between species and five flagellate groups: trachelomonads, green euglenoids, Chamydomonads, chrysophytes and cryptomonads. During daylight, twenty-seven species maintained population maxima at the surface of the sediment on eight occasions. The species composition of these maxima differed and eight species were found to have two maxima on the surface of the sediment at different times of day. Numbers of three species of chrysophycean flagellates and Rhodomonas minuta increased again on the sediment surface after dark. Under continuous irradiance at 10°C, the migration cycle of all five groups of flagellates was affected. Some evidence for an endogenous nature of this rhythm was found for green euglenoids and Chamydomonads. Numbers of chrysophytes, particularly Synura spp. increased in constant light in the surface layers of sediment.Thus a mosaic of vertical migration patterns was described in an epipelic community of algae dominated by five groups of flagellates. The importance of this in the survival strategy and ecology of these sediment-inhabiting algae is discussed.     

RHYTHMIC SETTLING BEHAVIOR IN PYRAMIMONAS PARKEAE (PRASINOPHYCEAE)1

Pyramimonas parkeae Norris et Pearson was examined for evidence of a settling rhythm while growing in laboratory culture. The alga settled rhythmically in a diet cycle when kept in a regularly alternating light-dark cycle. Cells moved out of suspension when settling and attached themselves to the sides and base of the culture vessel. Although rhythmic settling was inhibited in constant dim light (LL), it continued in constant darkness for 4 days with a period of approximately 24 h. The settling rhythm was temperature-compensated and could be reset by 6-h exposures to light. These observations demonstrate that the settling behavior of P. parkeae is controlled by an endogenous circadian oscillator. Regular low temperature pulses every 12 h removed the inhibition caused by LL and this points to the possible role of temperature changes as stimuli entraining the circadian settling rhythm of P. parkeae.     

Circadian rhythm in photosynthesis of the green alga Bryopsis maxima

The green marine alga Bryopsis maxima showed a circadian rhythmin the rate of oxygen evolution in photosynthesis. The rhythmlasted several days in constant light and seemed to be endogenous.It disappeared during darkness and reappeared under naturalor artificial light-dark cycle, which shows that it is light-dependentand entrainable by an exogenous light-dark cycle. In the rhythm,the oxygen evolution rate at midnight was 50 to 70% of thatat noon, and the amplitude of the rhythm was larger at higherintensities of actinic light. The light-intensity dependencyof the rhythm showed that the rhythmic change in the activitieswas due to an alteration of the dark-reaction rate in photosynthesisand not due to a change of the light-reaction rate. ¹ Present address: Radioisotope Research Institution for BasicMedicine, St. Marianna University School of Medicine, 2095 Sugao,Takatsu, Kawasaki 213, Japan. (Received June 29, 1977; )     

Chloroplast DNA of Acetabularia mediterranea: Cell cycle related changes in distribution

Chloroplast DNA (cpDNA) distribution in the giant unicellular, uninucleate alga Acetabularia mediterranea was analyzed with the DNA-specific fluorochrome 4'6-diamidino-2-phenylindole (DAPI) at various stages of the cell cycle. The number of chloroplasts exhibiting DNA/DAPI fluorescence changes during the cell's developmental cycle: (1) all chloroplasts in germlings contain DNA; (2) the number of plastids with DNA declines during polar growth of the vegetative cell; (3) it increases again prior to the transition from the vegetative to the generative phase; (4) several nucleoids of low fluorescence intensity are present in the chloroplasts of the gametes. The temporal distribution of the number of chloroplasts with DNA appears to be linked to the different mode of chloroplast division and growth during the various stages of development. The chloroplast cycle in relation to the cell cycle is discussed.Abbreviations cpDNA chloroplast DNA - DAPI 4,6-diamidino-2-phenylindole     

Light Dependence of Chloroplast Replication and Starch Metabolism in the Moss Polytrichum commune

Spores of Polytrichum conwtuine were grown on a mineral salt solution with or without sucrose and exposed to continuous white light, continuous darkness, red light and/or far-red light. With sucrose, germination and filament growth occurred in all conditions, Without sucrose, germination and filament growth occurred only in light. Two phytochrome mediated responses of the chloroplasts were demonstrated. Chloroplast replication occurred in continuous white light and red light of 15 min/6 hours. In continuous darkness and in far red light of 15 min/6 hours, the size of the chloroplasts increased; but no replication occurred. Both the chloroplast replication and chloroplast size were red, far-red light reversible. When changed from one continuous light environment to another, a lag period occurred before the chloroplasts responded to the new environment. Electron micrographs of sections and in vivo staining of the chloroplasts with iodine solution demonstrated that the change in size of the chloroplasts was at least partially due to the synthesis and degradation of starch.     

Influence of carbon supply on the circadian rhythmicity of photosynthesis and its stimulation by blue light in Ectocarpus siliculosus: clues to the mechanism of inorganic carbon acquisition in lower brown algae

Stimulation or light-saturated rates of photosynthesis in Ectocarpus siliculosus (Dillwyn) Lyngb. by blue light was eliminated by increasing dissolved inorganic carbon (DIC) or by lowering pH in natural seawater. The amplitude of the circadian rhythm of photosynthesis was also diminished under these conditions, and the pH compensation points in a closed system were higher in the presence of blue light and during the circadian day. These observations suggest that blue light and the circadian clock regulate the activity of a carbon acquisition system in these plants. The inhibitor of external carbonic anhydrase, acetazolamide, reduced overall rates of photosynthesis by only about 30%, but ethoxyzolamide suppressed the circadian rhythm of photosynthesis almost completely and markedly reduced the duration of responses to blue light pulses. Similar patterns were obtained when photosynthesis was measured in strongly limiting DIC concentrations (0–0.5 mol m^?3). Since blue light stimulated photosynthesis under these conditions of strong carbon limitation, we suggest that blue light activates the release of CO₂ from an internal CO₂ store. We propose a metabolic pathway with similarities to that of CAM plants. Non-photosynthetic fixation leads to the accumulation of a storage metabolite. The circadian clock and blue light control the mobilization of CO₂ at the site of decarboxylation of this metabolite. In the presence of continuous blue light the pathway is proposed to cycle and act as a pump for CO₂ into the chloroplasts. This hypothesis helps to explain a number of previously reported peculiarities of brown algal photosynthesis.