Circadian Rhythm Of Photosynthesis Research Articles

DISINTEGRATION OF THE CELLS OF SIPHONOUS GREEN ALGA CODIUM EDULE (BRYOPSIDALES, CHLOROPHYTA) UNDER MILD HEAT STRESS(1).

The siphonous green alga Codium edule P. C. Silva (Bryopsidales, Chlorophyta) has the highest covering ratio among the macroalgae on the coral reef of Nanwan Bay in southern Taiwan, but its population in the subtidal region drastically decreases from July to September each year. The objective of this study was to determine whether the high temperature of summer could be the basis for this population decrease. Chlorophyll fluorescence measurements revealed that when the algae were incubated at 35°C (a temperature that can be reached in southern Taiwan during the summer), their photosynthetic activities were almost completely inhibited after about 8 h. The circadian rhythm of photosynthesis was disrupted at a temperature as low as 32°C. TEM studies showed that 4 h incubation at 35°C induced a decrease in turgidity accompanied by vacuole shrinkage and plasmolysis. The marked disintegrative changes, including damage to organelles, such as chloroplasts and nuclei, occurred after about 8 h, at which time central vacuoles collapsed and the cell interior was then filled with numerous small vesicles. Our results suggested that the rise in seawater temperature during the summer could be one of the major causes of the massive death of C.edule in the field.

Circadian rhythm of photosynthesis in Kappaphycus alvarezii (Rhodophyta): independence of the cell cycle and possible photosynthetic clock targets

Various processes in the output pathway of the circadian clock are thought to act as important clock targets resulting in the circadian rhythms of photosynthesis observed in various algae. Examples of such processes are synchronization of the cell cycle, pigmentation, and light or dark reaction of photosynthesis. The newly detected, robust photosynthetic circadian rhythm in the red macroalga Kappaphycus alvarezii was investigated in more detail with respect to rhythmically changing components within the photosynthetic apparatus. The following major results were obtained; (1) The growing tips of Kappaphycus (0–2 cm) were found to exhibit a diurnal and circadian rhythm of nuclear division like many other algal species, (2) The circadian photosynthetic rhythm was apparent in the actively growing and dividing tip portions (0–;2 cm) as well as in older portions (2–4 cm) with little remaining mitotic activity. The Kappaphycus rhythm seems therefore to be independent of the cell cycle, at least in the older portions of the thallus, (3) During real (L:D cycle) or subjective (LL) dark phases, net photosynthetic capacity (Pmax) dropped drastically in young (tip) parts of the thallus, and α, the ‘light affinity’ parameter, decreased likewise. The net result of these two changes was an increase in the light saturation point, Ek. Dark respiration did not change rhythmically from one circadian maximum to the next circadian minimum. ΔF/Fm′ dropped during real and subjective night phases, while non-photochemical quenching (NPQ) increased. Low temperature (77 K) emission spectra with an excitation wavelength of 580 nm exhibited a larger increase of the 720:685 nm as well as the 720:696 nm emission quotients compared with spectra at 440 nm excitation for samples harvested in the middle of the subjective dark phase indicating changes in energy trapping from the phycobilisomes to the photosystems.

Circadian rhythm of photosynthesis and concurrent oscillations of transcript abundance of photosynthetic genes in the marine red alga Grateloupia turuturu

Many biological processes are under the control of an endogenous circadian clock, a prominent example within the plant kingdom being photosynthesis. Here we report a robust circadian rhythm of photosynthetic oxygen evolution in the marine red macroalga Grateloupia turuturu. The rhythm was obvious in continuous white light at irradiances ranging from 50 to 500 μmol photons m−2s−1. To assess whether this physiological rhythm was correlated with changes at the level of gene transcription in G. turuturu, abundance of the transcripts encoding the phycoerythrin α and β subunits and the ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) subunits was analysed under light-dark cycles (LD) and continuous illumination (LL). Abundance of both transcripts exhibited diurnal and circadian changes in G. turuturu. In LD conditions, abundance of the phycoerythrin transcript peaked between midday and late afternoon. This pattern was maintained under constant conditions (LL) for up to three cycles. For the Rubisco transcript, mRNA abundance started to increase in the morning and peaked around midday in LD cycles. In LL, Rubisco transcript abundance continued to oscillate, but the increase of mRNA started earlier, already during subjective night. Our results suggest control of both transcripts by the circadian clock in G. turuturu.

Daily Oscillation of Fatty Acids and Malondialdehyde in the Dinoflagellate Lingulodinium polyedrum

The levels of the fatty acids, cis eicosahexenoic acid and cis linolenic acid, as well as the extent of lipoperoxidation, measured as malondialdehyde (MDA), were analyzed in the photosynthetic marine dinoflagellate Lingulodinium polyedrum at different times during the light : dark (L : D) cycle. Levels of MDA were twice as high during the day phase than during the night phase. This may be related to the circadian rhythm in photosynthesis as during photosynthetic electron flux, electrons can 'leak' and react with molecular oxygen producing reactive oxygen species (ROS) which in turn react with lipids, proteins, and DNA among other biomolecules. Fatty acid levels were highest during the day phase. Our findings indicate that unsaturated fatty acids are more susceptible to attack and degradation when L. polyedrum is exposed to light and that the cells compensate for this by an increased fatty acid content during the day. Excessive lipoperoxidation during the light phase could result in a higher level of chloroplast or plasma membrane disruption leading to cell death.

Circadian rhythm and fast responses to blue light of photosynthesis in Ectocarpus (Phaeophyta, Ectocarpales)

Photosynthesis of Ectocarpus siliculosus (Dillwyn) Lyngb. under continuous saturating red irradiation follows a circadian rhythm. Blue-light pulses rapidly stimulate photosynthesis with high effectiveness in the troughs of this rhythm but the effectiveness of such pulses is much lower at its peaks. In an attempt to understand how blue light and the rhythm affected photosynthesis, the effects of inorganic carbon on photosynthetic light saturation curves were studied under different irradiation conditions. The circadian rhythm of photosynthesis was apparent only at irradiances which were not limiting for photosynthesis. The same was found for blue-light-stimulated photosynthesis, although stimulation was observed also under very low red-light irradiances after a period of adaptation, provided that the inorganic-carbon concentration was not in excess. Double-reciprocal plots of light-saturated photosynthetic rates versus the concentration of total inorganic carbon (up to 10 mM total inorganic carbon) were linear and had a common constant for half-saturation (3.6 mM at pH 8) at both the troughs and the peaks of the rhythm and before and after blue-light pulses. Only at very low carbon concentrations was a clear deviation found from these lines for photosynthesis at the rhythm maxima (red and blue light), which indicated that the strong carbon limitation specifically affected photosynthesis at the peak phases of the rhythm. Very high inorganic carbon concentrations (20 mM) in the medium diminished the responses to blue light, although they did not fully abolish them. The kinetics of the stimulation indicate that the rate of photosynthesis is affected by two blue-light-dependent components with different time courses of induction and decay. The faster component seemed to be at least partially suppressed at red-light irradiances which were not saturating for photosynthesis. Lowering the pH of the medium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates that Ectocarpus takes up free CO2 only and not bicarbonate, although additional physiological mechanisms may enhance the availability of CO2.

Biochemical Correlates of the Circadian Rhythm in Photosynthesis in Phaseolus vulgaris

A circadian rhythm in photosynthesis occurs in Phaseolus vulgaris after transfer from a natural or artificial light:dark cycle to constant light. The rhythm in photosynthesis persists even when intercellular CO(2) partial pressure is held constant, demonstrating that the rhythm in photosynthesis is not entirely due to stomatal control over the diffusion of CO(2). Experiments were conducted to attempt to elucidate biochemical correlates with the circadian rhythm in photosynthesis. Plants were entrained to a 12-hour-day:12-hour-night light regimen and then monitored or sampled during a subsequent period of constant light. We observed circadian oscillations in ribulose-1,5-bisphosphate (RuBP) levels, and to a lesser extent in phosphoglyceric acid (PGA) levels, that closely paralleled oscillations in photosynthesis. However, the enzyme activity and activation state of the enzyme responsible for the conversion of RuBP to PGA, ribulose-1,5-bisphosphate carboxylase/oxygenase, showed no discernible circadian oscillation. Hence, we examined the possibility of circadian effects on RuBP regeneration. Neither ribulose-5-phosphate kinase activity nor the level of ATP fluctuated in constant light. Oscillations in triose-phosphate levels were out of phase with those observed for RuBP and PGA.

DIEL PERIODICITY OF PHOTOSYNTHESIS AND CELL DIVISION COMPARED IN THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE)

Diel patterns of photosynthesis and cell division were examined in Thalassiosira weissflogii Grun. (clone Actin) grown in nitrogen-limited cyclostat culture. Ammonia (NH4+) was either supplied continuously or as a daily pulse to cultures grown in constant light or in a light: dark cycle. When either nitrogen or light was supplied periodically, both cell division and photosynthetic capacity were periodic. When both nitrogen and light were supplied periodically, cell division was coupled to the N-pulse whereas periodicities of photosynthetic capacity were modified but remained coupled to the light-dark cycle. Diel oscillations in photosynthesis were i) largely independent of cellular pigmentation and ii) similar for light-limiting and saturating irradiances. Periodicity in photosynthetic capacity also persisted following transfer of non-dividing batch cultures to constant light. Results suggest that photosynthesis but not cell division was coupled to a circadian clock in T. weissflogii. A circadian rhythm of photosynthesis may optimize carbon assimilation in phytoplankton exposed to intermittent nutrient supply by ensuring that maximum photosynthetic capacity occurs during the day.

The Loss of the Circadian Rhythm in Photosynthesis in an Old Strain of Gonyaulax polyedra

Cultures of Gonyaulax polyedra Stein maintained in the laboratory for 15 to 20 years, including an axenic strain isolated in 1960, have gradually lost the ability to survive in darkness. G. polyedra (70A), isolated in 1970 and maintained in a 12:12 light:dark cycle, now tolerates continuous darkness for a much shorter time than a strain isolated in 1981. I have compared the properties of strain 70A with those of this newer strain (81N), to investigate changes in Gonyaulax with length of time in culture, which may account for poor survival in darkness. When grown in continuous light (13, 12, or 4.5 watts per square meter), strains 70A and 81N have similar growth rates, yields, cell diameters, protein contents, C/N ratios, respiration rates, pigment complements, and photosynthetic rates. When entrained by a light:dark cycle (12L:12D), 70A showed no photosynthesis rhythm, although such a rhythm was formerly present. However, the circadian rhythms in bioluminescence and cell division were normal in both strains. Thus, the circadian clock is apparently still intact in 70A as in 81N. The rate of photosynthesis in strain 70A was constant at a low level, the consequent smaller accumulation of photosynthetic products probably accounting for the limited survival in darkness. The defect in strain 70A may be the loss of a component either directly affecting P(max) or necessary for transduction from the circadian clock to photosynthesis.

Changes in Photosystem II Account for the Circadian Rhythm in Photosynthesis in Gonyaulax polyedra

Cell-free extracts that show activity in photosynthetic electron flow have been prepared from the unicellular dinoflagellate, Gonyaulax polyedra. Electron flow, as O(2) uptake, was measured through both photo-system I and II from water to methyl viologen, through photosystem I alone from reduced 2,6-dichlorophenol indophenol to methyl viologen which does not include the plastoquinone pool or from duroquinol to methyl viologen which includes the plastoquinone pool. Electron flow principally through photosystem II was measured from water to diaminodurene and ferricyanide, as O(2) evolution. Cultures of Gonyaulax were grown on a 12-hour light:12 hour dark cycle to late log phase, then transferred to constant light at the beginning of a light period. After 3 days, measurements of electron flow were made at the maximum and minimum of the photosynthetic rhythm, as determined from measurements of the rhythm of bioluminescence. Photosynthesis was also measured in whole cells, either as (14)C fixation or O(2) evolution. Electron flow through both photosystems and through photosystem II alone were clearly rhythmic, while electron flow through photosystem I, including or excluding the plastoquinone pool, was constant with time in the circadian cycle. Thus, only changes in photosystem II account for the photosynthesis rhythm in Gonyaulax.

The circadian rhythm in photosynthesis in Acetabularia in the presence of actinomycin D, puromycin, and chloramphenicol.

Anucleate Acetabularia crenulata shows a circadian rhythm in photosynthesis. In this study, an oxygen electrode was employed to measure this photosynthetic rhythm in the presence and absence of the inhibitors, actinomycin D, chloramphenicol, and puromycin. High concentrations of the inhibitors were used: actinomycin D, 20-40 micrograms ml-1; puromycin, 30 and 100 micrograms ml-1; and chloramphenicol, 250 micrograms ml-1. The effectiveness of these inhibitors on protein synthesis was also measured under the same conditions used for the determination of rhythmicity. In spite of large effects of all three inhibitors on the incorporation of 14C leucine, no effect on the period or the phase of the photosynthetic rhythm was observed. The higher concentration of puromycin and chloramphenicol produced toxic effects which were expressed as a reduction in the amount of photosynthesis, but rhythmicity was still apparent. After 3 or 4 days' exposure to actinomycin, Acetabularia became resistant to its effect. Recovery was also observed in the ability to incorporate leucine. The implications of these results for theories of the basic oscillator responsible for circadian rhythmicity are discussed.