Number Of Phycobilisomes Research Articles

Effect of prolonged dark incubation on pigments and photosynthesis of the cave-dwelling cyanobacterium Phormidium autumnale (Oscillatoriales, Cyanobacteria)

F. Montechiaro and M. Giordano. 2006. Effect of prolonged dark incubation on pigments and photosynthesis of the cave-dwelling cyanobacterium Phormidium autumnale (Oscillatoriales, Cyanobacteria). Phycologia 45: 704–710. DOI: 10.2216/06-15.1The effect of prolonged darkness on the photosynthetic apparatus of the cyanobacterium Phormidium autumnale was investigated under nonheterotrophic conditions. The purpose of this study was to better understand the processes that allow this organism to rapidly resume growth after prolonged exposure to darkness, as it is often the case in show caves, where periods of darkness are applied to reduce algal proliferation. Phormidium autumnale was subjected to 4 weeks in the dark; this treatment elicited a large decrease in the cells' photosynthetic capacity (Pmax), while the photosynthetic affinity for photons (α) was affected to a smaller degree. Chlorophyll a and carotenoid contents were approximately constant over the 4 weeks of dark incubation, whereas the amount of phycobilins (phycocyanin, allophycocyanin and phycoerythrin) per cell decreased by 50% between the first and the last week of incubation. The relative abundance of the three phycobilins did not vary throughout the treatment, suggesting that the decrease in the number of phycobilisomes was not paralleled by changes in their relative composition. Upon re-exposure to light, cells promptly resumed photosynthesis and were able to cope with high irradiance up to 1600 μmol photons m−2 s−1. The resilience of the photosynthetic apparatus of P. autumnale in the dark may be one of the features that determine the prevalence of this organism in the cave flora at the expenses of more dark-sensitive photolithotrophs (i.e. organisms whose photosynthetic apparatus is substantially reduced or disassembled in the dark).

Acclimation of photosynthetic pigments and photosynthesis of the cyanobacterium Nostoc sp. strain UAM206 to combined fluctuations of irradiance, pH, and inorganic carbon availability

Summary We analysed the combined effect of pH, irradiance, and inorganic carbon availability on growth and pigment composition of the cyanobacterium Nostoc sp. strain UAM206, isolated from rice fields. This cyanobacterium contains phycoerythrin in its phycobilisomes and can show chromatic acclimation. Under inorganic carbon limitation, the growth rate of Nostoc sp. strain UAM206 was affected by pH, but not by irradiance. Chlorophyll a phycoerythrin (PE), and phycocyanin (PC) contents were inversely correlated to irradiance. Chlorophyll a (Chla) content was not affected by pH; however, with increasing pH, phycocyanin, phycoerythrin, and allophycocyanin (APC) content increased. Inorganic carbon availability masked or decreased some of the effects of pH under inorganic carbon limitation; however, the significant effect of pH on the allophycocyanin contents was clearly independent of the inorganic carbon availability. Analysis of our results indicates that elevation of external pH and available inorganic carbon results in an increase in the number of phycobilisomes along with a decrease in their size (PC+PE/APC ratio), while irradiance mostly affects the size of the phycobilisome. Likewise, increasing irradiance, pH, and available inorganic carbon results in an increase in the PSII/PSI ratio (APC/Chla ratio). Finally, Nostoc sp. strain UAM206 seems able to acclimate its photosynthetic apparatus to variations of the three studied environmental factors that are known to occur in rice fields.

Acclimation processes in the light harvesting complex of the red alga Porphyridium purpureum (Bory) Drew et Ross, according to irradiance and nutrient availability

ABSTRACTThe time‐course of acclimation (0‐5h) of the red alga Porphyridium purpureum with respect to total proteins, phycoerythrin (PE) and phycobilisomes (PBS) has been studied at different N availability and different light regimes. After a high N input, acclimation takes place in two phases. The first one, which is photoindependent is characterized by simultaneous increase of proteins and PE. At low N input, this first phase is not detected. In the second phase the PE content increases only under low light together with an increase of the PBS size, followed probably by an increase in the number of PBS. The effectiveness of the energy transfer increases under these conditions. A rapid decrease in the PBS size correlated with a decrease of the energy transfer is observed at high irradiance. Free PE plays an important role in the organization‐disorganization of the PBS at low N concentration (inverse correlation between free PE and PE attached to PBS). Free PE is not accumulated in the cell after a high N input at high irradiance. Independently of photoacclimation, two species of PBS appear with different PE content and different capacities to aggregate with other compounds. A clear correlation appears between the level of coupling of the PBS and the fluorescence ‘in vivo’ of the whole cells. The comparison between dissociated and undissociated PBS as well as between PBS obtained after the different acclimation processes allows the determination of the presence of two linker polypeptides probably associated with B‐PE (37 and 32–5 kDa) and two associated with PC and APC (27 and 25 kDa). That suggests that acclimation of PBS requires a parallel stoichiometric response of biliproteins and the linker polypeptides involved in the efficiency of the energy transfer.

Presence of Both Hemidiscoidal and Hemiellipsoidal Phycobilisomes in a Phormidium Species (Cyanobacteria)

Hemidiscoidal and hemiellipsoidal phycobilisomes have been determined in cells of the complementary chromatically adapting cyanobacterium Phormidium sp. C86 . They could be isolated from red and green light-adapted cells, respectively. Hemidiscoidal red light phycobilisomes show molar pigment ratios of allophycocyanin: phycocyanin of 1:4.5 with phycoerythrin lacking. Hemiellipsoidal phycobilisomes induced by green light present allophycocyanin: phycocyanin: phycoerythrin ratios of 1:1:6.8. The differences between the two phycobilisome types could additionally be demonstrated by their ultrastructure and sedimentation values. Isolated red light phycobilisomes have six rods, show dimensions of 70×30×15nm and a sedimentation value of 66 S whereas green light phycobilisomes are nearly twice larger. They contain ten rods and present dimensions of 70×40×25nm and a sedimentation value of 98 S. The number of phycobilisomes in red light cells is almost twice as large as in green light cells. There is evidence that cells grown under white light contain both types as well as “intermediate” forms.

Light Intensity Adaptation and Phycobilisome Composition of Microcystis aeruginosa

Phycobilisomes isolated from Microcystis aeruginosa grown to midlog at high light (270 microeinsteins per square meter per second) or at low light intensities (40 microeinsteins per square meter per second) were found to be identical. Electron micrographs established that they have a triangular central core apparently consisting of three allophycocyanin trimers surrounded by six rods, each composed of two hexameric phycocyanin molecules. The apparent mass of a phycobilisome obtained by gel filtration is 2.96 x 10(6) daltons. The molar ratio of the phycobiliproteins per phycobilisome is 12 phycocyanin hexamers:9 allophycocyanin trimers. The electron microscopic observations combined with the phycobilisome apparent mass and the phycobiliprotein stoichiometry data indicate that M. aeruginosa phycobilisomes are composed of a triangular central core of three stacks of three allophycocyanin trimers and six rods each containing two phycocyanin hexamers. Adaptation of M. aeruginosa to high light intensity results in a decrease in the number of phycobilisomes per cell with no alteration in phycobilisome composition or structure.

Effect of Light Intensity on Photosynthetic 14C O2 Fixation of Anabaena flos-aquae

The cyanobacterium Anabaena flos-aquae (strain 1444) grown at different intensities of white light (900, 3500 and 30000 lux) showed changes in the content and composition of the pigments. Phycocyanin was more affected by high light conditions during growth than chlorophyll a. In comparison to in low white light grown cyanobacteria number of phycobilisomes and thylakoids decreased under strong light. A diminution of 14CO2 fixation, total amino acid content, glutamic acid and glutamine pools was found in strong white light grown cells. Under these conditions the majority of 14C-labelling was measured in sugar phosphates. After pressure treatment a marked increase of 14C-incorporation into amino acids could be obtained. Results were discussed with reference to regulation of buoyancy in Anabaena flos-aquae.

Phycobilisome composition and possible relationship to reaction centers

The photosynthetic apparatus was studied in Anacystis nidulans wild type and in a spontaneous pigment mutant 85Y which had improved growth in far-red light (>650 nm). Two phycobiliproteins, C-phycocyanin ( λ max 625) and allophycocyanin ( λ max 650), were present in a molar ratio of ~3:1 in the wild type and ~0.4:1 in the mutant. Phycobilisomes of wild type cells were larger (57 × 30 nm) than those of the mutant 85Y (28 × 15 nm). In the mutant they seemed to consist primarily of the allophycocyanin core. Fluorescence emission maxima of wild type and mutant 85Y phycobilisomes were at 680 nm (23 °C) and 685 nm (−196 °C). Excitation maxima of phycobilisomes were at 630 and 650 nm for the wild type and the mutant 85Y, respectively. The phycobilisomes of wild type cells whether grown in white or far-red light had the same size and pigment composition. A typical wild type cell in white light had a thylakoid area of 22.8 μm 2, but in far-red light the area was reduced to 13.5 μm 2, which was close to that of 85Y at 13.6 μm 2. Chlorophyll molecules per cell decreased in far-red light from 1.1 × 10 7 in wild type (white light) to 4.5 × 10 6 in mutant 85Y (far-red). The number of phycobilisomes per cell (approx 2 × 10 4), calculated from the phycobiliprotein content and phycobilisome size, was about the same in wild type (white light) and mutant 85Y (far-red light), but the number of phycobilisomes per unit area of thylakoid was significantly greater in mutant 85Y than in wild type. The present results suggest that the phycobilisomes are linked with reaction centers and that the PSII complement (photosystem II and phycobilisome) was fully maintained in far-red light.

CHLOROPLAST STRUCTURE AND PIGMENT COMPOSITION IN THE RED ALGA GRIFFITHSIA PACIFICA: REGULATION BY LIGHT INTENSITY1

SUMMARYThe ratio of accessory phycobiliproteins to chlorophyll a is controlled by light intensity in the marine red alga Griffithsia pacifica. The greatest changes in pigment ratios are observed below 300 ft‐c; above 300 ft‐c the response approaches saturation. Ultrastructural examination of chloroplasts of plants grown at different intensities reveals that the number of phycobilisomes per unit of photosynthetic thylakoid changes in direct proportion to the pigment ratios and in inverse proportion to the light intensity.