Ecological studies of aquatic moss pillars in Antarctic lakes 3. Light response and chilling and heat sensitivity of photosynthesis

The light-photosynthesis relation was measured using a PAM chlorophyll fluorometric method in a moss, Leptobryum sp., which is the primary component of aquatic moss pillars, in cultured Leptobryum sp. on an agar plate, and in both aquatic and terrestrial forms of Bryum pseudotriquetrum. The morphology of the plate-cultured Leptobryum sp. was clearly different from the sample growing on an aquatic moss pillar; the leaves and shoots were considerably thickened and enlarged in the former. In spite of the great difference of morphology, photosynthetic light responses such as light-PS II yield, -non-photochemical quenching and the relative rate of electron transport of both samples were nearly the same. On the other hand, the responses of B. pseudotriquetrum collected from a moss pillar and terrestrial habitat differed greatly. Light-PS II yield and light-ETR relationships of the Leptobryum sp. showed rather shade-plant type response, low effective PS II yield at any light intensity and low maximum ETR with low light saturation point, while B. pseudotriquetrum from a terrestrial habitat showed rather \u27sun-plant\u27 type responses. Aquatic B. pseudotriquetrum showed the lowest values of effective PS II yield and ETR at almost all light intensities among the present samples. Chilling/heating stress was experimentally added to the aquatic Leptobryum sp., and it was found that both maximum and effective yield of PS II showed quite narrow and cryophilic relationships with treatment temperatures. These photosynthetic features observed in the Leptobryum sp., shade-plant type light response and very naive sensitivity to the changes of temperature, suggest that the species can perform photosynthetic growth within the aquatic habitat; however, it cannot survive or prevail in the terrestrial habitat in severe East Antarctica

Xanthophyll-cycle of ice algae on the sea ice bottom in Saroma Ko lagoon, Hokkaido, Japan

Using the ice algal community prevailing on the sea ice bottom in Saroma Ko lagoon, Hokkaido, Japan, the response of a photosynthetic system to exposure to light was investigated, focusing on xanthophylls-cycle features, diel changes of the pool size of xanthophylls-cycle pigments and the effective quantum yield of PS II in early February, 1998. By pigment analysis, β-carotene, chlorophylls a and c, diadinoxanthin, diatoxanthin and fucoxanthin were detected as major pigments, which suggests that diatoms dominated as ice algae during this study. When such ice algae were exposed to irradiance nearly 4 times higher than the daily maximum level at the ice bottom, the interconversion between diadinoxanthin and diatoxanthin continued for ca. 20 min immediately after the onset of irradiation in spite of the sub-zero Celsius ambient temperature. Although the pool size of this xanthophylls-cycle (relative amount of diadinoxanthin plus diatoxanthin per chlorophyll a) was not so large compared to that of mesophilic diatoms, it showed a circadian change increasing during the daytime and decreasing at night. This change correlated well with the effective quantum yield of PS II. These results suggest that ice algae at the sea ice bottom possess a relatively effective xanthophylls-cycle to regulate light energy usage. However, the xanthophylls-cycle in ice algae may be poor compared to that of algae living in intermediate irradiance, which can be interpreted from the point of view of bioenergetic aspects of shade adapted ice algae

Absence of the PsbQ protein results in destabilization of the PsbV protein and decreased oxygen evolution activity in cyanobacterial photosystem II

We have previously reported that cyanobacterial photosystem II (PS II) contains a protein homologous to PsbQ, the extrinsic 17-kDa protein found in higher plant and green algal PS II (Kashino, Y., Lauber, W. M., Carroll, J. A., Wang, Q., Whitmarsh, J., Satoh, K., and Pakrasi, H. B. (2002) Biochemistry 41, 8004-8012) and that it has regulatory role(s) on the water oxidation machinery (Thornton, L. E., Ohkawa, H., Roose, J. L., Kashino, Y., Keren, N., and Pakrasi, H. B. (2004) Plant Cell 16, 2164-2175). In this work, the localization and the function of PsbQ were assessed using the cyanobacterium Synechocystis sp. PCC 6803. From the predicted sequence, cyanobacterial PsbQ is expected to be a lipoprotein on the luminal side of the thylakoid membrane. Indeed, experiments in this work show that upon Triton X-114 fractionation of thylakoid membranes, PsbQ partitioned in the hydrophobic phase, and trypsin digestion revealed that PsbQ was highly exposed to the luminal space of thylakoid membranes. Detailed functional assays were conducted on the psbQ deletion mutant (ΔpsbQ) to analyze its water oxidation machinery. PS II complexes purified from ΔpsbQ mutant cells had impaired oxygen evolution activity and were remarkably sensitive to NH2OH, which indicates destabilization of the water oxidation machinery. Additionally, the cytochrome c550 (PsbV) protein partially dissociated from purified ΔpsbQ PS II complexes, suggesting that PsbQ contributes to the stability of PsbV in cyanobacterial PS II. Therefore, we conclude that the major function of PsbQ is to stabilize the PsbV protein, thereby contributing to the protection of the catalytic Mn 4-Ca1-Clx cluster of the water oxidation machinery. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc

A simple procedure to determine Ca2+ in oxygen-evolving preparations from Synechococcus sp

AbstractA simple procedure to determine Ca2+ bound to low- and high-affinity sites of Synechococcus oxygen-evolving particles was developed. The method consists of determination of Ca2+ in the particle suspensions with and without treatment with a chelating resin, Chelex 100, to remove the metal cations contaminating the suspension medium as well as those weakly bound to the particles. It was found that the particles contain one tightly bound Ca2+ per PS II reaction center which cannot be extracted with Chelex 100 and a larger amount of weakly associated and resin-extractable Ca2+

Ycf12 is a core subunit in the photosystem II complex

AbstractThe latest crystallographic model of the cyanobacterial photosystem II (PS II) core complex added one transmembrane low molecular weight (LMW) component to the previous model, suggesting the presence of an unknown transmembrane LMW component in PS II. We have investigated the polypeptide composition in highly purified intact PS II core complexes from Thermosynechococcus elongatus, the species which yielded the PS II crystallographic models described above, to identify the unknown component. Using an electrophoresis system specialized for separation of LMW hydrophobic proteins, a novel protein of ∼5 kDa was identified as a PS II component. Its N-terminal amino acid sequence was identical to that of Ycf12. The corresponding gene is known as one of the ycf (hypothetical chloroplast reading frame) genes, ycf12, and is widely conserved in chloroplast and cyanobacterial genomes. Nonetheless, the localization and function of the gene product have never been assigned. Our finding shows, for the first time, that ycf12 is actually expressed as a component of the PS II complex in the cell, revealing that a previously unidentified transmembrane protein exists in the PS II core complex

Utilizing the Effective Xanthophyll Cycle for Blooming of Ochromonas smithii and O. itoi (Chrysophyceae) on the Snow Surface

Snow algae inhabit unique environments such as alpine and high latitudes, and can grow and bloom with visualizing on snow or glacier during spring-summer. The chrysophytes Ochromonas smithii and Ochromonas itoi are dominant in yellow-colored snow patches in mountainous heavy snow areas from late May to early June. It is considered to be effective utilizing the xanthophyll cycle and holding sunscreen pigments as protective system for snow algae blooming in the vulnerable environment such as low temperature and nutrients, and strong light, however the study on the photoprotection of chrysophytes snow algae has not been shown. To dissolve how the chrysophytes snow algae can grow and bloom under such an extreme environment, we studied with the object of light which is one point of significance to this problem. We collected the yellow snows and measured photosynthetically active radiation at Mt. Gassan in May 2008 when the bloom occurred, then tried to establish unialgal cultures of O. smithii and O. itoi, and examined their photosynthetic properties by a PAM chlorophyll fluorometer and analyzed the pigment compositions before and after illumination with high-light intensities to investigate the working xanthophyll cycle. This experimental study using unialgal cultures revealed that both O. smithii and O. itoi utilize only the efficient violaxanthin cycle for photoprotection as a dissipation system of surplus energy under prolonged high-light stress, although they possess chlorophyll c with diadinoxanthin

Inhibition-excitation balance in the parietal cortex modulates volitional control for auditory and visual multistability

International audiencePerceptual organisation must select one interpretation from several alternatives to guide behaviour. Computational models suggest that this could be achieved through an interplay between inhibition and excitation across competing types of neural population coding for each interpretation. Here, to test for such models, we used magnetic resonance spectroscopy to measure non-invasively the concentrations of inhibitory γ-aminobutyric acid (GABA) and excitatory glutamate-glutamine (Glx) in several brain regions. Human participants first performed auditory and visual multistability tasks that produced spontaneous switching between percepts. Then, we observed that longer percept durations during behaviour were associated with higher GABA/Glx ratios in the sensory area coding for each modality. When participants were asked to voluntarily modulate their perception, a common factor across modalities emerged: the GABA/Glx ratio in the posterior parietal cortex tended to be positively correlated with the amount of effective volitional control. Our results provide direct evidence implicating that the balance between neural inhibition and excitation within sensory regions resolves perceptual competition. This powerful computational principle appears to be leveraged by both audition and vision, implemented independently across modalities, but modulated by an integrated control process. Perceptual multistability describes an intriguing situation, whereby an observer reports random changes in conscious perception for a physically unchanging stimulus 1,2. Multistability is a powerful tool with which to probe perceptual organisation, as it highlights perhaps the most fundamental issue faced by perception for any reasonably complex natural scene. And because the information encoded by sensory receptors is never sufficient to fully specify the state of the outside world 3 , at each instant perception must always choose between a number of competing alternatives. In realistic situations, the process produces a stable and useful representation of the world. In situations with intrinsically ambiguous information, the same process is revealed as multistable perception. A number of theoretical models have converged to pinpoint the generic computational principles likely to be required to explain multistability, and hence perceptual organisation 4-9. All of these models consider three core ingredients: inhibition between competing neural populations, adaptation within these populations, and neuronal noise. The precise role of each ingredient and their respective importance is still being debated. Noise is introduced to induce fluctuations in each population and initiate the stochastic perceptual switching in some models 7-9 , whereas switching dynamics are solely determined by inhibition in others 5,6. Functional brain imaging in humans has provided results qualitatively compatible with those computational principles at several levels of the visual processing hierarchy 10. But, for most functional imaging techniques in humans such as fMRI or MEG/EEG, change

Acclimation of photosynthetic properties in psychrophilic diatom isolates under different light intensities

Acclimation of growth and photosynthetic properties was examined for diatom strains, isolated from Saroma Ko lagoon (44°N, 144°E) in early spring, under different light intensities at 1℃. The relatively high specific growth constants under low irradiances were recognized for both Chaetoceros sp. and Thalassiosira sp. Further examination of photosynthesis in Chaetoceros sp. showed that growth under low irradiance caused an increase in the photosynthetic effciency for Chl α-specific rate of gross O_2 evolution (α^B) and a decrease in the Chl α-specific rate of dark O_2 respiration (R_d^B), which was extrapolated from the initial slope of net O_2 evolution rate vs. irradiance curve. These changes explain the low light compensation point for net photosynthetic O_2 evolution (I_c) and the high efficiency for growth under low irradiance conditions. Neither Chl α-specific amounts of light-harvesting pigments, such as fucoxanthin and Chl c, nor cellular content of Chl α, but Chl α-specific amount of diadinoxanthin was varied by the change in irradiance condition. The increase of α^B under low growth irradiance corresponded with a decrease in the amount of diadinoxanthin relative to Chl α. However, the Chl α-specific maximum photosynthetic rate (P_m^B) was retained at the same level and photoinhibition could not be observed under illumination up to &acd;800μE m^ s^. The light intensity at which photosynthesis was light-saturated (I_k, =P_m^B/α^B) was much higher than the incident growth irradiances (76 and 88μE m^ s^ under the growth irradiances of 11 and 42 μE m^ s^, respectively), although the value of I_k for the former was significantly smaller (t-test, P<0.001) than that for the latter. Thus, the capacity of photochemical reaction around photosystems seems to remain large even under low irradiance. These properties may indicate that the diatom cells could efficiently utilize light-energy under large variation of irradiance even on a short time-scale

Tolerance to freezing stress in cyanobacteria, Nostoc commune and some cyanobacteria with various tolerances to drying stress

Tolerance to and effects of the freezing stress in a desiccation-tolerant, terrestrial cyanobacterium, Nostoc commune, in cultivated strains of N. commune, and in desiccation-sensitive species, Synechocystis sp. PCC6803 and Fischerella muscicola, were studied by measuring their photosynthetic activities and fluorescence emission spectra. The results showed that a strain or species with higher desiccation tolerance was more tolerant to freezing stress than one with lower desiccation tolerance, which is consistent with the idea that tolerance to freezing stress is related to resistance to drying stress. Under freezing conditions, light energy absorbed by photosystem (PS) II complexes was dissipated to heat energy in N. commune, which may protect the cells from photoinactivation. N. commune encountered cellular dehydration due to ice formation outside the cell under freezing conditions. But NMR data showed that relatively high amounts of water still remained in a liquid state inside the cells at -36_C when N. commune colonies were fully wetted before freezing. High PSI activities measured by P700 photooxidation also support the result that non-freezing water remains within the cells. Besides, 5% methanol enhanced the resistance to freezing stress in the sensitive species. This effect seems to be related to maintenance of the PSI activity and pigment-protein complexes in their functional forms by methanol

Structure of the far-red light utilizing photosystem I of Acaryochloris marina

赤外光駆動型光合成をクライオ電顕で捉えることに成功 --低いエネルギーで通常の光化学反応が駆動される仕組み--. 京都大学プレスリリース. 2021-04-21.Acaryochloris marina is one of the cyanobacterial species that can use far-red light to drive photochemical reactions for oxygenic photosynthesis. Here, we report the structure of A. marina photosystem I (PSI) reaction center, determined by cryo-electron microscopy at 2.58 Å resolution. The structure reveals an arrangement of electron carriers and light-harvesting pigments distinct from other type I reaction centers. The paired chlorophyll, or special pair (also referred to as P740 in this case), is a dimer of chlorophyll d and its epimer chlorophyll d′. The primary electron acceptor is pheophytin a, a metal-less chlorin. We show the architecture of this PSI reaction center is composed of 11 subunits and we identify key components that help explain how the low energy yield from far-red light is efficiently utilized for driving oxygenic photosynthesis