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Ryo Nagao - One of the best experts on this subject based on the ideXlab platform.

  • Effects of CO_2 and temperature on photosynthetic performance in the diatom Chaetoceros gracilis
    Photosynthesis Research, 2020
    Co-Authors: Ryo Nagao, Yoshifumi Ueno, Seiji Akimoto, Jian-ren Shen
    Abstract:

    CO_2 concentration and temperature for growth of photosynthetic organisms are two important factors to ensure better photosynthetic performance. In this study, we investigated the effects of CO_2 concentration and temperature on the photosynthetic performance in a marine centric diatom Chaetoceros gracilis . Cells were grown under four different conditions, namely, at 25 °C with air bubbling, at 25 °C with a supplementation of 3% CO_2, at 30 °C with air bubbling, and at 30 °C with the CO_2 supplementation. It was found that the growth rate of cells at 30 °C with the CO_2 supplementation is faster than those at other three conditions. The pigment compositions of cells grown under the different conditions are altered, and fluorescence spectra measured at 77 K also showed different peak positions. A novel fucoxanthin chlorophyll a / c -binding protein complex is observed in the cells grown at 30 °C with the CO_2 supplementation but not in the other three types of cells. Since oxygen-evolving activities of the four types of cells are almost unchanged, it is suggested that the CO_2 supplementation and growth temperature are involved in the regulation of photosynthetic light-harvesting apparatus in C. gracilis at different degrees. Based on these observations, we discuss the favorable growth conditions for C. gracilis .

  • Effects of CO2 and temperature on photosynthetic performance in the diatom Chaetoceros gracilis.
    Photosynthesis research, 2020
    Co-Authors: Ryo Nagao, Yoshifumi Ueno, Seiji Akimoto, Jian-ren Shen
    Abstract:

    CO2 concentration and temperature for growth of photosynthetic organisms are two important factors to ensure better photosynthetic performance. In this study, we investigated the effects of CO2 concentration and temperature on the photosynthetic performance in a marine centric diatom Chaetoceros gracilis. Cells were grown under four different conditions, namely, at 25 °C with air bubbling, at 25 °C with a supplementation of 3% CO2, at 30 °C with air bubbling, and at 30 °C with the CO2 supplementation. It was found that the growth rate of cells at 30 °C with the CO2 supplementation is faster than those at other three conditions. The pigment compositions of cells grown under the different conditions are altered, and fluorescence spectra measured at 77 K also showed different peak positions. A novel fucoxanthin chlorophyll a/c-binding protein complex is observed in the cells grown at 30 °C with the CO2 supplementation but not in the other three types of cells. Since oxygen-evolving activities of the four types of cells are almost unchanged, it is suggested that the CO2 supplementation and growth temperature are involved in the regulation of photosynthetic light-harvesting apparatus in C. gracilis at different degrees. Based on these observations, we discuss the favorable growth conditions for C. gracilis.

  • Adaptation of light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis to different light qualities
    Photosynthesis Research, 2020
    Co-Authors: Seiji Akimoto, Yoshifumi Ueno, Jian-ren Shen, Makio Yokono, Ryo Nagao
    Abstract:

    Diatoms are a major group of microalgae in marine and freshwater environments. To utilize the light energy in blue to green region, diatoms possess unique antenna pigment–protein complexes, fucoxanthin chlorophyll a / c -binding proteins (FCPs). Depending on light qualities and quantities, diatoms form FCPs with different energies: normal-type and red-shifted FCPs. In the present study, we examined changes in light-harvesting and energy-transfer processes of a diatom Chaetoceros gracilis cells grown using white- and single-colored light-emitting diodes (LEDs), by means of time-resolved fluorescence spectroscopy. The blue LED, which is harvested by FCPs, modified energy transfer involving CP47, and suppressed energy transfer to PSI. Under the red-LED conditions, which is absorbed by both FCPs and PSs, energy transfer to PSI was enhanced, and the red-shifted FCP appeared. The red-shifted FCP was also recognized under the green- and yellow-LEDs, suggesting that lack of the shorter-wavelength light induces the red-shifted FCP. Functions of the red-shifted FCPs are discussed.

  • Biochemical characterization of photosystem I complexes having different subunit compositions of fucoxanthin chlorophyll a/c-binding proteins in the diatom Chaetoceros gracilis
    Photosynthesis Research, 2019
    Co-Authors: Ryo Nagao, Takehiro Suzuki, Naoshi Dohmae, Yoshifumi Ueno, Seiji Akimoto, Fusamichi Akita, Jian-ren Shen
    Abstract:

    Diatoms are dominant phytoplankton in aquatic environments and have unique light-harvesting apparatus, fucoxanthin chlorophyll a / c -binding protein (FCP). Diatom photosystem I (PSI) interacts with specific FCPs (FCPI); however, it remains unclear how PSI cores receive excitation energy from FCPI. To analyze the energy transfer dynamics, it is necessary to isolate both PSI cores and PSI–FCPI complexes. In this study, we prepared three PSI complexes, which are PSI–FCPI membrane fragments, detergent-solubilized PSI–FCPI supercomplexes and PSI core-like complexes, from the marine centric diatom, Chaetoceros gracilis , and examined their biochemical properties. Both the PSI–FCPI membrane fragments and supercomplexes showed similar subunit compositions including FCPI, whereas the PSI complexes were devoid of most FCPI subunits. The purity and homogeneity of the two detergent-solubilized PSI preparations were verified by clear-native PAGE and electron microscopy. The difference of pigment contents among the three PSI samples was shown by absorption spectra at 77 K. The intensity in the whole spectrum of PSI–FCPI membranes was much higher than those of the other two complexes, while the spectral shape of PSI complexes was similar to that of cyanobacterial PSI core complexes. 77-K fluorescence spectra of the three PSI preparations exhibited different spectral shapes, especially peak positions and band widths. Based on these observations, we discuss the merits of three PSI preparations for evaluating excitation energy dynamics in diatom PSI–FCPI complexes.

  • alterations of pigment composition and their interactions in response to different light conditions in the diatom Chaetoceros gracilis probed by time resolved fluorescence spectroscopy
    Biochimica et Biophysica Acta, 2018
    Co-Authors: Ryo Nagao, Yoshifumi Ueno, Jian-ren Shen, Makio Yokono, Seiji Akimoto
    Abstract:

    Abstract Maintenance of energy balance under changeable light conditions is an essential function of photosynthetic organisms to achieve efficient photochemical reactions. Among the photosynthetic organisms, diatoms possess light-harvesting fucoxanthin chlorophyll (Chl) a/c-binding protein (FCP) as peripheral antennas. However, how diatoms regulate excitation-energy distribution between FCP and the two photosystem cores during light adaptation is poorly understood. In this study, we examined spectroscopic properties of a marine diatom Chaetoceros gracilis adapted in the dark and at photosynthetic photon flux density at 30 and 300 μmol photons m−2 s−1. Absorption spectra at 77 K showed significant changes in the Soret region, and 77-K steady-state fluorescence spectra showed significant differences in the spectral shape and relative fluorescence intensity originating from both PSII and PSI, among the cells grown under different light conditions. These results suggest alterations of pigment composition and their interactions under the different light conditions. These alterations affected the excitation-energy dynamics monitored by picosecond time-resolved fluorescence analyses at 77 K significantly. The contributions of Chls having lower energy levels than the reaction center Chls in the two photosystems to the energy dynamics were clearly identified in the three cells but with presumably different roles. These findings provide insights into the regulatory mechanism of excitation-energy balance in diatoms under various light conditions.

Robert A. Kinzie - One of the best experts on this subject based on the ideXlab platform.

  • effects of ultraviolet radiation on photosynthesis in the subtropical marine diatom Chaetoceros gracilis bacillariophyceae 1
    Journal of Phycology, 1997
    Co-Authors: Christina Hazzard, Michael P. Lesser, Robert A. Kinzie
    Abstract:

    ARSTRACT Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short-term exposure to UVR (<24 h) reduced the efficiency of photosynthetic energy conversion, carbon fixation, activity of 1,5-bisphosphate carboxylase-loxygenase (RUBISCO), and the rapid turnover of the putative Dl reaction center (32 kda) protein, whereas longer-term exposure to ambient UVR (24–48 h) revealed a steady-state acclimation, defined as recovery of carbon fixation and RUBISCO activity to rates equivalent to treatments without exposure to UVR. The turnover of D1 and chlorophyll a (Chl a) remained high during exposure to UVR. Efficiency of energy conversion by photosystem II, measured with double flash (pump and probe) fluorometry, increased by 24% in cells acclimated to UVR. Acclimation to UVR had no detectable effect on the functional absorption cross-section or cellular concentrations of Chl a, Chl c, or total carotenoids. However, the maximum rate of carbon fixation was reduced by UVR on a Chl a basis but remained unaffected on a per-cell basis. Response to UVR exposure in this subtropical diatom has two components: a short-term inhibitory response and a longer-term acclimation process that ameliorates the inhibition of carbon fixation.

  • EFFECTS OF ULTRAVIOLET RADIATION ON PHOTOSYNTHESIS IN THE SUBTROPICAL MARINE DIATOM, Chaetoceros gracilis (BACILLARIOPHYCEAE)1
    Journal of Phycology, 1997
    Co-Authors: Christina Hazzard, Michael P. Lesser, Robert A. Kinzie
    Abstract:

    ARSTRACT Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short-term exposure to UVR (

Renato A. Quiñones - One of the best experts on this subject based on the ideXlab platform.

Eduardo Walter Helbling - One of the best experts on this subject based on the ideXlab platform.

  • temperature benefits the photosynthetic performance of the diatoms Chaetoceros gracilis and thalassiosira weissflogii when exposed to uvr
    Journal of Photochemistry and Photobiology B-biology, 2010
    Co-Authors: Silvana R Halac, Virginia E Villafane, Eduardo Walter Helbling
    Abstract:

    Abstract The aim of this study was to assess the combined effects of temperature and UVR on the photosynthesis performance of two diatoms – Chaetoceros gracilis and Thalassiosira weissflogii . In particular, we evaluated the role of UVR in inducing photoinhibition and the potential mitigation of this negative effect by an increase in temperature. Cultures were pre-acclimated at two temperatures – 18 °C and 23 °C – and exposed to different radiation treatments – UVR + PAR (280–700 nm); UV-A + PAR (315–700 nm) and PAR only (400–700 nm) under two temperatures: 18 °C (local surface summer water temperature) and 23 °C (simulating a potential increase estimated by the year 2100). Exposure to natural solar radiation resulted in UVR-induced photoinhibition that was significantly higher in T. weissflogii than in C. gracilis . Both species benefited from the higher temperature (23 °C) resulting in a lower photoinhibition as compared to samples exposed at 18 °C. Inter-specific differences were determined in regard to the heat dissipation processes (NPQ) which were higher at high temperatures, and much more evident in C. gracilis than in T. weissflogii . The analyses of inhibition and recovery rates under different irradiances indicate that the balance between negative (inhibition) and positive (repair-dissipation) effects shifted towards a more positive balance with increasing temperature. Our results highlight for a beneficial effect of temperature on photosynthesis performance during exposure to UVR, although important inter-specific differences are found, probably due to differences in cell size as well as in their distribution within the oceanic realm (i.e., coastal versus oceanic species).

Christina Hazzard - One of the best experts on this subject based on the ideXlab platform.

  • effects of ultraviolet radiation on photosynthesis in the subtropical marine diatom Chaetoceros gracilis bacillariophyceae 1
    Journal of Phycology, 1997
    Co-Authors: Christina Hazzard, Michael P. Lesser, Robert A. Kinzie
    Abstract:

    ARSTRACT Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short-term exposure to UVR (<24 h) reduced the efficiency of photosynthetic energy conversion, carbon fixation, activity of 1,5-bisphosphate carboxylase-loxygenase (RUBISCO), and the rapid turnover of the putative Dl reaction center (32 kda) protein, whereas longer-term exposure to ambient UVR (24–48 h) revealed a steady-state acclimation, defined as recovery of carbon fixation and RUBISCO activity to rates equivalent to treatments without exposure to UVR. The turnover of D1 and chlorophyll a (Chl a) remained high during exposure to UVR. Efficiency of energy conversion by photosystem II, measured with double flash (pump and probe) fluorometry, increased by 24% in cells acclimated to UVR. Acclimation to UVR had no detectable effect on the functional absorption cross-section or cellular concentrations of Chl a, Chl c, or total carotenoids. However, the maximum rate of carbon fixation was reduced by UVR on a Chl a basis but remained unaffected on a per-cell basis. Response to UVR exposure in this subtropical diatom has two components: a short-term inhibitory response and a longer-term acclimation process that ameliorates the inhibition of carbon fixation.

  • EFFECTS OF ULTRAVIOLET RADIATION ON PHOTOSYNTHESIS IN THE SUBTROPICAL MARINE DIATOM, Chaetoceros gracilis (BACILLARIOPHYCEAE)1
    Journal of Phycology, 1997
    Co-Authors: Christina Hazzard, Michael P. Lesser, Robert A. Kinzie
    Abstract:

    ARSTRACT Acclimation to ambient ultraviolet radiation (UVR) was examined in a subtropical marine diatom, Chaetoceros gracilis Schutt. Short-term exposure to UVR (