scholarly journals Photosynthetic responses of <i>Emiliania huxleyi</i> to UV radiation and elevated temperature: roles of calcified coccoliths

2011 ◽  
Vol 8 (6) ◽  
pp. 1441-1452 ◽  
Author(s):  
K. Xu ◽  
K. Gao ◽  
V. E. Villafañe ◽  
E. W. Helbling
Keyword(s):  
Elevated Temperature ◽  
Carbon Fixation ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Photosynthetic Carbon Fixation ◽  
Level 3 ◽  
Two Temperatures ◽  
Photosynthetic Responses ◽  
Radiation Treatments ◽  
Non Photochemical Quenching

Abstract. Changes in calcification of coccolithophores may affect their photosynthetic responses to both, ultraviolet radiation (UVR, 280–400 nm) and temperature. We operated semi-continuous cultures of Emiliania huxleyi (strain CS-369) at reduced (0.1 mM, LCa) and ambient (10 mM, HCa) Ca2+ concentrations and, after 148 generations, we exposed cells to six radiation treatments (>280, >295, >305, >320, >350 and >395 nm by using Schott filters) and two temperatures (20 and 25 °C) to examine photosynthesis and calcification responses. Overall, our study demonstrated that: (1) decreased calcification resulted in a down regulation of photoprotective mechanisms (i.e., as estimated via non-photochemical quenching, NPQ), pigments contents and photosynthetic carbon fixation; (2) calcification (C) and photosynthesis (P) (as well as their ratio) have different responses related to UVR with cells grown under the high Ca2+ concentration being more resistant to UVR than those grown under the low Ca2+ level; (3) elevated temperature increased photosynthesis and calcification of E. huxleyi grown at high Ca2+ concentrations whereas decreased both processes in low Ca2+ grown cells. Therefore, a decrease in calcification rates in E. huxleyi is expected to decrease photosynthesis rates, resulting in a negative feedback that further reduces calcification.

scholarly journals Decreased calcification affects photosynthetic responses of <i>Emiliania huxleyi</i> exposed to UV radiation and elevated temperature

2011 ◽  
Vol 8 (1) ◽  
pp. 857-884
Author(s):  
K. Xu ◽  
K. Gao ◽  
V. E. Villafañe ◽  
E. W. Helbling
Keyword(s):  
Elevated Temperature ◽  
Carbon Fixation ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Pigment Contents ◽  
Level 3 ◽  
Two Temperatures ◽  
Photosynthetic Responses ◽  
Radiation Treatments ◽  
Non Photochemical Quenching

Abstract. Changes in calcification of coccolithophores may affect their photosynthetic responses to both, ultraviolet radiation (UVR, 280–400 nm) and temperature. We operated semi-continuous cultures of Emiliania huxleyi (strain CS-369) at reduced (0.1 mM, LCa) and ambient (10 mM, HCa) Ca2+ concentrations and, after 148 generations, we exposed cells to six radiation treatments (>280, >295, >305, >320, >350 and >395 nm by using Schott filters) and two temperatures (20 and 25 °C) to examine photosynthesis and calcification responses. Overall, our study has demonstrated that: (1) decreased calcification resulted in a down regulation of photoprotective mechanisms (i.e., as estimated via non-photochemical quenching, NPQ), pigment contents and photosynthetic carbon fixation; (2) Calcification (C) and photosynthesis (P) (as well as their ratio) have different responses related to UVR with cells grown under the high Ca2+ concentration having a better performance as compared to those grown under the low Ca2+ level; (3) elevated temperature increased photosynthesis and calcification of E. huxleyi grown at high Ca2+ concentrations whereas the opposite was observed in low Ca2+ grown cells. Therefore, a decrease in calcification rates in E. huxleyi is expected to decrease photosynthesis rates and producing also a negative feedback, further reducing calcification.

scholarly journals The role of coccoliths in protecting <i>Emiliania huxleyi</i> against stressful light and UV radiation

2016 ◽  
Vol 13 (16) ◽  
pp. 4637-4643 ◽  
Author(s):  
Juntian Xu ◽  
Lennart T. Bach ◽  
Kai G. Schulz ◽  
Wenyan Zhao ◽  
Kunshan Gao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Uv Radiation ◽  
Growth Rates ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Visible Radiation ◽  
Light Levels ◽  
Relative Electron ◽  
Non Photochemical Quenching

Abstract. Coccolithophores are a group of phytoplankton species which cover themselves with small scales (coccoliths) made of calcium carbonate (CaCO3). The reason why coccolithophores form these calcite platelets has been a matter of debate for decades but has remained elusive so far. One hypothesis is that they play a role in light or UV protection, especially in surface dwelling species like Emiliania huxleyi, which can tolerate exceptionally high levels of solar radiation. In this study, we tested this hypothesis by culturing a calcified and a naked strain under different light conditions with and without UV radiation. The coccoliths of E. huxleyi reduced the transmission of visible radiation (400–700 nm) by 7.5 %, that of UV-A (315–400 nm) by 14.1 % and that of UV-B (280–315 nm) by 18.4 %. Growth rates of the calcified strain (PML B92/11) were about 2 times higher than those of the naked strain (CCMP 2090) under indoor constant light levels in the absence of UV radiation. When exposed to outdoor conditions (fluctuating sunlight with UV radiation), growth rates of calcified cells were almost 3.5 times higher compared to naked cells. Furthermore, the relative electron transport rate was 114 % higher and non-photochemical quenching (NPQ) was 281 % higher in the calcified compared to the naked strain, implying higher energy transfer associated with higher NPQ in the presence of calcification. When exposed to natural solar radiation including UV radiation, the maximal quantum yield of photosystem II was only slightly reduced in the calcified strain but strongly reduced in the naked strain. Our results reveal an important role of coccoliths in mitigating light and UV stress in E. huxleyi.

scholarly journals Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

2017 ◽  
Author(s):  
Shanying Tong ◽  
David A. Hutchins ◽  
Kunshan Gao
Keyword(s):  
Ocean Acidification ◽  
Uv Radiation ◽  
Carbon Fixation ◽  
Co2 Concentration ◽  
Emiliania Huxleyi ◽  
Marine Phytoplankton ◽  
Negative Effects ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon ◽  
Increasing Temperature

Abstract. Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar UV radiation (UVR, 280–400 nm) in the ocean's upper mixed layers. Nevertheless, effects of increasing CO2-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC; pHT: 7.70) and low (400 μatm, LC; pHT: 8.02) CO2 levels, at 15 °C (LT), 20 °C (MT) and 24 °C (HT) with or without UVR. The HC treatment didn't affect photosynthetic carbon fixation at 15 °C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395 nm) than UVB (295–320 nm), except in the HC and 24 °C-grown cells, in which UVB caused more inhibition than UVA. Reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HCHT-grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with the elevated CO2 concentration, exposure to UVB or UVA affected it differentially, with the former inhibiting and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20 °C, whereas at 24 °C, observed enhancement was not significant. The calcification to photosynthesis ratio (Cal / Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24 °C, exposures to UVR significantly increased the Cal / Pho ratio, especially in HC-grown cells, by up to 100 %. This implies that UVR can counteract the negative effects of the greenhouse treatment on the Cal / Pho ratio, and so may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.

scholarly journals Physiological and biochemical responses of <i>Emiliania huxleyi</i> to ocean acidification and warming are modulated by UV radiation

2019 ◽  
Vol 16 (2) ◽  
pp. 561-572 ◽  
Author(s):  
Shanying Tong ◽  
David A. Hutchins ◽  
Kunshan Gao
Keyword(s):  
Ocean Acidification ◽  
Carbon Fixation ◽  
Co2 Concentration ◽  
Emiliania Huxleyi ◽  
Marine Phytoplankton ◽  
Negative Effects ◽  
Solar Ultraviolet Radiation ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon ◽  
Increasing Temperature

Abstract. Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar ultraviolet radiation (UVR, 280–400 nm) in the ocean's upper mixed layers. Nevertheless, the effects of increasing carbon dioxide (CO2)-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 µatm, HC; pHT: 7.70) and low (400 µatm, LC; pHT: 8.02) CO2 levels, at 15 ∘C, 20 ∘C and 24 ∘C with or without UVR. The HC treatment did not affect photosynthetic carbon fixation at 15 ∘C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395 nm) than UVB (295–320 nm), except in the HC and 24 ∘C-grown cells, in which UVB caused more inhibition than UVA. A reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HC–high-temperature grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with elevated CO2 concentration, exposure to UVB or UVA affected the process differentially, with the former inhibiting it and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20 ∘C, whereas at 24 ∘C observed enhancement was not significant. The calcification to photosynthesis ratio (Cal ∕ Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24 ∘C, exposure to UVR significantly increased the Cal ∕ Pho ratio, especially in HC-grown cells, by up to 100 %. This implies that UVR can counteract the negative effects of the “greenhouse” treatment on the Cal ∕ Pho ratio; hence, UVR may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.

scholarly journals Chlamydomonas reinhardtii LHCSR1 and LHCSR3 proteins involved in photoprotective non-photochemical quenching have different quenching efficiency and different carotenoid affinity

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Federico Perozeni ◽  
Giorgia Beghini ◽  
Stefano Cazzaniga ◽  
Matteo Ballottari
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Functional Properties ◽  
Carbon Fixation ◽  
Thermal Dissipation ◽  
Photochemical Quenching ◽  
High Sequence Identity ◽  
Pigment Analysis ◽  
Quenching Efficiency ◽  
Non Photochemical Quenching

AbstractMicroalgae are unicellular photosynthetic organisms considered as potential alternative sources for biomass, biofuels or high value products. However, their limited biomass productivity represents a bottleneck that needs to be overcome to meet the applicative potential of these organisms. One of the domestication targets for improving their productivity is the proper balance between photoprotection and light conversion for carbon fixation. In the model organism for green algae, Chlamydomonas reinhardtii, a photoprotective mechanism inducing thermal dissipation of absorbed light energy, called Non-photochemical quenching (NPQ), is activated even at relatively low irradiances, resulting in reduced photosynthetic efficiency. Two pigment binding proteins, LHCSR1 and LHCSR3, were previously reported as the main actors during NPQ induction in C. reinhardtii. While previous work characterized in detail the functional properties of LHCSR3, few information is available for the LHCSR1 subunit. Here, we investigated in vitro the functional properties of LHCSR1 and LHCSR3 subunits: despite high sequence identity, the latter resulted as a stronger quencher compared to the former, explaining its predominant role observed in vivo. Pigment analysis, deconvolution of absorption spectra and structural models of LHCSR1 and LHCR3 suggest that different quenching efficiency is related to a different occupancy of L2 carotenoid binding site.

scholarly journals The role of coccoliths in protecting <i>Emiliania huxleyi</i> against stressful light and UV radiation

2016 ◽  
Author(s):  
Juntian Xu ◽  
Lennart T. Bach ◽  
Kai G. Schulz ◽  
Wenyan zhao ◽  
Kunshan Gao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Uv Radiation ◽  
Growth Rates ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Visible Radiation ◽  
Light Levels ◽  
Relative Electron ◽  
Non Photochemical Quenching

Abstract. Coccolithophores are a group of phytoplankton species which cover themselves with small scales (coccoliths) made of calcium carbonate (CaCO3). The reason why coccolithophores form these calcite platelets has been a matter of debate since decades but has remained elusive so far. One hypothesis is that they serve a role in light/UV protection, especially in surface dwelling species like Emiliania huxleyi which can tolerate exceptionally high levels of solar radiation. In this study, we tested this hypothesis by culturing a calcifying and a non-calcifying strain under different light conditions with and without UV radiation. The coccoliths of E. huxleyi reduced the transmission of visible radiation (400–700 nm) by 7.5 %, UV-A (315–400 nm) by 14.1 % and UVB (280–315 nm) by 18.4 %. Growth rates of the calcifying strain (PML B92/11) were about 2 times higher than those of the non-calcifying strain (CCMP 2090) under indoor constant light levels in the absence of UV radiation. When exposed to outdoor conditions (fluctuating sunlight with UV radiation), growth rates of calcified cells were almost 3.5 times higher compared to naked cells. Furthermore, relative electron transport rate was 114 % higher and non-photochemical quenching (NPQ) 281 % higher in the calcifying compared to the non-calcifying strain, implying higher energy transfer associated with higher NPQ in the presence of calcification. When exposed to natural solar radiation including UV radiation, maximal quantum yield of photosystem II was only slightly reduced in the calcifying but strongly reduced in the non-calcifying strain. Our results reveal an important role of coccoliths in mitigating light and UV stress in E. huxleyi.

Sectioned rubisco crystals in TEM

1990 ◽  
Vol 48 (3) ◽  
pp. 664-665
Author(s):  
Gunnel Karlsson ◽  
Jan-Olov Bovin ◽  
Michael Bosma
Keyword(s):  
Plant Cell ◽  
Carbon Fixation ◽  
Unit Cell ◽  
Protein Crystals ◽  
Unit Cell Parameters ◽  
Cell Parameters ◽  
Photosynthetic Carbon Fixation ◽  
Photosynthetic Carbon

RuBisCO (D-ribulose-l,5-biphosphate carboxylase/oxygenase) is the most aboundant enzyme in the plant cell and it catalyses the key carboxylation reaction of photosynthetic carbon fixation, but also the competing oxygenase reaction of photorespiation. In vitro crystallized RuBisCO has been studied earlier but this investigation concerns in vivo existance of RuBisCO crystals in anthers and leaves ofsugarbeets. For the identification of in vivo protein crystals it is important to be able to determinethe unit cell of cytochemically identified crystals in the same image. In order to obtain the best combination of optimal contrast and resolution we have studied different staining and electron accelerating voltages. It is known that embedding and sectioning can cause deformation and obscure the unit cell parameters.

Light Absorption and Partitioning in Response to Nitrogen in Apple Leaves

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 541a-541
Author(s):  
Lailiang Cheng ◽  
Leslie H. Fuchigami ◽  
Patrick J. Breen
Keyword(s):  
High Light ◽  
Thermal Dissipation ◽  
Photochemical Quenching ◽  
Light Conditions ◽  
Psii Efficiency ◽  
Fluorescence Measurements ◽  
Free Radical Formation ◽  
Highly Correlated ◽  
Non Photochemical Quenching ◽  
Leaf N

Bench-grafted Fuji/M26 apple trees were fertigated with different concentrations of nitrogen by using a modified Hoagland solution for 6 weeks, resulting in a range of leaf N from 1.0 to 4.3 g·m–2. Over this range, leaf absorptance increased curvilinearly from 75% to 92.5%. Under high light conditions (1500 (mol·m–2·s–1), the amount of absorbed light in excess of that required to saturate CO2 assimilation decreased with increasing leaf N. Chlorophyll fluorescence measurements revealed that the maximum photosystem II (PSII) efficiency of dark-adapted leaves was relatively constant over the leaf N range except for a slight drop at the lower end. As leaf N increased, non-photochemical quenching under high light declined and there was a corresponding increase in the efficiency with which the absorbed photons were delivered to open PSII centers. Photochemical quenching coefficient decreased significantly at the lower end of the leaf N range. Actual PSII efficiency increased curvilinearly with increasing leaf N, and was highly correlated with light-saturated CO2 assimilation. The fraction of absorbed light potentially used for free radical formation was estimated to be about 10% regardless of the leaf N status. It was concluded that increased thermal dissipation protected leaves from photo-oxidation as leaf N declined.

scholarly journals Gradual Response of Cyanobacterial Thylakoids to Acute High-Light Stress—Importance of Carotenoid Accumulation

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1916
Author(s):  
Myriam Canonico ◽  
Grzegorz Konert ◽  
Aurélie Crepin ◽  
Barbora Šedivá ◽  
Radek Kaňa
Keyword(s):  
Single Cell ◽  
Thylakoid Membrane ◽  
Intermediate Phase ◽  
Light Stress ◽  
Fast Response ◽  
High Light ◽  
Photochemical Quenching ◽  
Second Phase ◽  
Ros Scavenging ◽  
Non Photochemical Quenching

Light plays an essential role in photosynthesis; however, its excess can cause damage to cellular components. Photosynthetic organisms thus developed a set of photoprotective mechanisms (e.g., non-photochemical quenching, photoinhibition) that can be studied by a classic biochemical and biophysical methods in cell suspension. Here, we combined these bulk methods with single-cell identification of microdomains in thylakoid membrane during high-light (HL) stress. We used Synechocystis sp. PCC 6803 cells with YFP tagged photosystem I. The single-cell data pointed to a three-phase response of cells to acute HL stress. We defined: (1) fast response phase (0–30 min), (2) intermediate phase (30–120 min), and (3) slow acclimation phase (120–360 min). During the first phase, cyanobacterial cells activated photoprotective mechanisms such as photoinhibition and non-photochemical quenching. Later on (during the second phase), we temporarily observed functional decoupling of phycobilisomes and sustained monomerization of photosystem II dimer. Simultaneously, cells also initiated accumulation of carotenoids, especially ɣ–carotene, the main precursor of all carotenoids. In the last phase, in addition to ɣ-carotene, we also observed accumulation of myxoxanthophyll and more even spatial distribution of photosystems and phycobilisomes between microdomains. We suggest that the overall carotenoid increase during HL stress could be involved either in the direct photoprotection (e.g., in ROS scavenging) and/or could play an additional role in maintaining optimal distribution of photosystems in thylakoid membrane to attain efficient photoprotection.

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