Regulation of assimilate partitioning in leaves

Concepts of the regulation of assimilate partitioning in leaves frequently consider only the allocation of carbon between sucrose and starch synthesis, storage and export. While carbohydrate metabolism accounts for a large proportion of assimilated carbon, such analyses provide only a restricted view of carbon metabolism and partitioning in leaf cells since photosynthetic carbon fixation provides precursors for all other biosynthetic pathways in the plant. Most of these precursors are required for biosynthesis of amino acids that form the building blocks for many compounds in plants. We have used leaf carbon : nitrogen ratios to calculate the allocation of photosynthetic electrons to the assimilation of nitrogen necessary for amino acid formation, and conclude that this allocation is variable but may be higher than values often quoted in the literature. Respiration is a significant fate of fixed carbon. In addition to supplying biosynthetic precursors, respiration is required for energy production and may also act, in both light and dark, to balance cellular energy budgets. We have used growth CO2 concentration and irradiance to modify source activity in Lolium temulentum in order to explore the interactions between photosynthetic carbon and nitrogen assimilation, assimilate production, respiration and export. It is demonstrated that there is a robust correlation between source activity and foliar respiration rates. Under some conditions concomitant increases in source activity and respiration may be necessary to support faster growth. In other conditions, increases in respiration appear to result from internal homeostatic mechanisms that may be candidate targets for increasing yield.

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

10.5194/bg-2017-269 ◽

2017 ◽

Cited By ~ 1

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.

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

Biogeosciences ◽

10.5194/bg-16-561-2019 ◽

2019 ◽

Vol 16 (2) ◽

pp. 561-572 ◽

Cited By ~ 5

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.

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Symbiosis of the acoel flatworm Convoluta roscoffensis with the alga Platymonas convolutae

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1974.0071 ◽

1974 ◽

Vol 187 (1087) ◽

pp. 221-234 ◽

Cited By ~ 19

Keyword(s):

Amino Acids ◽

Carbon Fixation ◽

Main Product ◽

Indirect Evidence ◽

Fixed Carbon ◽

Free Living ◽

Photosynthetic Carbon Fixation ◽

Algal Symbiont ◽

Photosynthetic Carbon ◽

Convoluta Roscoffensis

Convoluta roscoffensis can carry out photosynthetic carbon fixation at rates comparable to free-living algae. The main product of fixation is mannitol, previously shown to be the main product accumulating in the isolated algal symbiont in pure culture. Since both eggs and mucus of Convoluta became radioactive when incubated in NaH 14 CO 3 in the light, photosynthetically fixed carbon can evidently move from alga to animal. Available evidence indicates that it is amino acids, not mannitol, which are released from the algae in Convoluta . The difficulty of separating algae from animal tissue prevented direct estimates of the amount of carbon moving, but indirect evidence indicated it may not be as high as in other autotroph-heterotroph associations. When Convoluta is incubated in the light in seawater containing NaH 14 CO 3 and certain amino acids (especially alanine), fixed 14 C is released to the medium as amino acids. Up to 8% of the total fixed carbon may be released in this way, and the effect is believed to be due to the external amino acids being able to penetrate the tissues and exchange with the radioactive amino acids as they move through the animal tissues. Pyruvic acid was also effective in causing the release of fixed 14 C.

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Sectioned rubisco crystals in TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010016087x ◽

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.

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