| 1. |
- Curien, Gilles, et al.
(författare)
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The Water to Water Cycles in Microalgae.
- 2016
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 57:7, s. 1354-1363
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Tidskriftsartikel (refereegranskat)abstract
- In oxygenic photosynthesis, light produces ATP plus NADPH via linear electron transfer, i.e. the in-series activity of the two photosystems: PSI and PSII. This process, however, is thought not to be sufficient to provide enough ATP per NADPH for carbon assimilation in the Calvin-Benson-Bassham cycle. Thus, it is assumed that additional ATP can be generated by alternative electron pathways. These circuits produce an electrochemical proton gradient without NADPH synthesis, and, although they often represent a small proportion of the linear electron flow, they could have a huge importance in optimizing CO2 assimilation. In Viridiplantae, there is a consensus that alternative electron flow comprises cyclic electron flow around PSI and the water to water cycles. The latter processes include photosynthetic O2 reduction via the Mehler reaction at PSI, the plastoquinone terminal oxidase downstream of PSII, photorespiration (the oxygenase activity of Rubisco) and the export of reducing equivalents towards the mitochondrial oxidases, through the malate shuttle. In this review, we summarize current knowledge about the role of the water to water cycles in photosynthesis, with a special focus on their occurrence and physiological roles in microalgae.
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| 2. |
- Petroutsos, Dimitris, et al.
(författare)
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A blue-light photoreceptor mediates the feedback regulation of photosynthesis
- 2016
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 537:7621, s. 563-566
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Tidskriftsartikel (refereegranskat)abstract
- In plants and algae, light serves both as the energy source for photosynthesis and a biological signal that triggers cellular responses via specific sensory photoreceptors. Red light is perceived by bilin-containing phytochromes and blue light by the flavin-containing cryptochromes and/or phototropins (PHOTs)1, the latter containing two photosensory light, oxygen, or voltage (LOV) domains2. Photoperception spans several orders of light intensity3, ranging from far below the threshold for photosynthesis to values beyond the capacity of photosynthetic CO2 assimilation. Excess light may cause oxidative damage and cell death, processes prevented by enhanced thermal dissipation via high-energy quenching (qE), a key photoprotective response4. Here we show the existence of a molecular link between photoreception, photosynthesis, and photoprotection in the green alga Chlamydomonas reinhardtii. We show that PHOT controls qE by inducing the expression of the qE effector protein LHCSR3 (light-harvesting complex stress-related protein 3) in high light intensities. This control requires blue-light perception by LOV domains on PHOT, LHCSR3 induction through PHOT kinase, and light dissipation in photosystem II via LHCSR3. Mutants deficient in the PHOT gene display severely reduced fitness under excessive light conditions, indicating that the sensing, utilization, and dissipation of light is a concerted process that plays a vital role in microalgal acclimation to environments of variable light intensities.
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