Large reallocations of carbon,nitrogen, and photosynthetic reductant among phycobilisomes,photosystems, and Rubisco during light acclimation in <Emphasis Type="Italic">Synechococcus elongatus</Emphasis> strain PCC7942 are constrained in cells under low environmental inorganic carbon |
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Authors: | Tyler?DB?MacKenzie Jeanette?M?Johnson Amanda?M?Cockshutt Robert?A?Burns Email author" target="_blank">Douglas?A?CampbellEmail author |
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Institution: | (1) Department of Biology, University of New Brunswick, Fredericton, NB, E3B 6E1, Canada;(2) Department of Biology and Coastal Wetlands Institute, Mount Allison University, NB, E4L 1G7, Canada;(3) Environmental Proteomics, Sackville, NB, E4L 1G7, Canada |
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Abstract: | Synechococcus elongatus strain PCC7942 cells were grown in high or low environmental concentrations of inorganic C (high-Ci, low-Ci) and subjected to a light shift from 50 µmol m–2 s–1 to 500 µmol m–2 s–1. We quantified photosynthetic reductant (O2 evolution) and molar cellular contents of phycobilisomes, PSII, PSI, and ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) through the light shift. Upon the increase in light, small initial relative decreases in phycobilisomes per cell resulted from near cessation of phycobilisome synthesis and their dilution into daughter cells. Thus, allocation of reductant to phycobilisome synthesis dropped fivefold from pre- to post-light shift. The decrease in phycobilisome synthesis liberated enough material and reductant to allow a doubling of Rubisco and up to a sixfold increase in PSII complexes per cell. Low-Ci cells had smaller initial phycobilisome pools and upon increased light; their reallocation of reductant from phycobilisome synthesis may have limited the rate and extent of light acclimation, compared to high-Ci cells. Acclimation to increased light involved large reallocations of C, N, and reductant among different components of the photosynthetic apparatus, but total allocation to the apparatus was fairly stable at ca. 50% of cellular N, and drew 25–50% of reductant from photosynthesis. |
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Keywords: | Carbon-concentrating mechanism Macromolecular acclimation Photosynthetic acclimation Resource allocation |
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