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Front Microbiol. 2014 Sep 19;5:488. doi: 10.3389/fmicb.2014.00488. eCollection 2014.

Effect of mono- and dichromatic light quality on growth rates and photosynthetic performance of Synechococcus sp. PCC 7002.

Author information

1
Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA ; Chemical and Biological Signature Science, Pacific Northwest National Laboratory Richland, WA, USA.
2
Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA ; Department of Biological Sciences, Purdue University W. Lafayette, IN, USA.
3
Biological Sciences Division, Pacific Northwest National Laboratory Richland, WA, USA.
4
Department of Biochemistry and Molecular Biology, The Pennsylvania State University University Park, PA, USA.
5
Department of Biological Sciences, Purdue University W. Lafayette, IN, USA.
6
Department of Biochemistry and Molecular Biology, The Pennsylvania State University University Park, PA, USA ; Department of Chemistry and Biochemistry, Montana State University Bozeman, MT, USA.

Abstract

Synechococcus sp. PCC 7002 was grown to steady state in optically thin turbidostat cultures under conditions for which light quantity and quality was systematically varied by modulating the output of narrow-band LEDs. Cells were provided photons absorbed primarily by chlorophyll (680 nm) or phycocyanin (630 nm) as the organism was subjected to four distinct mono- and dichromatic regimes. During cultivation with dichromatic light, growth rates were generally proportional to the total incident irradiance at values <275 μmol photons m(-2) · s(-1) and were not affected by the ratio of 630:680 nm wavelengths. Notably, under monochromatic light conditions, cultures exhibited similar growth rates only when they were irradiated with 630 nm light; cultures irradiated with only 680 nm light grew at rates that were 60-70% of those under other light quality regimes at equivalent irradiances. The functionality of photosystem II and associated processes such as maximum rate of photosynthetic electron transport, rate of cyclic electron flow, and rate of dark respiration generally increased as a function of growth rate. Nonetheless, some of the photophysiological parameters measured here displayed distinct patterns with respect to growth rate of cultures adapted to a single wavelength including phycobiliprotein content, which increased under severely light-limited growth conditions. Additionally, the ratio of photosystem II to photosystem I increased ~40% over the range of growth rates, although cells grown with 680 nm light only had the highest ratios. These results suggest the presence of effective mechanisms which allow acclimation of Synechococcus sp. PCC 7002 acclimation to different irradiance conditions.

KEYWORDS:

chlorophyll; cyanobacteria; fluorescence; photosynthesis; phycobiliprotein; turbidostat

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