Photosynthetic characteristics of coccoid marine cyanobacteria |
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Authors: | Hilary E Glover Ian Morris |
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Institution: | (1) Bigelow Laboratory for Ocean Sciences, 04575 West Boothbay Harbor, Maine, USA |
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Abstract: | Two strains of marine Synechococcus possessed a much greater potential for photorespiration than other marine algae we have studied. This conclusion was based
on the following physiological and biochemical characteristics: a) a light-dependent O2 inhibition of photosynthetic CO2 assimilation at atmospheric O2 concentrations. The degree of inhibition was dependent on the relative concentrations of dissolved O2 and CO2, being greatest at 100% O2 with no extra bicarbonate added to the medium; b) actively photosynthesizing cells had high levels of ribulose-1,5-bisphosphate
carboxylase compared with phosphoenolpyruvate carboxylase; ribulose-1,5-bisphosphate oxygenase activities were three times
greater than ribulose-1,5-bisphosphate carboxylase activities; c) cells photosynthesizing in 21% O2, showed significant 14C-labelling of phosphoglycolate and glycolate and the percentage of total carbon-14 incorporated into these two compounds
increased when the O2 concentration was 100%; d) at 100% O2, there was a post-illumination enhanced rate of O2 consumption, which was three times greater than dark respiration, and the rate declined with increasing bicarbonate concentrations.
The inhibitory effect of O2 on photosynthesis did not appear to be solely due to photorespiration, since O2 inhibition of photosynthetic O2 evolution was much greater than that of photosynthetic CO2 assimilation. Also, O2 inhibition of photosynthetic O2 evolution declined only slightly with decreasing light intensities, while the inhibition of CO2 assimilation declined rapidly with decreasing light intensity. |
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Keywords: | Marine Synechococcus sp Photosynthetic products Carboxylases Light intensity Photorespiration Warburg effect |
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