ISHS Acta Horticulturae 440: International Symposium on Plant Production in Closed Ecosystems
GROWTH OF PHOTOSYNTHETIC ALGAE EUGLENA IN HIGH CO2 CONDITIONS AND ITS PHOTOSYNTHETIC CHARACTERISTICS |
| Authors: | Y. Nakano, K. Miyatake, H. Okuno, K. Hamazaki, S. Takenaka, N. Honami, M. Kiyota, I. Aiga, J. Kondo |
| Keywords: | Euglena, photosynthesis, growth in high CO2 conditions, regulation, oxygen evolution |
| Abstract:
In the present experiment, we used Euglena gracilis Z, which is classified as both a green algae in the plant kingdom and a protist in the animal kingdom. We determined the growth rate, activities of photosynthetic O2 evolution and CO2 fixation, PSI and PSII, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), phosphoenol pyruvate carboxylase, and phosphoenol pyruvate carboxyl kinase at different CO2 concentrations. Photoautotrophic growth of Euglena gracilis Z was extremely enhanced under 5–40 % CO2 conditions, compared with bubbling air. However, Euglena cells could not proliferate at more than 45 % CO2 concentration. In 5–40 % CO2 conditions, the RuBisCO and chlorophyll contents increased considerably in the cells. Changes in the rate of photosynthesis measured as oxygen evolution and CO2 fixation were similar to those observed for growth. However, phosphoenol pyruvate carboxylase, and phosphoenol pyruvate carboxyl kinase were not suppressed in high CO2 conditions. RuBisCO activity was higher in high CO2 conditions, but the Km value for CO2 increased in high CO2 conditions, indicating a lowering of the affinity for CO2. During the growth inhibition at the above 45 % CO2 concentrations, the activity of PSII was suppressed. In contrast, the PSI activity was constant which suggested that the growth inhibition at over 45 % CO2 concentrations was due to suppression of the PSII activity. | |
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